2024-03-28T16:16:25Zhttps://kuscholarworks.ku.edu/oai/requestoai:kuscholarworks.ku.edu:1808/296072019-10-01T16:54:02Zcom_1808_231col_1808_13465col_1808_19739
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Lafikes, James
author
Darwin, David
author
O'Reilly, Matthew
author
Feng, Muzai
author
Bahadori, Alireza
author
Khajehdehi, Rouzbeh
author
2019-06-01
Construction and early-age crack evaluations of four bridge decks in Minnesota placed from 2016
to 2018 that incorporate specifications for Internally-Cured Low-Cracking High-Performance
Concrete (IC-LC-HPC) are documented in this study. Two additional decks that serve as Controls
followed specifications for high-performance concrete and paired with IC-LC-HPC decks are
included. Pre-wetted fine lightweight aggregate was used to provide a targeted internal curing
water content of 8% by total weight of binder. The IC-LC-HPC mixtures included 27 to 30% slag
cement by total binder weight while the Control mixtures included 25 or 35% Class F fly ash by
total weight of binder. For one IC-LC-HPC deck, mixture proportions were modified based on a
higher FLWA absorption than originally used to design the mixture. One IC-LC-HPC placement
failed due to errors in FLWA moisture corrections and concrete batching that led to rejections of
batches, leaving an inadequate supply of material to complete the deck. Crack surveys were
completed for the IC-LC-HPC and Control decks placed in 2016 and 2017. Crack densities at these
ages were low compared to most Low-Cracking High-Performance Concrete decks in Kansas and
Internally-Cured High-Performance Concrete decks in Indiana, with the exception of one IC-LCHPC
deck that exhibited extensive cracking within one year after placement, which had an overlay
with a high cement paste content and no internal curing. This project serves as a foundation for
implementing IC-LC-HPC in upcoming bridge decks in Kansas and Minnesota.
Lafikes, J., Darwin, D., O’Reilly, M., Feng, M., Bahadori, A., and, Khajehdehi, R., “Construction of Low-Cracking High-Performance Bridge Decks Incorporating New Technology,” SM Report No. 132, University of Kansas Center for Research, Inc., Lawrence, KS, June 2019, 98 pp.
http://hdl.handle.net/1808/29607
https://orcid.org/0000-0001-5039-3525
bridge decks
concrete construction
cracking
internally-cured low-cracking high-performance concrete
lightweight aggregate
paste content
supplementary cementitious materials
Construction Of Low-Cracking High-Performance Bridge Decks Incorporating New Technology
oai:kuscholarworks.ku.edu:1808/303552020-05-16T08:01:06Zcom_1808_231col_1808_13465col_1808_19739
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Al-Sabawy, Abdalkader
author
Lequesne, Rémy D.
author
O’Reilly, Matthew
author
Darwin, David
author
Lepage, Andrés
author
2020-05
Results are reported from 29 large-scale tests of reinforced concrete beams designed to investigate the use of Grade 80 (550) steel and headed deformed bars as shear reinforcement, both of which are expected to alleviate reinforcement congestion and improve constructability when used in heavily reinforced members. The specimens were tested under three-point bending with a shear span-to-effective depth ratio of 3. Shear reinforcement consisted of either stirrups or headed deformed bars made with Grade 60 or 80 (420 or 550) steel. Headed bars were evaluated both engaging and not engaging the longitudinal reinforcement to determine whether such engagement is necessary for acceptable performance. Other variables included beam depth, shear reinforcement size and spacing, longitudinal reinforcement ratio, and concrete compressive strength.
Test results showed that when headed deformed shear reinforcement (of diameter db) is placed with at least 6db of side cover and having at least one longitudinal bar within the side cover, or when headed reinforcement is engaged with longitudinal bars at each end, beam shear strength was similar to that of companion specimens with stirrups. Specimens designed for the same nominal shear strength, Vn, using either Grade 60 or 80 (420 or 550) shear reinforcement exhibited similar shear strengths and crack widths at service-level loads (taken as 0.6Vn). Test results indicate there may be cause to reevaluate the ACI Building Code minimum for ρtfytm of 50 psi (0.34 MPa): 9 out of 12 specimens with ρtfytm < 90 psi (0.62 MPa) had measured shear strengths less than Vn calculated using measured material properties, whereas only 2 out of 13 specimens with ρtfytm > 90 psi (0.62 MPa) did. The statistically significant difference between these groups persisted when Vn was based on the number of adequately anchored stirrup legs intercepted by the failure surface.
Al-Sabawy, A., Lequesne, R. D., O’Reilly, M., Darwin, D., and Lepage, A., “Headed and High-Strength Shear Reinforcement in Concrete Members,” SM Report No. 139, University of Kansas Center for Research, Inc., Lawrence, KS, May 2020, 498 pp.
http://hdl.handle.net/1808/30355
https://orcid.org/0000-0001-5039-3525
Crack width
Headed bars
Headed shear reinforcement
High-strength steel
High- strength concrete
Member depth
Shear reinforcement
Headed and High-Strength Shear Reinforcement in Concrete Members
oai:kuscholarworks.ku.edu:1808/189992019-04-12T14:27:11Zcom_1808_231col_1808_13465
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Young, Bryan
author
Nelson, Brian R.
author
Bradley, A. Allen
author
Smith, James A.
author
Peters-Lidard, Christa D.
author
Kruger, Anton
author
Baeck, Mary Lynn
author
1999-08-27
Next Generation Weather Radar (NEXRAD) precipitation estimates are used for hydrological, meteorological, and climatological studies at a wide range of spatial and temporal scales. The utility of radar-based precipitation estimates in such applications hinges on an understanding of the sources and magnitude of estimation error. This study examines precipitation estimation in the complex mountainous terrain of the northern Appalachian Mountains. Hourly digital precipitation (HDP) products for two WSR-88D radars in New York state are evaluated for a 2-year period. This analysis includes evaluation of range dependence and spatial distribution of estimates, radar intercomparisons for the overlap region, and radar-gage comparisons. The results indicate that there are unique challenges for radar-rainfall estimation in mountainous terrain. Beam blockage is a serious problem that is not corrected by existing NEXRAD algorithms. Underestimation and nondetection of precipitation are also significant concerns. Improved algorithms are needed for merging estimates from multiple radars with spatially variable biases.
Young, C. Bryan, Brian R. Nelson, A. Allen Bradley, James A. Smith, Christa D. Peters-Lidard, Anton Kruger, and Mary Lynn Baeck. "An Evaluation of NEXRAD Precipitation Estimates in Complex Terrain." J. Geophys. Res. Journal of Geophysical Research 104.D16 (1999): 19691. http://dx.doi.org/10.1029/1999JD900123
http://hdl.handle.net/1808/18999
10.1029/1999JD900123
An evaluation of NEXRAD precipitation estimates in complex terrain
oai:kuscholarworks.ku.edu:1808/232682019-04-12T14:23:18Zcom_1808_231col_1808_13465
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Guo, Guohui
author
Joseph, Leonard M.
author
Darwin, David
author
2013
The effects of story-by-story horizontal post-tensioning (PT) on multi-story buildings are investigated using staged construction analyses. Analytical column-supported and wall-supported multi-story models are studied to represent different degrees of restraint by supports. Findings include a determination that part of the PT force applied to an upper floor slab is diverted to floors below through flexure and shear of vertical structural elements. The first elevated PT floor and a PT roof may experience significantly reduced slab precompression from PT force diversion. Design recommendations are provided. The design of structural frames incorporating post-tensioned concrete members should consider secondary actions, such as moments and shears, for both horizontal and vertical members due to staged PT construction, in addition to gravity and lateral loads. Concrete PT floor slab serviceability stress checks should use realistic slab effective precompression forces, considering diversion of precompression forces through supports, rather than forces in tendons at that floor.
Guo, G., Joseph, L.M., and Darwin, D., "Effects of Story-by-Story Post-Tensioning on Multi-Story Buildings," ACI Structural Journal, Vol. 110, No. 4, July-August 2013, pp. 649-657.
http://hdl.handle.net/1808/23268
https://orcid.org/0000-0001-5039-3525
Effective precompression
Multi-story building
Post-tensioning
Precompression loss
Prestress level
Soft story
Staged construction
Unbonded tendons
Effects of Story-by-Story Post-Tensioning on Multi-Story Buildings
oai:kuscholarworks.ku.edu:1808/326932022-04-08T08:01:04Zcom_1808_231col_1808_13465
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Cheng, Min-Yuan
author
Wibowo, Leonardus S. B.
author
Giduquio, Marnie B.
author
Lequesne, Rémy D.
author
2021-01
The behavior of reinforced concrete (RC) squat walls constructed with conventional- and high-strength materials was evaluated through tests of 10 wall specimens subjected to reversed cyclic loading. Primary variables included specimen height-to-length aspect ratio, steel grade, concrete compressive strength, and normalized shear stress demand. Specimens were generally in compliance with ACI 318-14. Test results showed that specimens containing conventional- and high-strength steel had similar strength and deformation capacities when designed to have equivalent steel force, defined as total steel area times steel yield stress. The lateral strength of walls with aspect ratios of 1.0 and 1.5 can be estimated using their nominal flexural strength when the nominal shear strength exceeds Vmn. For specimens with an aspect ratio of 0.5, the lateral strength was close to the force required to cause flexural reinforcement yielding and less than the nominal shear strength calculated per ACI 318-14. Specimen deformation capacity decreased as the normalized shear stress increased. The use of high-strength concrete, which led to a reduced normalized shear stress demand, resulted in larger specimen deformation capacity.
Cheng, M.Y., Wibowo, L.S.B., Giduquio, M.B., Lequesne, R.D., (2021). "Strength and Deformation of Reinforced Concrete Squat
Walls with High-Strength Materials". ACI Structural Journal, vol. 118, no. 1, pp. 125-137.
http://hdl.handle.net/1808/32693
10.14359/51728082
Deformation
Drift
High strength
Low-rise wall
Shear
Squat wall
Strength
Strength and Deformation of Reinforced Concrete Squat Walls with High-Strength Materials
oai:kuscholarworks.ku.edu:1808/204752018-12-27T19:12:53Zcom_1808_231col_1808_13465col_1808_19739
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Darwin, David
author
Locke, Carl E., Jr.
author
Balma, Javier
author
Kahrs, Jason T.
author
1999-07
The corrosion performance of stainless steel clad reinforcing bars provided by Structural Metals, Inc. is compared with that of conventional (black) reinforcement. 304 stainless steel is used as the cladding material. The No. 19 (No. 61 bars are compared using rapid corrosion potential and macrocell tests. The tests are carried out in two stages, first with bare reinforcement and then with reinforcement encased in mortar. Test spe.cimens are placed in simulated concrete pore solution with a 1.6 molal ion concentration of sodium chloride. The continuity and uniformity of the cladding is measured using a scanning ele.ctron microscope. The study indicates that the cladding provides a significant improvement in corrosion performance, if the mild steel core of the clad bars is adequately isolated from chlorides. For bars not encased in mortar, the corrosion rate of the clad bars ranges between 0 and 0.3 µm/yr, about 1 1100 of the value observed for the black bars. For bars encased in mortar, the corrosion rate averages 0.1 µm/yr, 1 I 20 to 1/50 of the value exhibited by the black steel. Cladding thickness varies between 0.196 and 0.894 mm (7.7 and 35 mils), averaging 0.467 mm (18 mils). Based on an average corrosion rate of about 0.2 µm/yr for stainless steel bars not embedded in mortar (representing the corrosion rate that would be expected at a void adjacent to a bar in concrete), the cladding appears to be satisfactory if the current minimum thickness is maintained. Tests of bars clad with 316 stainless steel and longer-term tests are recommended.
Darwin, D., Locke, C.E., Jr., Balma, and J., Kahrs, J.T., "Evaluation of Stainless Steel Clad Reinforcing Bars," SL Report 99-3, University of Kansas Center for Research, Inc., Lawrence, Kansas, July 1999, 17 pp.
http://hdl.handle.net/1808/20475
https://orcid.org/0000-0001-5039-3525
Evaluation of Stainless Steel Clad Reinforcing Bars
oai:kuscholarworks.ku.edu:1808/234262018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Donahey, Rex C.
author
Darwin, David
author
1985
The effects of consolidation method and two-course construction on the bond strength of top-cast reinforcement in concrete bridge decks were studied as functions of slump, bleed. and slab depth. Consolidation was varied using vibrator spacing and insertion time. Four top covers were studied: !4 and 3 in. (19 and 76 mm) monolithic and 3 in. (76 mm) two-course with either !4 or 1 in. (19 or 25 mm) first course cover. Bond test specimens were of two types: shallow, with 8 in. (203 mm) of concrete below the reinforcement, and deep. with 24 in. (610 mm) of concrete below the reinforcement. Concrete densities were obtained from drilled cores. Based on the experimental work, high-density internal vibration provides improved bond over low-density internal vibration. A 3 in. (76 mm) monolithic cover provides higher bond strength than 3 in. (76 mm) two-course cover. Increased concrete slump has a negative effect on bond strength for top-cast reinforcement. Deep slabs made with stiff, well-consolidated concrete can provide the same bond strengths as shallow slabs.
Donahey, R.C., and Darwin, D., "Bond of Top-Cast Bars in Bridge Decks" ACI Journal Vol. 82, No. 5, January-February 1985, pp. 57-66.
http://hdl.handle.net/1808/23426
https://orcid.org/0000-0001-5039-3525
Air entrainment
Bond (concrete to reinforcement)
Bleeding (concrete)
Bridge decks
Concrete construction
Consistency
Consolidation
Cover
Pullout tests
Reinforced concrete
Reinforcing steels
Resurfacing
Vibration
Bond of Top-Cast Bars in Bridge Decks
oai:kuscholarworks.ku.edu:1808/234312018-02-23T18:25:17Zcom_1808_231col_1808_13465col_1808_19739
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Lequesne, Rémy D.
author
Pincheira, José A.
author
2014
Modifications correct anomalies for nonprestressed reinforced concrete members subjected to flexure and axial loads
Lequesne, R. D., and Pincheira, J. A., "Proposed Revisions to the Strength-Reduction Factor for Axially Loaded Members," Concrete International, 36(9), 2015, pp. 43-49.
http://hdl.handle.net/1808/23431
Proposed Revisions to the Strength-Reduction Factor for Axially Loaded Members
oai:kuscholarworks.ku.edu:1808/203412018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
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Clawson, William C.
author
Darwin, David
author
1980-10
The purpose of this investigation was to study the behavior and develop an ultimate strength model for composite beams with rectangular web openings. Six composite beams with concentric rectangular web openings were tested to failure. Varying moment to shear ratios were used to help develop and verify the ultimate strength model. One steel beam was tested to demonstrate the contribution of the concrete to the capacity of composite beams. Two steel sections were used, while the concrete slab size was held constant for all beams. Three elastic tests were performed on each beam before it was tested to failure. An ultimate strength model was developed to predict the strength of composite beams at the web openings in the form of moment-shear interaction diagrams. The steel is modeled as an elastic-perfectly plastic material. The yield stress of the steel is defined as a function of the assigned shear stress according to the von Mises yield criterion. The concrete is modeled for ultimate strength behavior. Concrete compressive strength is also defined as a function of the assigned shear stress, based on experimental results. Strain compatibility between the concrete and steel is assumed. The model is compared with experimental results and is used to study the effect of key parameters (material properties, opening size, and opening eccentricity) affecting the strength of composite beams with web openings. A simplified design interaction procedure is presented to conservatively guide the placement of web openings in composite beams. Based on the experimental study, it is clear that web openings can greatly reduce the strength of composite beams. It appears that the secondary bending has a sizable effect on beam behavior. The concrete in composite beams contributes, not only, to the flexural strength, but, also, to the shear capacity of the beams at web openings. The ultimate strength of composite beams at web openings is governed by the failure of the concrete. The ultimate strength model satisfactorily predicts the strength of the experimental beams.
Clawson, W.C., and Darwin, D., "Composite Beams with Web Openings," SM Report No. 4, Research Grant ENG 76-19045, The National Science Foundation, October 1980, 207 pp.
http://hdl.handle.net/1808/20341
https://orcid.org/0000-0001-5039-3525
Composite Beams With Web Openings
oai:kuscholarworks.ku.edu:1808/298542020-10-13T21:33:06Zcom_1808_231col_1808_13465
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Hansen, Amy T.
author
Singh, Arvind
author
2018-06-20
Excess nitrate in rivers draining intensively managed agricultural watersheds has caused coastal hypoxic zones, harmful algal blooms, and degraded drinking water. Hydrology and biogeochemical transformations influence nitrate concentrations by changing nitrate supply, removal, and transport. For the Midwest Unites States, where much of the land is used for corn and soybean production, a better understanding of the response of nitrate to hydrology and biogeochemistry is vital in the face of high nitrate concentrations coupled with projected increases of precipitation frequency and magnitude. In this study, we capitalized on the availability of spatially and temporally extensive sensor data in the region to evaluate how nitrate concentration (NO3−) interacts with discharge (Q) and water temperature (T) within eight watersheds in Iowa, United States, by evaluating land use characteristics and multiscale temporal behavior from 5‐year, high‐frequency, time series records. We show that power spectral density of Q, NO3−, and T, all exhibit power law behavior with slopes greater than 2, implying temporal self‐similarity for a range of scales. NO3− was strongly cross correlated with Q for all sites and correlation increased significantly with drainage area across sites. Peak NO3− increased significantly with crop coverage across watersheds. Temporal offsets in peak NO3− and peak Q, seen at all study sites, reduced the impact of extreme events. This study illustrates a relatively new approach to evaluating environmental sensor data and revealed characteristics of watersheds in which extreme discharge events have the greatest consequences.
Hansen, A., & Singh, A. (2018).High-frequency sensor data revealacross-scale nitrate dynamics inresponse to hydrology andbiogeochemistry in intensivelymanaged agricultural basins.Journal ofGeophysical Research: Biogeosciences,123, 2168–2182. https://doi.org/10.1029/2017JG004310
http://hdl.handle.net/1808/29854
10.1029/2017JG004310
https://orcid.org/0000-0002-6152-9595
https://orcid.org/0000-0003-2172-6321
High‐Frequency Sensor Data Reveal Across‐Scale Nitrate Dynamics in Response to Hydrology and Biogeochemistry in Intensively Managed Agricultural Basins
oai:kuscholarworks.ku.edu:1808/10742019-04-12T14:37:17Zcom_1808_231col_1808_13465
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Denne, Jane E.
author
Randtke, Stephen J.
author
Hathaway, Lawrence R.
author
Melia, Anne S.
author
1987-12
Denne, J.E., S.J. Randtke, L.R. Hathaway, and A.S. Melia, "Geological and Geochemical Factors Influencing Water Quality in a Buried Valley in Northeastern Kansas," Project Completion Report, Kansas Water Resources Research Institute, The University of Kansas, Contribution No. 265, December, 1987, 204 pp.
http://hdl.handle.net/1808/1074
Geological and Geochemical Factors Influencing Water Quality in a Buried Valley in Northeastern Kansas
oai:kuscholarworks.ku.edu:1808/204422018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Zuo, Jun
author
Darwin, David
author
1994-12
The visibility, durability, and cost-effectiveness of surface pavement markings and previous experience with permanent concrete pavement markings (PCPM) (markings with a service life similar to that of the pavement) are described. The use of durable materials, such as thermoplastics, polyesters, and epoxies, improves the service life of surface markings. However, these marking materials still exhibit problems of adhesion to pavement and rapid wear in high traffic areas. Snow removal procedures significantly reduce marking service life. Wet nighttime visibility is a continuing problem with surface markings. Previous attempts at developing PCPM have produced systems with very good durability, but poor nighttime visibility. The potential for developing cost-effective PCPM systems that can provide both long-term durability and adequate visibility throughout the service life and the requirements for such systems are discussed. Polymers, such as epoxies, can provide superior durability and adhesion to pavement. The application of larger than standard size glass beads can improve wet nighttime visibility. The cost of PCPM systems can be significantly reduced using effective methods of placing grooves in which the marking material is placed. Generally, there is a good probability that a cost-effective PCPM system with satisfactory durability and visibility can be developed. The PCPM systems with thicknesses of 9.5 mm (3/8 in.) or less will be cost-effective for a 20- year service life, and the systems with thicknesses of 3.2 mm (1/8 in.) or less will be costeffective for a I 0-year service life.
Zuo, J., Darwin, D., "Permanent Concrete Pavement Markings," SM Report No. 38, University of Kansas Center for Research, Inc., Lawrence, KS, December 1994, 67 pp.
http://hdl.handle.net/1808/20442
https://orcid.org/0000-0001-5039-3525
Permanent Concrete Pavement Markings
oai:kuscholarworks.ku.edu:1808/314572021-02-24T09:00:53Zcom_1808_231col_1808_13465
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Bazzaz, Mohammad
author
Darabi, Masoud K.
author
Little, Dallas N.
author
Garg, Navneet
author
2019-12-30
Rheological properties of asphalt binders significantly affect distress development and performance of asphalt concrete materials. This article presents the effect of Evotherm-M1 modifications on rheological properties of asphalt binders used in the construction of test sections at the Federal Aviation Administration’s National Airport Pavement & Materials Research Center. Four different binders (i.e., polymer styrene butadiene styrene [SBS]-modified PG 76-22, PG 64-22, SBS-modified PG 76-22 plus Evotherm-M1, and PG 64-22 plus Evotherm-M1) are studied. Multiple stress creep recovery (MSCR) and strain-controlled frequency sweep (FS) test results are analyzed to construct the master curves for the binders. Results indicate high sensitivity of SBS-modified PG 76-22 to Evotherm-M1 modifications as compared with PG 64-22. Subsequently, the results of dynamic modulus tests conducted on asphalt mixture specimens (prepared using job mix formula and different binders) are analyzed to investigate the effect of binder type and modification on rheological properties and rutting performance of asphalt mixtures. It is shown that the rutting resistance and rheological properties of asphalt mixtures can be ranked based on the results of MSCR and FS tests conducted on asphalt binders. It is shown that the rutting resistivity of traffic test sections and lab-tested asphalt mixtures can be ranked as follows: SBS-modified PG 76-22, SBS-modified PG 76-22 plus Evotherm-M1, PG 64-22, and PG 64-22 plus Evotherm-M1. This is consistent with the results obtained for tested asphalt binders.
M. Bazzaz, M. Darabi, D. Little, and N. Garg, "Effect of Evotherm-M1 on Properties of Asphaltic Materials Used at NAPMRC Testing Facility," Journal of Testing and Evaluation 48, no. 3 (2020): 2256-2269. https://doi.org/10.1520/JTE20190446
http://hdl.handle.net/1808/31457
10.1520/JTE20190446
Effect of Evotherm-M1 on Properties of Asphaltic Materials Used at NAPMRC Testing Facility
oai:kuscholarworks.ku.edu:1808/202172018-11-16T17:01:54Zcom_1808_231col_1808_13465col_1808_19739
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Attiogbe, Emmanuel K.
author
Palaskas, Michael N.
author
Darwin, David
author
1980-07
Attiogbe, E.K., Palaskas, M.N., and Darwin, D., "Shear Cracking and Stirrup Effectiveness of Lightly Reinforced Concrete Beams," SM Report No. 1, ARMCO Inc., July 1980, 144 pp.
http://hdl.handle.net/1808/20217
https://orcid.org/0000-0001-5039-3525
Shear Cracking and Stirrup Effectiveness of Lightly Reinforced Concrete Beams
oai:kuscholarworks.ku.edu:1808/250622018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Palaskas, Michael N.
author
Attiogbe, Emmanuel K.
author
Darwin, David
author
1981
Fifteen lightly reinforced concrete T-beams, 11 with stirrups and four without stirrups, were tested to failure. The major variables rit the study were the amounts of flexural and shear reinforcement. The flexural steel varied from 0.5 to 1 percent, and the shear reinforcement varied from 0 to 110 psi (0.75 MPa). The test results are analyzed and compared with the shear design provisions of "Building Code Requirements for Reinforced Concrete (AC1 318-77)" and the recommendations of AC1 Committee 426, Shear and Diagonal Tension. The test results confirmed the findings of other investigators, that the present AC1 equations for the shear cracking load are unconservative for beams without stirrups, having a longitudinal reinforcing ratio less than 1 percent. However, for beams with stirrups the web reinforcement was 1.5 times as effective as predicted by AC1 318-77 and compensated for the lower shear strength of the concrete. It is recommended that the shear design provisions of AC1 318-77 be retained in their current form.
Palaskas, M. N., Attiogbe, E. K. and Darwin, D., “Shear Strength of Lightly Reinforced T-Beams,” Journal of the American Concrete Institute, Vol. 78, No. 6, November-December 1981, pp. 447-455.
http://hdl.handle.net/1808/25062
https://orcid.org/0000-0001-5039-3525
Beams (supports)
Cracking (fracturing)
Diagonal tension
Flexural strength
Loads (forces)
Reinforced concrete
Reinforcing steel
Research
Shear strength
Stirrups
Structural design
T-beams
Web reinforcement
Shear Strength of Lightly Reinforced T-Beams
oai:kuscholarworks.ku.edu:1808/233342018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Lindquist, Will D.
author
Darwin, David
author
Browning, JoAnn
author
Miller, Gerald G.
author
2006
Field surveys to measure bridge deck cracking and chloride contents of uncracked as well as cracked concrete were performed as a part of a larger research program evaluating bridge deck performance. Three deck types were studied: monolithic decks, decks with a conventional high density concrete overlay, and decks with a high density concrete overlay containing either a 5 or 7% replacement of cement by silica fume.
The results of the field surveys indicate that bridge deck type does not have a major effect on chloride content. For samples taken away from cracks, the average chloride concentration at the top of transverse reinforcement rarely exceeded even the most conservative estimates of the corrosion threshold for conventional reinforcement. Chloride concentrations taken at crack locations, however, often exceeded the corrosion threshold of conventional reinforcement in less than 1 year.
Lindquist, W.D., Darwin, D., Browning, J.P., and Miller, G.G., "Effect of Cracking on Chloride Content in Concrete Bridge Decks," ACI Materials Journal, Vol. 103, No. 6, November-December 2006, pp. 467-473.
http://hdl.handle.net/1808/23334
https://orcid.org/0000-0001-5039-3525
Bridge deck
Chlorides
Cracking
Overlay
Permeability
Effect of Cracking on Chloride Content in Concrete Bridge Decks
oai:kuscholarworks.ku.edu:1808/204282018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
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Martin, Jeffrey L.
author
Darwin, David
author
Terry, Richard E.
author
1991-10
The behavior of saturated specimens of cement paste and mortar under monotonic, sustained and cyclic loading, is compated to that of concrete at water - cement ratios of 0.5 and 0.7. Specimen age, at testing, ranges from 27 to 29 days. For monotonic loading, the behavior of each material is described in terms of peak stress, strain at peak stress, and initial modulus of elasticity. For sustained loading, the behavior is described in terms of creep strain as a function of stress - strength ratio and time under load. Mathematical relationships ate developed on the sustained load response to estimate the cumulative static creep for a cyclic test. Cyclic test results ate exatnined in terms of strain at 15 seconds, the difference between the strain at 15 seconds and the peak strain for a given cycle (cyclic strain), the estimated creep strain for a cyclic test (equivalent creep, based on sustained load test results), the difference between cyclic strain and equivalent creep (cyclic action strain), and the change in secant unloading modulus (a measute of material damage). The equivalent creep duting a cyclic test is used to distinguish between cyclic strain and cyclic action strain, which may include accelerated creep strain as well as strain related to tnicrocracking. Cyclic action strain is correlated with change in modulus of elasticity to determine the extent to which these strains ate the result of damage. Monotonic test results show that for the materials used in this study, at a given water - cement ratio, cement paste has a higher strength and strain capacity than do the corresponding mortat and concrete, while mortat and concrete have a higher initial stiffness than cement paste. Sitnilatly, mortat has a higher strength and strain capacity than the corresponding concrete, but has approximately the same initial stiffness. The sustained load test results show that over a four hour period, creep strain increases nonlinearly with increasing stress - strength ratio. At the same stress - strength ratio, total strain and creep strain accumulate more rapidly for cement paste than for mortar and more rapidly for mortar than for concrete. The cyclic test results show that for cyclic tests with a maximum stress - strength ratio greater than 0.6f', cyclically loaded cement paste, mortar and concrete exhibit larger strains than similar materials exposed to a sustained load equal to the mean cyclic stress. For the load regimes studied, maximum cyclic stress appears to have a much greater impact on the cyclic action strain and change in stiffness than the mean cyclic stress or the cyclic stress range. The overall damage, as measured by the cyclic action strain and change in secant unloading modulus, in mortar in concrete is similar, suggesting that the behavior of concrete under cyclic loading is dominated by its mortar constituent. Under monotonic, sustained and cyclic loading, the behavior of mortar more closely resembles that of concrete than it does cement paste.
Martin, J.L., Darwin, D., Terry, R.E., "Cement Paste, Mortar and Concrete Under Monotonic, Sustained and Cyclic Loading," SM Report No. 31, Research Grant No. CEE-8116349, The National Science Foundation, October 1991, 176 pp.
http://hdl.handle.net/1808/20428
https://orcid.org/0000-0001-5039-3525
Cement Paste, Mortar and Concrete Under Monotonic, Sustained and Cyclic Loading
oai:kuscholarworks.ku.edu:1808/202162023-06-21T19:46:10Zcom_1808_231col_1808_13465col_1808_19739
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Bashur, Fuad K.
author
Darwin, David
author
1976-12
Bashur, F.K., and Darwin, D., "Nonlinear Model for Reinforced Concrete Slabs," CRINC Report SL-76-03, Research Grant ENG76-09444, The National Science Foundation, December 1976, 135 pp.
http://hdl.handle.net/1808/20216
https://orcid.org/0000-0001-5039-3525
Nonlinear Model for Reinforced Concrete Slabs
oai:kuscholarworks.ku.edu:1808/326912022-04-08T08:01:00Zcom_1808_231col_1808_13465
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Ameen, Shahedreen
author
Lequesne, Rémy D.
author
Lepage, Andrés
author
2020
Four large-scale coupling beams were tested under fully reversed cyclic loads to investigate the effects on behavior of diagonal bar grade (60 or 120 [420 or 830]), beam shear stress (9.5 or 14√fc′, psi [0.79 or 1.17√fc′, MPa]), and longitudinal bar detailing (either terminated near the beam-wall interface or developed into the walls). Coupling beam chord rotation capacity was 7.1% for the beam with Grade 60 (420) bars and between 5.1 and 5.6% for the beams with Grade 120 (830) bars, a difference likely due to having hoops spaced at 3.4db and 4db for Grade 60 and 120 (420 and 830) bars, where db is the diagonal bar diameter. Effective stiffness, energy dissipation, and residual chord rotations were approximately inversely proportional to bar grade. Developing the secondary longitudinal reinforcement reduced rotation demands at beam ends but did not improve deformation capacity. Beam shear stress did not affect beam chord rotation capacity.
Ameen, S., Lequesne, R.D., Lepage, A., (2020). "Diagonally Reinforced Concrete Coupling Beams with Grade 120 (830) High-Strength Steel Bars". ACI Structural Journal. Vol. 117, No. 6. DOI: 10.14359/51728067
http://hdl.handle.net/1808/32691
10.14359/51728067
https://orcid.org/ 0000-0003-2146-7243
Bar buckling
Chord rotation capacity
Coupled walls
High-strength reinforcement
Reversed cyclic loading
Shear stress
Diagonally Reinforced Concrete Coupling Beams with Grade 120 (830) High-Strength Steel Bars
oai:kuscholarworks.ku.edu:1808/318672021-10-09T08:00:41Zcom_1808_231col_1808_13465col_1808_19739
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O’Reilly, Matthew
author
Vosough-Grayli, Pooya
author
Darwin, David
author
2021-01
The corrosion resistance of ASTM A1035 CL (nominal Cr content of 2%), CM (nominal Cr content of 4%), and Type CS (nominal Cr content of 9%) steel reinforcing bars produced by MMFX Technologies under the respective trade names ChromX 2100, 4100, and 9100 were evaluated in uncracked concrete. The bars were tested both in the as-rolled condition as well as after sandblasting to remove mill scale. The corrosion performance of the ChromX bars was compared to that of conventional (ASTM A615) reinforcement in previous studies.
The ChromX bars exhibited a critical chloride corrosion threshold between 1.4 and 2.9 times greater than the critical chloride threshold of conventional reinforcement, with the ChromX 9100 bars exhibiting higher chloride thresholds and lower corrosion rates after initiation than the other ChromX bars. The average corrosion rate after initiation of ChromX bars ranged from 15% to 31% that of conventional reinforcing steel. Sandblasting was effective in decreasing the corrosion rate after initiation for ChromX bars, but did not significantly alter the chloride threshold.
O’Reilly, M., Vosough-Grayli, P., and Darwin, D., “Corrosion Performance of ChromX 2100, 4100, and 9100 Bars,” SL Report 21-1, The University of Kansas Center for Research, Inc., Lawrence, KS, January 2021, 34 pp
http://hdl.handle.net/1808/31867
https://orcid.org/0000-0003-3968-4342
https://orcid.org/0000-0002-6671-698X
https://orcid.org/0000-0001-5039-3525
ASTM A1035
Chromium
ChromX
Concrete
Corrosion
Reinforcing steel
Corrosion Performance of ChromX 2100, 4100, and 9100 Bars
oai:kuscholarworks.ku.edu:1808/204112018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
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Hester, Cynthia J.
author
Salamizavaregh, Shahin
author
Darwin, David
author
McCabe, Steven L.
author
1991-05
The effects of epoxy coating and transverse reinforcement on the splice strength of reinforcing bars in concrete are described. Tests included 65 beam and slab splice specimens for members containing No. 6 and No. 8 bars. The average coating thickness ranged from 6 to 11 mis. Three deformation patterns were used in the study. All but one group of specimens contained Class B ACI/Class C AASHTO splices. The results of the current study are analyzed, along with the results of 48 specimens from earlier studies and used to develop improved development length modification factors for use with epoxy coated bars. Epoxy coatings are found to significantly reduce splice strength. However, the extent of the reduction is less than used to select the development length modification factors in the 1989 AASHTO Bridge Specifications and 1989 ACI Building Code. The percentage decrease in splice strength caused by epoxy coating is independent of the degree of confining reinforcement, which provides approximately the same percentage increase in the strength of splices of both coated and uncoated reinforcement. A development length modification factor of 1.35 is applicable for design with epoxy-coated reinforcement. An alternate factor of 1.20 is applicable for epoxy-coated bars with a minimum amount of transverse reinforcement, if the positive effects of that transverse reinforcement are not already taken into account in the design provisions. The 1.20 factor is, thus, not applicable to the ACI Building Code but is applicable to the AASHTO Bridge Specifications. This report is the third in a continuing series describing research at the University of Kansas to gain a better understanding and develop accurate design procedures that reflect the changes in bond strength caused by the use of epoxy coating on reinforcing bars.
Hester, C.J., Salamizavaregh, S., Darwin, D., and McCabe, S.L., "Bond of Epoxy-Coated Reinforcement to Concrete: Splices," SL Report 91-1, The Kansas Department of Transportation, May 1991, 69 pp.
http://hdl.handle.net/1808/20411
https://orcid.org/0000-0001-5039-3525
Bond of Epoxy-Coated Reinforcement to Concrete: Splices
oai:kuscholarworks.ku.edu:1808/233362018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Darwin, David
author
Lutz, LeRoy A.
author
Zuo, Jun
author
2005
Criteria recommended by ACI Committee 408 on development and lap splice length design for straight reinforcing bars in tension are presented in code format and compared with those in ACI 318-05, Building Code Recommendations for Structural Concrete. The recommended criteria produce designs with improved reliability compared to those in ACI 318. Development lengths are longer than those in ACI 318 for conditions of low cover or confinement, but shorter for bars with higher degrees of confinement, provided by added cover and transverse reinforcement and wider spacing between bars, and for normalweight concretes with strengths between 10,000 and 16,000 psi (70 and 110 MPa).
Darwin, D., Lutz, L.A., and Zuo, J., "Recommended Provisions and Commentary on Development and Lap Splice Lengths for Deformed Reinforcing Bars in Tension," ACI Structural Journal V. 102, No. 6, November-December, 2005, pp 892-900.
http://hdl.handle.net/1808/23336
https://orcid.org/0000-0001-5039-3525
Bar ribs
Bond
Development length
High relative rib area
Reinforcing bars
Splice length
Recommended Provisions and Commentary on Development and Lap Splice Lengths for Deformed Reinforcing Bars in Tension
oai:kuscholarworks.ku.edu:1808/234202018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Darwin, David
author
McCabe, Steven L.
author
Idun, Emmanuel K.
author
Schoenekase, Steven P.
author
1992
An expression that accurately represents development and splice strength as a function of concrete cover and bar spacing is developed. The expression is then used to establish and evaluate modifications to the bond and development provisions of the ACI Building Code (AVI 318-89) for bars in concrete members that are not confined by transverse reinforcement. The expression for development and splice strength is similar in form to expression for development and splice strength is similar in form to expressions developed by Orangun, Jirsa, Breen (1975, 1977) but is obtained using techniques that limit the effects of unintentional bias in the test data. The resulting expression provides a more accurate representation of development and splice strength than do the earlier expressions, and it provides better guidance when there is a significant difference between the concrete cover and one-half of the clear spacing between bars. Proposals for new design cirteria, including one under study by ACI Committee 318, are compared. Each of the new proposals contains design criteria that are superior to the current development length provisions (ACI 318089); however, the criteria differ in terms of relative safety, economy, and ease of application. Side-by-side comparisons in design offices are recommended. In All cases, an additional development length modification factor of 1.1 is recommended for reinforcing steels with specified yield strengths in excess of 60,000 psi (414 MPa).
Darwin, D., McCabe, S. L., Idun, E. K., and Schoenekase, S. P., "Development Length Criteria: Bars Not Confined by Transverse Reinforcement," ACI Structural Journal Vol. 83, No. 94, November-December 1992, pp. 709-720.
http://hdl.handle.net/1808/23420
https://orcid.org/0000-0001-5039-3525
Bridge specifications
Building codes
Deformed reinforcement
Development
Lap connections
Reinforcing steels
Splicing
Structural engineering
Development Length Criteria: Bars Not Confined by Transverse Reinforcement
oai:kuscholarworks.ku.edu:1808/326942022-04-08T08:00:54Zcom_1808_231col_1808_13465
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Huq, Mohammad Sajedul
author
Burgos, Erick A.
author
Lequesne, Rémy D.
author
Lepage, Andrés
author
2021-01
Six large-scale reinforced concrete T-shaped slender walls were tested under reversed cyclic loading to study the effects of reinforcing bar mechanical properties on wall deformation capacity. Effects on lateral stiffness and hysteretic energy dissipation were also quantified. Primary variables included reinforcement yield stress and the ratio of tensile-to-yield strength (ft/fy). An additional aim of the tests was to determine the minimum uniform elongation (strain at peak stress) and fracture elongation required of high-strength reinforcing bars for use in earthquake-resistant structures. The walls were not subjected to axial loads other than the weight of the loading apparatus and self-weight. The T-shaped walls, with a specified concrete compressive strength of 8 ksi (55 MPa), had a 100 in. (2540 mm) long stem joining a single 100 in. (2540 mm) long flange, both 10 in. (254 mm) thick. All walls had a nominal shear span of 300 in. (7620 mm). The control specimen T1 was constructed with conventional Grade 60 (420) reinforcement (where Grade corresponds to the specified yield stress of reinforcement). Walls T2, T3, T4, and T6 were constructed with Grade 100 (690) reinforcement and T5 with Grade 120 (830) reinforcement. Test results showed that regardless of the reinforcement grade, walls designed for similar flexural strength using longitudinal reinforcement with ft/fy between 1.18 and 1.39, uniform elongation not less than 6%, and fracture elongation not less than 10% had similar strengths and drift ratio capacities. The effective initial stiffness and hysteretic energy dissipation index for walls with high-strength reinforcement (T2 through T6) were approximately 70%, on average, of those for the wall with conventional reinforcement (T1).
Huq, M.S., Burgos, E.A., Lequesne, R.D., Lepage, A., (2021). "High-Strength Steel Bars in Earthquake-Resistant Reinforced Concrete T-Shaped Walls". ACI Structural Journal, vol. 118, no. 1. DOI: 10.14359/51728091
http://hdl.handle.net/1808/32694
10.14359/51728091
https://orcid.org/ 0000-0003-2146-7243
Deformation capacity
Fracture elongation
High-strength reinforcement
Reversed cyclic loading
Slender walls
Tensile-to-yield strength ratio
Uniform elongation
High-Strength Steel Bars in Earthquake-Resistant Reinforced Concrete T-Shaped Walls
oai:kuscholarworks.ku.edu:1808/234272018-02-23T18:27:10Zcom_1808_231col_1808_13465col_1808_19739
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Cheng, Min-Yuan
author
Hung, Shih-Ching
author
Lequesne, Rémy D.
author
Lepage, Andrés
author
2016
Results are reported from reversed cyclic tests of five large-scale squat wall specimens reinforced with steel bars having a specified yield strength of either 60 or 115 ksi (413 or 792 MPa). Two specimens were designed for a shear stress of 5√fc′ psi (0.42√fc′ MPa) and the other three 9√fc′ psi (0.75√fc′ MPa). Boundary element confining reinforcement complied with the requirements of Chapter 18 of ACI 318-14 in all but one specimen, which had 50% of the required transverse boundary element reinforcement. Specimens constructed with Grade 115 steel had similar strength and exhibited 20% greater drift capacity than those with Grade 60 steel. Use of Grade 115 steel tended to control the softening effect of sliding at the base of the wall and to increase the component of drift due to reinforcement strain penetration into the foundation.
Cheng, M.-Y., Hung, S.-C., Lequesne, R. D., and Lepage, A., "Earthquake-Resistant Squat Walls Reinforced with High-Strength Steel," ACI Structural Journal, 113(5), 2016, pp.1065-1076.
http://hdl.handle.net/1808/23427
Crack width
Deformation capacity
Displacement reversals
Low-rise wall
Shear strength
Earthquake-Resistant Squat Walls Reinforced with High- Strength Steel
oai:kuscholarworks.ku.edu:1808/263062018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Lafikes, James
author
Khajehdehi, Rouzbeh
author
Feng, Muzai
author
O’Reilly, Matthew
author
Darwin, David
author
2018-04
Supplementary cementitious materials (SCMs) are used in conjunction with pre-wetted fine lightweight aggregate to provide internal curing, producing high-performance, low-shrinking concrete to mitigate bridge deck cracking. This study examines the density of cracks in bridge decks in Indiana and Utah that incorporated internal curing with various combinations of portland
cement and SCMs, specifically, slag cement, Class C and Class F fly ash, and silica fume, in concrete mixtures with water-cementitious material ratios ranging from 0.39 to 0.44. When compared with crack densities in low-cracking high-performance concrete (LC-HPC) and control bridge decks in Kansas, concrete mixtures with a paste content higher than 27% exhibited more
cracking, regardless of the use of internal curing or SCMs. Bridge decks with paste contents below 26% that incorporate internal curing and SCMs exhibited low cracking at early ages, although additional surveys will be needed before conclusions on long-term behavior can be made.
Lafikes, J., Khajehdehi, R., Feng, M., O’Reilly, M., and Darwin, D., “Internal Curing and Supplementary Cementitious Materials in Bridge Decks,” SL Report 18-2, University of Kansas Center for Research, Inc., Lawrence, KS, April 2018, 67 pp.
http://hdl.handle.net/1808/26306
https://orcid.org/0000-0001-5039-3525
Bridge decks
Internal curing high-performance concrete
Cracking
Lightweight aggregate
Paste content
Supplementary cementitious materials
Internal Curing and Supplementary Cementitious Materials in Bridge Decks
oai:kuscholarworks.ku.edu:1808/309862023-03-04T07:05:46Zcom_1808_231col_1808_13465
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Liu, Xiao-ming
author
Zhang, Rui
author
Han, Jie
author
Chen, Sha
author
2019-07-21
Axisymmetric concave slopes, one special type of three-dimensional (3D) slopes, may be encountered in mining and civil engineering practice. Analysis of 3D slopes is generally complex and mostly relies on complicated numerical simulations. This paper proposes an elastoplastic solution for determining the additional shear resistances due to spatial effects of axisymmetric concave slopes. By incorporating the extra antislide forces, this paper proposes a simplified two-dimensional (2D) limit equilibrium procedure for the stability analysis of axisymmetric concave slopes. Combined with an iteration algorithm, the procedure can obtain the factors of safety for axisymmetric concave slopes in a simple and efficient way. Comparisons of the results from the proposed method and the numerical software FLAC3D are performed to demonstrate the validity of the proposed method for practical applications. Finally, the effects of several key parameters on the stability of axisymmetric concave slopes are investigated through a parametric study.
Xiao-ming Liu, Rui Zhang, Jie Han, Sha Chen, "Stability Analysis of Axisymmetric Concave Slopes Based on Two-Dimensional Limit Equilibrium Approach considering Additional Shear Resistance", Advances in Civil Engineering, vol. 2019, Article ID 8491637, 10 pages, 2019. https://doi.org/10.1155/2019/8491637
http://hdl.handle.net/1808/30986
10.1155/2019/8491637
https://orcid.org/0000-0002-3090-3994
https://orcid.org/0000-0002-0367-3812
Stability Analysis of Axisymmetric Concave Slopes Based on Two-Dimensional Limit Equilibrium Approach considering Additional Shear Resistance
oai:kuscholarworks.ku.edu:1808/204372018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Hanks, David L.
author
Darwin, David
author
McCabe, Steven L.
author
1993-03
The effects of beam width on the cyclic behavior of reinforced concrete beamto-column connections are investigated. A new procedure, which takes into consideration the influence of a member's strength, stiffness, and load history on cyclic performance, is developed to predict the number of cycles to failure and energy dissipation capacity per cycle in terms of beam design and load parameters. A parametric investigation is performed to quantify and evaluate the effect of changes in flexural and shear strength and geometry on the predicted number of cycles to failure. Four lightly reinforced concrete cantilever beams, representing exterior beamto-column connections in a moment resistant frame, were tested and compared to earlier tests to evaluate the effect of beam width on member response under severe cyclic loading. The overall dimensions of the specimens and the design strength of the columns were identical. The flexural reinforcement ratios of the beams were 0.34 or 0.51% and the maximum applied shear stress varied from 64 to 105 psi. The ratio of positive to negative moment beam reinforcement at the column face was 0.5 or 1.0. The size and spacing of the transverse reinforcement did not vary between specimens and provided a nominal stirrup shear capacity of 79 psi. The nominal concrete strength was 4,000 psi. The ratio of beam width-to-effective depth remained constant at 0.95. Specimen response is evaluated based on the number of cycles to failure, energy dissipation capacity, and Energy Dissipation Index, D;. Test results from the current study are compared to previous research results for narrow beams fabricated with the same reinforcement and subjected to the same load history. A rational procedure, based on a physical interpretation of the load-deflection hysteresis response of reinforced concrete beams, is developed to predict the number of cycles to failure and the energy dissipation capacity per cycle in terms of a beam's design and loading parameters. A parametric investigation is perlormed to evaluate the effects of a change in flexural and shear strength and geometry on the preclicted number of cycles to failure. Based on the response of the beams investigated in the current study, an increase in the ratio of positive to negative moment reinforcement results in an increase in energy dissipated. For the wide beams with the same geometry and flexural and shear reinforcement, an increase in the clisplacement ductility factor decreases the number of cycles to failure and energy clissipation capacity. A comparison of wide and narrow beam test results shows that an increase in width increases the number of cycles to failure and energy dissipation capacity. An increase in the predicted number of cycles to failure is obtained with 1) a decrease in the maximum applied shear stress and root-mean-square clisplacement ductility factor, and 2) an increase in the nominal stirrup strength, ratio of positive to negative moment reinforcement, and ratio of beam width-to-stirrup spacing. The findings of the parametric investigation show that, for the beam used in the case study, the least improvement in cyclic perlormance is obtained through an increase in concrete strength. The most effective means available to increase cyclic perlorrnance is to increase the amount of positive moment reinforcement within the hinging regions.
Hanks, D.L., Darwin, D., McCabe, S.L., "Predicting the Cyclic Behavior of Reinforced Concrete Beams," SM Report No. 33, Research Grant PFR 79-24696, The National Science Foundation, March 1993, 250 pp.
http://hdl.handle.net/1808/20437
https://orcid.org/0000-0001-5039-3525
Predicting the Cyclic Behavior of Reinforced Concrete Beams
oai:kuscholarworks.ku.edu:1808/276762020-01-09T09:00:45Zcom_1808_231col_1808_13465col_1808_19739
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Weber-Kamin, Alexander S.
author
Lequesne, Rémy D.
author
Lepage, Andrés
author
2019-01
The use of high-strength steel bars in reinforced concrete coupling beams is expected to reduce reinforcement congestion. A series of tests was conducted to investigate the effects of high-strength reinforcement on coupling beam behavior. This report summarizes the test program and test results.
Eleven large-scale coupling beam specimens were tested under fully reversed cyclic displacements of increasing magnitude. The main variables of the test program included: yield stress of the primary longitudinal reinforcement (Grade 80, Grade 100, and Grade 120 [550, 690, and 830]), span-to-depth (aspect) ratio (1.5, 2.5, and 3.5), and layout of the primary longitudinal reinforcement (diagonal [D] and parallel [P]). All beams had the same nominal concrete compressive strength (8,000 psi [55 MPa]) and cross-sectional dimensions (12 by 18 in. [305 by 457 mm]). Beams were designed for a target shear strength based on the upper limits specified in ACI 318-14. All transverse reinforcement was Grade 80 (550), except one specimen that had Grade 120 (830) transverse reinforcement.
The test program is documented by presenting the details of specimen construction, test setup, instrumentation, and loading protocol. Documentation of test results include material properties and cyclic force-deformation response.
Weber-Kamin, A. S., Lequesne, R. D., and Lepage, A., “RC Coupling Beams with High-Strength Steel Bars: Summary of Test Results,” SL Report 19-1, The University of Kansas Center for Research, Inc., Lawrence, KS, January 2019, 133 pp.
http://hdl.handle.net/1808/27676
RC Coupling Beams with High-Strength Steel Bars: Summary of Test Results
oai:kuscholarworks.ku.edu:1808/340992023-04-18T06:05:42Zcom_1808_231col_1808_13465col_1808_19739
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Yasso, Samir
author
Darwin, David
author
O’Reilly, Matthew
author
2021-11-01
The effects of concrete tail cover and tail kickout on the anchorage strength of hooked bars were investigated. The study included 195 simulated beam-column joint specimens containing two No. 5, 8, or 11 (No. 16, 25, or 36) hooked bars. Bar stresses at anchorage failure ranged from 33,000 to 141,000 psi (228 to 972 MPa), and concrete compressive strengths ranged from 4490 to 16,180 psi (31 to 112 MPa). Tail cover ranged from 3/4 to 3-5/8 in. (19 to 92 mm) and tail kickout occurred for approximately 7% of the hooked bars used in the analysis. Hooked bars were placed inside or outside the column core with or without confining reinforcement in the joint region. Tail kickout was only observed in conjunction with other modes of failure and was not, in any case, the only mode of failure. The likelihood of tail kickout increases for hooked bars placed outside the column core, as compared to hooked bars placed inside the column core, as confining reinforcement within the joint region decreases, and as the size of the hooked bar increases. The anchorage strength of hooked bars with a 90-degree bend angle is not affected by hook tail covers as low as 3/4 in. (19 mm) or tail kickout at failure.
Yasso, S., Darwin, D., and O’Reilly, M. O., “Effects of Concrete Tail Cover and Tail Kickout on Anchorage Strength of 90-Degree Hooks,” ACI Structural Journal, Vol. 118, No. 6, Nov. 2021, pp. 227-236 DOI: 10.14359/51732990.
https://hdl.handle.net/1808/34099
10.14359/51732990
https://orcid.org/0000-0002-5160-5750
https://orcid.org/0000-0001-5039-3525
https://orcid.org/0000-0003-3968-4342
Beam-column joint
High-strength concrete
High-strength steel
Hooked bars
Reinforced concrete
Tail cover
Tail kickout
Effects of Concrete Tail Cover and Tail Kickout on Anchorage Strength of 90-Degree Hooks
oai:kuscholarworks.ku.edu:1808/346642023-08-01T06:05:47Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
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Dhungel, Sujan
author
Darwin, David
author
O’Reilly, Matthew
author
2023-07
The effects of total internal (TI) water, provided by normalweight coarse and fine aggregates and pre-wetted fine lightweight aggregate (LWA), in the range of 6.8 to 17.3%, corresponding to internal curing (IC) water in the LWA ranging from 0 to 15.1%, by weight of cementitious materials, on the freeze-thaw durability and scaling resistance of 12 concrete mixtures are evaluated. Cementitious materials consist of portland cement only or portland cement with a 30% weight replacement by slag cement. The coarse aggregate consists of limestone (with an oven-dry absorption of 1.8%) or granite (with an oven-dry absorption of 0.6%), which provide 5.5 to 5.6% or 1.9% internal curing water by the weight of cementitious materials, respectively.
All of the mixtures with the limestone coarse aggregate failed the test, with the average dynamic modulus of elasticity (EDYN) dropping below 95% of the initial value well before the 660 freeze-thaw cycles specified by the Kansas Department of Transportation, demonstrating that the limestone itself is susceptible to freeze-thaw damage. The mixtures containing granite coarse aggregate had an average relative EDYN above 95% of the initial value at 660 freezethaw cycles in the test of freeze-thaw durability at TI water contents up to 15.7% (corresponding to an IC water content of 13.4% from the LWA) by the weight of cementitious materials. The only mixture with granite coarse aggregate that failed the test had a 30% weight replacement of portland cement with slag cement and a TI water content of 17.3% by weight of the cementitious materials (corresponding to 15.1% IC water from LWA). This result indicates that it is possible to have too much internal curing water. In the scaling test, the mixtures with granite coarse aggregate, all of which contained LWA, had lower mass losses than mixtures with limestone coarse aggregate, although all but one of the 12 mixtures passed the test with a cumulative 56-day mass loss below 0.1 lb/ft2. For concrete with granite coarse aggregate, the mass loss increased slightly with increased TI water content when portland iv cement was used as the only cementitious material. When a 30% weight replacement of portland cement with slag cement was used, the mass loss increased for a TI water content above 12.5% (corresponding to 9.9% IC water from LWA), but remained below the failure limit, suggesting no benefits for a TI water content above 12.5% by the weight of cementitious materials. The mixtures with portland cement as the only cementitious material had lower mass losses than the mixtures with a 30% weight replacement of portland cement with slag cement for the same coarse aggregate. Pre-wetted fine lightweight aggregate (LWA) for internal curing (IC) should equal 7 to 8% by weight of cementitious materials. The results provide no evidence that it would be advantageous to stray much above these values and demonstrate that high TI/ IC water contents can be deleterious.
Dhungel, S., Darwin, D., and O’Reilly, M., “Effects of Total Internal Water Content on Freeze-Thaw Durability and Scaling Resistance of Internally-Cured Concrete,” SM Report No. 154, University of Kansas Center for Research, Inc., Lawrence, KS, July 2023, 106 pp.
https://hdl.handle.net/1808/34664
https://orcid.org/0000-0001-5039-3525
https://orcid.org/0000-0003-3968-4342
Bridge decks
Freeze-thaw durability
Internal curing
Lightweight aggregate
Low-cracking high-performance concrete
Scaling resistance
Slag cement
Specifications
Total internal water
Effects of Total Internal Water Content on Freeze-Thaw Durability and Scaling Resistance of Internally-Cured Concrete
oai:kuscholarworks.ku.edu:1808/203262018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Benitez, Manuel A.
author
Darwin, David
author
Donahey, Rex C.
author
1990
Procedures for calculating the deflections of composite beams with web openings are described. Initially, a matrix formulation is used. Modeling assumptions are verified by comparison with experimental data, and recommendations for practical application of the matrix analysis procedures are made. The results of the comparison are used to develop a design aid for estimating the maximum deflection of beams with web openings and an expression for calculating the deflection across a web opening. The work demonstrates that, in most cases, a single web opening often has little effect on the total deflection of a composite beam. There are, however, important cases where the effect can be significant. The effects of an opening and of shear deflections are of the same order. Ignoring both the web opening and shear deformation can lead to significant error. The matrix stiffness method, the design aid, and closed form equations provide reasonable estimates of both total deflection and deflection across an opening.
Benitez, M.A., Darwin, D., and Donahey, R.C., "Deflections of Composite Beams with Web Openings," SL Report 90-3, The University of Kansas Structural Engineering and Materials Laboratory, June 1990, 64 pp.
http://hdl.handle.net/1808/20326
https://orcid.org/0000-0001-5039-3525
Deflections of Composite Beams with Web Openings
oai:kuscholarworks.ku.edu:1808/187122018-07-13T17:15:23Zcom_1808_231col_1808_13465
00925njm 22002777a 4500
dc
McEnroe, Bruce M.
author
Young, Bryan
author
Shelley, John Edwin
author
2014-04-01
The reference reach method is commonly used for natural stream design. In the reference reach approach, a stable reach is selected to serve as the design template for a design reach. The planform and profile of this reference reach must be scaled to fit the design site. Currently, the leading method for scaling uses a simple ratio of cross-sectional areas. This paper presents a simple method that employs hydraulic scaling to size the design reach to accommodate the desired bankfull flow. The method introduced in this paper is easy to use, does not require additional survey data, and should lead to more robust channel design.
McEnroe, B. , Young, C. and Shelley, J. (2014) Scaling of Reference Reach for Desired Bankfull Discharge. International Journal of Geosciences, 5, 475-477. http://dx.doi.org/10.4236/ijg.2014.55045.
http://hdl.handle.net/1808/18712
10.4236/ijg.2014.55045
Channel design
Restoration
Streams
Stream Improvement
Scaling of Reference Reach for Desired Bankfull Discharge
oai:kuscholarworks.ku.edu:1808/325862022-03-16T08:00:56Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Rulon, Ryan
author
Lequesne, Rémy D.
author
Lepage, Andrés
author
Darwin, David
author
2022-03
Rulon, R., Lequesne, R. D., Lepage, A., and Darwin, D., “Lap Splicing of Large High-Strength Steel Reinforcing Bars,” SM Report No. 148, The University of Kansas Center for Research, Inc., Lawrence, KS, March 2022, 136 pp.
http://hdl.handle.net/1808/32586
https://orcid.org/0000-0001-5039-3525
Lap Splicing of Large High-Strength Steel Reinforcing Bars
oai:kuscholarworks.ku.edu:1808/202182018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Mockry, Eldon F.
author
Darwin, David
author
1980
Mockry, E.F., and Darwin, D., "Simplified Design of Slender Reinforced Concrete Columns," SM Report No. 2, University of Kansas Center for Research, Inc., Lawrence, Kansas, July 1980, 312 pp.
http://hdl.handle.net/1808/20218
https://orcid.org/0000-0001-5039-3525
Simplified Design of Slender Reinforced Concrete
oai:kuscholarworks.ku.edu:1808/256542018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Darwin, David
author
O’Reilly, Matthew
author
Browning, JoAnn
author
Xing, Lihua
author
2014-01-20
The bond strength of four sets of reinforcing bars is evaluated, two each with No. 5 and No. 10 (No. 16 and No. 32) bars, which have, respectively, nominal diameters of 0.625 and 1.27 in. (15.9 and 32.3 mm). One bar of each size satisfies the criterion for maximum deformation spacing in ASTM reinforcing bar specifications, while the other has deformations that exceed the maximum spacing. All bars exceed the requirements for minimum deformation height. Research related to the effect of deformation properties on bond strength, including the research used to establish the requirements for deformations in ASTM reinforcing bar specifications, is also reviewed. The test results match earlier research and demonstrate that (1) bond strength is not governed by the specific value of deformation height or spacing, but by the combination of the two as represented by the relative rib area of the bars and (2) the bond strength of the bars with deformation spacings that exceed those in ASTM reinforcing bar specifications is similar to the bond strength of the bars that meet the specification. Based on this and prior research, it is recommended that ASTM reinforcing bar specifications be modified to allow for deformation spacing up to 90 % (currently a maximum of 70 %) of the bar diameter provided the ratio of deformation height to deformation spacing is greater than or equal to the minimum ratio for bar deformations meeting the current requirements in ASTM reinforcing bar specifications.
Darwin, D., O’Reilly, M., Browning, J., and Xing, L. "Case for Changing Reinforcing Bar Deformation Spacing Requirements," Journal of Testing and Evaluation, Vol. 42, No. 2, 2014, pp. 368-374, https://doi.org/10.1520/JTE20120250. ISSN 0090-3973
http://hdl.handle.net/1808/25654
10.1520/JTE20120250
https://orcid.org/0000-0001-5039-3525
Bond (concrete to reinforcement)
Deformed reinforcement
Relative deformation area
Relative rib area
Structural engineering
Case for Changing Reinforcing Bar Deformation Spacing Requirements
oai:kuscholarworks.ku.edu:1808/255912017-12-07T09:01:58Zcom_1808_231col_1808_13465
00925njm 22002777a 4500
dc
Han, Jie
author
Song, S.
author
Xu, C.
author
2016-04
A geosynthetic-reinforced pile-supported (GRPS) embankment that consists of embankment fill, geosynthetic, piles, and foundation soils is a complex soil–structure system. Its key load transfer mechanisms include soil arching and tensioned membrane effects and subsoil resistance. Type of embankment fill (cohesive or cohesionless) and type of pile (end-bearing or floating) are expected to affect these load transfer mechanisms; however, their influence has not been well investigated. Six scaled model tests were conducted in this study to investigate the influence of the embankment fill properties, the clear spacing of pile caps, and the pile type on soil arching and tensioned membrane effects. This study used cohesive and cohesionless embankment fills and end-bearing and floating piles. The test results show that the cohesive embankment fill strengthened the soil-arching effect, increased the pile efficacy, and reduced the settlements of the subsoil between pile caps and the embankment crest under the same load as compared with the cohesionless embankment fill. The soil arching-effect was inversely proportional to the clear spacing of pile caps. Soil arching initiated at a low ratio of the embankment height to the clear spacing of pile caps (i.e. 0.5 to 0.7) and became stable at a higher ratio (i.e. 1.1 to 1.5). The embankment height when the soil arching becomes stable is also referred to as the critical height, at which full soil arching is formed. The measured vertical earth pressures at the edges of the pile caps were higher than those in the middle of the pile caps in all six model tests. When the end-bearing or floating piles were used, the loads on the piles (i.e. the pile efficacy) increased during the construction of the embankment. However, when the floating piles started to penetrate into the underlying soil under a higher load; the pile efficacy decreased with the embankment and the surcharge load. Floating piles resulted in less soil arching and larger settlement.
Xu, C., Song, S., & Han, J. (2015). Scaled model tests on influence factors of full geosynthetic-reinforced pile-supported embankments. Geosynthetics International, 23(2), 140-153.
http://hdl.handle.net/1808/25591
10.1680/jgein.15.00038
Geosynthetics
Earth pressure
Embankment
Pile
Settlement
Soil arching
Tensioned membrane
Scaled model tests on influence factors of full geosynthetic-reinforced pile-supported embankments
oai:kuscholarworks.ku.edu:1808/335562022-09-22T08:00:51Zcom_1808_231col_1808_13465
00925njm 22002777a 4500
dc
Khosravi, Mohammad
author
Leon-Corwin, Maggie
author
Ritchie, Liesel
author
Smallegan, Stephanie
author
Stark, Nina
author
Stephens, Max
author
Sutley, Elaina J.
author
Athanasopoulos-Zekkos, Adda
author
2020-07-10
The User Forum is a Natural Hazards Engineering Research Infrastructure (NHERI)-wide group focused on providing the NHERI Council with independent advice on community user satisfaction, priorities, and needs relating to the use and capabilities of NHERI. The User Forum has representation across NHERI activities, including representatives working directly with the Network Coordination Office (NCO), Education and Community Outreach (ECO), Facilities Scheduling, and Technology Transfer efforts. The User forum also provides feedback on the NHERI Science Plan. As the community voice within the governance of NHERI, the User Forum is composed of members nominated and elected by the NHERI community for a specified term of 1–2 years. User Forum membership spans academia and industry, the full breadth of civil engineering and social science disciplines, and widespread hazard expertise including earthquakes, windstorms, and water events. One of the primary responsibilities of the User Forum is to conduct an annual community user satisfaction survey for NHERI users, and publish a subsequent Annual Community Report. Measuring user satisfaction and providing this feedback to the NHERI Council is critical to supporting the long-term sustainability of NHERI and its mission as a multidisciplinary and multi-hazard network. In this paper, the role and key activities of the User Forum are described, including User Forum member election procedures, User Forum member representation and roles across NHERI activities, and the processes for measuring and reporting user satisfaction. This paper shares the user satisfaction survey distributed to NHERI users, and discusses the challenges to measuring community user satisfaction based on the definition of user. Finally, this paper discusses the evolving approaches of measuring user satisfaction using other methods, including engaging with the twelve NHERI research infrastructures.
Khosravi M, Leon-Corwin M, Ritchie L, Smallegan S, Stark N, Stephens M, Sutley EJ and Athanasopoulos-Zekkos A (2020) Measuring User Satisfaction for the Natural Hazards Engineering Research Infrastructure Consortium. Front. Built Environ. 6:101. doi: 10.3389/fbuil.2020.00101
http://hdl.handle.net/1808/33556
10.3389/fbuil.2020.00101
User satisfaction
NHERI
Evaluation
Hazards
Experimental facility
Consortium
Measuring User Satisfaction for the Natural Hazards Engineering Research Infrastructure Consortium
oai:kuscholarworks.ku.edu:1808/199362018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Lafikes, James
author
Storm, Scott
author
Darwin, David
author
Browning, JoAnn
author
O’Reilly, Matthew
author
2011-10-31
Lafikes, J., Storm, S., Darwin, D., Browning, J., and O'Reilly, M., "Stainless Steel Reinforcement as a Replacement for Epoxy Coated Steel in Bridge Decks," Annual Report for FY 2011, ODOT SPR Item Number 2231, also University of Kansas Center for Research, Inc., Lawrence, KS, October 2011, 71 pp.
http://hdl.handle.net/1808/19936
https://orcid.org/0000-0001-5039-3525
Stainless Steel Reinforcement as a Replacement for Epoxy Coated Steel in Bridge Decks
oai:kuscholarworks.ku.edu:1808/300072020-02-25T09:00:54Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Darwin, David
author
Khajehdehi, Rouzbeh
author
Feng, Muzai
author
Lafikes, James
author
Ibrahim, Eman
author
O’Reilly, Matthew
author
2017-10
The goal of this study was to implement cost-effective techniques for improving bridge deck service life through the reduction of cracking. Work was performed both in the laboratory and in the field, resulting in the creation of Low-Cracking High-Performance Concrete (LC-HPC) specifications that minimize cracking through the use of low slump, low paste content, moderate compressive strength, concrete temperature control, good consolidation, minimum finishing, and extended curing. This paper documents the performance of 17 decks constructed with LC-HPC specifications and 13 matching control bridge decks based on crack surveys. The LC-HPC bridge decks exhibit less cracking than the matching control decks in the vast majority of cases. Only two LC-HPC bridge decks have higher overall crack densities than their control decks, which are the two best performing control decks in the program, and the differences are small. The majority of the cracks are transverse and run parallel to the top layer of the deck reinforcement. The results of this study demonstrate the positive effects of reduced cement paste contents, concrete temperature control, limitations on or de-emphasis of maximum concrete compressive strength, limitations on maximum slump, the use of good consolidation, minimizing finishing operations, and application of curing shortly after finishing and for an extended time on minimizing cracking in bridge decks.
Darwin, D., Khajehdehi, R., Feng, M., Lafikes, J., Ibrahim, E., and O’Reilly, M., “Low-Cracking High-Performance Concrete (LC-HPC) for Durable Bridge Decks,” Cracking and Durability in Sustainable Concretes, American Concrete Institute Symposium Vol., SP-336, R. Leistikow and K. W. Kramer, ed., 2019, pp. 101-116.
http://hdl.handle.net/1808/30007
https://orcid.org/0000-0001-5039-3525
Bridge decks
Consolidation
Cracking
Curing
Finishing
High-performance concrete
Temperature control
Low-Cracking High-Performance Concrete (LC-HPC) for Durable Bridge Decks
oai:kuscholarworks.ku.edu:1808/266222018-11-16T16:19:41Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Ajaam, Ali Hussein
author
Yasso, Samir
author
Darwin, David
author
O’Reilly, Matthew
author
Sperry, Jayne
author
2018-07
The effect of close spacing on the anchorage strength of standard hooks is investigated. Sixty-seven simulated beam-column joint specimens were tested, each containing three, four, or six No. 5, 8, or 11 (No. 16, 25, or 36) hooked bars arranged in one or two layers with center-to-center spacing ranging from two to six bar diameters. Anchorage strengths are compared with those of specimens containing two hooked bars with spacings of six to 12 bar diameters. The results demonstrate that the provisions in ACI 318-14 tend to overestimate the anchorage strength of hooked bars as concrete compressive strength and bar size increase and as spacing between bars decreases. Decreasing center-to-center spacing below six bar diameters results in lower anchorage strengths than for hooked bars with wider spacing. The anchorage strength of hooked bars can be represented by considering the minimum of the horizontal and vertical spacing between bars.
Ajaam, A., Yasso, S., Darwin, D., O’Reilly, M., and Sperry, J., “Anchorage Strength of Closely-Spaced Hooked Bars,” ACI Structural Journal, Vol. 115, No. 4, July-Aug. 2018, pp. 1143-1152.
http://hdl.handle.net/1808/26622
10.14359/51702065
https://orcid.org/0000-0001-5039-3525
https://orcid.org/0000-0003-3968-4342
Anchorage
Beam-column joints
High-strength concrete
High-strength steel
Hooks
Reinforced concrete
Reinforcement
Spacing
Staggered hooks
Anchorage Strength of Closely Spaced Hooked Bars
oai:kuscholarworks.ku.edu:1808/203462018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Leibengood, Linda D.
author
Darwin, David
author
Dodds, Robert H., Jr
author
1984-05
The effects of the descending branch of the tensile stress-strain curve, fracture energy, grid refinement, and load-step size on the response of finite element models of notched concrete beams are studied. The width of the process zone and constraint of crack angles are investigated. Nonlinearity is 1 imited to cracking of the concrete. A limiting tensile stress criterion governs crack initiation. Concrete is represented as linear elastic prior to cracking. Cracks are modeled using a smeared representaion. The post-cracking behavior is controlled by the shape of the descending branch, fracture energy, crack angle, and element size. Unloading occurs at a slope equal to the i nitia 1 modulus of the material. load deflection curves and cracking patterns are used to evaluate the beam's response. Comparisons of the process zone size are made. All analyses are performed on a 200 x 200 x GOO mm concrete beam, with an initial notch length of 80 mm. The fracture energy, tensile strength, and shape of the descending branch interact to determine the stiffness and general behavior of the specimen. The width of the process zone has a negligible influence on the beam's response. The importance of proper crack orientation is demonstrated. The model is demonstrated to be objective with respect to grid refinement and load-step size.
Leibengood, L.D., Darwin, D., and Dodds, R.H., "Finite Element Analysis of Concrete Fracture Specimens," SM Report No. 11, University of Kansas Center for Research, Inc., Lawrence, Kansas, May 1984, 128 pp.
http://hdl.handle.net/1808/20346
https://orcid.org/0000-0001-5039-3525
Finite Element Analysis of Concrete Fracture Specimens
oai:kuscholarworks.ku.edu:1808/233832018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Darwin, David
author
1999
One hundred years ago, engineers were debating whether density, aggregate gradation, or water cement ratio controls the strength of concrete. Today, those debates have been settled, but the factors that control the behavior of concrete in compression remain controversial. The debate has now shifted to the roles played by cement paste, the interfacial transition zone between paste and aggregate, and the relative stiffness of the components. While all three ingredients play significant roles, the properties of cement paste and the heterogeneous nature of the material appear to be the key factors in the response of concrete in compression. This article highlights some of the research that demonstrates the roles played by the various constituents, with emphasis on microcracking, interfacial bond strength, and models of concrete. The reader is directed to Reference 1 for a more complete discussion of the subject.
Darwin, D., "Concrete in Compression," Concrete International, Vol. 21, No.8, Aug., 1999, pp. 82-85.
http://hdl.handle.net/1808/23383
https://orcid.org/0000-0001-5039-3525
Concrete in Compression
oai:kuscholarworks.ku.edu:1808/203982018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
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Attiogbe, Emmanuel K.
author
Darwin, David
author
1985-11
Submicroscopic cracking of cement paste and mortar under uniaxial compression is measured and correlated with applied strain and load history. Cement paste specimens with water-cement ratios of 0.7, 0.5 and 0.3 were subjected to monotonic, sustained or cyclic loading, while mortar specimens with a water-cement ratio of 0.5 were subjected to monotonic loading. One hundred and thirty ( 130) specimens were tested at ages ranging from 27 to 29 days, using a closed-loop servo-hydraulic testing machine. After loading, slices of material were removed for study at a magnification of 1 250x in a scanning electron microscope. Cracking on transverse and longitudinal surfaces was measured. Statistical and stereological models are developed to convert the surface crack distributions to three-dimensional distributions. A self-consistent model is developed tc estimate the elastic moduli of transversely isotropic cracked materials. These models are used to correlate submicrocracking with the reduction in stiffness and the shape of the stress-strain curve. The surface crack densities in cement paste and mortar are about ten times the density of bond and mortar microcracks in concrete at the same value of compressive strain. Submicrocracking accounts for a significant portion (20% to 90%) of the nonlinear respons of cement paste and mortar at all levels of applied compressive strain. As compressiVE strain increases, other mechanisms, such as large microcracks, macrocracks, and creep, play an increasingly greater role.
Attiogbe, E., and Darwin, D., "Submicroscopic Cracking of Cement Paste," SM Report No. 16, Research Grant AFOSR-85-0194, The Air Force Office of Scientific Research, November 1985, 466 pp.
http://hdl.handle.net/1808/20398
https://orcid.org/0000-0001-5039-3525
Cement paste
Compression
Concrete
Cracks (cracking)
Crack distribution
Cyclic
Engineering materials
Engineering mechanics
Microcracks
Microstructure
Monotonic
Mortar
Scanning electron microscope (SEM)
Self-consistent model
Statistics
Stereology
Strains
Stresses
Stress-strain curve
Submicrocracks
Sustained
Transverse isotropy
Submicroscopic Cracking of Cement Paste and Mortar in Compression
oai:kuscholarworks.ku.edu:1808/203472018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Brettmann, Barie B.
author
Darwin, David
author
Donahey, Rex C.
author
1984-04
The effects of superp 1 asti ci zers on concrete-steel bond strength are studied. Key variables are degree of consolidation, concrete slump, both with and without a superplasticizer, concrete temperature, and bar position. #8 deformed reinforcing bars were used with a 2 in. cover and a 10 in. bonded length. Concrete slumps ranged from 1-3/4 in. to 9 in. Three specimen depths were used. All specimens were modified cantilever beam specimens. Based on the experimental results, high slump superplasticized concrete pro vi des a 1 ower bond strength than 1 ow slump concrete of the same strength. Superpl asti ci zed concrete pro vi des a higher bond strength than high slump regular concrete with the same slump and water-cement ratio. Vibration of high slump concrete increases the bond strength compared to high slump concrete without vibration. Bond strength decreases as the amount of concrete below a bar increases, but the greatest effect appears to occur with top-cast (i.e. upper surface) bars.
Brettmann, B.B., Darwin, D., Donahey, R.C., "Effect of Superplasticizers on Concrete-Steel Bond Strength," SL Report 84-1, The University of Kansas Center for Research Inc., Lawrence, KS, April 1984, 35 pp
http://hdl.handle.net/1808/20347
https://orcid.org/0000-0001-5039-3525
Effect of Superplasticizers on Concrete-Steel Bond Strength
oai:kuscholarworks.ku.edu:1808/189152019-04-12T14:54:42Zcom_1808_231col_1808_13465
00925njm 22002777a 4500
dc
Ching, Wai-Yim
author
Rulis, Paul
author
Ouyang, Lizhi
author
Aryal, Sitaram
author
Misra, Anil
author
2010-06-24
Microstructures such as intergranular glassy films (IGFs) are ubiquitous in many structural ceramics. They control many of the important physical properties of polycrystalline ceramics and can be influenced during processing to modify the performance of devices that contain them. In recent years, there has been intense research, both experimentally and computationally, on the structure and properties of IGFs. Unlike grain boundaries or dislocations with well-defined crystalline planes, the atomic scale structure of IGFs, their fundamental electronic interactions, and their bonding characteristics are far more complicated and not well known. In this paper, we present the results of theoretical simulations using ab initio methods on an IGF model in β-Si3N4 with prismatic crystalline planes. The 907-atom model has a dimension of 14.533 Å×15.225 Å×47.420 Å. The IGF layer is perpendicular to the z axis, 16.4 Å wide, and contains 72 Si, 32 N, and 124 O atoms. Based on this model, the mechanical and elastic properties, the electronic structure, the interatomic bonding, the localization of defective states, the distribution of electrostatic potential, and the optical dielectric function are evaluated and compared with crystalline β-Si3N4. We have also performed a theoretical tensile experiment on this model by incrementally extending the structure in the direction perpendicular to the IGF plane until the model fully separated. It is shown that fracture occurs at a strain of 9.42% with a maximum stress of 13.9 GPa. The fractured segments show plastic behavior and the formation of surfacial films on the β-Si3N4. These results are very different from those of a previously studied basal plane model [J. Chen et al., Phys. Rev. Lett. 95, 256103 (2005)] and add insights to the structure and behavior of IGFs in polycrystalline ceramics. The implications of these results and the need for further investigations are discussed.
Ching, W. Y., Paul Rulis, Lizhi Ouyang, Sitaram Aryal, and Anil. Misra. "Theoretical Study of the Elasticity, Mechanical Behavior, Electronic Structure, Interatomic Bonding, and Dielectric Function of an Intergranular Glassy Film Model in Prismatic β -Si 3 N 4." Phys. Rev. B Physical Review B 81.21 (2010). http://dx.doi.org/10.1103/PhysRevB.81.214120
http://hdl.handle.net/1808/18915
10.1103/PhysRevB.81.214120
Theoretical study of the elasticity, mechanical behavior, electronic structure, interatomic bonding, and dielectric function of an intergranular glassy film model in prismatic β-Si3N4
oai:kuscholarworks.ku.edu:1808/204432018-12-27T19:15:35Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Smith, Jeffrey L.
author
Darwin, David
author
Locke, Carl E., Jr.
author
1995-04
The initial portion of the first phase of a five phase research effort to evaluate a corrosionresistant steel for reinforcing bars is descnoed. Rapid corrosion potential and time-to-corrosion (macrocell) tests are used. The test specimen consists of a No. 5 reinforcing bar embedded in a 30 mm diameter, 102 nnn long cylinder of mortar. The mortar is made using portland cement, graded Ottawa sand, and deionized water. Four different steel types are evaluated: hot-rolled regular steel, Thermex treated (quenched and tempered) regular steel, hot-rolled corrosion resistant steel, and Thermex treated corrosion resistant steeL Corrosion potential tests are perlbrmed to determine the tendency of a steel to corrode. The results for these tests are fuirly consistent, with little scatter. There is no significant difference in potentials for the four steels. The use of different test solutions did not influence the potential of the four steels. The macrocell tests are perlbrmed to determine the time-to-corrosion and the corrosion rates. The results for some of these tests are not consistent and show considerable scatter. The macrocell test is sensitive to the quality in the specimen fabrication. Because the initial tests in Phase I did not perform as intended, it is difficult to determine for certain which steel has the best corrosion resistance based on the resUlts reported here. However, the hot rolled regular steel specimens consistently exluoit the highest corrosion rate. The test solutions used at the anode and cathode in the macrocell tests appear to influence the corrosion rate and the difference in rates between the four steels. When the difference in pH of the anode and cathode solutions is decreased, the corrosion rates are reduced and the difference between the rates for the four steels is more pronounced. Based on the results of the Phase I initial tests, some modifications to the specimen fabrication procedure are reconnnended. The epoxy band should be applied in two coats. The reinforcing bar lengths should be heated after cleaning and after applying each coat in order to improve the bond between the reinforcing bar and the first epoxy coat as well as between the two coats of epoxy. Special care should be exercised when applying the epoxy band. Addition work in Phase I includes an evaluation of the effects of changing the ratio of the number of cathode to anode specimens from 3:3 to 2:1. Special care should also be exercised in the oversight of the corrosion potential and macrocell tests.
Smith, J.L., Darwin, D., Locke, C.E., Jr., "Corrosion-Resistant Steel Reinforcing Bars Initial Tests," SL Report 95-1, University of Kansas Center for Research, Inc., Lawrence, KS, April 1995, 47 pp.
http://hdl.handle.net/1808/20443
https://orcid.org/0000-0001-5039-3525
Chlorides
Concrete
Corrosion testing
Corrosion
Potentials
Macrocells
Reinforcing bars
Corrosion-Resistant Steel Reinforcing Bars Initial Test
oai:kuscholarworks.ku.edu:1808/234212018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Choi, Oan Chul
author
Hadje-Ghaffari, Hossain
author
Darwin, David
author
McCabe, Steven L.
author
1991
The effects of coating thickness, deformation pattern, and bar size on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end and splice specimens containing No.5, 6, 8, and 11 bars with average coating thicknesses ranging from 3 to 17 mils (0.08 to 0.43 mm). Three deformation patterns are evaluated. All bars are bottom~cast. Beam-end specimens have covers of two bar diameters, while splice specimens have covers that depend on bar size and are less than 2 bar diameters. The results are compared with the splice tests that were used to establish the epoxy-coated bar provisions in the 1989 A CI Building Code and 1989 AASHTO Bridge Specifications. Epoxy coatings are found to reduce bond strength significantly, but the extent of the reduction is less than that used to select the development length modification factors in the ACI Building Code and AASHTO Bridge Specifications. Coating thickness has little effect on the amount of bond strength reduction for No. 6 bars and larger. However, the thicker the coating, the greater the reduction in bond strength for No. 5 bars. In general, the reduction in bond strength caused by an epoxy coating increases with bar size. The magnitude of the reduction depends on the deformation pattern; bars with relatively larger ribbearing areas with respect to the bar cross section are affected less by the coating than bars with smaller bearing areas. This is the first in a
series of papers concerning bond of epoxy-coated reinforcement. Subsequent papers will address the effects of concrete cover, bar position, concrete strength, and transverse reinforcement.
Choi, O., Hadje-Ghaffari, H., Darwin, D., and McCabe, S. L., "Bond of of Epoxy-Coated Reinforcement: Bar Parameters," ACI Materials Journal Vol. 88, No. 26, March-April 1991, pp. 207-217.
http://hdl.handle.net/1808/23421
https://orcid.org/0000-0001-5039-3525
Bond (concrete to reinforcement)
Coatings
Deformed reinforcement
Epoxy resins
Lap connections
Pullout tests
Reinforcing steels
Splicing structural engineering
Bond of Epoxy-Coated Reinforcement: Bar Parameters
oai:kuscholarworks.ku.edu:1808/203312018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
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Darwin, David
author
Idun, Emmanuel K.
author
Zuo, Jun
author
Tholen, Michael L.
author
1995
The formulation and calculation of a reliability-based strength-reduction ( <P) factor for developed and spliced bars is described. Conventional and high relative rib area bars, both with and without confining reinforcement, are considered. The cp-factor is determined using statistically-based expressions for development/splice strength and Monte Carlo simulations of a range of beams.
A strength-reduction factor of 0.9 is obtained for the design expressions for development/splice length, based on a probability of failure in bond equal to about one-fifth of the probability of failure in bending or combined bending and compression. <P = 0.9 is incorporated into two expressions for development/splice length in a manner that is transparent to the user. A major advantage of each of the final expressions is that they provide identical values for development and splice length, removing the need to multiply development length by 1.3 or 1.7 to obtain the length of most splices.
Darwin, D., Idun, E.K., Zuo, J., Tholen, M.L., "Reliability-Based Strength Reduction Factor for Bond," SL Report 95-5, University of Kansas Center for Research, Inc., Lawrence, KS, May 1995, 51 pp.
http://hdl.handle.net/1808/20331
https://orcid.org/0000-0001-5039-3525
Bond (concrete to reinforcement)
Bridge specifications
Building codes
Deformed reinforcement
Development
Lap connections
Reinforcing steels
Relative rib area
Reliability
Splicing
Structural engineering
Variability
Reliability-Based Strength Reduction Factor For Bond
oai:kuscholarworks.ku.edu:1808/204412018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Ravikumar, S.
author
Darwin, David
author
McCabe, Steven L.
author
Pasley, Gregory P.
author
1994-03
The objective of this research is to study the shear strength of continuous lightly reinforced concrete joist systems. Six two span joists, with and without web reinforcement, and two multiple web joists without web reinforcement were tested. The main focus of this study was to determine the shear cracking capacity and to investigate load sharing between joists. Shear cracking loads are determined using crack pattern and stirrup strain analyses. Behavior is evaluated in both the .o,.irive and the negative moment regions. The primary variables in this research are the longitudinal reinforcement ratio, p,.. (0.76% and 1.04% for negative moment regions and from 0.79% to 2.43% for positive moment regions), and nominal stirrup strength, Pvfvy (0 to 70 psi) for single web joists and placement of the load in multiple web joists. Stirrup effectiveness in joists is analyzed based upon ACI provisions and the number of stirrups intercepted by the critical shear crack. Nominal shear stresses and load sharing between the joists are compared with current ACI design pro , The tests indicate that ACI 318-89 overestimates the shear cracking load and shear capacity of lightly reinforced concrete joists in negative moment regions, and under estimates the shear cracking load but not the shear capacity in positive moment regiOns. In the study, the stirrup contribution in both the negative and positive moment regions equaled or exceeded the value predicted by ACI 318-89. In the positive moment regions of members with stirrups, the concrete contribution to shear capacity was often below the shear cracking load, contrary to the usual assumption. The study indicates that significant load sharing occurs between the joists, but that the load sharing is adequate only to distribute local overloads. The additional I 0% in the concrete contribution to shear capacity, as allowed by ACI 318-89, is not available for joist systems as a whole.
Ravikumar, S., Darwin, D., McCabe, S.L., Pasley, G.P., "Shear Strength of Continuous Lightly Reinforced Concrete Joist Systems," SM Report No. 37, University of Kansas Center for Research, Inc., Lawrence, KS, March 1994, 137 pp.
http://hdl.handle.net/1808/20441
https://orcid.org/0000-0001-5039-3525
Shear Strength of Continuous Lightly Reinforced Concrete Joist Systems
oai:kuscholarworks.ku.edu:1808/259052018-02-02T09:01:00Zcom_1808_231col_1808_13465
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Huang, Shiping
author
Wu, Zhifeng
author
Misra, Anil
author
2017-12-11
Location localization technology is used in a number of industrial and civil applications. Real time location localization accuracy is highly dependent on the quality of the distance measurements and efficiency of solving the localization equations. In this paper, we provide a novel approach to solve the nonlinear localization equations efficiently and simultaneously eliminate the bad measurement data in range-based systems. A geometric intersection model was developed to narrow the target search area, where Newton’s Method and the Direct Search Method are used to search for the unknown position. Not only does the geometric intersection model offer a small bounded search domain for Newton’s Method and the Direct Search Method, but also it can self-correct bad measurement data. The Direct Search Method is useful for the coarse localization or small target search domain, while the Newton’s Method can be used for accurate localization. For accurate localization, by utilizing the proposed Modified Newton’s Method (MNM), challenges of avoiding the local extrema, singularities, and initial value choice are addressed. The applicability and robustness of the developed method has been demonstrated by experiments with an indoor system.
Huang, S., Wu, Z., & Misra, A. (2017). A Practical, Robust and Fast Method for Location Localization in Range-Based Systems. Sensors, 17(12), 2869.
http://hdl.handle.net/1808/25905
10.3390/s17122869
PMC5751652
Location localization
Indoor localization
Positioning algorithm
Newton’s Method
A Practical, Robust and Fast Method for Location Localization in Range-Based Systems
oai:kuscholarworks.ku.edu:1808/221852019-04-12T14:15:55Zcom_1808_231col_1808_13465
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Yuan, Xing
author
Roundy, Joshua K.
author
Wood, Eric F.
author
Sheffield, Justin
author
2015-11
Seasonal hydrologic extremes in the form of droughts and wet spells have devastating impacts on human and natural systems. Improving understanding and predictive capability of hydrologic extremes, and facilitating adaptations through establishing climate service systems at regional to global scales are among the grand challenges proposed by the World Climate Research Programme (WCRP) and are the core themes of the Regional Hydroclimate Projects (RHP) under the Global Energy and Water Cycle Experiment (GEWEX). An experimental global seasonal hydrologic forecasting system has been developed that is based on coupled climate forecast models participating in the North American Multimodel Ensemble (NMME) project and an advanced land surface hydrologic model. The system is evaluated over major GEWEX RHP river basins by comparing with ensemble streamflow prediction (ESP). The multimodel seasonal forecast system provides higher detectability for soil moisture droughts, more reliable low and high f low ensemble forecasts, and better “real time” prediction for the 2012 North American extreme drought. The association of the onset of extreme hydrologic events with oceanic and land precursors is also investigated based on the joint distribution of forecasts and observations. Climate models have a higher probability of missing the onset of hydrologic extremes when there is no oceanic precursor. But oceanic precursor alone is insufficient to guarantee a correct forecast—a land precursor is also critical in avoiding a false alarm for forecasting extremes. This study is targeted at providing the scientific underpinning for the predictability of hydrologic extremes over GEWEX RHP basins and serves as a prototype for seasonal hydrologic forecasts within the Global Framework for Climate Services (GFCS).
Yuan, X., Roundy, J. K., Wood, E. F., & Sheffield, J. (2015). Seasonal Forecasting of Global Hydrologic Extremes: System Development and Evaluation over GEWEX Basins. Bulletin of the American Meteorological Society, 96(11), 1895–1912. doi:10.1175/bams-d-14-00003.1
http://hdl.handle.net/1808/22185
10.1175/BAMS-D-14-00003.1
Seasonal Forecasting of Global Hydrologic Extremes: System Development and Evaluation over GEWEX Basins
oai:kuscholarworks.ku.edu:1808/189182019-04-12T14:22:29Zcom_1808_231col_1808_13465
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Misra, Anil
author
Marangos, Orestes
author
2008-10-05
The relationship between effective stiffness of rough contacts of rock blocks and transmission of plane waves is well known. Effective stiffness of a rough contact may be related to the force-deformation behavior of the asperity contacts and the statistical description of rock joint surface topography through micromechanical methods. In this paper, a micromechanical methodology for computing the overall rock contact effective stiffness is utilized along with the imperfectly bonded interface model to investigate how transmitted and reflected wave amplitudes are affected by the incident wave frequency, rock joint closure and the existing rock joint normal stress conditions. As a result, expressions for reflected and transmitted wave amplitudes as well as group time delay of the wave-packets are obtained and parametrically evaluated.
Misra, Anil, and Orestes Marangos. "Micromechanical Model of Rough Contact between Rock Blocks with Application to Wave Propagation." Acta Geophysica 56.4 (2008). http://dx.doi.org/10.2478/s11600-008-0050-x
http://hdl.handle.net/1808/18918
10.2478/s11600-008-0050-x
Rough contact
Micromechanics
Effective stiffness
Rock joint
Wave propagation
Micromechanical model of rough contact between rock blocks with application to wave propagation
oai:kuscholarworks.ku.edu:1808/205102018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Darwin, David
author
2000
Design techniques for composite beams with web openings have been under development for well over 30 years. During the past decade, these efforts have reached a level of maturity that allows for an accurate assessment of strength and the development of economical designs. This paper describes the behavior of steel}concrete composite beams with web openings and summarizes the key aspects of strength design and deflection calculation.
Darwin, D., "Design of Composite Beams with Web Openings," Progress in Structural Engineering and Materials, Vol. 2, No. 2, Apr.-June, 2000, 157-163.
http://hdl.handle.net/1808/20510
https://orcid.org/0000-0001-5039-3525
Design of composite beams with web openings
oai:kuscholarworks.ku.edu:1808/233312018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Browning, JoAnn
author
Darwin, David
author
Reynolds, Diane
author
Pendergrass, Benjamin
author
2011
The effectiveness of prewetted, vacuum-saturated (PVS) lightweight aggregate (LWA) as an internal curing agent to reduce concrete shrinkage is evaluated for curing periods of 7 and 14 days. Normalweight aggregate is replaced by LWA at volume replacement levels ranging from 8.9 to 13.8%. Some mixtures contain a partial replacement of portland cement with slag cement while maintaining the paste content at approximately 24.1% of concrete volume. Comparisons are made with mixtures containing low-absorption granite and high absorption limestone normalweight coarse aggregates. At the replacement levels used in this study, PVS LWA results in a small reduction in concrete density, no appreciable effect on concrete compressive strength, and a
substantial decrease in concrete shrinkage for drying periods up to 365 days. Increasing the curing period from 7 to 14 days reduces concrete shrinkage. Thirty and 60% volume replacements of portland cement by slag cement result in reduced shrinkage when used with a porous LWA or normalweight aggregate. After
30 and 365 days of drying, all mixtures with LWA exhibited less shrinkage than the mixtures with either low- or high-absorption normalweight aggregates.
Browning, J., Darwin, D., Reynolds, D., and Pendergrass, B., “Lightweight Aggregate as Internal Curing Agent to Limit Concrete Shrinkage,” ACI Materials Journal, Vol. 108, No. 6, Nov.-Dec. 2011, pp. 638-644.
http://hdl.handle.net/1808/23331
https://orcid.org/0000-0001-5039-3525
Bridge decks
Cracking
Curing
Drying shrinkage
Lightweight aggregate
Slag cement
Vacuum saturation
Lightweight Aggregate as Internal Curing Agent to Limit Concrete Shrinkage
oai:kuscholarworks.ku.edu:1808/298202019-12-06T20:28:39Zcom_1808_231col_1808_13465
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Asadollahi, Parisa
author
Huang, Yong
author
Li, Jian
author
2018-09-12
We focus on a Bayesian inference framework for finite element (FE) model updating of a long-span cable-stayed bridge using long-term monitoring data collected from a wireless sensor network (WSN). A robust Bayesian inference method is proposed which marginalizes the prediction-error precisions and applies Transitional Markov Chain Monte Carlo (TMCMC) algorithm. The proposed marginalizing error precision is compared with other two treatments of prediction-error precisions, including the constant error precisions and updating error precisions through theoretical analysis and numerical investigation based on a bridge FE model. TMCMC is employed to draw samples from the posterior probability density function (PDF) of the structural model parameters and the uncertain prediction-error precision parameters if required. It is found that the proposed Bayesian inference method with prediction-error precisions marginalized as “nuisance” parameters produces an FE model with more accurate posterior uncertainty quantification and robust modal property prediction. When applying the identified modal parameters from acceleration data collected during a one-year period from the large-scale WSN on the bridge, we choose two candidate model classes using different parameter grouping based on the clustering results from a sensitivity analysis and apply Bayes’ Theorem at the model class level. By implementing the TMCMC sampler, both the posterior distributions of the structural model parameters and the plausibility of the two model classes are characterized given the real data. Computation of the posterior probabilities over the candidate model classes provides a procedure for Bayesian model class assessment, where the computation automatically implements Bayesian Ockham razor that trades off between data-fitting and model complexity, which penalizes model classes that “over-fit” the data. The results of FE model updating and assessment based on the real data using the proposed method show that the updated FE model can successfully predict modal properties of the structural system with high accuracy.
Asadollahi, P.; Huang, Y.; Li, J. Bayesian Finite Element Model Updating and Assessment of Cable-Stayed Bridges Using Wireless Sensor Data. Sensors 2018, 18, 3057.
http://hdl.handle.net/1808/29820
10.3390/s18093057
https://orcid.org/0000-0003-3439-7539
Bayesian model updating
Bayesian model class assessment
Transitional Markov Chain Monte Carlo
Cable-stayed bridge
Prediction-error precision
Structural health monitoring
Wireless sensor network
Bayesian Finite Element Model Updating and Assessment of Cable-Stayed Bridges Using Wireless Sensor Data
oai:kuscholarworks.ku.edu:1808/204712018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Barham, Shawn
author
Darwin, David
author
1999-08
The effects of age and aggregate type on the behavior of normal, medium, and high-strength concrete, and the relationships between compressive strength, flexural strength, and fracture properties (fracture energy and characteristic length) are studied. The concrete mixes contain either basalt or crushed limestone aggregate with a maximum size of 19 mm (3/4 in.) and an aggregate volume factor (ACI 211.1- 91) of 0.67. Mixes are tested at ages of 7, 28, 56, 90, and 180 days. Water-tocementitious material (w/cm) ratios range between 0.25 and 0.46.
In the study, compressive strengths range from 20 MPa (2,920 psi) (7 day normal-strength limestone concrete) to 99 MPa (14,320 psi) (180 day high-strength basalt concrete). High-strength concrete containing basalt attains a higher compressive strength than high-strength concrete containing limestone, even at a slightly higher w/cm ratio. Medium-strength concrete containing limestone exhibits slightly higher compressive strength than concrete containing basalt. Compressive strengths for normal-strength concrete are similar for limestone and basalt. The w/cm ratio is the primary controlling factor for determining compressive strength. Higher strength concretes gain a greater portion of their long-term compressive strength at an earlier age than lower strength concretes.
The flexural strengths range from 4 MPa (550 psi) to 14 MPa (1,960 psi). High-strength concrete containing basalt yields significantly higher flexural strengths than high-strength concrete containing limestone at the same age. The limiting factor appears to be the tensile strength of the aggregate. For the normal and mediumstrength concretes, aggregate does not significantly affect the flexural strength. The w/cm ratio and aggregate strength are the primary controlling factors for determining flexural strength. Flexural strength generally increases with increasing age.
The fracture energies range from 27.7 N/m (0.158 lb/in.) to 202 N/m (1.152 lb/in.). Concrete containing basalt yields significantly higher fracture energies than concrete containing limestone at all w/cm ratios and ages. This is due to less aggregate fracture and a more irregular fracture surface in basalt concrete, causing greater energy dissipation. Compressive strength, w/cm ratio, and age seem to have no effect on fracture energy, which is principally governed by coarse aggregate type. The characteristic length is higher for concrete containing basalt than for concrete containing limestone. Characteristic length decreases with an increase in compressive strength. The peak bending stress in a fracture test is linearly related to flexural strength.
Barham, S. and Darwin, D., "Effects of Aggregate Type, Water-to-Cementitious Material Ratio, and Age on Mechanical and Fracture Properties of Concrete," SM Report No. 56, University of Kansas Center for Research, Inc., Lawrence, Kansas, August 1999, 95 pp.
http://hdl.handle.net/1808/20471
https://orcid.org/0000-0001-5039-3525
Effects of Aggregate Type, Water-to-Cementitious Material Ratio, and Age on Mechanical and Fracture Properties of Concrete
oai:kuscholarworks.ku.edu:1808/280782019-05-31T15:43:20Zcom_1808_231col_1808_13465col_1808_19739
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Ghimire, Krishna P.
author
Shao, Yun
author
Darwin, David
author
O'Reilly, Matthew
author
2019-05
Results of an experimental program on the anchorage strength of headed reinforcing bars are presented. Two hundred and two exterior beam-column joint specimens with concrete compressive strengths ranging from 3960 to 16,030 psi (27.3 to 110.6 MPa) were tested under monotonic loading. Key parameters included concrete compressive strength, embedment length, bar size, head size, spacing between headed bars, and confining reinforcement within the joint region. Bar stresses at failure ranged from 26,100 to 153,200 psi (180 to 1057 MPa). Specimens exhibited concrete breakout, side-face blowout, or a combination of the two failure
modes, with concrete breakout being the dominant failure mode. A comparison of bar stress at anchorage failure with the stress calculated based on ACI 318-14 shows that ACI 318-14 provides a very conservative estimate of anchorage strength for No. 5 (No. 16) bars and low concrete compressive strengths. The estimate becomes progressively less conservative with increasing bar size and concrete compressive strength.
Ghimire, K. P., Shao, Y., Darwin, D., and O’Reilly, M., “Conventional and High-Strength Headed Bars – Part 1: Anchorage Tests,” ACI Structural Journal, Vol. 116, No. 4, May 2019, pp. 255-264.
http://hdl.handle.net/1808/28078
10.14359/51714479
https://orcid.org/0000-0001-5039-3525
Anchorage
Beam-column joints
Bond and development
Development length
Headed bars
High-strength concrete
High-strength steel
Reinforcement
Conventional and High-Strength Headed Bars—Part 1: Anchorage Tests
oai:kuscholarworks.ku.edu:1808/233842018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Idun, Emmanuel K.
author
Darwin, David
author
1999
The coefficients of friction between epoxy-coated and uncoated reinforcing steel and mortar and the effects of rib face angle on
the relative bond strength of epoxy-coated bars are determined. Results for 130 test specimens indicate that the average coefficient of friction is about 0.49 between epoxy-coated reinforcing steel and mortar and about 0.56 between uncoated reinforcing steel and mortar. Based on 58 beam-end specimen tests using both machined and rolled 1-in. (25-mm) nominal diameter reinforcing bars with face angles of 30, 40, 45, 60, and 90 deg, epoxy coating has the least effect on the bond strength of steel reinforcing bars to concrete when the rib face angle is greater than or equal to 45 deg.
E. K., Idun, and Darwin, D., "Epoxy-Coated Reinforcement: Coefficient of Friction and Rib Face Angle," ACI Structural Journal, Vol. 96, No. 4, July-Aug., 1999, pp. 609-615.
http://hdl.handle.net/1808/23384
https://orcid.org/0000-0001-5039-3525
Bond (concrete to reinforcement)
Deformed reinforcement
Epoxy resins
Friction
Reinforcing steels
Splicing
Structural engineering
Bond of Epoxy-Coated Reinforcement: Coefficient of Friction and Rib Face Angle
oai:kuscholarworks.ku.edu:1808/234182018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Hadje-Ghaffari, Hossain
author
Choi, Oan Chul
author
Darwin, David
author
McCabe, Steven L.
author
1994
The effects of concrete cover, casting position, concrete slump, and degree of consolidation on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end specimens containing No. 5, No. 6, No. 8 and No. 11 (16, 19, 25, and 46 mm) bars. Bottom-cast and top-cast bars with 1, 2, or 3 bar diameters of cover are evaluated. Concrete slump ranges from 2 1/4 to 8 in. (55 to 205 mm). some specimens containing high slump concrete are not vibrated. The results of the study are used to develop improved development length modification facts for epoxy-coated bars.
Epoxy coatings significantly reduce bond strength. However, the extent of the reduction is less than used to select the development length modification factors in the 1989 ACI Building Code and the 1989 AASHTO Bridge Specifications for bars with cover < 3 bar diameters (db) or a clear spacing < 6 db. The development length modification factor can be reduced from 1.5 to 1.35 for these bars. The relative bond strength of epoxy-coated reinforcement increases as cover increases. As a result, the development length modification factor of 1.2 in ACI 318-89 is realistic for epoxy-coated bars with a cover > 3 db and a clear space > 5 db (ACI) or a center-to-center spacing > 6 in. (AASHTO). However, the modification factor of 1.15 in the 1989 AASHTO Bridge Specifications is slightly unconservative for these bars and should be modified. The ratio of the bond strength of bottom-cast bars to the bond strength of top-cast bars, B/T, is about the same for coated and uncoated bars and decreases slightly for coated bars as slump increases. As a result, the upper limit on the product of the epoxy-coating factor and the top-bar factor can be reduced from 1.7 to 1.5. A lack of vibration has a negative effect on the bond strength of both coated and uncoated reinforcement in high slump concrete.
This is the third in a series of papers describing research at the University of Kansas on epoxy-coated reinforcement. The research is aimed at gaining a better understanding of the bond of epoxy-coated reinforcement to concrete and developing design procedures that accurately reflect the changes in bond strength caused by epoxy coating.
Hadje-Ghaffari, H., Choi, O. C., and McCabe, S. L., "Bond of Epoxy-Coated Reinforcement: Cover, Casting Position, Slump, and Consolidation," ACI Structural Journal Vol. 83, No. 7, January-February 1994, pp. 59-68.
http://hdl.handle.net/1808/23418
https://orcid.org/0000-0001-5039-3525
Bond (concrete to reinforcement)
Coatings
Deformed reinforcement
Epoxy-coated reinforcement
Pullout tests
Reinforcing steels
Structural engineering
Bond of Epoxy-Coated Reinforcement: Cover, Casting Position, Slump, and Consolidation
oai:kuscholarworks.ku.edu:1808/234192018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Hester, Cynthia J.
author
Salamizavaregh, Shahin
author
Darwin, David
author
McCabe, Steven L.
author
1993
The effects of epoxy coating and transverse reinforcement on the splice strength of reinforcing bars in concrete are described. A total of 65 beam and slab splice specimens containing No. 6 and No. 8 bars were tested. The average coating thickness ranged from 6 to 11 mils (0.15 to 0.28 mm). Three deformation patterns were used. All but one group of specimens contained
Class B ACI/Class C AASHTO splices. The results of the current study are analyzed, along with the results of 48 specimens from earlier studies, and used to develop improved development length modification factors for use with epoxy-coated bars. Epoxy coatings are found to reduce splice strength significantly; however, the extent of the reduction is less than that used to
select the development length modification factors in the 1989 ACI Building Code and 1989 AASHTO Bridge Specifications. The percentage decrease in splice strength caused by epoxy coating is independent of the degree of confining reinforcement, which provides approximately the same percentage increase in the strength of splices for both coated and uncoated bars. A maximum development length modification factor of 1.35 is applicable for design with epoxy-coated reinforcement. An alternate factor of 1.20 is applicable for epoxy-coated bars with a defined minimum amount of transverse reinforcement if the positive effects of that transverse reinforcement are not already taken into account in the design provisions. Thus, the 1.20 factor is not applicable to the ACI Building Code, but is applicable to the AASHTO Bridge Specifications. This is the second in a series of papers describing research at the University of Kansas on epoxy-coated reinforcement. The research is aimed at gaining a better understanding of the bond of epoxy-coated reinforcement to concrete and developing design procedures
that accurately reflect the changes in bond strength caused by epoxy coating.
Hester, C. J., Salamizavaregh, S., Darwin, D., and McCabe, S. L., “Bond of Epoxy-Coated Reinforcement: Splices,” ACI Structural Journal, Vol. 90, No. 1, Jan.-Feb. 1993, pp. 89-102.
http://hdl.handle.net/1808/23419
https://orcid.org/0000-0001-5039-3525
Bond (concrete to reinforcement)
Coatings
Deformed reinforcement
Epoxy-coated reinforcement
Lap connections
Pullout tests
Reinforcing steels
Splicing
Structural engineering
Bond of Epoxy-Coated Reinforcement: Splices
oai:kuscholarworks.ku.edu:1808/333262022-11-30T09:00:27Zcom_1808_231col_1808_13465col_1808_19739
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Aljawad, Yasmeen
author
Lequesne, Rémy D.
author
O’Reilly, Matt
author
2022-08
Ultra-high-performance concrete (UHPC) has been used increasingly in the past decade due to its high strength, rapid strength gain, and enhanced durability. UHPC is a cement-based material that typically has a low w/cm ratio, high paste content, and a 2% volume fraction of high-strength steel fibers. Most commercially available UHPC mixtures are also proprietary, or company-owned, which tends to elevate its cost. To lower the cost of UHPC in Kansas, this research aimed to develop non-proprietary UHPC using primarily Kansas-based materials. It was important that the proposed mixture gain strength quickly for use in accelerated bridge construction; the proposed mixture proportions resulted in 1-, 7-, and 28-day compressive strengths of 13.1, 16.8, and 19.6 ksi. Also, because UHPC typically exhibits high early-age shrinkage relative to conventional concrete, this research explores shrinkage-limiting methods, including a shrinkage reducing admixture (SRA), a shrinkage compensating admixture (SCA), and prewetted lightweight aggregates (LWAs). The SRA effectively reduced UHPC shrinkage by one-third 30 to 60 days after mixing, but not at 90 days. The SCA reduced shrinkage throughout the 90 days of monitoring, and the effect was highly dose dependent. LWA did not reduce UHPC shrinkage in this study, but further research is needed since this finding conflicts with prior research. Results are also reported from tension and bending tests of UHPC with different volume fractions of high-strength straight and hooked steel fibers. Every specimen tested exhibited strain hardening in tension or deflection hardening in bending, suggesting that both fiber types are similarly effective. However, further research is needed to conclusively compare fibers due to the scope of the reported tests.
Aljawad, Y., Lequesne, R. D., and O’Reilly, M., “Low-Shrinkage Ultra-High-Performance Concrete,” SL Report 22-3, The University of Kansas Center for Research, Inc., Lawrence, KS, August, 2022, 69 pp.
http://hdl.handle.net/1808/33326
https://orcid.org/0000-0003-3968-4342
Low-Shrinkage Ultra-High-Performance Concrete
oai:kuscholarworks.ku.edu:1808/198272018-07-03T01:48:33Zcom_1808_231col_1808_13465col_1808_19739
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O’Reilly, Matthew
author
Darwin, David
author
2012-11
The corrosion resistance of 2304 and XM-28 stainless steel bars, produced by a single mill and supplied by a single supplier, was evaluated using the rapid macrocell test outlined in Annexes A1 and A2 of ASTM A955-12. Bars were tested both before and after undergoing mechanical straightening. Based on the test results, the stainless steel bars satisfy the requirements of ASTM A955-12. The straightening process allowed corrosion to initiate on the bars, but had limited to no effect on the macrocell corrosion rate.
O'Reilly, M. and Darwin, D., "Rapid Macrocell Tests of 2304 and XM-28 Reinforcing Bars," SL Report 12-3a, University of Kansas Center for Research, Inc., Lawrence, Kansas, November 2012, 17 pp.
http://hdl.handle.net/1808/19827
https://orcid.org/0000-0001-5039-3525
Chlorides
Concrete
Corrosion
Macrocell
Reinforcing steel
Stainless steel
Rapid Macrocell Tests of 2304 and XM-28 Reinforcing Bars
oai:kuscholarworks.ku.edu:1808/204622018-12-27T19:11:33Zcom_1808_231col_1808_13465col_1808_19739
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Shipley, Richard W.
author
Darwin, David
author
Locke, Carl E., Jr.
author
1997-12
The conditions in which stray currents contribute to the corrosion damage of highway structures, the tests to determine if these conditions exist, and the methods recommended to alleviate either the conditions or the damage caused by stray current corrosion are investigated. An extensive review of the literature concerning the fundamentals of stray current corrosion and the practices of utility cathodic protection is presented, including a comprehensive study of the history of stray current corrosion, from its conception with the direct current trolley systems of the late 1880's to its present day problems in the cathodic protection industry. Federal, state, and Kansas Department of Transportation rules and policy are reviewed as they pertain to utility cathodic protection and the damage it may cause to adjacent underground highway structures. Based on the research covered within this report, procedural changes for the prevention of stray current corrosion damage to highway structures and additions to the KDOT Utility Accommodation Policy (1994) are recommended. The research herein concludes that: (1) that all construction close to cathodically protected utilities should be reported to the utility owners so that stray current interference can be assessed, (2) any utility pipeline found uncovered should be reported to its owner so that it can be inspected for corrosion damage, and (3) no underground highway structure should be located within the area of influence of a cathodic protection groundbed. Additionally, its recommended that the KDOT Utility Accommodation Policy (1994) be modified to: (I) directly state the policy on stray current interference from utility cathodic protection systems, (2) require utilities installing cathodic protection systems to submit the design plans as part of the process necessary to obtain a permit agreement for operating in a highway right-of-way, and (3) state that KDOT may require additional inspections along pipelines where interference could jeopardize the structural integrity of an underground highway structure.
Shipley, R.W., Darwin, D., Locke, C.E., Jr., "Stray Current Corrosion Due to Utility Cathodic Protection," SM Report No. 45, University of Kansas Center for Research, Inc., Lawrence, KS, December 1997, 51 pp.
http://hdl.handle.net/1808/20462
https://orcid.org/0000-0001-5039-3525
Bridges
Cathodic protection
Highway structures
Stray currents
Stray current corrosion
Stray current interference
Stray Current Corrosion Due to Utility Cathodic Protection
oai:kuscholarworks.ku.edu:1808/189982019-04-12T14:27:12Zcom_1808_231col_1808_13465
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Young, Bryan
author
Bradley, A. Allen
author
Krajewski, Witold F.
author
Kruger, Anton
author
2000-06
Next-Generation Weather Radar (NEXRAD) multisensor precipitation estimates will be used for a host of applications that include operational streamflow forecasting at the National Weather Service River Forecast Centers (RFCs) and nonoperational purposes such as studies of weather, climate, and hydrology. Given these expanding applications, it is important to understand the quality and error characteristics of NEXRAD multisensor products. In this paper, the issues involved in evaluating these products are examined through an assessment of a 5.5-yr record of multisensor estimates from the Arkansas–Red Basin RFC. The objectives were to examine how known radar biases manifest themselves in the multisensor product and to quantify precipitation estimation errors. Analyses included comparisons of multisensor estimates based on different processing algorithms, comparisons with gauge observations from the Oklahoma Mesonet and the Agricultural Research Service Micronet, and the application of a validation framework to quantify error characteristics. This study reveals several complications to such an analysis, including a paucity of independent gauge data. These obstacles are discussed and recommendations are made to help to facilitate routine verification of NEXRAD products.
Young, C. Bryan, A. Allen Bradley, Witold F. Krajewski, Anton Kruger, and Mark L. Morrissey. "Evaluating NEXRAD Multisensor Precipitation Estimates for Operational Hydrologic Forecasting." J. Hydrometeor Journal of Hydrometeorology 1.3 (2000): 241-54. http://dx.doi.org/10.1175/1525-7541(2000)001<0241:ENMPEF>2.0.CO;2
http://hdl.handle.net/1808/18998
10.1175/1525-7541(2000)001<0241:ENMPEF>2.0.CO;2
Evaluating NEXRAD Multisensor Precipitation Estimates for Operational Hydrologic Forecasting
oai:kuscholarworks.ku.edu:1808/326902022-04-08T08:01:02Zcom_1808_231col_1808_13465
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Li, Chaohui
author
Lequesne, Rémy D.
author
Matamoros, Adolfo
author
2019-01
Results are reported from tests of three precast, prestressed concrete girders under fatigue-type cyclic and monotonic loading conducted after deck removal and replacement. Although deck demolition altered the top surface of the girders, the girder–deck interfaces exhibited shear strengths greater than their nominal strength (based on the 2012 AASHTO LRFD Specification) after 2 × 106 cycles of loading to 45 and 30% of their nominal strength for troweled and roughened interfaces, respectively. A partially debonded detail was used for two of the girders to protect the girder top flange, which was wide and thin, during deck demolition. The roofing felt used to debond the girder–deck interface over the flanges reduced the effort required for deck removal by 65%, compared with the typical detail, eliminated chipping hammer–induced damage to the girder flanges, and still resulted in sustained composite action under 2 × 106 cycles of loading. The width of the bonded interface had little effect on girder stiffness and no observed effect on the width of deck effective in bending.
Li, C., Lequesne, R.D., Matamoros, A., (2019). Girder–Deck Interface: Partial Debonding, Deck Replacement, and Composite Action. Journal of Bridge Engineering, Volume 24 Issue 1
http://hdl.handle.net/1808/32690
10.1061/(ASCE)BE.1943-5592.0001311
https://orcid.org/ 0000-0003-2146-7243
Girder–Deck Interface: Partial Debonding, Deck Replacement, and Composite Action
oai:kuscholarworks.ku.edu:1808/204392018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Darwin, David
author
Salamizavaregh, Shahin
author
1993-10
The effects of hole preparation method, grout type, hole diameter, bar size, embedment length, cover, reinforcing bar deformation pattern, bar surface condition (epoxy coated or uncoated), orientation of the installed bar, and concrete strength on the bond strength of grouted reinforcing bars are described. Hole preparation methods, using a high-speed vacuum drill or a hand-held pneumatic hammer drill, and cleaning methods, using a fiber bottle brush with water, a fiber bottle brush without water, or compressed air only, are compared. Two capsule systems, two two-component grout systems, and two nonshrink grout systems are evaluated. Hole diameters range from 3/4 to 11/z in. for No. 5 bars; ll/4 in. diameter holes are used for No. 8 bars. Embedment lengths range from 4 to 12 in. for No. 5 bars and from 6 to 15 in. for No. 8 bars. 11/z in. and 3 in. covers are used. Two deformation patterns bars are evaluated. Bar installations include vertical, sloped, and horizontal bars. Concrete strengths range from 2700 to 5900 psi. Test results are used to develop rational design and construction requirements. A standard test to, establish the Strength Class of a grout for anchoring reinforcing bars is proposed. In addition, a test method currently in use by one state department of transportation as a technique for prooftesting grouted reinforcement in the field is evaluated. The bond strength of grouted reinforcing bars is not highly sensitive to differences in the hole preparation or cleaning methods studied. Grouts that provide strong bond at the groutconcrete interface provide higher bond strengths than grouts that undergo failure at the groutconcrete interface. With the exception of bars anchored by capsule systems, the bond strength provided by grouts is not sensitive to hole diameter. Bond strength increases with increasing embedment length, cover, and bar size. The bond strength of grouted reinforcement is only slightly sensitive to reinforcing bar deformation pattern, and insensitive to the presence of epoxy coating. Vertically and horizontally anchored bars may exhibit different bond strengths, depending on the grout used. For the grouts tested, bond strength increases approximately with the square root of the concrete compressive strength. The proposed standard test method for establishing the Strength Class of a grout is incorporated in a conservative, easy-to-use design procedure. The test method evaluated for proof-testing reinforcement is not recommended because the failure modes are often different and the strengths are higher than those obtained under more realistic loading conditions. A modification to the test method is suggested.
Darwin, D., and Salamizavaregh, S., "Bond Strength of Grouted Reinforcing Bars," SM Report No. 32, University of Kansas Center for Research, Inc., Lawrence, KS, October 1993, 149 pp.
http://hdl.handle.net/1808/20439
https://orcid.org/0000-0001-5039-3525
Bond Strength of Grouted Reinforcing Bars
oai:kuscholarworks.ku.edu:1808/189232019-04-12T14:22:43Zcom_1808_231col_1808_13465
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Molz, F. J.
author
Melville, J. G.
author
Parr, Alfred D.
author
King, D. A.
author
Hopf, M. T.
author
1983-02
The two main objectives of this communication are to present a study of potential advantages and disadvantages of the doublet supply-injection well configuration in an aquifer thermal energy storage (ATES) system and to report on aquifer storage problems with injection temperatures in the 80°C range. A 3-month injection-storage-recovery cycle followed by a 7.3-month cycle constituted the main experiment. The injection volumes were 25,402 m3 and 58,063 m3 at average temperatures of 58.5°C and 81°C respectively. Unlikely previous experiments at the Mobile site, no clogging of the injection well due to clay particle swelling, dispersion, and migration was observed. This is attributed to the fact that the supply water used for injection contained a cation concentration equal to or slightly greater than that in the native groundwater. For cycles I and II, the fraction of injected energy recovered in a volume of water equal to the injection volume was 0.56 and 0.45 respectively. Both groundwater temperature and tracer data support the conclusion that this relatively low recovery was due to the detrimental effects of free thermal convection, possibly augmented by longitudinal zones of high permeability. Construction of a partially penetrating recovery well improved recovery efficiency but is not thought to be an adequate solution to thermal stratification. A maximum increase of 1.24 cm in relative land surface elevation was recorded near the end of second cycle injection. The engineering implications of such an elevation change would have to be considered, especially if an ATES system were being designed in an urban environment. A third cycle was started at the Mobile site on April 7, 1982. This final experiment contains a partially penetrating, dual-recovery well system which is expected to maximize energy recovery from a thermally stratified storage aquifer.
Molz, F. J., J. G. Melville, A. D. Parr, D. A. King, and M. T. Hopf. "Aquifer Thermal Energy Storage : A Well Doublet Experiment at Increased Temperatures." Water Resources Research Water Resour. Res. 19.1 (1983): 149-60. http://dx.doi.org/10.1029/WR019i001p00149
http://hdl.handle.net/1808/18923
10.1029/WR019i001p00149
Aquifer thermal energy storage : A well doublet experiment at increased temperatures
oai:kuscholarworks.ku.edu:1808/280792019-05-31T15:42:32Zcom_1808_231col_1808_13465col_1808_19739
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Ghimire, Krishna P.
author
Shao, Yun
author
Darwin, David
author
O'Reilly, Matthew
author
2019-05
Equations to characterize the anchorage strength of headed bars were developed, incorporating key factors affecting anchorage strength: concrete compressive strength; embedment length; bar diameter; spacing between the bars; and confining reinforcement parallel to the headed bars. Results from tests of 138 exterior beam-column joints, 64 without and 74 with confining reinforcement within the joint region, were used to develop the equations. Concrete compressive strengths ranged from 4050 to 16,030 psi (27.9 to 110.6 MPa) and bar stresses at failure ranged from 33,100 to 153,160 psi (228 to 1056 MPa). The bearing area of the headed bars ranged from 3.8 to 9.5 times the area of the bar. Some headed bars contained obstructions adjacent to the head that exceeded the dimensions permitted for HA heads in ACI 318-14 and ASTM A970-13a but are now permitted by ASTM A970-18. The test results show that headed bar anchorage strength is proportional to the concrete compressive strength raised to the power 0.24. The contribution of confining reinforcement is proportional to the area of confining reinforcement parallel to the headed bar within eight to 10 bar diameters of the headed bar. Headed bars with obstructions larger than those permitted in ACI 318-14 that meet the provisions in ASTM A970-18 exhibit anchorage strengths that are similar to those that meet the provisions in ACI 318-14.
Ghimire, K. P., Shao, Y., Darwin, D., and O’Reilly, M., “Conventional and High-Strength Headed Bars – Part 2: Data Analysis,” ACI Structural Journal, Vol. 116, No. 4, May 2019, pp. 265-272.
http://hdl.handle.net/1808/28079
10.14359/51714480
https://orcid.org/0000-0001-5039-3525
Anchorage
Beam-column joints
Bond and development
Headed bars
High-strength concrete
High-strength steel
Reinforcement
Conventional and High-Strength Headed Bars—Part 2: Data Analysis
oai:kuscholarworks.ku.edu:1808/204482018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Darwin, David
author
1995-05
The corrosion of reinforcing steel in highway structures results in maintenance and replacement costs in the United States that are measured in billions of dollars. These costs would be greatly reduced and the durability and design life of reinforced concrete structures greatly enhanced if the corrosion resistance of reinforcing steel were improved. This study involves the evaluation of a concrete reinforcing steel which has shown superior corrosion-resistant properties. Previous evaluations have concentrated on the corrosion resistance of the steel in the atmosphere, which can be quite different than obtained for steel in contact with concrete. Emphasis in this study is placed on the corrosion resistance of the steel in concrete structures. The new steel differs from steel used in standard U.S. practice in a number of ways. Additional alloying elements (copper, chromium, and phosphorus) are used, along with a special heat treatment, to provide the corrosion-resistant properties of the steel. The bars possess lower carbon content than is usual, and the phosphorous content exceeds that allowed in ASTM specifications. The bars are quenched and tempered immediately following the rolling operation, a step that places the exterior of the bars in compression. The apparent corrosion-resisting mechanisms include the formation of a corrosion-retarding layer of copper chloride-<:apper hydroxide at the steel surface in the presence of chloride, the formation of phosphorous oxides, which serve as corrosion inhibitors, the formation of iron-chromium oxide at the steel surface, which is a poor conductor and, thus, reduces the corrosion rate, and the reduction of microfractures in the surface from the rolling operation due to the quenching and tempering process. The corrosion products that form are much denser than for normal reinforcing steel, which further reduces the availability of oxygen and water at the steel surface. The reduced microfractoring lowers the surface area available for corrosion. The study is carried out in four overlapping stages. Stages l and 3 are dedicated to understanding the corrosion protection mechanisms and the degree of corrosion protection when the steel is subjected to different chloride concentrations and different deicing chemicals. Stage 2 involves the evaluation and comparison of the new reinforcement to standard reinforcing steel using accepted time-to-corrosion tests. Stage 4 consists of a determination of the mechanical properties of the new steel, as affected by the alloying process. The study involves the evaluation of four types of steel, representing combinations of alloying elements and heat treatment. The steels include two conventional steels, one hot-rolled and one subjected to heat treatment immediately following the hot-rolling operation, and two forms of corrosion-resistant steel, one hot-rolled and one heat-treated. The experimental results and analyses demonstrate that the microalloying procedure improves the corrosion resistance of steel reinforcing bars cast in concrete and subjected to deicing chemicals. The resulting corrosion rate is approximately one-half of the corrosion rate exhibited by conventional reinforcing bars. The use of the quenching and tempering heat treatment following hot rolling appears to provide some additional corrosion resistance, when used in conjunction with the microalloying procedure. The heat treatment produces a reinforcing steel with higher yield and tensile strengths. A phosphorous content in excess of that allowed under current AS'IM requirements does not cause the corrosion resistant steel in this study to be brittle. The tests indicate that the new reinforcing steel should not be combined with conventional reinforcement in reinforced concrete structures. The new steel performs well when used in conjunction with an epoxy coating and offers the potential of economically providing a measurable improvement in the corrosion performance of reinforced concrete structures subjected to chlorides and deicing chemicals. Implementation of the new reinforcing steel will require additional corrosion tests to fully document the corrosionresistant properties of the reinforcement, the development of standard specif'JCations for the material, and the execution of demonstration projects in which the new reinforcing steel is applied in practice. Special attention should be given to using the new steel in conjunction with epoxy coating.
Darwin, D., "Corrosion-Resistant Steel Reinforcing Bars," SL Report 95-2, University of Kansas Center for Research, Inc., Lawrence, KS, May 1995, 25 pp.
http://hdl.handle.net/1808/20448
https://orcid.org/0000-0001-5039-3525
Corrosion-Resistant Steel Reinforcing Bars
oai:kuscholarworks.ku.edu:1808/296342019-10-22T16:13:52Zcom_1808_231col_1808_13465col_1808_19739
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Darwin, David
author
O'Reilly, Matthew
author
Farshadfar, Omid
author
Browning, JoAnn
author
Locke, Carl, Jr.
author
2018-11
Corrosion-related cracking in reinforced concrete is caused by
expansive corrosion products and the resulting tensile stresses.
While the amount of corrosion to cause cracking has been studied
for uncoated conventional reinforcement, significantly less is
known about the corrosion loss at cracking for galvanized reinforcement.
Conventional and galvanized bars were cast in chloride-
contaminated concrete. Clear cover to the bar ranged from
0.5 to 2 in. (12.7 to 51 mm). Specimens were tested both with and
without the use of impressed current to drive corrosion. It was found
that galvanized reinforcement requires greater corrosion losses
to crack concrete than conventional steel reinforcement. Visual
observations at autopsy suggest that the cracking of the concrete
specimens containing galvanized reinforcement was not due to zinc
corrosion products, but rather to corrosion products from intermetallic
iron-zinc layers or from the underlying steel. Further study is
needed to determine the exact nature of these corrosion products.
Tests using impressed current may be used to establish the corrosion
loss required to cause cracking.
O’Reilly, M., Farshadfar, O., Darwin, D., Browning, J., and Locke, C., “Corrosion-Induced Concrete Cracking for Uncoated and Galvanized Reinforcing Bars,” ACI Materials Journal, Vol. 115, No. 6, Nov. 2018, pp. 825-832.
http://hdl.handle.net/1808/29634
10.14359/51706839
https://orcid.org/0000-0001-5039-3525
Chlorides
Corrosion
Cracking
Galvanized reinforcement
Steel reinforcement
Zinc
Corrosion-Induced Concrete Cracking for Uncoated and Galvanized Reinforcing Bars
oai:kuscholarworks.ku.edu:1808/253262017-12-19T15:08:28Zcom_1808_231col_1808_13465
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Hale, David K.
author
Ma, Jiaqi
author
Kondyli, Alexandra
author
Hu, Jia
author
Huang, Zhitong
author
Su, Peng
author
2016
The Highway Capacity Manual 2010 (HCM 2010) contains computational procedures for evaluating traffic operational efficiency of urban street segments. These procedures have been implemented within several commercial software packages and are likely used by thousands of engineers and planners across the United States. The procedures for urban street capacity analysis contain no logic for handling right turns on red (RTORs) or for handling special cases of RTORs such as shielded and free right turns. A new proposed RTOR modeling framework is described for urban streets in the HCM 2010. When significant upstream RTOR flows exist, the proposed logic is designed to generate more realistic flow profiles. Three types of experimental results are presented: they demonstrate the improved modeling accuracy of the proposed logic. First, it is shown that macroscopic flow profile shapes are now more visually sensible because they now illustrate RTOR flows moving at the appropriate times. Second, macroscopic flow profile shapes are now more consistent with microscopic vehicle trajectories. Third, a statistical analysis shows that when the proposed logic is used, HCM 2010 performance measures become more consistent with the performance measures generated by microsimulation. Finally, case study results show that when the proposed RTOR logic is not used, control delays are sometimes be inaccurate by more than 30%. Given the experimental evidence presented, it is urgent that the proposed improvements be adopted and implemented so that RTOR corridors can be accurately analyzed by the HCM 2010 procedures.
Hale, D. K., Ma, J., Kondyli, A., Hu, J., Huang, Z., & Su, P. (2016). Right-Turn-on-Red Flow Profile Impactson Urban Street Capacity Analysis. Transportation Research Record: Journal of the Transportation Research Board, 2553, 29-40. doi:10.3141/2553-04
http://hdl.handle.net/1808/25326
10.3141/2553-04
Right-Turn-on-Red Flow Profile Impactson Urban Street Capacity Analysis
oai:kuscholarworks.ku.edu:1808/204632018-12-27T19:15:18Zcom_1808_231col_1808_13465col_1808_19739
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Kepler, Jennifer L.
author
Darwin, David
author
Locke, Carl E., Jr.
author
2000-05
Since the 1970s, research projects and field studies have been conducted on different methods for protecting reinforced concrete bridges from corrosion damage. The methods include alternative reinforcement and slab design, barrier methods, electrochemical methods, and corrosion inhibitors. Each method and its underlying principles are described, performance results of laboratory and/or field trials are reviewed, and systems are evaluated based on the results of the trials. Using performance results from the studies and costs obtained from transportation agencies, an economic analysis is used to estimate the cost of each system over a 75 year economic life using discount rates of 2, 4, and 6%.
Epoxy-coated reinforcing steel is the most common corrosion protection method used in the United States today. Although controversial in many areas, epoxy-coated reinforcement has performed well in many states, including Kansas, since it was introduced in the early 1970s and is a low-cost backup to many other corrosion protection options. Research on stainless steel reinforcement indicates that it may remain free of corrosion in chloride contaminated concrete for more than 75 years. At a low discount rate (2%), solid stainless steel reinforcement is a cost-effective option compared to other options, but at higher discount rates (4%+), the present value cost of a deck with solid stainless steel is significantly higher than that of an unprotected deck. Stainless steel clad reinforcement is much less expensive than solid stainless steel reinforcement. The performance of stainless steel-clad reinforcement will be similar to that of solid stainless steel bars if the stainless steel coating is continuous and if the black steel core, exposed at the bar ends, is protected so that it does not come into contact with concrete pore solution. The present value of the cost of a bridge deck built with stainless steel-clad reinforcement is significantly lower than the present value for the cost of any other corrosion protection system. This method should be considered for experimental use. Solid stainless steel should be considered, as well, if a low discount rate (around 2%) is used. Hot rubberized asphalt membranes are the least expensive option, other than stainless steel-clad reinforcement. Hot rubberized asphalt and spray-applied liquid membranes should be considered for use on future projects. In laboratory tests, corrosion inhibitors have been shown to provide protection to steel in chloride contaminated concrete, but information on their performance in the field is limited. Both calcium nitrite and organic corrosion inhibitors have the potential to be cost-effective, if they perform as well in the field as they have in the laboratory, and should be considered for experimental use.
Kepler, J.L., Darwin, D., and Locke, C.E., Jr. "Evaluation of Corrosion Protection Methods for Reinforced Concrete Highway Structures," SM Report No. 58, University of Kansas Center for Research, Inc., Lawrence, Kansas, May 2000, 221 pp.
http://hdl.handle.net/1808/20463
https://orcid.org/0000-0001-5039-3525
Evaluation of Corrosion Protection Methods for Reinforced Concrete Highway Structures
oai:kuscholarworks.ku.edu:1808/234252018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Brettmann, Barie B.
author
Darwin, David
author
Donahey, Rex C.
author
1986
The effects of superplasticizers on concrete-steel bond strength were studied. Key variables were degree of consolidation; concrete slump, both with and without a superplasticizer; concrete temperature; and bar position. No. 8 deformed reinforcing bars were used with a 2-in (51mm) cover and a 10 in. (254 mm) bonded length. Concrete slumps ranged from 1 3/4 in to 9in. (44 to 229 mm). Three specimens depths were used. All specimens were modified cantilever beam specimens.
The experimental results show that high-slump superplasticized concrete provides a lower bond strength than low-slump concrete of the same strength. Vibration of high-slump concrete increases the bond strength compared to high-slump concrete without vibration. The current ACI top-bar requirements appear to be unconservative for top-cast bars with less than 12 in. (305 mm) of concrete below the bar and are possibly overconservative for nontop-cast bars with more than 12 in. 305 (mm) of concrete below the bar when low-slump concrete is used.
Brettmann, B.B., Darwin, D., Donahey, R.C., "Bond of Reinforcement to Superplasticized Concrete," ACI Journal Vol. 83, No. 12, January-February 1986, pp. 98-107.
http://hdl.handle.net/1808/23425
https://orcid.org/0000-0001-5039-3525
Bond (concrete to reinforcement)
Concrete construction
Consolidation
Cover
Plasticizers
Pullout tests
Reinforced concrete
Reinforcing steels
Vibration
Water-reducing agents
Bond of Reinforcement to Superplasticized Concrete
oai:kuscholarworks.ku.edu:1808/233822018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Zuo, Jun
author
Darwin, David
author
2000
The load-slip behavior of high relative rib area and conventional reinforcing bars subjected to reversed cyclic loading is compared. No. 8 (No. 25) production reinforcing bars with relative rib areas of 0.119 and 0.085 are subjected to reversed tension-tension cyclic loading to evaluate the effect of relative rib area on slip and bond deterioration. The tests demonstrate that the high relative rib area bars exhibit 50 to 70% less unloaded end slip, and 30 to 40% less loaded end slip than the conventional bars under multiple cycles of loading. The results suggest that high relative rib area bars could be used to improve
the behavior of reinforced concrete members and frame joints that are affected by bond deterioration, such as caused by seismic loading.
Zuo, J. and Darwin, D., "Bond Slip of High Relative Rib Area Bars under Cyclic Loading," ACI Structural Journal, Vol. 97, No. 2, Mar. - Apr. 2000, pp. 331-334.
http://hdl.handle.net/1808/23382
https://orcid.org/0000-0001-5039-3525
Bond (concrete to reinforcement)
Cyclic loads
Deformed reinforcement
Reinforcing steels
Seismic loading
Structural engineering
Bond Slip of High Relative Rib Area Bars under Cyclic Loading
oai:kuscholarworks.ku.edu:1808/264962018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
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Maher, Ataullah
author
Darwin, David
author
1982-03-01
A study of the behavior of the mortar constituent of concrete under monotonic and cyclic uniaxial compression is summarized. Two mixes were used, with proportions corresponding to concretes with water-cement ratios of 0.5 and 0.6. Forty-four groups of three specimens each were tested at ages ranging from 5 to 70 days. Complete monotonic and cyclic envelopes were obtained using six different loading regimes, including cycles to specified strains. Major emphasis was placed on tests using relatively high stress cycles. Accumulation of residual strain and changes in the initial modulus of elasticity were used to evaluate damage and structural change. The maximum strain appears to be the major factor con trolling damage in mortar, but the total cyclic strain range and/or the number of load cycles also play significant roles. The behavior of concrete and mortar is highly similar, indicating that the mortar constituent may control the primary stress-strain behavior of concrete.
Maher, A. and Darwin, D., “Mortar Constituent of Concrete in Compression,” Journal of the American Concrete Institute, Vol. 79, No. 2, March-April 1982, pp. 100-109.
http://hdl.handle.net/1808/26496
10.14359/10885
https://orcid.org/0000-0001-5039-3525
Compression
Compressive strength
Concretes
Cyclic loads
Damage
Modulus of elasticity
Mortars (material)
Strains
Stresses
Stress-strain relationships
Mortar Constituent of Concrete in Compression
oai:kuscholarworks.ku.edu:1808/255922017-12-07T09:01:59Zcom_1808_231col_1808_13465
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Sukmak, K.
author
Han, Jie
author
Sukmak, P.
author
Horpibulsuk, S.
author
2016-12
This paper presents a numerical parametric study on behavior of bearing reinforcement earth (BRE) walls with different backfill properties using the finite-element method software PLAXIS 2D. The primary objective of this study was to improve the understanding of bearing stress, settlement, lateral earth pressure, and horizontal wall movement of BRE walls with different backfill materials. The second objective of this study was to evaluate the effects of various soil–structure interactions, foundations, and stiffness of reinforcements on horizontal wall deformations. The backfill materials consisted of four types of soil, which were mixtures of silty clay and sand at different fine contents of 2, 20, 40, and 80% by dry weight. The model parameters for the numerical simulation were obtained from the conventional laboratory tests and back-calculated from the laboratory pullout tests of the bearing reinforcement. The geotextile elements were used to model the bearing reinforcements by converting the contribution of friction and bearing resistances to the equivalent friction resistance, which was represented by the soil–bearing reinforcement interaction ratio, Rinter. The values of Rinter decreased following a polynomial function as an increase of fine content in the ranges of 0.65–0.38 and 0.75–0.40 for the numbers of transverse members, n = 2 and 3, respectively. The simulated bearing stress in the reinforced zone decreased from the front to the back of the wall because the BRE wall behaved as a rigid body built on the relatively firm foundation retaining the unreinforced backfill. The foundation settlement decreased from the facing of the wall to the unreinforced zone for all backfill properties due to the slight rotation of the wall. The relationship between the maximum horizontal wall movement and the fine content can be expressed by a polynomial function. The maximum horizontal wall movement significantly increased as the fine content increased. The excessive movement was realized when the fine content was greater than 45%. The increase of the fine content moved the location of the maximum wall movement higher up from the mid to the top of the wall. A numerical parametric study was conducted to investigate the soil–structure interaction, foundation, and stiffness of reinforcement. These parameters affected the horizontal wall deformation, which is especially important for serviceability of BRE walls. The knowledge gained from this study provides a preliminary guideline in predicting the behavior of BRE walls and may be used to investigate other BRE walls with different wall heights and features of bearing reinforcements.
Sukmak, K., Han, J., Sukmak, P., & Horpibulsuk, S. (2016). Numerical parametric study on behavior of bearing reinforcement earth walls with different backfill material properties. Geosynth. Int, 23(6), 435-451.
http://hdl.handle.net/1808/25592
10.1680/jgein.16.00008
Geosynthetics
Bearing reinforcement
Fine content
Finite-element analysis
Mechanically stabilized earth wall
Numerical parametric study on behavior of bearing reinforcement earth walls with different backfill material properties
oai:kuscholarworks.ku.edu:1808/203422018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
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Maher, Ataullah
author
Darwin, David
author
1980-10
The behavior of the mortar constituent of concrete under cyclic compression was studied and a simple analytical model was developed to represent its cyclic behavior. The experimenta 1 work consisted of monotonic and cyclic compressive loading of mortar. Two mixes were used, with proportions corresponding to concretes with water-cement ratios of 0.5 and 0.6. Forty-four groups of specimens were tested at ages ranging from 5 to 7 days. Complete monotonic and cyclic stress-strain envelopes were obtained. A number of loading regimes were investigated, including cycles to a constant maxi mum strain. Major emphasis was placed on The degradation was tests using relatively high stress cycles. strain and load history. shown to be a continuous process and a function of both total No stability of damage in concrete and limit (fatigue limit) was indicated. The nature mortar may dominate the behavior of concrete.
Maher, A., and Darwin, D., "Mortar Constituent of Concrete Under Cyclic Compression," SM Report No. 5, University of Kansas Center for Research, Inc., Lawrence, KS, October 1980, 180 pp.
http://hdl.handle.net/1808/20342
https://orcid.org/0000-0001-5039-3525
Mortar Constituent of Concrete Under Cyclic Compression
oai:kuscholarworks.ku.edu:1808/314192021-02-11T09:01:03Zcom_1808_231col_1808_13465
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Jaramillo, Fernando
author
Desormeaux, Amanda
author
Hedlund, Johanna
author
Jawitz, James W.
author
Clerici, Nicola
author
Piemontese, Luigi
author
Rodríguez-Rodriguez, Jenny Alexandra
author
Anaya, Jesús Adolfo
author
Blanco-Libreros, Juan F.
author
Borja, Sonia
author
Celi, Jorge
author
Chalov, Sergey
author
Chun, Kwok Pan
author
Cresso, Matilda
author
Destouni, Georgia
author
Dessu, Shimelis Behailu
author
Di Baldassarre, Giuliano
author
Downing, Andrea
author
Espinosa, Luisa
author
Ghajarnia, Navid
author
Girard, Pierre
author
Gutiérrez, Álvaro G.
author
Hansen, Amy
author
Hu, Tengfei
author
Jarsjö, Jerker
author
Kalantari, Zahra
author
Labbaci, Adnane
author
Licero-Villanueva, Lucia
author
Livsey, John
author
Machotka, Ewa
author
McCurley, Kathryn
author
Palomino-Ángel, Sebastián
author
Pietron, Jan
author
Price, René
author
Ramchunder, Sorain J.
author
Ricaurte-Villota, Constanza
author
Ricaurte, Luisa Fernanda
author
Dahir, Lula
author
Rodríguez, Erasmo
author
Salgado, Jorge
author
Sannel, A. Britta K.
author
Santos, Ana Carolina
author
Seifollahi-Aghmiuni, Samaneh
author
Sjöberg, Ylva
author
Sun, Lian
author
Thorslund, Josefin
author
Vigouroux, Guillaume
author
Wang-Erlandsson, Lan
author
Xu, Diandian
author
Zamora, David
author
Ziegler, Alan D.
author
Åhlén, Imenne
author
2019-03-25
Wetlands are often vital physical and social components of a country’s natural capital, as well as providers of ecosystem services to local and national communities. We performed a network analysis to prioritize Sustainable Development Goal (SDG) targets for sustainable development in iconic wetlands and wetlandscapes around the world. The analysis was based on the information and perceptions on 45 wetlandscapes worldwide by 49 wetland researchers of the Global Wetland Ecohydrological Network (GWEN). We identified three 2030 Agenda targets of high priority across the wetlandscapes needed to achieve sustainable development: Target 6.3—“Improve water quality”; 2.4—“Sustainable food production”; and 12.2—“Sustainable management of resources”. Moreover, we found specific feedback mechanisms and synergies between SDG targets in the context of wetlands. The most consistent reinforcing interactions were the influence of Target 12.2 on 8.4—“Efficient resource consumption”; and that of Target 6.3 on 12.2. The wetlandscapes could be differentiated in four bundles of distinctive priority SDG-targets: “Basic human needs”, “Sustainable tourism”, “Environmental impact in urban wetlands”, and “Improving and conserving environment”. In general, we find that the SDG groups, targets, and interactions stress that maintaining good water quality and a “wise use” of wetlandscapes are vital to attaining sustainable development within these sensitive ecosystems.
Jaramillo, F.; Desormeaux, A.; Hedlund, J.; Jawitz, J.W.; Clerici, N.; Piemontese, L.; Rodríguez-Rodriguez, J.A.; Anaya, J.A.; Blanco-Libreros, J.F.; Borja, S.; Celi, J.; Chalov, S.; Chun, K.P.; Cresso, M.; Destouni, G.; Dessu, S.B.; Di Baldassarre, G.; Downing, A.; Espinosa, L.; Ghajarnia, N.; Girard, P.; Gutiérrez, Á.G.; Hansen, A.; Hu, T.; Jarsjö, J.; Kalantari, Z.; Labbaci, A.; Licero-Villanueva, L.; Livsey, J.; Machotka, E.; McCurley, K.; Palomino-Ángel, S.; Pietron, J.; Price, R.; Ramchunder, S.J.; Ricaurte-Villota, C.; Ricaurte, L.F.; Dahir, L.; Rodríguez, E.; Salgado, J.; Sannel, A.B.K.; Santos, A.C.; Seifollahi-Aghmiuni, S.; Sjöberg, Y.; Sun, L.; Thorslund, J.; Vigouroux, G.; Wang-Erlandsson, L.; Xu, D.; Zamora, D.; Ziegler, A.D.; Åhlén, I. Priorities and Interactions of Sustainable Development Goals (SDGs) with Focus on Wetlands. Water 2019, 11, 619. https://doi.org/10.3390/w11030619
http://hdl.handle.net/1808/31419
10.3390/w11030619
https://orcid.org/0000-0002-6769-0136
https://orcid.org/0000-0002-8137-050X
https://orcid.org/0000-0002-6745-0765
https://orcid.org/0000-0003-4547-7606
https://orcid.org/0000-0002-1600-5450
https://orcid.org/0000-0001-8082-8374
https://orcid.org/0000-0001-8242-5712
https://orcid.org/0000-0003-0507-2401
https://orcid.org/0000-0002-6937-7020
https://orcid.org/0000-0001-9873-6240
https://orcid.org/0000-0001-9408-4425
https://orcid.org/0000-0002-8180-4996
https://orcid.org/0000-0002-5206-9355
https://orcid.org/0000-0003-1452-3104
https://orcid.org/0000-0001-8928-3198
https://orcid.org/0000-0002-6152-9595
https://orcid.org/0000-0002-7978-0040
https://orcid.org/0000-0001-7986-2209
https://orcid.org/0000-0002-5270-4988
https://orcid.org/0000-0001-6373-5096
https://orcid.org/0000-0003-1050-7270
https://orcid.org/0000-0002-0102-0797
https://orcid.org/0000-0003-1554-4994
https://orcid.org/0000-0003-4303-6460
https://orcid.org/0000-0003-0670-0334
https://orcid.org/0000-0002-1350-6516
https://orcid.org/0000-0002-0888-9700
https://orcid.org/0000-0001-5247-4097
https://orcid.org/0000-0002-4292-5808
https://orcid.org/0000-0001-6111-4819
Wetlands
Wetlandscapes
SDGs
Network analysis
Sustainable development goals
Priorities
Interactions
Priorities and Interactions of Sustainable Development Goals (SDGs) with Focus on Wetlands
oai:kuscholarworks.ku.edu:1808/204092018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
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Zhao, Hong
author
Darwin, David
author
1990-06
Backscattered electron imaging and x-ray microanalysis are used to identify phases within polished epoxy impregnated cement paste sections. A silicon-magnesium standard is applied and an objective procedure is developed for the calibration of the scanning electron microscope and the image analysis system, so that the L;tensity of individual phases in cement paste appears within reproducible ranges when using backscattered electron imaging, The techniques allow for consistency in quantitative analysis of cement microstructure. Image analysis of cement phases is carried out and a statistical basis is established for the number of frames that must be analyzed to obtain a satisfactory level of confidence in the data. Backscattered electron imaging of polished surfaces of cement paste can be used to distinguish the phases within unhydrated cement particles and the phases of cement I hydration products. The existence of calcium hydroxide within inner product is confirmed, For image analysis, the number of frames required for a selected level of confidence decreases as the magnification decreases, while the total area required increases as the magnification decreases. To achieve a desired level of confidence in image analysis for the phases of hydrated cement paste, unhydrated cement particles require the greatest number of frames, while inner product and calcium silicate hydrate require the least number of frames.
Zhao, H., and Darwin, D., "Quantitative Backscattered Electron Analysis Techniques for Cement-Based Materials," SM Report No. 24 Research Grant AFOSR-89-0296, The Air Force Office of Scientific Research, June 1990, 57 pp.
http://hdl.handle.net/1808/20409
https://orcid.org/0000-0001-5039-3525
Backscattered electron imaging
Backscattering coefficient
Calibration
Cement paste
Cracking
Epoxy impregnation
Gray levels
Hydration
Image analysis
Intensities
Microstructures
Phases
Polishing
Quantitative analysis
Standard
Voids
X-ray dot mapping
X-ray microanalysis
Quantitative Backscattered Electron Analysis Techniques for Cement-Based Materials
oai:kuscholarworks.ku.edu:1808/311102021-01-13T09:00:53Zcom_1808_231col_1808_13465
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Sun, Xiaoqin
author
Medina, Mario A.
author
Zhang, Yuan
author
2019-02-22
This paper presents results of the potential thermal enhancement in building walls derived from using phase change materials (PCMs). Typical North American construction, namely, frame walls outfitted with hydrated-salt-based PCM with a melting temperature of 29°C were evaluated in well-controlled test houses under full weather conditions. It was found that PCMs produced reductions in energy gains during summer. The reductions were assessed via total heat transfer and peak heat transfer. For a 10 percentage by weight (wt%) PCM concentration, the largest peak flux reduction of 31.25% was observed when the PCM was integrated within a north-facing wall. For a 20 wt% PCM concentration, the largest peak flux reduction was 25.54% when the PCM pipes was installed on an east-facing wall. Doubling the amount of PCM did not produce improvement on heat flux reduction except for the east-facing wall. The indoor wall surface temperature and temperature amplitude was reduced by 1.5 and 1.4°C, respectively. The maximum time lag for peak heat flux was observed on the north-facing wall, which was 1.5 h for a 10 wt% PCM concentration and 2.25 h for a 20 wt% PCM concentration, respectively. To achieve the maximum energy savings, it is recommended that the PCMs be installed within west-facing walls.
Sun X, Medina MA and Zhang Y (2019) Potential Thermal Enhancement of Lightweight Building Walls Derived From Using Phase Change Materials (PCMs). Front. Energy Res. 7:13. doi: 10.3389/fenrg.2019.00013
http://hdl.handle.net/1808/31110
10.3389/fenrg.2019.00013
Phase change materials (PCMs)
Heat transfer through building walls
Energy management in buildings
Enhanced building enclosures
Heat flux reduction
Potential Thermal Enhancement of Lightweight Building Walls Derived From Using Phase Change Materials (PCMs)
oai:kuscholarworks.ku.edu:1808/313422021-02-04T09:01:05Zcom_1808_231col_1808_13465col_1808_19739
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Zhao, Hong
author
Darwin, David
author
1992-07
Procedures are developed to obtain reproducible quantitative data from polished specimens of cement paste using automated backscattered electron imaging. Signal production, contrast, image resolution, and imaging techniques are discussed. Preparation of a silicon-magnesium standard is described. Typical results and a statistical basis for establishing the number of frames required to provide confidence in the results are presented. The silicon-magnesium standard provides an objective method for setting both a scanning electron microscope and an image analysis system for quantitative backscattered electron analysis of phases within cement paste. The number of frames required for a selected degree of confidence decreases, but the total area required increases as magnification decreases. The number of frames is also a function of the specific phase, being greatest for unhydrated cement particles and least for inner product and calcium silicate hydrate.
Zhao, H. and Darwin, D., “Quantitative Backscattered Electron Analysis of Cement Paste,” Cement and Concrete Research, Vol. 22, No. 4, July 1992, pp. 695-706.
http://hdl.handle.net/1808/31342
10.1016/0008-8846(92)90022-N
https://orcid.org/0000-0001-5039-3525
Quantitative backscattered electron analysis of cement paste
oai:kuscholarworks.ku.edu:1808/267132020-05-15T08:00:36Zcom_1808_231col_1808_13465col_1808_19739
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Poudel, Ashwin
author
Lequesne, Rémy D.
author
Lepage, Andrés
author
2018-09-01
Diagonally reinforced concrete coupling beams are commonly used in mid- and high-rise buildings to connect adjacent structural walls separated by openings. Under lateral loading, these beams can undergo large inelastic deformations but must retain their strength for the system to behave as desired. It is not known how or whether resistance to axial elongation of the beams, provided by the floor diaphragms and stiff structural walls, affects the strength and deformation capacity of coupling beams.
The influence of axial restraint on diagonally reinforced concrete coupling beams was investigated by comparing the results of an axially-restrained coupling beam specimen with those of a nominally equivalent control specimen tested without axial restraint but using the same loading protocol. The presence of axial restraint increased the strength of the coupling beam specimen by approximately 30%, decreased the chord rotation capacity by approximately 10%, and resulted in buckling of diagonal reinforcement at smaller chord rotations.
Poudel, A., Lequesne, R. D., and Lepage, A., “Diagonally Reinforced Concrete Coupling Beams: Effects of Axial Restraint,” SL Report 18-3, The University of Kansas Center for Research, Inc., Lawrence, KS, September 2018, 48 pp.
http://hdl.handle.net/1808/26713
Reinforced concrete
Coupling beam
Coupled wall
Axial restraint
Cyclic loading
Diagonally Reinforced Concrete Coupling Beams: Effects of Axial Restraint
oai:kuscholarworks.ku.edu:1808/244672018-11-01T16:05:29Zcom_1808_231col_1808_13465
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Graham, David W.
author
Trippett, Clare
author
Dodds, Walter K.
author
O'Brien, Jonathan M.
author
Banner, Eric B. K.
author
Head, Ian M.
author
Smith, Marilyn S.
author
Yang, Richard K.
author
Knapp, Charles W.
author
2010-10
Denitrification is a process that reduces nitrogen levels in headwaters and other streams. We compared nirS and nirK abundances with the absolute rate of denitrification, the longitudinal coefficient of denitrification (i.e., Kden, which represents optimal denitrification rates at given environmental conditions), and water quality in seven prairie streams to determine if nir-gene abundances explain denitrification activity. Previous work showed that absolute rates of denitrification correlate with nitrate levels; however, no correlation has been found for denitrification efficiency, which we hypothesise might be related to gene abundances. Water-column nitrate and soluble-reactive phosphorus levels significantly correlated with absolute rates of denitrification, but nir-gene abundances did not. However, nirS and nirK abundances significantly correlated with Kden, as well as phosphorus, although no correlation was found between Kden and nitrate. These data confirm that absolute denitrification rates are controlled by nitrate load, but intrinsic denitrification efficiency is linked to nirS and nirK gene abundances.
Graham, D. W., Trippett, C., Dodds, W. K., O’Brien, J. M., Banner, E. B. K., Head, I. M., … Knapp, C. W. (2010). Correlations between in situ denitrification activity and nir-gene abundances in pristine and impacted prairie streams. Environmental Pollution (Barking, Essex : 1987), 158(10), 3225–3229. http://doi.org/10.1016/j.envpol.2010.07.010
http://hdl.handle.net/1808/24467
10.1016/j.envpol.2010.07.010
https://orcid.org/0000-0003-2449-890X
PMC3071025
Denitrification
Nitrogen-removal
nirS
nirK
Sediment
Water-column
qPCR
Correlations between in situ denitrification activity and nir-gene abundances in pristine and impacted prairie streams
oai:kuscholarworks.ku.edu:1808/204162018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
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Tritsch, Nathan
author
Darwin, David
author
Browning, JoAnn
author
2005-01
Free shrinkage and restrained ring tests are used to evaluate concrete mixes designed for use in bridge decks. The study consists of a series of preliminary tests and three test programs. In each program, the concrete is exposed to drying conditions of about 21C (70F) and 50% relative humidity. The concrete mixes include a typical concrete bridge deck mix from both the Kansas (KDOT) and Missouri (MoDOT) Departments of Transportation, plus seven laboratory mixes, including a basic mix used as a control, a mix similar to the control but made with Type II coarse-ground cement, the control mix cured for 7 and 14 days, a mix with a shrinkage-reducing admixture, a mix with a reduced cement content compared to that of the control, and a mix with quartzite in place of the limestone coarse aggregate used for the other mixes. The free shrinkage specimens were 76 x 76 x 286 mm (3 x 3 x 11_ in.). The concrete ring specimens were 76 mm (3 in.) or 57 mm (2_ in.) thick and 76 mm (3 in.) tall and were cast around a 13 mm (_ in.) thick steel ring with an outside diameter of 324 mm (12_ in.). The results show that as the paste content of the concrete increases, the ultimate free shrinkage also increases. Replacing Type I/II Portland cement with Type II coarse-ground cement lowers the free shrinkage and shrinkage rate, and adding a shrinkage-reducing admixture significantly reduces these values. Extending the curing time lowers free shrinkage at early ages due to delayed drying and expansion during curing, but does not affect the restrained shrinkage rate at the start of drying. The free shrinkage and restrained shrinkage decrease as the surface to volume ratio of the concrete decreases. One out of 39 restrained rings cracked during testing, and the mix that did crack, MoDOT, had the highest paste content and highest shrinkage rate of all the mixes.
Tritsch, N., Darwin, D., and Browning, J., “Evaluating Shrinkage and Cracking Behavior of Concrete Using Restrained Ring and Free Shrinkage Tests,” SM Report No. 77, University of Kansas Center for Research, Inc., Lawrence, Kansas, January 2005, 178 pp.
http://hdl.handle.net/1808/20416
https://orcid.org/0000-0001-5039-3525
Concrete
Shrinkage
Cracking
Free shrinkage
Restrained shrinkage
Ring test
Cement
Shrinkage-reducing admixture (SRA)
Curing
Evaluating Shrinkage and Cracking Behavior of Concrete Using Restrained Ring and Free Shrinkage Tests
oai:kuscholarworks.ku.edu:1808/313212021-02-03T09:00:59Zcom_1808_231col_1808_13465col_1808_19739
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O’Reilly, Matthew
author
Darwin, David
author
Browning, JoAnn
author
Xing, Lihua
author
Locke, Carl E., Jr.
author
Virmani, Y. Paul
author
2013-09
Three commercially available corrosion inhibitors—calcium nitrite, a solution of amines and esters, and an alkenyl-substituted succinic acid salt—are evaluated in conjunction with conventional reinforcement in concrete based on corrosion rate, metal loss, the critical chloride corrosion threshold (CCCT), pore solution analyses, and concrete compressive strength. All three inhibitors increase time to corrosion initiation and decrease corrosion rate, but are less effective in cracked concrete than in uncracked concrete. Of the three inhibitors, the alkenyl-substituted succinic acid salt results in the greatest decrease in corrosion rate, but exhibits the lowest CCCT—below that measured in concrete with no inhibitor. The compressive strengths of concretes containing the amine-ester inhibitor and the alkenyl substituted succinic acid salt were 15% and 60% lower, respectively, than concrete without an inhibitor. For the latter inhibitor, pore solution analyses indicated elevated sulfate contents at 1 and 7 days, which may explain the low CCCT and strength. Paste containing the amine-ester inhibitor had an elevated sulfate content at 7 days.
O'Reilly, M., Darwin, D., Browning, J., Xing, L., Locke Jr., C.E., and Virmani, P., "Effect of Corrosion Inhibitors on Concrete Pore Solution Composition and Corrosion Resistance," ACI Materials Journal, Vol. 110, No. 5, September-October 2013, pp. 577-585.
http://hdl.handle.net/1808/31321
https://orcid.org/0000-0001-5039-3525
https://orcid.org/0000-0003-3968-4342
Chlorides
Corrosion
Corrosion inhibitor
Cracking
Durability
Pore solution
Steel reinforcement
Effect of Corrosion Inhibitors on Concrete Pore Solution Composition and Corrosion Resistance
oai:kuscholarworks.ku.edu:1808/232642018-07-03T01:48:35Zcom_1808_231col_1808_13465
00925njm 22002777a 4500
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Yuan, Jiqiu
author
Matamoros, Adolfo B.
author
Darwin, David
author
2016
The effect of preexisting subsurface cracks on the strength of lap splices was investigated. Ten full-scale beams with No. 11 (No. 36) bars and lap splice lengths of 33, 79, and 120 in. (838, 2007, and 3048 mm) were tested. The beams had mitigating features that prevented catastrophic failure upon propagation of the preexisting cracks, such as staggered splices and the presence of some reinforcement crossing the plane of the cracks. The effect of preexisting cracks on the bar stress at failure was found to be most severe for the shortest splices and not significant for the two other splice lengths evaluated. The effect was found to be dependent on the amount of reinforcement crossing the plane of the cracks. Splice strength was unaffected in beams with the largest amount of reinforcement, and reduced on the order of 50% in beams without any reinforcement crossing the plane of the cracks.
Yuan, J., O'Reilly, M., Matamoros, A., and Dawrin, D., "Effect of Preexisting Cracks on Lap Splice Strength of Reinforcing Bars," ACI Structural Journal, Vol. 113, No. 1, July-August 2016, pp. 901-812.
http://hdl.handle.net/1808/23264
https://orcid.org/0000-0001-5039-3525
Bond strength
Cold joint
Crack width
Cracks
Cyclic loading
Lap Splice
Preexisting cracks
Effect of Preexisting Cracks on Lap Splice Strength of Reinforcing Bars
oai:kuscholarworks.ku.edu:1808/314392021-02-18T09:00:55Zcom_1808_231col_1808_13465
00925njm 22002777a 4500
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Rahmaninezhad, Seyed Mustapha
author
Han, Jie
author
Kakrasul, Jamal Ismael
author
Weldu, Mehari
author
2018-11-05
In design of reinforced soil structures, pullout capacity of reinforcement in an anchorage zone is an important parameter for stability analysis. This parameter is generally quantified by conducting laboratory or field pullout tests. In the laboratory pullout test, the reinforcement is embedded in the soil mass at a normal stress, which is commonly applied by a pressurized airbag or a hydraulic jack through a rigid plate, and then a horizontal tensile force is applied to the reinforcement. This article reports an experimental study conducted to evaluate the effect of the load application method using an airbag with and without stiff wooden plates on the vertical stress distribution and the pullout capacities and deformations of extensible (geogrid) and inextensible reinforcement (steel strip) in the soil in a large pullout box. This study monitored the distributions of the vertical earth pressures at the top and bottom of the soil mass in the pullout box, and at the level of reinforcement using earth pressure cells. The measured earth pressures show that the airbag with stiff plates resulted in a nonuniform pressure distribution, whereas the tests with an airbag directly on the soil had an approximately uniform pressure distribution. The nonuniform pressure distribution resulting from the airbag with stiff plates reduced the pullout resistance of the reinforcement as compared with that using the same airbag without stiff plates. The nonuniform pressure distribution effect was more significant for narrow inextensible reinforcements than wide extensile reinforcements. The test results also show that the displacements in the cross section of the same transverse bar were not equal when the normal load was applied through stiff plates.
S. Rahmaninezhad, J. Han, J. Kakrasul, and M. Weldu, "Stress Distributions and Pullout Responses of Extensible and Inextensible Reinforcement in Soil Using Different Normal Loading Methods," Geotechnical Testing Journal 42, no. 6 (2019): 1606-1623. https://doi.org/10.1520/GTJ20180102
http://hdl.handle.net/1808/31439
10.1520/GTJ20180102
https:// orcid.org/0000-0003-3137-733X
Stress Distributions and Pullout Responses of Extensible and Inextensible Reinforcement in Soil Using Different Normal Loading Methods
oai:kuscholarworks.ku.edu:1808/198492018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
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O’Reilly, Matthew
author
Darwin, David
author
Browning, JoAnn
author
2009-11
The bond strength of No. 6 zinc-clad bars was compared to that of uncoated conventional bars using beam-end tests performed in accordance with ASTM A944. The zinc-clad bars were also subjected to bend tests using bend diameters of 3.75, 4.5, and 6.0 in. (5, 6, and 8 bar diameters), as required for conventional and epoxy-coated No. 6 deformed bars, respectively, in accordance with ASTM A615 and ASTM A775.
The zinc-clad bars provided bond strength equal to 94.9 percent of that exhibited by conventional bars from the same heat of steel. The difference in bond strength is not statistically significant. The two types of reinforcement exhibited similar force-bond slip behavior. The cladding exhibited significant local deformation and, in some cases, tearing following bond failure. Full-scale splice and bending strength tests on reinforced concrete members to compare the performance of clad and conventional reinforcement are recommended to develop design criteria for use in the ACI Building Code (ACI 318). The bend test specimens with the 3.75-in. bend diameter exhibited small transverse tension cracks in the cladding on the outside of the bend. Cracks ranged in length from 0.1 in. to one-half the circumference of the bar. One of six bend test specimens with the 4.5 in. diameter bend exhibited transverse cracking in the cracking at the outside of the bend. The crack was located on the cladding seam and had a length less than 0.1 in. No other damage was observed for the specimens with the 4.5 in. diameter bend. The bend test specimens with the 6.0-in bend diameter exhibited no visible damage to the cladding. To limit access of moisture and chlorides between the cladding and the underlying reinforcing bar, tightly fitting corrosion-resistant caps for the ends of the bars should be developed and marketed along with the clad reinforcement.
O'Reilly, M., Darwin, D., and Browning, J. P., "Beam-End Bond Tests and Bend Tests of Zinc-Clad No. 6 reinforcing Bars" SL Report 09-2, University of Kansas Center for Research, Inc., Lawrence, Kansas, December 2009, 20 pp.
http://hdl.handle.net/1808/19849
https://orcid.org/0000-0001-5039-3525
Bent reinforcement
Bond
Clad reinforcement
Deformed reinforcement
Zinc cladding
Beam-End Bond Tests and Bend Tests of Zinc-Clad No. 6 reinforcing Bars
oai:kuscholarworks.ku.edu:1808/300682020-03-11T08:00:23Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
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Farshadfar, Omid
author
O’Reilly, Matthew
author
Darwin, David
author
2018-10
The corrosion resistance of coated ASTM A1035 Type CL (2% Cr) and CM (4% Cr) steel bars produced by MMFX Technologies were evaluated in both cracked and uncracked concrete as well as in the rapid macrocell test. Coated bars were evaluated after simulating damage typical to that which would occur during normal handling and placement at a construction site. Bars were compared to the performance of epoxy-coated (ASTM A775) reinforcement from previous studies, and a life-cycle cost analysis over a 75-year design life was performed.
Both epoxy-coated bars tested (2% and 4% chromium) exhibited reduced disbondment of the coating at the end of testing compared to conventional epoxy-coated reinforcement. The 4% chromium coated bars also exhibited significantly lower corrosion rates relative to conventional epoxy-coated reinforcement, with corrosion rates between 15 and 30% of that of conventional ECR. Coated bars with 2% chromium performed comparably or slightly better than conventional epoxy-coated reinforcement (depending on the test method), but the differences were not statistically significant. The life-cycle cost analysis found that epoxy-coated MMFX with 4% chromium was the most cost-effective reinforcement of the bars in this study.
Farshadfar, O., O’Reilly, M., and Darwin, D., “Corrosion Performance of Plain and Epoxy-Coated MMFX Bars,” SL Report 18-4a, University of Kansas Center for Research, Inc., Lawrence, KS, October 2018, 78 pp.
http://hdl.handle.net/1808/30068
https://orcid.org/0000-0001-5039-3525
Chromium
Concrete
Corrosion
MMFX
Reinforcing steel
Corrosion Performance of Epoxy-Coated MMFX Bars
oai:kuscholarworks.ku.edu:1808/221952019-04-12T14:15:54Zcom_1808_231col_1808_13465
00925njm 22002777a 4500
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Chaney, Nathaniel W.
author
Roundy, Joshua K.
author
Herrera-Estrada, Julio
author
Wood, Eric F.
author
2015-01-28
The spatial heterogeneity of soil moisture remains a persistent challenge in the design of in situ measurement networks, spatial downscaling of coarse estimates (e.g., satellite retrievals), and hydrologic modeling. To address this challenge, we analyze high-resolution (∼9 m) simulated soil moisture fields over the Little River Experimental Watershed (LREW) in Georgia, USA, to assess the role and interaction of the spatial heterogeneity controls of soil moisture. We calibrate and validate the TOPLATS distributed hydrologic model with high to moderate resolution land and meteorological data sets to provide daily soil moisture fields between 2004 and 2008. The results suggest that topography and soils are the main drivers of spatial heterogeneity over the LREW. We use this analysis to introduce a novel network design method that uses land data sets as proxies of the main drivers of local heterogeneity (topography, land cover, and soil properties) to define unique and representative hydrologic similar units (subsurface, surface, and vegetation) for probe placement. The calibration of the hydrologic model and network design method illustrates how the use of hydrologic similar units in hydrologic modeling could minimize computation and guide efforts toward improved macroscale land surface modeling.
Chaney, N. W., Roundy, J. K., Herrera-Estrada, J. E., & Wood, E. F. (2015). High-resolution modeling of the spatial heterogeneity of soil moisture: Applications in network design. Water Resour. Res., 51(1), 619–638. doi:10.1002/2013wr014964
http://hdl.handle.net/1808/22195
10.1002/2013WR014964
Topography
Network Design
Land Surface
Soil Moisture Modeling
High-resolution modeling of the spatial heterogeneity of soil moisture: Applications in network design
oai:kuscholarworks.ku.edu:1808/204742018-12-27T19:13:12Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
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Axelsson, Henrik
author
Darwin, David
author
Locke, Carl E., Jr.
author
1999-08
The mechanism of corrosion of reinforcing steel in concrete is discussed based on electrochemical and electron microscopy observations. The importance of calcium hydroxide precipitation on the steel surf ace in the steel/mortar interface is evaluated by placing filter paper around reinforcing steel bar specimens prior to casting in mortar, thus preventing direct contact between steel and mortar. The voids created presumably prevent calcium hydroxide crystals from forming on the steel surface. Specimens with filter paper are compared to specimens with good steel/mortar adhesion using rapid macrocell and corrosion potential tests and a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). The study included 21 macrocell and 16 corrosion potential tests run for periods of 25 to 89 days. Seven specimens were subjected to SEM/EDS analysis. Electrochemical results are mixed due to the influence of crevice corrosion. but it is generally shown that better protection is provided for steel with good steel/mortar adhesion than with filter paper. The filter paper, indeed, prevents calcium hydroxide crystals from forming on the steel surface. Corrosion products on active specimens with good mortar cover are shown to grow preferentially in voids created by air bubbles trapped in the mortar. The protective mechanism of calcium hydroxide crystals is proposed to be due to pH buffering by the hydroxyl ions released when the crystals are dissolved, a fact that cannot be proven easily, since many other factors may contribute to the protection of steel in concrete. This report is based on research by Henrik J. Axelsson in partial fulfillment of the requirements of the M.Sc. degree in Engineering Physics at Chalmers University of Technology, Gothenburg. Sweden. The research was sponsored by the Department of Civil and Envirorunental Engineering at the University of Kansas and by Structural Metals, Inc.
Axelsson, H., Darwin, D., and Locke, C.E., Jr., "Influence of Adhesion at Steel/Mortar Interface on Corrosion Characteristics of Reinforcing Steel," SL Report 99-4, University of Kansas Center for Research, Inc., Lawrence, Kansas, July 1999, 55 pp.
http://hdl.handle.net/1808/20474
https://orcid.org/0000-0001-5039-3525
Influence of Adhesion at Steel/Mortar Interface on Corrosion Characteristics of Reinforcing Steel
oai:kuscholarworks.ku.edu:1808/343422023-06-14T06:06:21Zcom_1808_231col_1808_13465
00925njm 22002777a 4500
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Collins, William N.
author
Yount, Tristan D.
author
Sherman, Ryan J.
author
Leon, Roberto T.
author
Connor, Robert J.
author
2023-04-26
Impact energy tests are an efficient method of verifying adequate toughness of steel prior to it being put into service. Based on a multitude of historical correlations between impact energy and fracture toughness, minimum impact energy requirements that correspond to desired levels of fracture toughness are prescribed by steel bridge design specifications. Research characterizing the fracture behavior of grade 485 and 690 (70 and 100) high-performance steel utilized impact, fracture toughness, and crack arrest testing to verify adequate performance for bridge applications. Fracture toughness results from both quasi-static and dynamic stress intensity rate tests were analyzed using the most recently adopted master curve methodology. Both impact and fracture toughness tests indicated performance significantly greater than the minimum required by material specifications. Even at the AASHTO Zone III service temperature, which is significantly colder than prescribed test temperatures, minimum average impact energy requirements were greatly exceeded. All master curve reference temperatures, both for quasi-static and dynamic loading rates, were found to be colder than the Zone III minimum service temperature. Three correlations between impact energy and fracture toughness were evaluated and found to estimate reference temperatures that are conservative by 12 to 50 °C (22 to 90 °F) on average for the grades and specimen types tested. The evaluation of two reference temperature shifts intended to account for the loading rate was also performed and the results are discussed.
Collins, W.N.; Yount, T.D.; Sherman, R.J.; Leon, R.T.; Connor, R.J. Dynamic Fracture and Crack Arrest Toughness Evaluation of High-Performance Steel Used in Highway Bridges. Materials 2023, 16, 3402. https://doi.org/10.3390/ma16093402
https://hdl.handle.net/1808/34342
10.3390/ma16093402
https://orcid.org/0000-0002-2835-6389
https://orcid.org/0000-0001-7525-4775
https://orcid.org/0000-0001-8753-2496
PMC10180142
Impact energy
Fracture toughness
Master curve
Stress intensity rate
High-performance steel
Dynamic Fracture and Crack Arrest Toughness Evaluation of High-Performance Steel Used in Highway Bridges
oai:kuscholarworks.ku.edu:1808/323542022-01-07T09:00:57Zcom_1808_231col_1808_13465
00925njm 22002777a 4500
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Lakhina, Shefali Juneja
author
Sutley, Elaina J.
author
Wilson, Jay
author
2021-03-25
In recent years there has been an increasing emphasis on achieving convergence in disaster research, policy, and programs to reduce disaster losses and enhance social well-being. However, there remain considerable gaps in understanding “how do we actually do convergence?” In this article, we present three case studies from across geographies—New South Wales in Australia, and North Carolina and Oregon in the United States; and sectors of work—community, environmental, and urban resilience, to critically examine what convergence entails and how it can enable diverse disciplines, people, and institutions to reduce vulnerability to systemic risks in the twenty-first century. We identify key successes, challenges, and barriers to convergence. We build on current discussions around the need for convergence research to be problem-focused and solutions-based, by also considering the need to approach convergence as ethic, method, and outcome. We reflect on how convergence can be approached as an ethic that motivates a higher order alignment on “why” we come together; as a method that foregrounds “how” we come together in inclusive ways; and as an outcome that highlights “what” must be done to successfully translate research findings into the policy and public domains.
Lakhina, S.J., Sutley, E.J. & Wilson, J. “How Do We Actually Do Convergence” for Disaster Resilience? Cases from Australia and the United States. Int J Disaster Risk Sci 12, 299–311 (2021). https://doi.org/10.1007/s13753-021-00340-y
http://hdl.handle.net/1808/32354
10.1007/s13753-021-00340-y
PMC7993904
Convergence research
Disaster resilience
Disaster risk reduction
Research ethics
“How Do We Actually Do Convergence” for Disaster Resilience? Cases from Australia and the United States
oai:kuscholarworks.ku.edu:1808/306472021-01-31T03:09:22Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
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Weber-Kamin, Alexander S.
author
Lequesne, Rémy D.
author
Lepage, Andrés
author
2020-08
The use of high-strength steel bars in reinforced concrete coupling beams has the potential to reduce reinforcement congestion and support more efficient design and construction methods. A series of tests was conducted to investigate the effects of high-strength reinforcement on coupling beam behavior.
Eleven large-scale coupling beam specimens were tested under fully reversed cyclic displacements of increasing magnitude. The main variables of the test program included: yield stress of the primary longitudinal reinforcement (Grades 80, 100, and 120 [550, 690, and 830]), span-to-depth (aspect) ratio (1.5, 2.5, and 3.5), and layout of the primary longitudinal reinforcement (diagonal [D] and parallel [P]). All beams had the same nominal concrete compressive strength (8,000 psi [55 MPa]) and cross-sectional dimensions (12 by 18 in. [310 by 460 mm]). Beams were designed for target shear stresses of 8√f’c psi (0.67√f’c) for D-type beams and 6√f’c psi (0.5√f’c) for P- type beams. Transverse reinforcement was Grade 80 (550) in all but one beam, which had Grade 120 (830) reinforcement.
The test program is documented by presenting the details of specimen construction, test setup, instrumentation, and loading protocol. Documentation of test data includes material properties, cyclic force-deformation response, progression of damage, calculated and measured strengths, initial stiffness, and measured reinforcement strains. Analysis of test data includes hysteretic energy, changes in beam length and depth, components of chord rotation, and the development of an equation for estimating chord rotation capacity.
Weber-Kamin, A. S., Lequesne, R. D., and Lepage, A., “Reinforced Concrete Coupling Beams with High-Strength Steel Bars,” SM Report No. 143, The University of Kansas Center for Research, Inc., Lawrence, KS, August 2020, 598 pp.
http://hdl.handle.net/1808/30647
Reinforced Concrete Coupling Beams with High-Strength Steel Bars
oai:kuscholarworks.ku.edu:1808/200762018-12-27T19:13:41Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Darwin, David
author
Browning, JoAnn
author
Locke, Carl E., Jr.
author
Van Nguyen, Trung
author
2007-07
the rapid macrocell, Southern Exposure, cracked beam, and linear polarization resistance tests. The systems include bars that are pretreated with zinc chromate to improve the adhesion between the epoxy and the reinforcing steel; two epoxies with improved adhesion to the reinforcing steel; one inorganic corrosion inhibitor, calcium nitrite; two organic corrosion inhibitors; an epoxy-coated bar with a primer containing microencapsulated calcium nitrite; the three epoxy-coated bars with improved adhesion combined with the corrosion inhibitor calcium nitrite; and multiple coated bars with an initial 50-μm (2-mil) coating of 98 percent zinc and 2 percent aluminum followed by a conventional epoxy-coating. The systems are compared with conventional uncoated reinforcement and conventional epoxy-coated reinforcement. The results presented in this report represent the findings obtained during the first half of a 5-year study that includes longer-term ASTM G 109 and field tests. In the short-term tests used to date, the epoxy-coatings evaluated provide superior corrosion protection to the reinforcing steel. The results also indicate that the bars will continue to perform well in the longer term, although the tests do not evaluate the effects of long-term reductions in the bond between the epoxy and the reinforcing steel. The corrosion rate on the exposed regions of damaged epoxy-coated reinforcement is somewhat higher than the average corrosion rate on the surface of uncoated reinforcement subjected to similar exposure conditions. The use of concrete with a reduced water-cement ratio improves the corrosion performance of both conventional and epoxy-coated reinforcement in uncracked concrete but has little effect in cracked concrete. Increased adhesion between the epoxy and reinforcing steel provides no significant improvement in the corrosion resistance of epoxy-coated reinforcement. It appears that corrosion inhibitors in concrete and the primer coating containing microencapsulated calcium nitrite improve the corrosion resistance of the epoxy-coated steel in uncracked concrete, but not in cracked concrete. The zinc coating on the multiple coated bars acts as a sacrificial barrier and provides some corrosion protection to the underlying steel in both uncracked and cracked concrete. The degree of protection, however, cannot be evaluated based on the results available to date.
Darwin, D., Browning, J., Locke, C.E., Jr., and Nguyen, T., "Multiple Corrosion Protection Systems for Reinforced Concrete Bridge Components," Publication No. FHWA-HRT-07-043, Federal Highway Administration, also SM Report No. 84, University of Kansas Center for Research, Inc., Lawrence, Kansas, July 2007, 116 pp.
http://hdl.handle.net/1808/20076
https://orcid.org/0000-0001-5039-3525
Adhesion
Chlorides
Concrete
Corrosion
Corrosion inhibitor
Durability
Epoxy-coated steel
Zinc-coated steel
Multiple Corrosion Protection Systems for Reinforced Concrete Bridge Components
oai:kuscholarworks.ku.edu:1808/204052018-07-03T01:48:34Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
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Cong, Xiaofeng
author
Gong, Shanglong
author
Darwin, David
author
McCabe, Steven L.
author
1990-04
Controversy exists as to why silica fume increases the strength of concrete when it is used as a partial replacement for cement. Some evidence supports the view that the increase in strength is due to an increase in the strength of the cement paste constituent of concrete. However, contradictory evidence exists that shows no increase in the strength of cement paste, but substantial increases in concrete strength, when silica fume is used. The latter evidence is used to support the theory that silica fume strengthens concrete by strengthening the bond between cement paste and aggregate. This study is designed to explain the contradictory evidence and establish the role played by silica fume in controlling the strength of concrete and its constituent materials. These goals are accomplished using cement pastes, mortars, and concretes with water-cementitious material ratios ranging from 0.30 to 0.39. Mixtures incorporate no admixtures, a superplasticizer only, or silica fume and a superplasticizer. The research demonstrates that replacement of cement by silica fume and the addition of a superplasticizer increases the strength of cement paste. It also demonstrates that cement paste specimens, with or without silica fume, can exhibit reduced strength compared to other specimens with the same water-cementitious material ratio if the material segregates during fabrication, thus explaining some earlier experimental observations. The segregation of cement paste is caused by high superplasticizer dosages that do not cause segregation of concrete with the same water-cementitious material ratio. Concrete containing silica fume as a partial replacement for cement exhibits an increased compressive strength because of the improved strength of its cement paste constituent. Changes in the paste-aggregate interface caused by silica fume appear to have little effect on the uniaxial compressive strength of concrete.
Cong, X., Gong, S., Darwin, D., and McCabe, S.L., "Role of Silica Fume in Compressive Strength of Cement Paste, Mortar, and Concrete," SL Report 90-2, The University of Kansas Structural Engineering & Materials Laboratory, April 1990, 37 pp.
http://hdl.handle.net/1808/20405
https://orcid.org/0000-0001-5039-3525
Role of Silica Fume in Compressive Strength of Cement Paste, Mortar, and Concrete
oai:kuscholarworks.ku.edu:1808/204762018-07-03T01:48:35Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Sperry, Jayne
author
Darwin, David
author
O’Reilly, Matthew
author
Lequesne, Rémy D.
author
2015-12
Key factors affecting the anchorage strength of hooked bars are investigated and design guidelines for the development length of hooked bars that apply to both conventional and highstrength steel and concrete are presented. In this study, 337 beam column joint specimens were tested. Parameters included number of hooks (2, 3, or 4), concrete compressive strength (4,300 to 16,510 psi [30 to 114 MPa]), bar stress at failure (22,800 to 141,600 psi [157 to 976 MPa]), bar diameter (No. 5, 8, and 11 [No. 19, 25, and 36]), concrete side cover (1.5 to 4 in. [38 to 102 mm]), quantity of confining reinforcement in the joint region, hooked bar spacing (3 to 11 bar diameters measured center-to-center), hook bend angle (90° or 180°), placement of the hook (inside or outside the column core, and inside or outside of the column compressive region), and embedment length. Using a subset of 214 simulated exterior beam-column joints, expressions are developed to characterize the anchorage capacity of hooked bars as a function of embedment length, concrete compressive strength, bar diameter, and amount and orientation of confining reinforcement. The results of this study show that front failure plays an important role in the behavior of hooked bars, which contrasts with the findings of previous studies. The provisions in the 2014 ACI Building Code become less conservative as the concrete compressive strength and bar diameter increase. The contribution of concrete compressive strength to the anchorage capacity of hooked bars can be represented by the concrete compressive strength to the 0.29 power, in contrast to the 0.5 power currently used in the ACI 318-14 Code. Confining reinforcement, expressed as the area of confining reinforcement per confined hooked bar, provides in an incremental rather than percentage increase in the anchorage capacity of hooked bars. Confining reinforcement parallel to the straight portion of the hooked bars contributes to the anchorage capacity of both 90° and 180° hooked bars. The contribution of confining reinforcement oriented perpendicular to the straight portion of the hooked bar differs from that of confining reinforcement parallel to the straight portion of the hooked bar and may be similar to the contribution of confining reinforcement to the development and splice strength of straight bars. Hooked bars with 90° and 180° bend angles produce similar anchorage capacities and can be used interchangeably. Increasing concrete side cover from 2.5 to 3.5 in. (64 to 89 mm) does not increase the anchorage capacity of hooked bars. These observations are incorporated into a new design equation that allows for the conservative design of hooked bars at concrete strengths up to 16,000 psi and steel stresses up to 120 ksi, well above current Code limits.
Sperry, J., Darwin, D., O'Reilly, M., and Lequesne, R., "Anchorage Strength of Conventional and High-Strenth Hooked Bars in Concrete," SM Report No. 115, The University of Kansas Center for Research, Inc., Lawrence, KS, December 2015, 281 pp.
http://hdl.handle.net/1808/20476
https://orcid.org/0000-0001-5039-3525
Anchorage
Beam-column joints
Bond and development
Concrete
High-strength concrete
High-strength steel
Hooks
Reinforcement
Reinforced concrete
Side cover
Bend angle
Reliability
Variability
Anchorage Strength of Conventional and High-Strength Hooked Bars in Concrete
oai:kuscholarworks.ku.edu:1808/198192018-11-16T16:19:17Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Farshadfar, Omid
author
Ajaam, Ali Hussein
author
Hano, Muna
author
O’Reilly, Matthew
author
Darwin, David
author
2014-08
The bond strength of two sets of No. 7 reinforcing bars was evaluated in accordance with ASTM A944. One set satisfied the criterion for maximum deformation spacing specified in ASTM A615, while the other had deformations that exceeded the maximum spacing. All bars exceeded the requirements for minimum deformation height. Research related to the effect of deformation properties on bond strength, including the research used to establish the requirements for deformations in ASTM A615, is also reviewed. The test results match earlier research and demonstrate that (1) the bond strength of the bars with deformation spacings that exceed those specified in ASTM A615 is similar to the bond strength of the bars that meet the specification, and (2) the differences in bond strength observed in the tests are not statistically significant. The bars tested in this study with deformation spacings that exceed those specified in ASTM A615 will provide satisfactory bond performance and can be used in all concrete construction.
Farshadfar, O., Ajaam, A., Hano, M., O'Reilly, M., Darwin, D., "Bond Strength of Reinforcing Bars with Deformation Spacings that Exceed Maximum Specified in ASTM A615," SL Report 14-2, The University of Kansas Center for Research, Inc., Lawrence, KS, August 2014, 26 pp.
http://hdl.handle.net/1808/19819
https://orcid.org/0000-0001-5039-3525
Bond (concrete to reinforcement)
Deformed reinforcement
Relative rib area
Structural engineering
Bond Strength of Reinforcing Bars with Deformation Spacings that Exceed Maximum Specified in ASTM A615
oai:kuscholarworks.ku.edu:1808/198432021-02-09T09:00:38Zcom_1808_231col_1808_13465col_1808_19739
00925njm 22002777a 4500
dc
Sturgeon, W. Joseph
author
O’Reilly, Matthew
author
Darwin, David
author
Browning, JoAnn
author
2010-11
The corrosion performance of epoxy-coated steel meeting the requirements of ASTM A775 with the coating in an undamaged condition and two damaged conditions (0.04% and 0.83% damaged area) is evaluated in accordance with Annexes A1 and A2 of ASTM 955 and compared with the corrosion performance of conventional reinforcing steel meeting the requirements of ASTM A615 steel and low-carbon, chromium steel meeting the requirements of A1035, with the latter in both the as-received and pickled conditions.
Epoxy-coated bars provide significantly better corrosion performance than conventional reinforcing steel. The macrocell corrosion rates for bars with a damaged area equal to 0.04% of the area exposed to the solutions in the test are relatively low, and are, on average, similar to those observed for the undamaged epoxy-coated bars. Both undamaged and 0.04% damaged area epoxy-coated specimens meet the requirements for stainless steels specified in Annexes A1 and A2 of ASTM 955, with an average corrosion rate not exceeding 0.25 μm/yr and the corrosion rate of no individual specimen exceeding 0.50 μm/yr. The macrocell corrosion rates for bars with a damaged area equal to 0.83% of the area exposed to the solutions in the test average 1 to 1.5 μm/yr based on total bar area under the severe exposure conditions provided. Conventional and A1035 steel exhibit average values near 30 μm/yr for and 20 μm/yr, respectively. Pickling provides initial protection to A1035 steel bars, and to some bars for the duration of the test, but once corrosion initiates, corrosion appears to be similar to that observed on non-pickled bars.
Sturgeon, W.J., O'Reilly, M., Darwin, and Browning, J.P., "Rapid Macrocell Tests of Enduramet® 2304 Stainless Steel Bars," SL Report 10-3, University of Kansas Center for Research, Inc., Lawrence, Kansas, September 2010. 40 pp.
http://hdl.handle.net/1808/19843
https://orcid.org/0000-0001-5039-3525
Chlorides
Concrete
Corrosion
Epoxy coating
Macrocell
Reinforcing steel
Rapid Macrocell Tests of Enduramet® 2304 Stainless Steel Bars
marc///col_1808_13465/100