Infrastructure Research Institute Scholarly Works

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This collection contains technical reports and publications of the Infrastructure Research Institute.

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Deformation Capacity of Reinforced Concrete Column-to-Foundation Connections with Anchorage/Breakout Failures
(University of Kansas Center for Research, Inc., 2024-09-11) Niyonyungu, Ferdinand; Lequesne, Rémy D.; Lepage, Andrés; Darwin, David
Recent tests of column-foundation connections showed that these types of connections are prone to fail by concrete breakout at low deformation demands when subjected to cyclic loading. This report describes tests of four large-scale reinforced concrete column-foundation connections that were designed to investigate how foundation reinforcement details affect deformation capacity. Primary variables were the amount of foundation flexural reinforcement (spaced at 5.5 in., 9 in., or 12 in. in two directions), whether foundation transverse reinforcement was provided around the column, and foundation depth (18 in. or 30 in.). All specimens had the same column nominal dimensions, column reinforcement, concrete compressive strength (6000 psi), and nominal reinforcing bar yield stress (60 ksi). Lateral loads were applied to the column, while the foundations had vertical simple supports located 10 ft apart and a horizontal support 9 in. from the top of the foundation. The foundations were designed for the shear and flexural demands associated with the expected flexural strength of the column. All specimens exhibited similar strengths, which were limited by column flexural yielding, and failed by breakout within the foundation that limited the deformation capacity. The results show that deformation capacity of column-foundation connections is sensitive to the amount of foundation longitudinal reinforcement, and that adding longitudinal bars or small quantities of foundation shear reinforcement delays breakout in specimens like those tested. Conversely, increasing the foundation depth without also increasing column bar embedment length led to somewhat earlier breakout and reduced deformation capacity. Strain measurements suggested that initiation of breakout is linked to bond strength decay along the straight portion of the column hooked bars, which in turn may be linked to the magnitude of strains in the top mat of foundation longitudinal reinforcement. Strains in the top mat of foundation longitudinal bars were larger than in the bottom mat and larger than expected based on strength calculations, suggesting that the top mat was more active in resisting transfer moment than the bottom mat.
Compression Lap Splices and Compression Development of Headed and Hooked Bars in Beam-Column Joints
(University of Kansas Center for Research, Inc., 2024-07) Valentini, Guido; Lequesne, Rémy D.; Lepage, Andrés; Darwin, David
ACI 318-19 Building Code provisions for compression lap splices and for headed and hooked bar development in special moment frame (SMF) joints were evaluated against databases of test results. Recommendations are made for simplifying and improving code requirements. Compression lap splice length provisions (ACI 318-19 §25.5.5) produce calculated lengths longer than Class B tension lap splice lengths under certain design conditions. The provisions were shown to also be a poor fit to a database of 89 test results (with 72 specimens in the database violating the ACI 318-19 minimum lap splice length). Several equations exist that better fit the dataset, including several tension development length equations. Defining compression lap splice length requirements as a function of the tension development length is a more accurate alternative to §25.5.5 that eliminates the need to calculate both tension and compression development lengths and prevents design cases where calculated lengths are longer in compression than in tension. Provisions for headed and hooked bar development were compared against databases of exterior beam-column connection tests with 35 and 27 specimens, respectively. Analyses show that satisfying the compression development length requirements of §25.4.9, as mandated by §18.8.2.2, is not necessary for preventing anchorage distress in special moment frame joints with either headed or hooked bars. None of the 59 specimens (35 with headed bars and 24 with hooked bars) with drift ratio capacities above 3% satisfied §25.4.9. The analyses also show that joints that did not satisfy the ACI 318-19 provisions for headed or hooked bar tension development length (§18.8.5.2 for headed bars and §25.4.3 for hooked bars) still exhibited satisfactory behavior, suggesting that §18.8.5.2 and §25.4.3 are considerably conservative. Other equations were evaluated and found to better fit the data, including the equation in ACI 318-19 §18.8.5.1, which analyses suggest might be applicable to both headed and hooked bars.
Development of Large High-Strength Reinforcing Bars with Standard Hooks and Heads
(University of Kansas Center for Research, Inc., 2023-07) Banaeipour, Ali; Darwin, David; O'Reilly, Matthew; Lequesne, Rémy D.; Lepage, Andrés; Blessent, Matthew
Hooked and headed reinforcing bars are viable alternatives for development of reinforcing steel when member geometry does not allow for a straight deformed bar to fully develop its yield strength. Current design provisions in ACI 318-19 Building Code impose limitations on the use of hooked and headed bars larger than No. 11 (that is, No. 14 and No. 18 bars), mainly due to a lack of experimental data. This research continues a comprehensive study of the anchorage and development of high-strength hooked and headed bars to expand the available data to include No. 14 and No. 18 bars. Forty-two large-scale simulated beam-column joint specimens containing No. 11, No. 14 and No. 18 hooked and headed bars are tested. Of the 42 specimens, 12 contain hooked bars and 30 contain headed bars. The effects of bar size, bar spacing, bar location, embedment length, confining transverse reinforcement in the joint region, placement of bars within the cross-section, concrete compressive strength, compression strut angle, and effective beam depth on anchorage strength are investigated. Two loading conditions are used. In loading condition A, the joint shear is 80% of the total applied force to the bars, simulating the forces in an exterior beam-column joint with the beam located at the midheight of the column. The joint shear is reduced to ⁓69% of the total applied force in loading condition B. All hooked bar specimens and 15 headed bar specimens are tested under loading condition A, while the other 15 headed bar specimens are tested using loading condition B. Concrete compressive strengths range from 6,390 to 15,770 psi for hooked bars and from 5,310 to 16,210 psi for headed bars. Bar stress at failure ranges from 87,300 to 130,600 psi for hooked bars and from 54,900 to 148,300 psi for headed bars. Center-to-center bar spacing, s, ranges from 3.5db to 10.6db for hooked bars and from 2.7db to 10.6db for headed bars, where db is the nominal hooked or headed bar diameter. Confining reinforcement, Ath, or parallel ties, Att, in the joint region ranges from 0 to 0.465Ahs and 0 to 0.827Ahs for hooked and headed bars, respectively, where Ath or Att equal the total cross-sectional area of tie legs within 10db from the top of the bars and Ahs is the total area of the bars being developed. Headed bars with net bearing areas between 4.2 and 4.4 times the bar area are used. The test results are compared with the current provisions for the development length of hooked and headed bars in Chapter 25 of ACI 318-19. Descriptive equations to characterize anchorage strength of hooked and headed bars developed previously for No. 11 and smaller bars are evaluated. New descriptive equations are developed to represent the anchorage strength for bars as large as No. 18. The equations are compared with the test results in the current study and available in the literature. New design provisions for development length are developed for hooked and headed bars and evaluated with respect to test results and ACI 318-19 provisions. The descriptive equations for hooked and headed bars developed in this study accurately account for concrete compressive strength, confining reinforcement, and bar spacing. The ability of the equations to accurately represent anchorage strength is insensitive to variations in compression strut angle and effective beam depth. While the contribution of confining reinforcement to anchorage strength increases with bar size, the effect of increasing confining reinforcement for headed bars is much lower than for hooked bars and much lower for headed bars than observed in prior studies. Under loading condition A, all hooked bar specimens, even those without confining reinforcement, carried the joint shear and exhibited an anchorage failure, whereas shear-like failures were observed in some headed bar specimens under similar conditions. These observations reveal the distinct role of the tail of the hook in helping to carry the joint shear, and indicate the difference in joint shear under loading conditions A and B is a key factor in the type of failure and anchorage strength of headed bars. Larger headed bars need confining reinforcement on the order of 0.5Ahs to carry the joint shear demand under loading condition A. The development length provisions in ACI 318-19 are unnecessarily conservative for No. 14 and No. 18 hooked and headed bars. For both hooked and headed bars, providing confining reinforcement below the minimum amounts required by ACI 318-19 contributes to anchorage strength. Similar to No. 11 and smaller hooked and headed bars, the effect on anchorage strength of concrete compressive strength is best represented by the 0.25 power for design. The bar location factor o of 1.25 in ACI 318-19, applied to bars terminating inside column longitudinal reinforcement (column core) with side cover < 2.5 in. or bars with side cover < 6db, can be safely reduced to 1.15 for design. The proposed design equations for hooked and headed bars are applicable to concrete with compressive strengths up to 16,000 psi, steel with yield strengths up to 120,000 psi, and bars as large as No. 18. The proposed modification factors for confining reinforcement (expressed as Ath/Ahs or Att/Ahs) and bar spacing (expressed as s/db), in the form of a single expression or simplified expressions that address the effects of confining reinforcement and bar spacing independently, provide more flexibility for designers to take advantage of a range of values for Ath/Ahs or Att/Ahs and s/db and, ultimately, permit the use of shorter development lengths than the provisions in ACI 318-19 for all bar sizes.
Evaluation of Cracking Performance of Bridge Decks With And Without Overlays and With and Without Fibers
(University of Kansas Center for Research, Inc., 2024-05) Dhungel, Sujan; Bahadori, Alireza; Darwin, David; O’Reilly, Matthew; Truman, Katelyn
Ninety-three spans on 19 bridges, constructed between 2013 and 2020, were surveyed for cracks. The decks were constructed on either steel or prestressed concrete girders. The spans were constructed with or without overlays, some of which used silica fume as a partial replacement for portland cement, with or without nonmetallic fibers, or with monolithic decks with or without nonmetallic fibers. Of the six bridges with conventional overlays (without silica fume), four contained fibers. All nine of the bridges with silica fume overlays had fibers. Of the four monolithic decks, two had spans with fibers, one did not have fibers, and one had two surveyed units (each with three spans) with fibers and four surveyed units without fibers. The bridge superstructures had from two to seven spans with lengths ranging from 147 to 808 ft (44.9 to 246. m), and roadways with widths ranging from 32 to 70.5 ft (9.8 to 21.5 m). The surveys revealed that decks with concrete overlays crack more than monolithic decks for decks on both steel and prestressed concrete superstructures. Decks with cement paste contents less than 27% of the concrete volume cracked less than decks with a higher volumes of cement paste. More generally, good construction practices are needed for low-cracking decks, and with poor construction practices, even decks with a low paste content, with or without fibers, can exhibit high cracking.
Long-term Implications of Redecking Bridges with Prestressed Concrete Girders
(University of Kansas Center for Research, Inc., 2024-03) Adhikari, Beeva; Lequesne, Rémy D.; Collins, William
Precast/prestressed concrete girders with cast-in-place decks are commonly used for bridge construction throughout the United States. There is a need to replace concrete decks on many of these bridges because girders last much longer than concrete decks. This study surveyed United States Department of Transportation (DOT) engineers to determine common deck removal practices. Survey results showed that, although most states have a need to replace bridge decks, few states have comprehensive plans for assessing the long-term effects of deck replacement on girder behavior. This study developed a Python model to estimate girder behavior over its lifespan that accounts for the effects of deck replacement, changes in loading conditions, changes in restraint conditions, and concrete deformations. Time-step analysis was used to calculate incremental changes in girder behavior throughout time, considering several lifespan stages delineated by changes in loading or boundary conditions. The B4 model (Wendner et al., 2013) was used to estimate the creep and shrinkage strain in the concrete. The model was validated against examples in the literature and applied to an example bridge to illustrate function. Modelling results suggest that deck replacement had minimal effect on long-term girder behavior for the bridge considered. A parametric study was also conducted to evaluate the influence of input parameter variations on long-term prestress loss, deflections, and stresses and strains for the example bridge. Parametric study results showed that girder behavior varies widely based on input parameters, suggesting that more research is needed to determine whether other bridge configurations would also be insensitive to deck replacement.
Bond Behavior of Epoxy-Coated Reinforcing Bars in Non-Proprietary UHPC
(Oklahoma Department of Transportation, 2023-10) Darwin, David; O'Reilly, Matthew; Lequesne, Rémy D.; Thapa, Sanjeeb
Non-proprietary ultra-high-performance concrete (UHPC) mixtures were developed for use in closure strips between precast members on reinforced concrete bridges. The mixtures contained ODOT approved Type I portland cement, slag cement, silica fume, graded fine aggregate, two high-range water-reducers (HRWRs), one of which incorporated a viscosity modifying admixture, and 2% by volume of 0.5-in. steel fibers. Several HRWRs of each type were included in the evaluations. Mixtures were evaluated based on flow, fiber distribution, flexural properties, compressive strength, and effect on bond strength using a modified pullout test and the ASTM A944 beam-end test for No. 5 uncoated, ASTM A755 epoxy-coated, and ASTM A1124 textured-epoxy-coated reinforcing bars. The UHPC mixture with the best properties was used to cast a closure strip between two precast sections to determine the splice strength of No. 4, No. 5, and No. 8 uncoated, epoxy-coated, and textured-epoxy-coated reinforcing bars with minimum clear covers ranging from 1.00 to 2.63 in. The results of the splice test were used to develop design recommendations. The study showed that UHPC can be made using ODOT approved materials. The splice strength of reinforcing bars in UHPC is two times the value in conventional concrete. The negative effects of epoxy coating on bond strength are lower in UHPC than in conventional concrete. ASTM A1124 textured epoxy-coated bars have the same bond strength as uncoated bars. The design procedures described in this report are based on UHPC with a minimum compressive strength at the time of load application of not less than 12 ksi, with a flow between 8 and 10 in. and good fiber distribution.
Construction of Low-Cracking High-Performance Bridge Decks Incorporating New Technology Phase II
(Kansas Department of Transportation, 2023-12) Bahadori, Alireza; Darwin, David; O'Reilly, Matthew; Salavati-Khoshghalb, Mohsen
The construction, crack surveys, and evaluation of 12 bridge decks with internal curing provided by prewetted fine lightweight aggregate and supplementary cementitious materials following internally cured low-cracking high-performance concrete (IC-LC-HPC) specifications of Minnesota or Kansas are described, as well as those from two associated Control decks without IC (MN-Control). Nine IC-LC-HPC decks and one Control deck were monolithic, while three IC-LC-HPC decks and one Control deck had an overlay. The internally cured low-cracking high-performance concrete had paste contents between 23.8 and 25.8 percent by volume. Of the 12 IC-LC-HPC decks, nine were constructed in Minnesota between 2016 and 2020, and three were constructed in Kansas between 2019 and 2021. The performance of the decks is compared with that of earlier IC-LC-HPC bridge decks and low-cracking high-performance concrete (LC-HPC) bridge decks without internal curing. The effects of construction practices on cracking are addressed. The results indicate that the use of overlays on bridge decks is not beneficial in mitigating cracking. The IC-LC-HPC decks constructed exhibited lower average crack densities than those without internal curing. Good construction practices are needed for low-cracking decks. If poor construction practices, which may include poor consolidation and disturbance of concrete after consolidation, over-finishing, delayed application of wet curing, are employed, even decks with low paste contents and internal curing can exhibit high cracking. Delayed curing and over-finishing can also result in scaling damage to bridge decks.
DATASET: Test Results from Shake Table Tests of Reinforced Concrete Frames with Grade 60 or 100 (420 or 690) Reinforcement
(University of Kansas, 2023-12-13) Chin, Chin-Hsuan; Cheng, Min-Yuan; Lepage, Andrés; Lequesne, Rémy D.
This dataset reports the acceleration and displacement data collected during tests of two reinforced concrete frames that differed in one way: the longitudinal bars were Grade 60 (420) in C1 and Grade 100 (690) in H1. The frames were placed side-by-side on the NCREE shake table in Taipei, Taiwan, and subjected to 16 earthquake simulations. Details of the specimens and ground motions are reported in references [1] and [2], along with inferences made by the authors. This dataset includes one image file (“Instrument Locations”), which shows the locations and IDs of the instruments used during testing, and 39 excel files. The excel file named “Description of Runs” identifies the excitation type associated with each of the 38 runs, which include low-amplitude excitation recorded to determine dynamic properties before and after each earthquake simulation. Excel files named “Run 1” to “Run 38” each contain the recorded displacement (mm) and acceleration (g) data versus time. References: [1] Chin, C.-H., Cheng, M.-Y., Lepage, A., & Lequesne, R. D., (2024). Shake Table Tests to Compare the Seismic Response of Concrete Frames with Conventional and High-Strength Reinforcement. Earthquake Engineering and Structural Dynamics, 53(1), 89-115. doi: 10.1002/eqe.4008 [2] Chin, C.-H., (2022). Shaking Table Test of RC Column Using High-Strength Flexural Reinforcement Under Low Axial Load. M.S. Thesis, National Taiwan University of Science and Technology, Taipei, Taiwan, 175 pp. (In Chinese)
Chord Rotation Capacity and Strength of Diagonally Reinforced Concrete Coupling Beams
(American Concrete Institute, 2023-11) Lepage, Andrés; Lequesne, Rémy D.; Weber-Kamin, Alexander S.; Ameen, Shahedreen; Cheng, Min-Yuan
A database of results from 27 tests of diagonally reinforced concrete coupling beams was analyzed to develop improved force-deformation envelopes (backbone curves) for modeling and analysis of coupling beams. The database, which was selected from a larger set of 60 test results, comprises specimens that generally satisfy ACI 318-19 requirements. The analyses show that the chord rotation capacity of diagonally reinforced concrete coupling beams compliant with ACI 318-19 is closely correlated with beam clear span-to-overall depth ratio and, to a lesser extent, the ratio of hoop spacing to diagonal bar diameter. A simple expression is proposed for estimating beam chord rotation capacity. Coupling beam strength was shown to be more accurately estimated from flexural strength calculations at beam ends than other methods. Recommendations are made for obtaining more accurate backbone curves in terms of chord rotation capacity, strength, and stiffness.
Evaluation of Multiple Corrosion Protection Systems for Reinforced Concrete Bridge Decks
(University of Kansas Center for Research, Inc., 2023-07) Vosough Grayli, Pooya; O’Reilly, Matthew; Darwin, David
This study evaluated the corrosion resistance of epoxy-coated (ASTM A775), hot-dip galvanized (ASTM A767), and continuously galvanized (ASTM A1094) reinforcement, and the conventional reinforcement (ASTM A615) used to produce them, as well as ChromX reinforcement (ASTM A1035 Type CS) under the rapid macrocell, Southern Exposure, and cracked beam tests. To simulate the effects of handling, placing, and construction practices in the field, epoxy-coated and galvanized bars were tested in the as-received condition, with intentional damage to the coating, and after bending. To simulate the effects of outdoor exposure on epoxycoated reinforcement, selected epoxy-coated reinforcing bars were tested under accelerated ultraviolet exposure cycles, both without and with physical damage. The corrosion performance of conventional and ChromX reinforcement was also evaluated in conjunction with IPANEX and Xypex, two waterproofing admixtures. Additionally, a 100-year life cost analysis was conducted to compare the cost-effectiveness of the reinforcing bars and admixtures evaluated in providing corrosion resistance based on construction costs in the states of Oklahoma and Kansas. Finally, the effect of variability in corrosion on the predicted service life is investigated using a Monte Carlo simulation using data from conventional, ECR, and ChromX reinforcement from the current study and previous studies. Epoxy-coated reinforcement exhibited much greater corrosion resistance than conventional reinforcement, even after damage; however, ultraviolet exposure equivalent to as low as 1.2 months of outdoor exposure reduced the effectiveness of the coating resulting in increased corrosion rates. Both A767 and A1094 reinforcement exhibited better corrosion resistance than conventional reinforcement, but corrosion rates on both types of galvanized reinforcement increased when the bars were bent. Xypex was generally effective at reducing the corrosion rate iv of conventional reinforcement, but not ChromX reinforcement; further study is recommended on the effects of Xypex on the corrosion resistance of reinforced concrete. IPANEX did not affect the corrosion resistance of either type of reinforcement. Over a 100-year design life, epoxy coated, galvanized, and ChromX reinforcement are all cost-effective solutions.
Effects of Total Internal Water Content on Freeze-Thaw Durability and Scaling Resistance of Internally-Cured Concrete
(University of Kansas Center for Research, Inc., 2023-07) Dhungel, Sujan; Darwin, David; O’Reilly, Matthew
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.
Anchorage of Large High-Strength Reinforcing Bars with Standard Hooks and Heads: Initial Tests
(University of Kansas Center for Research, Inc., 2020-02) Blessent, Matthew; Darwin, David; Lepage, Andres; Lequesne, Rémy; O’Reilly, Matthew
The reaction frame to be used to test No. 14 and No. 18 bar beam-column joint specimens, the modified reaction frame used to test initial No. 11 beam-column joint specimens, and the design of beam-column joint specimens are described. Concrete strengths of 5,000 psi to 15,000 psi will be used with bar sizes of No. 11, No. 14, and No. 18 with bar stresses at anchorage failure in excess of 100 ksi in future work. Thus far, the testing apparatus has been designed, test procedures have been established, and initial specimens have been tested. The initial test results show that the descriptive equation used to calculate the anchorage strength of headed bars presented by Shao et al. (2016) is accurate for No. 11 bars. Testing will continue using the apparatus and procedures described in this report, and the results will be added to the database developed at The University of Kansas to better understand how large high-strength headed and hooked bars behave in beam-column joints.
A Finite Element Model to Study the Microscopic Behavior of Plain Concrete
(University of Kansas Center for Research, Inc., 1976-11) Maher, Atauallah; Darwin, David
The object of this study is to develop a finite element model of non-homogeneous concrete, consisting of mortar and aggregate, for in-plane loading conditions. Linear elastic properties of aggregate and nonlinear properties of mortar are employed. Experimental strength criteria are used to represent the mortar-aggregate interface. Experimental results for monotonic biaxial loading and biaxial strength of mortar are combined with a previously developed numerical procedure to represent nonlinear mortar. The finite element study considers the simplified model of concrete suggested by Shah and Winter. Formation and propagation of interfacial and mortar cracks, and the load-deflection behavior of concrete as affected by the strength of the interface and linear and nonlinear representations of mortar are studied. The analytical load-deflection behavior of concrete is compared with the experimental results of Buyukozturk.
Minimum Joint Depth for Moment Frames with High-Strength Materials
(American Concrete Institute, 2023-01-01) Lee, Hung-Jen; Lequesne, Rémy D.; Lepage, Andrés; Lin, Jian-Xing; Wang, Jui-Chen; Yin, S. Y.-L.
This paper reports results from four large-scale interior beam column connections without transverse beams or slabs tested under reversed cyclic displacements. The specimens, which included the first of interior beam-column connections constructed with Grade 100 (690) reinforcement with bar deformations similar to those available in U.S. practice, had Grade 60 or 100 (420 or 690) bars, 4 or 10 ksi (28 or 69 MPa) concrete, and varied column depthto-beam bar diameter ratios. The specimens all exhibited strengths greater than the nominal strength, retained at least 80% of their strength to drift ratios exceeding 5%, and exceeded ACI 374 acceptance criteria at a 3% drift ratio for components of special moment frames, demonstrating that well-detailed joints constructed with high-strength materials behave satisfactorily. The data add evidence that joints constructed with high-strength concrete exhibit less bond decay, and recommendations are made for accounting for this effect in design. Results from the specimen constructed with normal-strength materials, considered in the context of prior tests, suggest a need to increase the minimum joint depth for special moment frames. Considerable improvement in behavior associated with reduced bond damage within the joint is obtained from a 20% increase in the minimum column depth-to-beam bar diameter ratio required in ACI 318-19.
Anchorage of High-Strength Reinforcing Bars in Concrete
(University of Kansas Center for Research, Inc., 2023-01) Nazzal, Luay Ali; Darwin, David; O’Reilly, Matthew
Hooked and headed reinforcing bars are commonly used as a means of shortening development length of reinforcing bars, but a limited amount of previous research has resulted in restrictions on their use in practice. This study included two phases: In the first phase, 31 tests of simulated column-foundation joints were conducted to investigate the anchorage strength and behavior of large and high-strength headed bars as functions of the distance between the anchored headed bar and the compression reaction, number of headed bars tested simultaneously (1 or 2), size of the headed bars (No. 11 or No. 14), center-to-center spacing between headed bars loaded simultaneously (3.2 or 8.2db), amount of confining reinforcement within the joint region (zero to six No. 4 closed stirrups), and concrete compressive strength (5,060 to 14,470 psi). The embedment length of the headed bars ranged from 125 /8 to 14 in., and the stresses in the headed bars at failure ranged from 41,800 to 144,400 psi. The test results are compared with anchorage strengths based on the descriptive equations for headed bars developed at the University of Kansas, ACI 318-19 Code provisions, and proposed Code provisions. Recommended changes to Chapters 17 and 25 of ACI 318-19 are presented. In the second phase of the study, descriptive equations for beam-column joints tested under monotonic loading are investigated their applicability to predict the anchorage strength of hooked bars anchored in members subjected to reversed cyclic loading. Comparisons are made with test results from 24 studies of 146 exterior beam-column joint specimens subjected to reversed cyclic loading in which the beam bars are anchored by hooks. Key variables include embedment lengths of the hooked bars (6 to 21 in.), concrete compressive strength (3,140 to 13,700 psi), center-to-center spacing between the hooked bars (1.75 to 6.5 in.), bar size (No. 3 to No. 9), and confining reinforcement within the joint region parallel to the straight portion of the hooked bars (none to nine hoops spaced at 1.25 to 6.0 in.). The yield strength of the hooked bars ranged from 42,900 to 103,000 psi. Proposed changes to Chapters 18 of ACI 318-19 are presented. The results of the experimental study show that the anchorage strength of headed bars anchored in column-foundation joints is improved by parallel tie reinforcement located on all sides of the headed bars, a contribution that is not included in the provisions of ACI 318-19. Similar to observations for beam-column joints, the anchorage strength of headed bars anchored in simulated column-foundation joints decreases as the center-to-center spacing decreases below 8db. The descriptive equations developed based on tests of beam-column joints are suitable for predicting the anchorage strength of headed bars anchored in column-foundation joints. Chapter 17 of ACI 318-19 does not accurately predict the anchorage strength of headed bars tested when parallel tie/anchor reinforcement is used and should be modified to combine the contributions of concrete strength and parallel tie reinforcement. The descriptive equations developed for beam-column joints apply to column-foundation joints and could serve as a basis for the anchorage provisions in Chapter 17 of ACI 318. The provisions in Chapter 25 of ACI 318-19 should be updated to include the effect of parallel tie reinforcement in connections other than beam-column joints. The descriptive equations for the anchorage strength of hooked bars in beam-column joints tested under monotonic loading are suitable for predicting the anchorage strength of hooked bars anchored in members subjected to reversed cyclic loading. The ACI Code provisions for the development length of hooked bars in tension in beam-column joints in special moment frames (Section 18.8.5.1 of ACI 318-19), derived from the development length provisions for non-seismic loading in earlier Codes, permit development lengths that are shorter needed for gravity load by Chapter 25. Changes in Chapter 18 of ACI 318-19 are proposed that require the use of the provisions in Chapter 25 to establish the minimum development length for hooked bars anchored in joints for frames subjected to seismic loading
Effects of Concrete Tail Cover and Tail Kickout on Anchorage Strength of 90-Degree Hooks
(American Concrete Institute, 2021-11-01) Yasso, Samir; Darwin, David; O’Reilly, Matthew
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.
Internally-Cured Low-Cracking High-Performance Concrete (IC-LC-HPC) Bridge Decks: Durability and Cracking Performance
(University of Kansas Center for Research, Inc., 2023-01) Bahadori, Alireza; Darwin, David; O’Reilly, Matthew
The laboratory portion of this study investigates the effects of internal curing (IC) water in pre-wetted lightweight aggregates (LWA) between 8.2 and 9.0% and between 12.0 and 13.1% by weight of binder and total internal (TI) water in all aggregates between 3.4 and 12.5% by weight of binder on freeze-thaw durability, scaling resistance, shrinkage, and ion transport properties of concrete mixtures with different binder compositions (100% portland cement or a ternary composition with 30% slag cement and 3% silica fume as partial replacements for portland cement [by total weight of cementitious materials]), paste as a percentage of concrete volume (23.7, 24.6, 26.7, or 33.7%), and water-to-cementitious material ratios (w/cm, 0.45 or 0.41). Normalweight aggregates consisted of three types of coarse aggregates and river sand. The results show that for paste contents between 23.7 and 33.7% of concrete volume, the freeze-thaw durability of internally-cured concrete mixtures is a function of the percentage of IC water by the weight of binder, rather than total IC water per unit volume of concrete; all IC mixtures assessed for freeze-thaw durability in accordance with ASTM C666-Procedure A exhibited durability factors below 90% and failed the freeze-thaw test and would not be considered acceptable under MnDOT specifications, while some mixtures at w/c ratio of 0.45 and all mixtures at a w/c ratio of 0.41satisfied the requirements of ASTM C666-Procedure B and KTMR-22 and would be considered acceptable under KDOT specifications. The results also demonstrate that the freeze-thaw resistance of the mixtures decreased markedly when the TI water exceeded 12.0% by the weight of binder. Scaling test results show that as the paste content increases from 23.7 to 33.7%, the scaling resistance of the specimens decreases. At a w/cm ratio of 0.45 and a paste content of 23.7%, mixtures with an IC water content of 8.8% passed the scaling test; at a w/cm ratio of 0.41 and a paste content of 23.7%, mixtures with IC water contents less than or equal to 13% passed the scaling test. None of the mixtures with a paste content of 33.7% passed the scaling test at either w/cm ratio. Moreover, for a given binder composition and type of coarse aggregate, increased TI water resulted in higher scaling resistance. The type of coarse aggregate also had effects on scaling resistance. The ternary mixtures with granite as the coarse aggregate, had lower mass losses than the ternary mixtures with low-absorption limestone and similar quantities of TI water. As the TI water content increased, shrinkage decreased for concretes with both binder compositions. Mixtures with IC water exhibited more expansion at the end of the curing period than mixtures with no IC water. Increases in the TI water content in mixtures did not affect the rapid chloride permeability or surface resistivity measurements, while the binder composition did, with the ternary mixtures, on average, showing higher and lower SRM and RCP values, respectively, than mixtures containing 100% portland cement. The second portion of the study involved the construction, crack surveys, and evaluation of 12 bridge decks (nine in Minnesota and three in Kansas) containing IC water and supplementary cementitious materials (SCMs) that were constructed between 2016 and 2021 following IC-LCHPC specifications (of Minnesota or Kansas) and two associated Control decks without IC. The decks were monolithic with the exception of three of the Minnesota decks, which had overlays. The results show that the use of overlays on bridge decks results in high crack densities and should be avoided. Low-cracking bridge decks require concrete with a paste content of 27.2% or less based on concrete volume. Paste contents above 27.2% correlate with increased cracking, and for decks with paste contents greater than 27.2%, the addition of IC and SCMs does not overcome the negative effects of high paste content. The results also indicate that the combination of low paste, internal curing, and good construction procedures offer the potential to reduce cracking. Under circumstances, good construction practices are needed for low-cracking decks. If poor construction practices are employed, even decks with low paste content and IC can exhibit high cracking and scaling damage.
Evaluation of Cracking Performance of Bridge Decks Incorporating Nonmetallic Fibers
(University of Kansas Center for Research, Inc., 2022-07) Bahadori, Alireza; Darwin, David; O’Reilly, Matthew; Dhungel, Sujan
The Minnesota Department of Transportation (MnDOT) identified 20 monolithic (onecourse) bridge decks, constructed between 2015 and 2018, for cracking surveys to investigate the effectiveness of nonmetallic fibers in reducing bridge deck cracking. Of the 20 monolithic decks, 13 were constructed with concrete mixtures containing nonmetallic fibers and seven without fibers. Of the bridge decks constructed with nonmetallic fibers, nine are supported by precast-prestressed concrete girders and four are supported by steel girders. Of the decks constructed without fibers, six are supported by precast-prestressed concrete girders and one is supported by steel girders. The first portion of the report (Chapters 1 through 4) presents a description of the crack survey procedures, followed by information about the decks. A comparison of the decks is then made by converting the survey results to equivalent crack densities at 36 months of age. The second portion of the report (Chapters 5 and 6) investigates the effects of paste content, fibers, and construction procedures on the cracking performance of the 20 bridge decks surveyed in this study using comparisons with the results of crack surveys of 74 other bridge deck placements, conducted in Kansas, Virginia, and Indiana. Results show that for the decks surveyed in this study, the majority of cracks that contributed to crack density had lengths greater than 1 ft and there is no apparent correlation between the use of fibers and crack width. Low cracking bridge decks require the use of concrete with a low paste content (27.1% or less), and when the paste content is 27.1% or less, there is no significant difference in the average 36-month crack densities between bridge decks with and without fibers. More generally, good construction practices are needed for low-cracking decks, and with poor construction practices, even decks with low paste content, with or without fibers, can exhibit high cracking
Chloride Content and Carbonation of KU Memorial Stadium Cores
(University of Kansas Center for Research, Inc., 2022-08) O’Reilly, Matt; Darwin, David
Three cores were taken from KU Memorial Stadium on 08/17/22 by personnel from Wiss, Janney, Elstner Associates and analyzed for water-soluble chloride content and depth of carbonation. Cores A4 and B4 were taken from original construction dating to the 1920s, and Core C4 was taken from construction dating to the 1960s. All three cores exhibited low chloride contents, approximately 0.01% by mass of concrete at the depth of reinforcement. Core A4 exhibited carbonation to the deepest depth, 3.5 in., while Cores B4 and C4 exhibited carbonation to depths of 1.25 in. and less than 0.25 in., respectively.
Low-Shrinkage Ultra-High-Performance Concrete
(University of Kansas Center for Research, Inc., 2022-08) Aljawad, Yasmeen; Lequesne, Rémy D.; O’Reilly, Matt
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.

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