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Mechanically-Spliced High-Strength Steel Bars in Earthquake-Resistant Walls
Lepage, Andrés
Lepage, Andrés
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Abstract
Three large-scale reinforced concrete rectangular slender structural walls were subjected to reversed-cyclic displacement demands to investigate the use of mechanical splices with Grade 100 (690) longitudinal bars in regions where yielding is expected. These tests were undertaken because ACI 318-19 prohibits both lap and mechanical splices for Grade 100 (690) bars in special structural walls where longitudinal reinforcement yielding is likely. The reinforcement detailing of the walls satisfied ACI 318-19 requirements for special structural walls, except that all longitudinal bars of the walls each had one of three types of mechanical splices located 2 in. (50 mm) from the top of foundation. The mechanical splice types considered were: taper-threaded, swaged-threaded, and shear screwed. The impact of the mechanical splice on wall cracking, surface strains, bar strain demands, drift ratio capacity, and failure mode are examined.
All three walls reached the same deformation capacity (at least one cycle to 3% drift ratio) irrespective of the splice connection type or length but differed in the failure mode, with Wall 1 losing strength due to bar fractures. Mechanical splices with a strength not less than the actual bar tensile strength, such that bars systematically fail in direct tension tests away from the splice, performed well. Such bar failure in direct tension tests should be required of mechanical splices used where yielding is expected. Mechanical splices satisfying ACI 318-19 Type 2 criteria resulted in better wall behavior than reported for lap splices, but bar fractures still occurred at the splice, so Type 2 splice requirements alone are insufficient to allow mechanical splices where yielding is expected.
Splice length influenced crack distribution near the splices and wall failure mode. The taper-threaded splices (length < 0.05*l_w) resulted in a relatively uniform crack distribution whereas swaged and shear-screwed splices (length > 0.1*l_w) led to more concentrated cracks above the splices. The concentrated cracking led to larger longitudinal and shear strains (> 0.01 radians) measured on the concrete surface at larger drifts, resulting in shear-induced compression failures of those walls. Although the maximum shear force remained relatively constant after 1% drift ratio, average shear surface strain in a row-layer near the base of all three specimens continued to increase nearly proportionally to the average longitudinal surface strains in the same row-layer. Further study is necessary to examine whether average longitudinal and shear strains remain proportional as wall configuration and loading conditions change.
A simple model was proposed for relating bar strains to wall drift ratio that estimated boundary element longitudinal bar strains that were nearly within 10% of the measured values at 2% and 2.5% drift ratio for the walls tested in this study. A parametric study conducted with the model suggests that for a given drift demand, bar strain demands increase as splice length increases and as splice relative elongation, wall aspect ratio, reinforcement grade, and longitudinal bar diameter decrease. The contribution of shear distortion to overall drift and concrete compressive strength have relatively small effects on calculated bar strain demands. Based on the test results and parametric study, it is recommended to limit mechanical splice length to 0.2*l_w at the base of slender walls with Grade 100 (690) longitudinal reinforcement.
Appendix E reports preliminary results from an investigation of squat wall strength. No conclusions are drawn based on the results presented.
Description
Results from these tests can be found at this reference:
Neupane, U., Lequesne, R. D., Lepage, A., and Darwin, D., DATASET: Results from Cyclic Tests of Earthquake-Resistant Rectangular Walls Mechanically-Spliced High-Strength Reinforcement, KU Scholarworks, Lawrence, KS, January 2025. https://hdl.handle.net/1808/35804
Date
2025-02
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Publisher
University of Kansas Center for Research, Inc.
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Keywords
Couplers, Drift ratio capacity, Earthquake-resistant walls, High-strength reinforcement, Mechanical splices, Splice length, Shear walls, Strain-drift ratio relationship, Uniform elongation;
Citation
Neupane, U., Lequesne, R. D., Lepage, A., and Darwin, D., “Mechanically-Spliced High-Strength Steel Bars in Earthquake-Resistant Walls,” SM Report No. 165, The University of Kansas Center for Research, Inc., Lawrence, KS, February, 2025, 320 pp. https://hdl.handle.net/1808/35869