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Reinforced Concrete Coupling Beams with High-Strength Steel Bars
Lepage, Andrés
Lepage, Andrés
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Abstract
Eleven large-scale reinforced concrete coupling beam specimens were tested under reversed cyclic displacements of increasing magnitude. The main variables included yield stress (fy) of the primary longitudinal reinforcement (Grade 80, 100, or 120 ksi [550, 690, or 830 MPa]), span-depth (aspect) ratio (1.5, 2.5, or 3.5), and layout of the primary longitudinal reinforcement (diag¬onal [D] or parallel [P]). Specimens had the same nominal concrete strength (8000 psi [55 MPa]) and cross section (12 x 18 in. [310 x 460 mm]) and were designed for nominal shear stresses of 8 √ __ f c′ psi (0.67 √ __ f c′ MPa) for D-type beams and 6√ __ f c′ psi (0.5 √ __ f c′ MPa) for P-type beams. Transverse reinforcement was Grade 80 (550) in all but one beam (D120-2.5), which had Grade 120 (830) reinforcement.
Test results show that, on average, D-type beams had chord rota¬tion capacities in excess of 5%, 6%, and 7% for beams with aspect ratios of 1.5, 2.5, and 3.5, respectively. P-type beams with Grade 80 or 100 (550 or 690) longitudinal bars, tested only for an aspect ratio of 2.5, had chord rotation capacities of approximately 4%. Based on these results, the authors recommend permitting the use of high-strength steel, Grade 80 (550) and higher, in D-type and P-type coupling beams for earthquake-resistant design. The spacing of confining reinforcement should be limited to 5db for fy = 80 ksi (550 MPa) and 4db for fy = 100 or 120 ksi (690 or 830 MPa). Consis¬tent with prior findings, the results show that deformation capacity is correlated with span-depth ratio and more sensitive to spacing of the confining reinforcement than to uniform elongation of the longi¬tudinal reinforcement. Finally, the test results illustrate the effects of reinforcement grade on stiffness and energy dissipation of pseudo-statically loaded coupling beams.
Description
Date
2025-05-01
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Publisher
American Concrete Institution
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Research Projects
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Keywords
Chord rotation capacity, Confining reinforcement, Deformation capacity, Force deformation envelope, Hoop spacing, Reinforcement grade, Reversed cyclic displacements
Citation
Lepage, A., Lequesne, R. D., & Weber-Kamin, A. S., (2025). Reinforced Concrete Coupling Beams with High-Strength Steel Bars, ACI Structural Journal, 122(5), 173-186. doi: 10.14359/51745464