Title:
Reinforced Concrete Coupling Beams with High-Strength Steel Bars
Author(s):
Andres Lepage, Remy D. Lequesne, and Alexander S. Weber-Kamin
Publication:
Structural Journal
Volume:
122
Issue:
3
Appears on pages(s):
173-186
Keywords:
chord rotation capacity; confining reinforcement; deformation capacity; force-deformation envelope; hoop spacing; reinforcement grade; reversed cyclic displacements
DOI:
10.14359/51745464
Date:
5/1/2025
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 (diagonal
[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 rotation 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). Consistent 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 longitudinal reinforcement. Finally, the test results illustrate the effects of reinforcement grade on stiffness and energy dissipation of pseudostatically loaded coupling beams.