Reinforced Concrete Coupling Beams with High-Strength Steel Bars

Abstract

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.