Behavior and Design of High-Performance Fiber-Reinforced Concrete Coupling Beams and Coupled-Wall Systems.

Abstract

A series of tests has been conducted to investigate the use of strain-hardening, high-performance fiber-reinforced concrete (HPFRC) in the critical regions of coupled-wall systems. A component test phase, consisting of tests of three large-scale precast coupling beam specimens with span-to-depth ratios (l_n⁄h) of 1.75 subjected to reversed cyclic loading, was conducted to evaluate various reinforcement details for HPFRC coupling beams. A new design approach for HPFRC coupling beams, developed from these tests, has been shown to result in a ductile flexurally-dominated failure mode. The results from these tests confirmed that HPFRC can provide adequate confinement to the diagonal reinforcement, and that 5√(f_c^')[psi] (0.42√(f_c^')[MPa]) is an appropriate estimate of the shear stress contribution from HPFRC in coupling beams. The viability of precasting the coupling beam and connecting it to adjacent structural walls without interfering with wall boundary reinforcement was demonstrated.

Subsequently, two large-scale, four-story coupled-wall specimens, which were designed based on the results from the component test phase, were tested under lateral displacement reversals. Each coupled wall consisted of four precast coupling beams linking two T-shaped reinforced concrete structural walls. The reinforcement details of the precast beams were varied slightly, allowing a comparison of the response of different detailing schemes when integrated into a coupled wall system. The second coupled-wall specimen also incorporated fiber reinforcement in the plastic hinge regions of the walls, which allowed for a reduction in confinement reinforcement and a higher contribution from the concrete to wall shear capacity. The response of both coupled-wall specimens showed good strength and stiffness retention, and substantial energy dissipation up to system drifts of approximately 3.0%. It is recommended that 4√(f_c^')[psi], (0.33√(f_c^')[MPa]) is appropriate for the shear stress contribution from HPFRC in coupled walls. Relaxing the maximum spacing of wall boundary confinement reinforcement to t_w⁄2 was shown to be permissible in HPFRC coupled walls.