Seismic Behavior and Detailing of High-Performance Fiber-Reinforced Concrete Coupling Beams and Coupled Wall Systems

The seismic behavior of coupling beams and walls constructed with tensile strain-hardening, high-performance fiber-reinforced concrete (HPFRC) was studied through tests of large-scale precast coupling beams and coupled walls. A precast coupling beam design was developed to speed up construction and minimize interference with wall reinforcement. Three isolated precast coupling beam specimens with a span/depth of 1.75 were tested under large displacement reversals. Test results indicate the use of HPFRC allows a reduction of the reinforcement required to achieve a stable coupling beam response by providing confinement and contributing to beam shear strength. A concrete design shear stress capacity of $0.41\mathrm{\surd }{f}_c^{\prime } \text{MPa} (5\mathrm{\surd }{f}_c^{\prime } \text{psi})$, where $f_c^{\prime }$ is the compressive strength of the concrete, was found to be appropriate. In addition to the coupling beam tests, two 4-story coupled wall specimens with precast HPFRC and regular concrete coupling beams were tested under lateral displacement reversals. Besides allowing the evaluation of seismic behavior of coupled walls with HPFRC coupling beams, the use of HPFRC in the plastic hinge regions of the walls as a means of relaxing transverse wall reinforcement was evaluated. The two coupled wall specimens exhibited drift capacities of at least 2.5%. The HPFRC coupling beams were more ductile and damage-tolerant than the regular concrete beams. The incorporation of a HPFRC material in the wall allowed the use of a concrete design shear stress capacity of $0.33\mathrm{\surd }{f}_c^{\prime } \text{MPa} (4\mathrm{\surd }{f}_c^{\prime } \text{psi})$ and a wider spacing of transverse reinforcement confining the wall boundary regions.