Seismic Behavior of Slender Coupling Beams Constructed with High-Performance Fiber-Reinforced Concrete.

Abstract

Coupling beams greatly influence the behavior of coupled wall systems. In order to ensure adequate coupling beam behavior under earthquake-induced deformations and stresses, intricate reinforcement detailing is required for reinforced concrete coupling beams, typically in the form of diagonal bars and extensive confinement reinforcement. Such reinforcement detailing, however, creates major construction difficulties. Furthermore, in slender coupling beams, where beam span-to-depth ratios are on the order of 3.0, the effectiveness of diagonal reinforcement is questionable because of its shallow angle (less than 20 degrees) with respect to the beam longitudinal axis. In this study, a design alternative for slender coupling beams that puts less reliance on diagonal reinforcement was experimentally investigated. The use of tensile strain-hardening, high-performance fiber reinforced concrete (HPFRC) as a means to reduce or totally eliminate the need for diagonal bars and substantially reduce confinement reinforcement was evaluated. To validate this design alternative, six precast coupling beams were tested under large displacement reversals. The parameters considered were the coupling beam span-to-depth ratio (2.75 and 3.3), presence of diagonal reinforcement, and material type (HPFRC and regular concrete). Results from large-scale tests indicated excellent damage tolerance, and strength and stiffness retention capacity for slender HPFRC coupling beams. Moreover, tests results showed that diagonal reinforcement can be completely eliminated without a detrimental effect on seismic behavior. The contribution of the HPFRC material to shear strength of the coupling beam was estimated to be on the order of 5*sqrt(fc) (psi) times the cross section area. To simulate the behavior of the tested precast coupling beams under displacement reversals, analytical modeling was conducted using VecTor2, a nonlinear finite element program in which an HPFRC material model can be incorporated. It was found that the behavior of the tested coupling beams could be reasonably predicted in VecTor2. Simulated shear resultant was in good agreement with that of the test specimens. Excluding drift contributed by sliding, which could not be properly captured in VecTor2, drift capacity obtained from the numerical models agreed well with that of the test specimens. Modeling guidelines critical to simulating the seismic behavior of HPFRC coupling beams were also provided.