Fragility functions of different groups of diagonally reinforced concrete coupling beams (DRCBs)

Abstract

Diagonally reinforced concrete coupling beams (DRCBs) act as a fuse element that dis-sipates most of the seismic energies imparted to coupled shear wall systems during earth-quakes. The objective of this study is to develop the fragility functions of different groups of DRCBs: (1) all DRCBs, (2) DRCBs conforming to the ACI 318-14 (Building code requirements for structural concrete and commentary (ACI 318-14), American Concrete Institute, Farmington Hills, 2014) confinement options A and B, and (c) DRCBs not con-forming to the ACI 318-14 confinement options. Forty-three specimens were collected from nineteen previous experimental studies to estimate their empirical fragility using four different damage states. It was found that maximum shear stress (υmax) played an important role in the fragility curves. Without considering υmax, the fragility of DRCBs was signifi-cantly underestimated for DRCBs with υmax ˂ 4.0 whereas their fragility was overestimated for DRCBs with υmax ˃ 4.0. In this study, fragility curves were constructed considering the level of υmax. Mean chord rotations (μθ) of DRCB specimens were estimated for life safety and collapse prevention limit states, and compared to corresponding limiting values speci-fied in ASCE 41-17 (Seismic evaluation and retrofit of existing buildings, American Soci-ety of Civil Engineers, Reston, 2017. https ://doi.org/10.1061/97807 84414 859). DRCBs conforming to the ACI 318-14 confinement options produced μθ larger than the limiting values whereas μθ of DRCBs not conforming to the ACI 318-14 did not exceed the limiting values.