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 dissipates most of the seismic energies imparted to coupled shear wall systems during earthquakes. 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 conforming 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 (upsilon(max)) played an important role in the fragility curves. Without considering upsilon(max), the fragility of DRCBs was significantly underestimated for DRCBs with upsilon(max) ˂ 4.0 whereas their fragility was overestimated for DRCBs with upsilon(max) ˃ 4.0. In this study, fragility curves were constructed considering the level of upsilon(max). Mean chord rotations (mu(theta)) of DRCB specimens were estimated for life safety and collapse prevention limit states, and compared to corresponding limiting values specified in ASCE 41-17 (Seismic evaluation and retrofit of existing buildings, American Society of Civil Engineers, Reston, 2017. 10.1061/9780784414859). DRCBs conforming to the ACI 318-14 confinement options produced mu(theta) larger than the limiting values whereas mu(theta) of DRCBs not conforming to the ACI 318-14 did not exceed the limiting values.