Seismic vulnerability assessment of medium-rise moment resisting frames with reduced beam section connections

The paper presents the development of fragility curves for two types of frames considering reduced beam section (RBS) connections, based on the results obtained from extensive nonlinear time history analysis (NLTHA). Two different classes of MRF are considered with bolted and welded connections. Due to some limitations inherent in both experimental and empirical based fragility curves, analytical fragility curves are considered to be the most reliable ones for the assessment of seismic vulnerability. In the present work, first, the force-displacement behaviour of bidirectional bolted connections (ordinary and RBS) was obtained by experimental test and numerical simulation, while the force-displacement behaviour of welded connections (ordinary and RBS) was obtained by numerical simulation using finite element analysis in ABAQUS. Subsequently, moment–rotation (M-θ) curves for all the connections were extracted from the backbone curves to obtain the behaviour of the plastic hinges of each connection. These plastic hinges were then used to derive the accurate force-displacement behaviour of the medium-rise frame modelled in SAP 2000. Finally, NLTHA was performed to obtain the maximum roof drift, considered the engineering demand parameter (EDP) in this study. Finally, standard goodness-of-fit test was performed using standard statistical methods and probability distribution function was fit to maximum roof drift data. A comparison of the fragility functions for each type of frame with different RBS-column connections was carried out. The results indicate the significant low seismic vulnerability of the considered medium-rise frames with RBS for both the bolted and welded connections, in comparison to the ordinary frame.