Vertical collapse safety margin assessment for steel frames against earthquake-induced loss of column

Abstract

A quantifiable approach measuring the seismic structural collapse under sudden column removal is proposed using the interaction of the vertical collapse margin ratio (CMRV), the demand-to-capacity ratio (DCR) and the robustness (R). The assessment of CMRV needs the identification of the vertical maximum considered earthquakes. A classification of the ground motions based on the vertical-to-horizontal (V/H) ratios was used to obtain the vertical design spectrum. Six schemes of steel structures with various scenarios of sudden column removal were investigated to extract CMRV, DCR, and R. Then, a nonlinear regression analysis allows finding a general formulation of CMRV. A 15-story steel structure validates the proposed formulation of the CMRV. The two paths for estimating the minimum CMRV (CMRV, min) were the use of the recommended value of DCR and the minimum value of R inside the approximated CMRV expression, and the probabilistic distribution of CMRV, min from the analyses of different beam deformation states. The study of eighteen archetypes with 119 scenarios of sudden column removal reveals the value of the CMRV decreases when the V/H or/and DCR increase. The new maximum values of DCR with respect to R and its precise ranges are found with the use of the contour curves of CMRV, min.