Progressive‐Failure Analysis of Buildings Subjected to Abnormal Loading

Abstract

Abstract: This article presents a progressive‐failure analysis procedure to evaluate the performance of a building framework after it has been damaged by unexpected abnormal loading, such as an impact or blast load caused by a natural, accidental, or deliberate event, or as a result of human error in design and construction. To begin with, it is assumed that some type of short‐duration abnormal loading has already caused some form of local damage to the structure. The residual load‐carrying capacity of the remaining framework is then analyzed by incrementally applying the prevailing long‐term loads and any impact debris loads, and progressively tracing the strength deterioration of the structure until either a globally stable state is reached or progressive collapse occurs for part or all of the structure. The computer‐based procedure is based on the displacement method of analysis. The effect of both axial force and shear deformation on member and structure stiffness is accounted for in this article (Liu, 2004; Xu et al., 2004). The stiffness matrices for framework members account for elastic–plastic bending, shearing, and axial deformations, and are progressively updated under incrementally increasing loads through the use of degradation factors that characterize stiffness deterioration. The computational model allows the incremental analysis to proceed beyond loading levels at which structural instabilities occur, including the formation of plastic collapse mechanisms and the disengagement of members from the building superstructure. The progressive‐failure analysis procedure is quite general and, with the appropriate choice of material constitutive model, may be applied to building frameworks of any type (concrete, steel, composite, etc.). Herein, a constitutive model for structural steel is adopted to account for elastic–plastic behavior under single or combined forces, and the progressive‐failure analysis procedure is illustrated for two example planar steel moment frames.