Approximations in Progressive Collapse Modeling

Abstract

Assumptions must necessarily be made when the collapse response of structures is investigated using simulation models. The type and extent of modeling assumptions depend on the computational resources available, modeling expertise, and results sought. Modeling choices that are commonly made include planar versus three-dimensional (3D) representation, simplification of member response for modeling purposes, and the use of macroelements to mimic behavior instead of using elements that are based on fundamental constitutive relationships. Using four different types of models, this paper sheds light on the effect of some commonly employed approximations in collapse modeling. The models represent a 10-story seismically designed steel building and encompass computationally expedient planar and 3D macromodels as well as continuum models of individual frames and the full 3D structural system. After a validation exercise, the simulation models are exercised to investigate system collapse response when columns are forcibly removed and to highlight the effects of the various modeling approaches. The simulation studies show that the floor system contributes significantly to collapse response. It is also shown that well calibrated macromodels can be relied on for accuracy when modeling progressive collapse and that the results of planar analyses cannot always be viewed as conservative.