DYNAMIC PROGRESSIVE COLLAPSE OF FRAME STRUCTURES Griengsak Kaewkulchai 1 , and Eric B. Williamson 2 , Member ASCE ABSTRACT Current research on the dynamic progressive collapse of frame structures is presented in this paper. Unlike previous studies that have approached the problem without consideration of inertial effects, our research addresses the importance of dynamic load redistribution. For the present study, a computer program has been developed for analyzing dynamic progressive collapse of 2-D frame structures. Newmark’s method, in conjunction with Newton-Raphson iterations, is used for computing system response as a function of time. Both geometric and material nonlinearities are considered. A damage index is also computed to account for the effects of strength and stiffness degradation, and it is used to determine the onset of member failure. Following member failure, the analysis continues through the use of a modified member stiffness procedure with releases of end forces. The paper concludes with a discussion of other important factors related to progressive collapse including the prediction of impact forces that may result after a member has failed and strikes a portion of the remaining structure. Keywords: structural dynamics, progressive collapse, building collapse, damage INTRODUCTION Progressive collapse is characterized by widespread propagation of failure following localized damage to a small portion of a structure, i.e., a chain reaction of failures. Progressive collapse has been recognized as a major consideration for structural design since the collapse of the Ronan Point Apartment building in London in 1968. In recent years, terrorist attacks against the Alfred P. Murrah Building in Oklahoma City in 1995 and the World Trade Center in New York in 1993 and 2001 have drawn awareness to the design of civilian buildings against progressive collapse. Although there has been a significant amount of research related to progressive collapse dating back to the early 1970s (e.g., Breen, 1976; Leyendecker and Ellingwood, 1977), few researchers have considered the implications of dynamic load transfer in the response of frame structures during a collapse event (Hakuno and Meguro, 1993; Isobe and Toi, 1996). Currently, protection against progressive collapse is indirectly built into most design standards through strength, ductility, redundancy, and continuity requirements. However, these requirements do not guarantee the prevention of progressive collapse. In most of the current design standards, a direct method called the ‘Alternate Load Path Method’ is referred to as a 1 Graduate Research Asst., Dept. of Civil Eng., University of Texas, Austin, TX 78712. E-mail: nguang@ mail.utexas.edu 2 Asst. Prof., Dept. of Civil Eng., University of Texas, Austin, TX 78712. E-mail: ewilliamson@mail.utexas.edu