S. Kadysiewski¹ and K.M. Mosalam²

1. Structural Engineer, Bechtel National, Inc., San Francisco, California, skadysie@msn.com
2. Professor and Vice Chair, 733 Davis Hall, Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710, mosalam@ce.berkeley.edu

ABSTRACT

This paper describes a practical analytical model which can be used for the seismic evaluation of unreinforced masonry (URM) infill walls located within a reinforced concrete (RC) frame. The model, consisting of diagonal beam-column members utilizing fiber-element cross sections, is suitable for use in nonlinear time history analyses. The model considers both the in-plane (IP) and the out-of-plane (OOP) responses of the infill, as well as any chosen convex interaction between IP and OOP capacities. The behaviour is elastoplastic, and limit states may be defined by deformations or ductilities in the two directions. These limit states may be chosen to conform to code guidelines or they may be developed independently by the engineer. The model is composed of elements available in commonly used structural analysis software programs. The performance of the model is shown to be satisfactory for static pushover and dynamic analyses using a single panel structure. The proposed infill model is incorporated into a five-storey RC moment frame building with URM infill walls. It is subjected to 20 sets of ground acceleration time histories at five different levels of spectral acceleration. Collapse of the infill panel is assumed to occur at critical displacement ductilities in the IP and OOP directions with interaction between the ductilities considered. Fragility functions, giving the probability of collapse as a function of spectral acceleration level, are calculated and discussed.

KEYWORDS: earthquake, fragility, infill, in-plane, out-of-plane, model

C4-3