Modeling of Unreinforced Masonry Infill Wall Considering In- Plane and Out-of-Plane Interaction

摘要

This report describes a practical analytical model that can be used for the seismic evaluation of unreinforced masonry (URM) infill walls located within a reinforced concrete (RC) frame. The model, which consists of diagonal beam-column members utilizing fiber element cross sections, is suitable for use in a nonlinear time history analysis. The model considers both the in-plane (IP) and out-of-plane (OOP) response of the infill, as well as the interaction between IP and OOP capacities. The behavior 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 various codes and guidelines, or they may be developed independently by the engineer. The model is composed of elements that are available in commonly used structural analysis software programs, and is based on small displacement theory, so it is rather straightforward to implement. For each infill wall panel modeled, one additional degree of freedom and two beam-column members are added to the overall structural model. This report is part of a larger research program of investigation into RC frames with URM infill, carried out in recent years at the University of California, Berkeley. Some of the previous work is described, including a previously proposed strut and tie (SAT) model. The behavior of that SAT model is investigated, and it is found that under certain circumstances, problematic issues are encountered. The newly proposed infill wall model is idealized as a single diagonal beam-column member, composed of two beam-column elements, with a node at the midspan. The midspan node is assigned a mass in the OOP direction to account for the inertial forces in that direction. The beam-column elements used in this report are force-based elements with inelastic behavior concentrated at the hinge regions. These regions are modeled using inelastic fibers, whose strength and locations are calculated to produce the desired IP-OOP strength interaction relationship for the panel. The interaction relationship is based on previous work conducted in an earlier phase of the research program.