Three-Strut Model for Concrete Masonry-Infilled Steel Frames

Masonry infill panels in framed structures have been long known to affect strength, stiffness, and ductility of the composite structure. In seismic areas, ignoring the composite action is not always on the safe side, since the interaction between the panel and the frame under lateral loads dramatically changes the stiffness and the dynamic characteristics of the composite structure, and hence, its response to seismic loads. This study presents a simple method of estimating the stiffness and the lateral load capacity of concrete masonry-infilled steel frames (CMISFs) failing in corner crushing mode, as well as the internal forces in the steel frame members. In this method, each masonry panel is replaced by three struts with force-deformation characteristics based on the orthotropic behavior of the masonry infill. A simplified steel frame model is also presented based on the documented modes of failure of the CMISF. The method can be easily computerized and included in nonlinear analysis and design of three-dimensional CMISF structures.