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This paper quantifies the collapse performance of a set of masonry-infilled reinforced concrete (RC) frame buildings that are representative of 1920s-era construction in Los Angeles, California. These building have solid clay brick infill walls, and vary in height (2-8 stories), wall configuration (bare, partially and fully-infilled frames) and wall thickness (1-3 wythes). The buildings' collapse behavior is assessed through dynamic analysis of nonlinear models. These models represent the walls by diagonal struts whose properties are developed from finite element analyses, as described in the companion paper, and represent beamcolumns with lumped-plasticity models. The results indicate that the presence of infill walls can increase the risk of collapse. The most collapse prone of the buildings considered are those with strong, heavy infill walls, which induce large force demands in the frame elements. The partially infilled frames, which have a soft and weak first story, also perform poorly.

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Reinforced concrete (RC) frames with masonry infill walls are prevalent in high-seismicity areas worldwide and have experienced significant damage in earthquakes. This paper proposes a finite element–enhanced strut model to simulate the in-plane seismic response of masonry-infilled RC frames through time-history analysis. The strut backbone defining the behavior of the wall is developed from the response extracted from the finite element (FE) model(s) for the infill and frame configuration of interest. These struts are combined with models capturing flexural and shear failures of beam-columns to simulate building response. The strut model takes advantage of the accuracy of the FE modeling results, yet is computationally efficient for use in nonlinear dynamic analysis. The robustness of the proposed strut model is examined through comparison with experimental results for frames with different failure modes. This modeling approach is used in the companion paper to simulate the collapse response of 1920s-era California frames.