Response of infilled reinforced concrete frames with failure in infill dominated by sliding shear

Masonry-infilled reinforced concrete (RC) frames are commonly used in residential and commercial buildings across the world. The seismic response of such structures is complex on account of significant differences in the behavior of RC frame and the masonry infill. During an earthquake, the RC frame members generally undergo flexural or shear failure, while the infill can fail through two broad sets of failure modes: (1) diagonal mode (e.g., corner crushing, diagonal tension, diagonal compression), and/or (2) sliding mode. Majority of studies in the past have focused on the behavior of infilled frames with infills failing through the diagonal failure modes. This paper investigates the response of infilled frames with failure in infill dominated by sliding shear. Commercially available software platform ANSYS was used in the present study. Four alternate modeling approaches were considered to develop a detailed finite element model for a one-bay-one-story infilled RC frame specimen, subjected to monotonic in-plane lateral loads. Efficacy of these approaches were evaluated against experimentally studied specimens, wherein the sliding shear failure was observed. The approach wherein the brick and mortar were modeled explicitly, and all interfaces were modeled using a cohesive zone model was found to be most appropriate. A detailed parametric study was carried out to understand the influence of change in masonry prism strength, strength of concrete and number of sliding planes on the lateral force-displacement response of infilled RC frames. The results show that the peak strength of infilled frame with a pre-defined sliding plane was smaller by about 10 – 45% compared to the frame with regular infill. The deformability of infilled frames substantially increased due to introduction of sliding plane(s), especially when the number of planes were high or the planes were near mid-height of the specimen. The contact length between frame and infill reduced significantly by the introduction of sliding plane when compared with regular infill. This information may be useful in determining the location of struts and their properties in macro models for infilled frames.