Experimental investigation of interface stiffness between concrete masonry infill and reinforced concrete frames

•Experimental investigation for interface stiffness of three types of CMU was carried out.•Interface stiffness varied considerably for various CMU types.•Construction practice and use of shear connectors also affected the interface stiffness.•Experimental values of interface stiffness can be used in FEM simulations. Masonry infilled wall panels are commonly used as internal partitions or external curtain walls within building frames. These infill panels are generally treated as non-structural elements as quantification of their strength and stiffness is varied and difficult. Interface properties between masonry infill and building frame play an important role in the lateral performance of masonry infilled frames. Behavior of masonry infilled frames have been studied since 1960s experimentally as well as analytically. However, studies to determine the properties of the interface between the masonry infill and the building frame elements are very few. In this study, 28 concrete masonry unit (CMU) samples consisting of solid, lightweight and hollow CMU blocks were tested under lateral load to determine the interface stiffness at three different locations (i.e. frame bottom, side and top) of a reinforced concrete (R/C) frame under varying normal load as well as presence or otherwise of steel shear connectors. The experimental data was analyzed and compared to delineate effect of different parameters on interface stiffness. Experimental results showed that the interface stiffness varied widely for the three types of CMU blocks at various interface locations. The use of shear connectors in the top and side interface specimen increased the interface stiffness considerably as compared to the samples without shear connectors. Similarly, normal load increased the interface stiffness of the bottom specimen as compared to the ones without normal load. Interface stiffness determined from these experimental results can be used for accurate modeling and analysis of CMU infilled R/C frames.