In-plane and out-of-plane behaviour of concrete masonry infills

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Masonry walls have been commonly used to infill steel or reinforced concrete frames either as interior partitions or exterior cladding in modern building construction. Due to a lack of scientific information in assessing the extent of interaction between the infill and the frame, the masonry infill is often treated as non-structural element and the bounding frame is designed for both gravity and lateral loading. The contribution of masonry infills to the frame stiffness and strength is therefore ignored. It is, however, a misconception that ignoring the contribution of the infill is a conservative approach. Infill walls significantly stiffen the frame, which in turn attracts larger forces to the infill region in a structure. Improperly designed Infill walls have been identified as a contributing factor to catastrophic structural failures in earthquakes. On the other hand, properly designed infills have shown to provide significant strength and ductility for the frame system in resisting various types of lateral loads-even after considerable cracking. The nonlinear, inelastic behaviour of the frame system coupled with the various material and geometric characteristics of masonry infills has made accurate evaluation of the infill contribution to the lateral stiffness and strength of the infilled system a challenge. Despite that much experimental testing and numerical analysis have been conducted in the past three decades, the results have been scattered and some findings from these studies were either inconclusive or even conflicting. The design guidelines for masonry infills contained in the Canadian masonry design standard, CSA S304.1-04 (2004), are based on work conducted more than 40 years ago. The design values obtained using these guidelines are found to be in significant disparity with existing experimental results and also with values obtained from other recognized standards such as American code MSJC 2013, New Zealand masonry design code NZS 4230 and Eurocode 8. These inconsistencies have resulted in the situation that research findings have not been transferred to industry practice to a large degree. In order to incorporate masonry infills in the lateral and gravity load resisting systems of a structure, scientifically verified and industry-accepted design guidelines that cover practical applications of infills are crucial. This proposal is hence motivated to investigate, both experimentally and analytically, the behaviour and capacity of concrete masonry infills bounded by frames so as to contribute to advancement of rational design approaches. The research, upon its completion, is expected to quantify the infill and frame behaviour with a range of parameters to a point that constructive recommendations applicable to industry practice can be made. This will fill in the gap in the current standard which will ultimately impact the current masonry infill construction practice.