EXPERIMENTAL AND NUMERICAL STUDY OF THE IN-PLANE AND OUT-OF-PLANE BEHAVIOUR OF UNREINFORCED MASONRY INFILLS BOUNDED BY RC FRAMES

Abstract

A literature review revealed that there is limited technical information available on the subject of masonry infilled frames, in particular, the interaction between the infill and its bounding frame and how this interaction affects the infilled system behaviour and strength. This research was then conducted to further the understanding of the infill-to-frame interaction considering a range of geometric, material, loading characteristics of the infilled frame systems. To that end, both experimental and numerical studies were performed with the focus on the concrete masonry infills bounded by reinforced concrete frames. Both in-plane and out-of-plane loading situations on the infilled frames were considered. The experimental testing was designed to provide physical results of failure modes, behaviour and strength of infilled frames as affected by several key parameters. The numerical study began with development of a 3D finite element model capable of incorporating properties of masonry infilled frames using ABAQUS. An extensive validation process on the model ensued using the physical results. Once verified, the model was used in a finite element study where several geometric and material parameters with extended range of variations were systematically studied. In the experimental study, a total of 17 specimens were tested of which 1) ten were subjected to in-plane loading; 2) four were subjected to out-of-plane loading; and 3) three were tested under in-plane loading first and then tested under out-of-plane loading to failure. Infill openings and infill-to-frame interfacial gaps were designed as two varying parameters for 1) and 2) test scenarios. The varying in-plane damage was the parameter for 3) testing scenario. While the diagonal cracking followed by corner crushing predominated the in-plane failure, two-way arching with the shear cracking through the concrete masonry unit webs was identified as the main load-resisting mechanism in out-of-plane tests. As for the in-plane damaged specimens, the out-of-plane capacity was reduced as a function of experienced in-plane drift ratio. In the numerical study, the finite element model was shown to be capable of predicting the load-displacement responses as well as the cracking pattern and failure modes accurately for both in-plane and out-of-plane loading scenarios. The correlations between each studied parameter and the behaviour and strength of masonry infilled frames were presented and discussed. Modifications on the out-of-plane design method currently adopted by the American masonry standard (TMS 402/602-16) were proposed and was shown to improve the performance of the method. A lower-bound equation for evaluating the out-of-plane strength of masonry infills with prior in-plane damage was proposed and it showed to produce better estimate when compared to the existing method.