Experimental Investigation of the In-Plane Behaviour of Concrete Masonry Infills Bounded by Reinforced Masonry Frames

Abstract

This study was carried out to investigate the in-plane behaviour of all-masonry infilled frames, i.e., concrete masonry infills bounded by reinforced masonry frames. To this end, six specimens including one masonry bare frame and five all-masonry infilled frame specimens were subjected to lateral loading applied at the frame top beam level to failure. The parameters studied included masonry infill strength, infill reinforcement, and presence of vertical loading. Masonry infill strength study considered a regular and a weaker strength of infills; infill reinforcement study considered two scenarios of horizontal reinforcement in the infill where one was the bed joint reinforcement implemented every other course in the infill and the other was the two bond beams implemented in the infill; and vertical load study involved one specimen under combined vertical and lateral loading where the vertical load was applied to the top beam and held constant while the lateral loading was increased to the specimen failure. Load vs. displacement response, cracking pattern and load, and failure mode and ultimate load for each specimen were obtained and discussed in detail. The experimental results were used to evaluate the validity of stiffness and strength provisions contained in the Canadian (CSA S304.14) and American (TMS 402/602.16) masonry design standards. The performance of specimens was also compared with the infills of the same geometry but bounded by RC frames. For all infilled frame specimens, the final failure mode seems to be controlled by severe diagonal cracking extending into the boundary columns or a combination of diagonal cracking and shear sliding as in the case of horizontally reinforced infills. No evident corner crushing was observed. An increase in infill strength increased the ultimate load of the infilled frame but showed no evident correlation with the infill-frame system stiffness. Implementing infill reinforcement did not have a significant effect on the ultimate strength but resulted in an increase in both the initial and cracking stiffnesses as well as ductility of the specimen. Presence of vertical load resulted in a marked increase in ultimate load of the infilled specimen but at the expense of a reduced ductility. In general, CSA S304-14 overestimated whereas TMS 402/602 underestimated the stiffness with a similar range of disparity to the test results. In the case of strength prediction, CSA S304 performed better than TMS 402/602 with predicted values closer to the test results. The comparison with infilled RC frames showed that behaviour, strength, and ductility of all-masonry infilled frames are similar to, and in some cases, slightly better than infilled RC frames.