Effect of masonry joints on the behavior of infilled frames

The present paper investigates the behavior of masonry infill walls and the effect of the interfaces between the masonry wall units (joints), on the global behavior and on the local infill-frame interaction. The investigation focuses on the case of failure of a supporting column that may trigger a progressive collapse of the building. Experimental results of a new testing method are presented. The experimental technique enables analysis of the contact zone and the contact tractions, and their variations during the loading process. The purpose of this study is to explore and quantify the effect of the joints on the global and local behavior of the composite infill-frame structure. The study examines the contact zone between the infill wall and the frame and its variation with loading, and compares the new data with available expressions that are found in the literature. A comparative experimental study that includes three large-scale unreinforced masonry infill walls with identical geometry and identical Autoclaved Aerated Concrete (AAC) masonry units, but different joints' properties is presented. The results show that the joint properties have a significant effect on the ultimate load, the initial stiffness and the energy dissipation with differences of about 50%, 85% and 70%, respectively. It is also shown that the length of the contact zone changes during loading in all three specimens and its size depends on the joints characteristics. The different contact lengths that are calculated by available simplified models are smaller than the experimentally measured contact region by more than 30%.