Experiment-based out-of-plane resistance of strong masonry infills for codified applications

In the last two decades, the typology of unreinforced masonry infills to be adopted in newly designed RC structures has been subjected to significant changes, passing from the use of slender/weak masonry panels with one or two layers, to stronger single-whyte walls. These modifications have allowed to reduce the construction time and to improve the thermal and acoustic performance. However, the adoption of a more robust masonry solution can significantly affect the response of infilled structures as respect to slender/weak typologies, but the current standards do not provide proper design procedures for the in-plane and out-of-plane verification of such masonry infills. In order to fill some of these gaps, this paper presents the experimental results of two masonry infills made of modern strong masonry tested only in the out-of-plane direction, without any previous in-plane load. The tests have permitted to apply and analyze the existing formulations in the codes and literature for the computation of the out-of-plane resistance and the fundamental period. Moreover, some new formulations have been proposed to better estimate these values according to the experimental evidence. In the proposed equations, dimensionless parameters have been introduced to include some important physical aspects, such as the bidirectional response of the masonry infill, the second order effects, the deformability of the frame and the occurrence of local mechanisms such as the sliding at the frame/infill interface.