Experimental investigation of the influence of slenderness ratio and of the in-plane/out-of-plane interaction on the out-of-plane strength of URM infill walls

•An experimental program concerning URM infills is presented.•The results of eight combined IP/OOP tests are described.•The influence of slenderness ratio on the IP/OOP interaction is discussed.•Tests’ results are compared with literature formulations’ predictions.•Empirical formulations for IP/OOP interaction modelling are proposed. This study presents the results of eight experimental tests on unreinforced masonry infills for the assessment of their out-of-plane (OOP) response and of the effects on it of in-plane (IP) damage (IP/OOP interaction). Infills equal for geometric and mechanical properties except for the slenderness (height-over-thickness, h/t) ratio were tested. The conservativeness of literature formulations in predicting the effects of IP/OOP interaction is assessed. The experimental results are collected together with those presented in literature to propose formulations for the prediction of the reduction of OOP response parameters as a function of the IP displacement demand and of the h/t ratio.