Effect of static and kinematic boundary conditions on the out-of-plane response of brick masonry walls

The Unreinforced Wall (URM) elements that are most susceptible to out-of-plane failure are wall elements of the upper storeys where the accelerations are largest. In modern URM buildings with reinforced concrete slabs, the out-of-plane mechanism involves typically a storey-high wall element, which is subjected at its base and top to the accelerations of the corresponding floor slabs. The accelera-tion time histories of the two slabs differ as a result of the deformability of the in-plane loaded walls and their rigid body rotations. Existing studies on the out-of-plane response of URM walls analysed walls that were subjected to the same input motion at the top and bottom of the wall. In few studies, the motion was modified by a spring modelling the in-plane flexibility of the slabs. This article investigates how the response of walls subjected to different accelerations at the top and bottom differ from the response of walls that are subjected to the same, mean acceleration at the top and bottom. The topic is investigated by means of a parametric study using discrete element modelling and by means of simple mechanical models using rigid body mechanisms. The article concludes that in particular the relative displacement between the top and base of the wall contributes to the reduced out-of-plane resistance. The non-constant force distribution over the wall height has only a lesser influence. The paper concludes with recommendations for future research.