Interaction of in-plane and out-of-plane responses in unreinforced masonry walls under seismic loads

Abstract

Under seismic loading, a building is subject to simultaneous in-plane and out-of-plane actions. Existing simplified methods, such as the storey-shear mechanism, to determine the shear capacity of masonry structures neglect the interactions of out-of-plane actions. While neglecting the out-of-plane capacity can lead to a conservative estimate of global load carrying capacity, ignoring the interaction of in-plane and out-of-plane effects may lead to a non-conservative seismic assessment. In this paper, an analytical model is developed to evaluate the interaction of out-of-plane displacements with the in-plane shear capacities of unreinforced masonry (URM) walls under static loading. Results demonstrate that the out-of-plane displacements alter both the in-plane shear capacity and failure mechanism of a wall. The sensitivity of the interaction on the aspect ratio of, slenderness ratio of and axial load on the wall is also studied. Due to lack of experimental data specific to the phenomenon addressed, the proposed model is validated with non-linear finite element analysis. The model can be used to determine the reduced shear capacity of URM walls, if an estimate of the mid-height out-of-plane displacement is available. This interaction in URM walls are also studied under dynamic loading. The model is finally incorporated within the framework of the storey-shear mechanism to study the effect of out-of-plane displacements on the global shear capacity of a structure.