Publication

Abstract : One of the fundamental assumptions of the equivalent frame (EF) modeling of unreinforced masonry (URM) buildings is that there is no interaction between in-plane and out-of-plane actions in the wall. However, an existing building, particularly with significant eccentricity between centers of mass and stiffness, is expected to have such bidirectional interaction that can potentially cause its EF model to overestimate global lateral force capacity. Nevertheless, the current practice in structural analysis of URM buildings using equivalent frames is to verify seismic demand separately, against pure in-plane and out-of-plane capacities, without considering bidirectional interaction; in reality, out-of-plane demand can adversely influence in-plane capacity and vice versa. After investigating such a problem, some literature in the past provides interaction curves for URM walls considering different boundary conditions, precompression, and aspect ratios. However, no specific study is available for the component identified as the pier within the EF modeling of a URM wall. Hence, this paper proposes an analytical model for the interaction curves between URM piers’ in-plane and out-of-plane force capacities by simulating 25 piers involving different aspect ratios and precompressions. Detailed block-based finite element micro-modeling is used to develop numerical models, employing a damage-plasticity-based material model and a layered shell element capable of simulating in-plane and out-of-plane responses. The outcome indicates that the interaction is significant in shear-controlled but not in flexure-controlled piers. After a critical point, however, there was a steep decrease in the in-plane capacity due to out-of-plane action, irrespective of aspect ratio and precompression level. The proposed analytical model would benefit structural engineers in the seismic assessment of URM buildings. In addition, it can serve as the basis for developing a 3D macro-element capable of accounting for bidirectional interaction for use in EF modeling.