In-plane lateral load transfer capacity of unreinforced masonry walls considering presence of openings

Abstract

This study proposes mathematical models for the prediction of the in-plane lateral load capacity of unreinforced masonry (URM) walls considering potential failure modes and the presence of openings. The rocking strength is derived from the elasticity theorem for the compound stress condition under the assumption that rocking begins when the stresses at the extreme tensile fiber reach the tensile resistance capacity of the masonry. For toe crushing strength, the equivalent rectangular stress block specified in federal emergency management agency (FEMA) 273 is considered in the calculation of resultant compressive forces. The sliding and diagonal shear crack strengths are formulated based on the upper-bound theorem of concrete plasticity. The proposed models account for the effects of door or window openings on the failure mode and lateral load capacity of URM walls. The reliability of the proposed models is verified by comparing with test datasets comprising 202 URM walls without opening, 3 walls with door opening, and 4 walls with window opening. The proposed models confirm that URM walls are initially governed by the rocking rotation and subsequently ultimately fail via different mechanisms. It is also found that the empirical design equations specified in FEMA 273 and new zealand society for earthquake engineering (NZSEE) overestimate the rocking strength of URM walls and that their predicted their lateral load capacity significantly deviates from the test data. The proposed model results present comparatively better agreement with the test results. The mean and standard deviation of the ratios between the experimental and predicted results are 0.93 and 0.20, respectively, for URM walls without openings, and 0.92 and 0.14 respectively, for URM walls with openings. The proposed models rationally consider the effect of openings on the transition of the failure modes and the consequent reduction in the lateral load capacity.