Seismic Assessment of Out-of-Plane Loaded Unreinforced Masonry Walls

Abstract

This thesis investigates the behaviour of URM walls subjected to out-of-plane seismic forces, and the study is focused primarily on single-storey and two-storey one-way spanning walls connected to flexible diaphragms. Expressions that describe the intermediate-height cracking of out-of-plane loaded one-way spanning URM walls were formulated, and wall force-displacement behaviour and the sensitivity to various parameters were studied. Crack height was identified to be particularly sensitive to low values of masonry bond strength and/or to low values of applied overburden. Crack height was found to have significant effects on both wall instability displacement and lateral resistance. A comprehensive quasi-static testing programme was developed by subjecting full-scale two-leaf and three-leaf URM walls to out-of-plane uniform forces. The objective of the tests was to develop an idealised predictive model for the out-of-plane behaviour of URM walls, by accounting the effects of different mortar mixes, multi-leaf construction and overburden loads. An in-field out-of-plane pushover testing programme was next completed, and some of the key questions about actual wall performance were answered. Wall support types and characteristics and their effect on wall behaviour were investigated by testing multiple walls having different support configurations, which included timber diaphragms, concrete ring beam, and grouted steel anchorage bars. The effect of plaster and wall finishings was investigated, and the conditions upon which the previously developed idealised predictive model had acceptable results were determined. A simplified reduced-degree-of-freedom numerical model was developed to study the dynamic behaviour of URM walls, with critical requirements of the model being an ability to account for the effects of flexible supports and an ability to predict the behaviour of two-storey walls. An existing assessment procedure for seismic assessment of out-of-plane loaded URM walls was reviewed in detail, an alternative methodology for wall assessment was introduced, and seismic assessment charts were presented for single-storey and two-storey walls.