A study of two-way bending in unreinforced masonry

Research Doctorate - Doctor of Philosophy (PhD)Masonry walls will almost invariably be required to resist lateral out-of-plane loads due to the action of wind or earthquakes; less commonly walls may be subjected to water or earth pressure or blast loading. Of particular interest is the common case which arises when the walls are supported on two or more adjacent edges. Under these conditions the masonry is subjected to a complex state of biaxial (two-way) out-of-plane bending combined with vertical in-plane compression due to the self weight of the wall and any superimposed loads. Different approaches currently exist for the design of masonry wall panels subjected to out-of-plane loads. However, these approaches are all empirical and often yield widely varying design recommendations and there has been significant criticism by proponents of the different methods regarding the use of alternative approaches. In this study an extensive program of laboratory testing in parallel with numerical analysis was conducted to examine the bending, biaxial bending in particular, behaviour of masonry walls. The aim was to provide a better understanding of the behaviour at the fundamental level towards ultimately developing a fully rational biaxial-bending failure model that can predict behaviour under any simultaneous combination of bending moments in the two principal directions, along with a superimposed compression force on the bed joints. Experimentally, 'single joint' four brick unit specimens were studied comprehensively, using a newly commissioned test rig, by subjecting them to various vertical and horizontal bending moments both separately and in combinations, along with a superimposed compression force on the bed joints. These tests provided important information about the flexural behaviour of mortar joints and the torsional behaviour of bed joints. In addition, a complete set of characterization tests was also performed to study the fundamental material properties of masonry, which were important input parameters in the numerical modelling. Numerically, a 3D non-linear finite element micro-model with cohesive contact was proposed and implemented in the ABAQUS/Standard software package. Numerical viii analyses were performed to provide rational explanations to the bending behaviours observed in the four brick unit specimen tests and evaluate a newly proposed torsion shear test method. A simplified 3D non-linear finite element micro-model was also proposed to simulate the bending behaviour of small walls. Its effectiveness was clearly demonstrated in its application to masonry walls, with or without openings, subjected to both in-plane and out-of-plane loads