Department of Civil, Environmental and Mining Engineering, University of Adelaide


Unreinforced masonry subjected to horizontal bending can fail by two distinct modes: stepped failure, characterised as zigzagging cracks following the masonry bond along bed and perpend joints; and line failure, characterised as a straight line crack through the brick units and perpend joints. Due to the variability of material properties throughout a panel a vertical crack typically exhibits a mixture of these two failure modes, with the crack propagating along the weak links in the masonry. Current design procedures, including the Australian Masonry Code AS 3700 calculate the design moment capacity in horizontal bending as the weaker of the characteristic values of strength for the two individual modes. However, this approach does not explicitly account for a further strength reduction due to the weak link effects. This paper presents a stochastic analysis method for determining the moment capacity of the mixed mode of failure. The procedure is based on analytical equations for the ultimate moment capacities for the stepped and line failure modes, in which key material properties are treated as random variables. It was found that whilst the reduction in strength due to weak link effects can be significant at high levels of material variability, it appears to be sufficiently accounted for by the severe strength reduction factor (?=0.6) used in design.

Key words
Unreinforced masonry; stochastic analysis; structural reliability, horizontal bending; ultimate strength; capacity reduction factor