The Size Effect and Strain Effect in Reinforced Masonry

The research described in this thesis focuses on improving our understanding of the behaviour of reinforced concrete masonry subjected to shear. All shear design methods in current masonry building codes are empirically based, and have been shown to produce widely varying predictions of shear strengths of masonry walls, beams and columns. Furthermore, the research community acknowledges that there is little to no consensus on the exact mechanisms of shear transfer in masonry elements, thereby slowing the replacement of empirical design expressions with more rational approaches. Given that shear failures can be brittle and sudden, with little to no warning of impending failure; experimental research focusing on these two issues is of primary importance.An extensive experimental program consisting load-testing fifteen large-scale reinforced masonry beams is presented in this thesis. The results definitively show that principles that govern the shear design of reinforced concrete beams in Canada can be applied to reinforced masonry beams. Various phenomena that have been observed in reinforced concrete subjected to shear were also observed in these tests, includes “the size effect” and “the strain effect”. It is shown that design codes that do not account for these effects exhibit higher variability and in the case of size effect, may produce unsafe designs.Detailed instrumentation of the test specimens showed that aggregate interlock is the major mechanism of shear transfer in masonry beams, and as such this mechanism can explain much of the observed experimental behaviour. The size effect, wherein the failure shear stress decreases as the effective depth increases, can be explained by the reduced aggregate interlock capacity. Likewise, the strain effect, wherein the failure shear stress decrease as longitudinal strains increase, can be explained based on reduced aggregate interlock. It is also found that stirrups and longitudinal reinforcement distributed over the height of the beam have highly beneficial effects on shear behaviour of reinforced masonry. The test results of this research were used to justify the use of the CSA A23.3 as a base to revise the shear provisions in of CSA S304-2014 masonry code.