Numerical evaluation of test setups for determining the shear strength of masonry

The bond shear strength between masonry units and mortar is the weakest link in a masonry wall. Different material tests have been developed in order to characterize this bond behaviour. The objective of this study is to evaluate three common test setups through non-linear finite element analysis. The simulation method is based on our recent development of cohesive elements, which allows for the first time to fully capture the force-deformation characteristic of shear tests in 3D from the onset of loading until the residual shear strength and to retrieve typical shear failure modes observed in experiments. This study provides new insights into our understanding and interpretation of such shear tests: (1) elastic analysis, which has been widely used in the past, does not yield a stress distribution that is representative of the stress distribution at maximum resistance; (2) while friction coefficient is well estimated (the error is less than 10%), the local cohesion is underestimated by all three test setups of which the error lies between 13 and 32%; (3) the randomness of the material properties leads to a further underestimation of the mean value of the local cohesion; (4) differences in the material properties of the two joints of the triplet test units do not jeopardize the applicability of this test setup and estimations of the mean properties are obtained with similar reliability as for couplet tests.