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This paper examines the horizontal bed joint shear failure mode and the shear load‐displacement behavior of unreinforced brick masonry during static and cyclic loading. Laboratory tests are conducted on masonry samples using a servo‐controlled direct shear apparatus. A total of 44 tests are conducted on old clay unit‐1:2:9 mortar specimens and 9 tests on new clay unit‐1:1.5:4.5 mortar specimens (laboratory specimens). In addition, three tests are conducted on field specimens collected from older brick walls damaged during the Whittier earthquake. In general, under cyclic shear loading, masonry bed joints show a peak strength for the first cycle followed by residual shear strength. Both peak and residual shear strengths are well represented by the Mohr Coulomb criterion, with friction coefficients ranging between 0.64 and 0.75 for the laboratory specimens. The field specimens show lower shear strength values. The pre‐peak response of masonry bed joints can best be represented by a hyperbolic curve and their shear stiffness depends on both the shear displacement and normal load level.
Atkinson et al. (Fri,) studied this question.