Experimental study on the direct shear behavior of multiple shear keys at concrete glue joints subjected to uneven normal stress

Ten 'Z'-shaped shear specimens were fabricated to study the effect of uneven normal stress on the shear performance of glue joints. The test parameters included the roughness of the joint surface, the level of lateral normal stress, and the uniformity of lateral normal stress. The crack development, failure mode, ultimate bearing capacity, and relative slip data of the specimens were recorded in detail, and the load-strain curve and load-relative slip curve were plotted according to the test results. The results show that all specimens were brittle failures. After roughening the surfaces of the joints, the deformation resistance, overall strength, and overall stiffness of the specimens all got a little better. Increasing the level of lateral normal stress and the uniformity of lateral normal stress, the cracking load and ultimate bearing capacity of the specimen were increased. In addition, a coefficient η that quantifies the degree of uniformity of the lateral normal stress was defined, and a formula for predicting the direct shear bearing capacity of glue joints was proposed. The results show that the average ratio between the calculated values from the proposed formula and the test values was 0.96.