Analysis and evaluation of direct shear tests on concrete joints in hydraulic structures

Neither the shear transfer behavior of unreinforced hydraulic concrete structures nor experimental procedures for its determination have been standardized in recent building codes and regulations. This poses uncertainty for the assessment of the integrity of hydraulic structures. This paper adapts direct shear tests, which are an established method in rock mechanics, for the assessment of unreinforced concrete joints and expands the evaluation method through recognizing surface inclination as a contribution to the coefficient of friction. The evaluation is subsequently performed on direct shear test results performed on specimens taken from a lock built in the early 20th century. Based on the initial state of the concrete joints—intact or cracked bond—results for the basic friction angle and the inclination angle are discussed. Using entire shear stress-deformation-curves as opposed to singular values was found to yield more stable results of shear transfer parameters and additional insight on the validity of the test.