Experimental and numerical evaluation of the effects of concrete lift joints on static and seismic response of gravity dams

Concrete gravity dams in Canada are ageing. With an average of 50 years of service, there are definite signs of deterioration, particularly along lift joints, sometimes due to inadequate construction techniques. The safety assessment of dams, including the response of lift joints under extreme loads, has not been addressed adequately in the context of advanced numerical analysis using relevant load-displacement constitutive models.; Cracking and failure along lift joints in dams involve frictional strength characteristics which, under transient loadings such as earthquakes, may lead to energy dissipation by friction sliding. Eighteen specimens with concrete-concrete joint surface area of 500mm x 250mm were subjected to sliding friction tests. The friction coefficient was found to decrease with increasing applied normal stress. Hysteresis loops are very stable; there is no significant degradation in response. The friction angle characterizing the shear strength is the sum of a basic angle and a roughness angle. Roughness of waterblasted joints is equal to 80% of monolithic cracked specimens roughness, while roughness of untreated joints is equal to 15% of monolithic cracked concrete roughness. The dynamic sliding hysteresis loops are enhanced by reducing the basic friction coefficient to 85% of the static value.; Based on the experiments, a hysteretic concrete-concrete lift joint constitutive model was developed. The initial linear elastic response of the joint interface, the crack initiation and propagation, and the fully cracked sliding friction response, were combined in a three-state constitutive model. The model was implemented into the newly developed finite element program INTRFACE that uses nonlinear gap-friction interface element as numerical support. A typical 90 m concrete gravity dam with lift joints was analysed for three possible situations: (i) a base joint at the foundation, (ii) a base joint and a lift joint near the crest, and (iii) eight lift joints evenly distributed along the dam height. Nonlinear transient dynamic analyses indicate that the total energy dissipated by friction, and the maximum residual sliding displacements could be adopted as a basis for assessing the potential damage under a severe earthquake.