The shear strength of bonded lift joints and shear keys is important to overall dam stability during an earthquake but it is poorly understood. This paper provides a brief review of shear strength data from recent testing and available literature to estimate the strength of shear keys in vertical contraction joints and bonded horizontal lift joints in concrete dams. Three shear failure criteria for concrete are compared to assess the shear strength of shear keys and lift joints. The Griffith failure criteria is selected as the most appropriate because it tends to provide a lower bound estimate of strength and it is appropriate for brittle materials like concrete subjected to shear loading. Relatively simple shear strength equations are developed and compared to results available from the literature. Both static and dynamic shear strengths are given. The resulting shear strength parameters are compared to shear strengths which have traditionally been used in dam design and assessment. It is concluded that relatively high shear strengths are available particularly under dynamic conditions.
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