Shear keys in bridge abutments are intended to provide lateral restraints to the bridge superstructure in the event of a moderate earthquake and to serve as fuses to prevent the transmission of large lateral forces to the abutment piles when a severe earthquake occurs.

This study is to acquire a comprehensive understanding of the behavior and resistance mechanisms of external shear keys in bridge abutments and to develop reliable analytical methods for the evaluation of the capacity of shear keys with different material properties, construction methods, reinforcing details, geometries, and degrees of skew. Six shear key-stem wall assemblies were tested. The tests on isolated shear keys have provided useful information on the influence of the construction joint preparation on the shear key behavior and have been used to validate simplified strength assessment methods. The study has shown that non-isolated shear keys can be so reinforced that their failure mechanism is governed by horizontal sliding rather than diagonal cracking of the stem wall, which is costly to repair. A reliable analytical method has been proposed to calculate the resistance of non-isolated shear keys based on the shear key geometry, the concrete strength, and the amount of the vertical dowel reinforcement. An innovative design concept using post-tensioned rocking shear keys has been explored and proven to be feasible. Finally, the test data have shown that a shear key with a 60-degree skew can be significantly weaker than a shear key with zero-degree skew and the same amount of vertical dowel reinforcement.

Nonlinear finite element analysis can be an accurate means to understand the failure mechanism and predict the resistance of shear keys. For such analysis, a 3-D cohesive crack interface model has been developed to represent concrete fracture in a realistic manner, and an interface material law has been proposed to simulate the dowel action of steel reinforcing bars crossing cracks and construction joints.

Based on the experimental and numerical studies, general recommendations are provided for the design of shear keys. The simplified analytical methods proposed here can be used to design shear keys and stem walls to achieve the desired performance.