Maintaining Bridge Alignment during Seismic Events: Shear Key Design and Implementation Guidelines

Abstract

Shear keys are widely used in small-to-medium–span highway bridges to restrain the superstructure laterally. Owing to deficiencies in the existing design codes in China, shear keys were damaged extensively in bridges that experienced the Wenchuan earthquake on May 12, 2008. Post-earthquake investigations showed that failure of shear keys was the main reason for girder unseating and bearing sliding. To maintain bridge alignment during seismic events, a new type of shear key is proposed to retrofit existing highway bridges. Experimental and analytical work was conducted to investigate the seismic behavior of the proposed shear keys under repeated monotonic loading. Seven specimens were designed and fabricated with shear keys on top at full scale of a prototype bent cap commonly used in China. The test results showed that the proposed shear keys failed as designated in a ductile mode in which shear keys experienced sliding while bent caps were protected from damage. An analytical model was then developed to predict the capacity of the proposed shear keys, and an overstrength factor was recommended in a capacity design philosophy. Compared with the experimental results, the analytical model developed in this study was more accurate than existing analytical models. Based on the experimental and analytical results, design and implementation guidelines were proposed for replacement of existing obsolete shear keys in highway bridges.