Reconstruction Method of Shear Keys on Existing Bridges Based on Structural Fuse Concept

Shear keys in existing bridges are ineffective in controlling the seismic displacement due to the lack of design codes to guide the details of construction and reinforcement. To improve the ability of existing bridges to resist earthquake damage, the reconstruction of shear keys based on the structural fuse concept is proposed. Firstly, quasi-static experiments are conducted to verify that the shear keys with a particular design of structural configuration and reinforcement meet the requirements of the structural fuse concept. Then, a prediction model is proposed to calculate the strength of shear keys based on the sliding shear mechanism, and the detailed procedures are presented for the reconstruction of shear keys. Finally, numerical simulations according to an actual bridge are performed to comparatively examine the effects of displacement control and force transfer of the reconstructed shear keys. The results show that the failure of reconstructed shear keys in a ductile mode with sliding shear and a large sliding displacement, causes no damage to the cap beam/stem wall. The strength of shear keys can be predicted accurately with a unified equation for different design parameters. The prediction errors of the equation are lower than 10% and most of them lower than 5%. Numerical simulations reveal that under the earthquakes of E1 and E2 levels, the reconstructed shear keys can decrease the lateral displacement of superstructure by 13.5% and 22.0%, respectively, and reduce the transverse deformation of laminated rubber bearings by 83.1% and 45.8%, respectively. The reconstructed shear keys remain perfectly elastic under the earthquake of E1 level and experience strength degradation under the earthquake of E2 level, which plays the role of structural fuse.