Effect of Shear Keys on the Quasi-Isolated Behavior of Small-to-Medium-Span Girder Bridges

Small-to-medium-span girder bridges equipped with shear keys play a significant role in the Chinese highway bridge system. However, shear key failure was observed during the 2008 Wenchuan earthquake, which resulted in excessive superstructure displacements and even catastrophic span collapse. For this, six refined bridges were investigated for the quasi-isolated behaviors under different shear key strengths by using the Pushover and IDA methods. Results indicate that the bridges exhibit two distinct damage states upon the shear key strengths. The shear key failure and bearing sliding create a natural quasi-isolated mechanism, with the following damage sequence: shear key failure → bearing sliding → pier undamaged or slight damage. Quasi-isolated behavior leads to higher displacement demands for beams, especially when the peak ground acceleration (PGA) exceeds 0.45 g. By selecting suitable shear key strength, below 9% for 20 m piers and 30% for 10 m piers, quasi-isolated damage is expected to occur in bridges. The study offers a fresh perspective on the concept of seismic design for highway girder bridges in China.

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