Seismic Damage Model and Multilevel Performance Indexes of Elevated Pile Cap Bridge

摘要

The elevated pile cap foundation is widely used in large span or long bridges. The paper deals with experimental activity on 4 scale-models of elevated pile cap foundation belonging to a long span continuous bridge. The foundation was composed of 9 piles. The pile cap and pier and the special soil box were built to consider soil-pile-superstructure interaction. Two specimens were strengthened by steel protective pipe at each pile top. The tests consist of cyclically imposed displacement to 4 specimens, performed in the state key laboratory for disaster reduction in civil engineering of Tongji University. According to the test result, the peak strength of strengthening specimens is about 1. 77 times of the others and the ultimate displacement is 1. 66 times of the original models. Additionally, the dissipated hysteric energy capability of strengthening specimens is more than 2.15 times of the others as the equivalent viscous damping ratio is reduced by 50%. Other relevant phenomena are the pinching effect of original specimens is more obvious and the hysteretic loops of reinforced specimens are more plumpness. Moreover, the modified Park-Ang seismic damage model is proposed to consider the loading path, the pronounced pinching effect of concrete and bond-slip of the reinforcing bars. Finally the failure mechanisms and five-level performance indexes of the elevated pile cap foundation were summarized.