Effects of Local Damage on Global Seismic Response of Bridge

The effects of seismic limit state performance of bearings on a whole bridge system during strong ground motions have been greatly concerned from past earthquake damages. Although rubber bearings or seismic isolation devices have replaced steel bearings since the 1995 Hyogo-ken Nanbu earthquake, they are still in use in existing bridges. This indicates that the effects of steel bearing failure on earthquake resistance of a bridge are a crucial issue. There are several physical models for steel bearing required in developing dynamic seismic response analysis model of a bridge system. The easiest way may be in such a manner that fixed and movable bearings are modeled as a nodal in a frame structure analysis. Bi-linear models are sometimes employed to represent bearing performance. A tri-linear model for fixed and movable bearings are developed based on real failure modes during the 1995 Hyogo-ken Nanbu earthquake. However, a systematic nonlinear model for steel bearing performance is yet to be established and geometric behavior modeling should be also discussed as well as material strength in developing a nonlinear model. Under these circumstances, a seismic hybrid experiment can be a powerful toll to examine earthquake response nature of a total bridge system. Seismic hybrid tests have been extensively used in earthquake resistance study of bridges, focusing on nonlinear performance of a reinforced concrete column, a steel column and various bearing devices such as a seismic isolation bearing. However, no seismic hybrid experiments have been conducted on nonlinear behavior of steel bearing so far. The objective of the present study is then to experimentally discuss the effect of near limit state in regard to fixed steel bearing on seismic performance of a total bridge system. First, we will describe a general earthquake response of a target bridge. Second, we will explain the hybrid seismic test. Third, test results will be discussed in view of superstructure response, restoring force characteristics and others. Finally, concluding remarks throughout the present study will be summarized. The terms `fixed' and `steel' will be dropped unless confusion arises in the present paper.