Transfer Functions of Bridge and Train: Case Study of the Yunjung Bridge in Honam High-Speed Railway System

Abstract

We propose the inverse transfer function (TFinv) changing the ground motion amplitude recorded at the train to the free-field equivalent ground motion supposing that the train is on the bridge. This process is needed to estimate the free-field motions from the seismic records observed at the on-board accelerometer which is used for the on-board earthquake warning system. To estimate the TFinv, evaluation of two transfer functions is needed: a transfer function of the bridge (TFbridge), and the other transfer function of the train (TFtrain). For the estimation of the TFbridge, we simplified an example bridge (named Yunjung bridge) located in the Honam high-speed railway as SDOF models finding its natural frequency dependent on the girder type and span length. Then, using time-domain integration methods (Newmark and Duhamel), SDOF response and TFbridge is calculated. For the TFtrain, we modeled the rail base and train following the similitude law and performed the shaking table test with various earthquake ground motions, and evaluated the TFtrain empirically comparing the responses at the train and the rail base. Two models of TFinv based on the moment magnitude ranges of input ground motions are proposed.