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

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

Yoo, Mintaek / Yang, Seunghoon / Moon, Jae Sang / Kwak, Dongyoup

We propose the inverse transfer function (TF_inv) 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 TF_inv, evaluation of two transfer functions is needed: a transfer function of the bridge (TF_bridge), and the other transfer function of the train (TF_train). 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 TF_bridge is calculated. For the TF_train, 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 TF_train empirically comparing the responses at the train and the rail base. Two models of TF_inv based on the moment magnitude ranges of input ground motions are proposed.