DYNAMIC PERFORMANCES OF A RAILWAY BRIDGE UNDER MOVING TRAIN LOAD USING EXPERIMENTAL MODAL PARAMETERS

In the design of railway bridges, it is necessary to be able to predict their dynamic behavior under a moving train load so as to avoid a resonance state from repetitive moving axle forces with uniform intervals. According to design trends, newly developed girder bridges weigh less and have longer spans. Since the dynamic interaction between bridge superstructures and passing trains is one of the critical issues concerning such railway bridges that are designed with greater flexibility, it is very important to evaluate the modal parameters of newly designed PSC girders before carrying out dynamic analyses. In this paper, a full scale incrementally prestressed 25-meter long concrete girder was fabricated as a test specimen and modal testing was performed at every prestressing stage in order to evaluate the modal parameters, including the natural frequency and the modal damping ratio. Young's modulus was also obtained from the global stiffness of the test specimen. During the modal testing, a digitally controlled vibration exciter and an impact hammer were applied in order to obtain precise frequency response functions, and the modal parameters were evaluated at various construction stages. With the availability of reliable properties from the modal experiments, dynamic performance estimation of a PSC girder railway bridge during the passage of a moving train can be carried out.