INVESTIGATION OF DYNAMIC PERFORMANCES OF RAILWAY BRIDGES UNDER MOVING TRAIN LOAD USING EXPERIMENTAL MODAL PARAMETERS

초록

Repetitive moving forces with uniform intervals induced from the passing train can cause unpleasant behavior of railway bridges. Resonance of the structure can be broken out when the natural frequency of the bridge coincides with exciting frequency of moving forces. Therefore, exact application of dynamic properties of the structure will conduct exact understanding of dynamic behavior of the structure under moving train loads. As an alternative of conventional prestressed concrete(PSC) girders, various types of PSC girders are being developed and applied in bridge structures. Incrementally prestressed concrete girders and concrete girder with encased steel I-shaped beam are one of these newly developed girders. According to design concept, these new type of PSC girders are of some advantages to reduce their self-weight and make spans longer. However, dynamic interaction between bridge superstructures and passing trains would be sometimes one of critical issues in these more flexible railway bridges. Therefore, it is very important to evaluate modal parameters of PSC girders newly designed before doing dynamic analyses. In the present paper, a full scale incrementally prestressed concrete girder of 25 meters long as a test specimen was fabricated and modal testing on it at every prestressing stage was carried out to evaluate modal parameters including natural frequencies and modal damping ratios. Young’s modulus can also be obtained from static loading tests. In the modal testing, a vibration exciter controlled digitally as well as an impact hammer is applied to obtain frequency response functions more exactly and the modal parameters are evaluated varying with construction stages. With application of reliable properties from modal experiments, estimation of dynamic performances of PSC girder railway bridges can be obtained from various parametric studies on dynamic behavior under the passage of moving train.