Ductility demand seismic design of the curved rigid-frame bridge at the highway ramp

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Many curved rigid-frame bridges are under construction to connect the several highway networks. Though the earthquake response of the curved bridges are complicated compared to the straight bridges, the seismic design procedure for the curved rigid-frame bridges is not established yet. The aim of this research project is to clarify the basic earthquake response phenomena of the curved rigid-fame bridges.First, we evaluated the answers to the questionnaires of the bridge engineers. It was found that how to estimate the suitable initial cross section was the important problem for the bridge engineers, because the three-dimensional inelastic earthquake response analyses were still difficult and expensive to do.Then, the earthquake response analyses were carried out to study the effect of the cross angle of the curved rigid-frame bridge on the earthquake response. The modal analyses showed that the participation factors of the dominant modes decreased as the cross angle became smaller. The horizontal rotation of the beam elements was characteristic for the curved rigid-frame bridges. As the beam elements rotated during the earthquake responses, the displacement response of the piers were different from each other. On the other hand, the responses of the piers of the straight bridge were almost the same. This means that the modal analysis is important for the curved rigid-frame bridge.The three-dimensional inelastic model was necessary especially for the curved bridge whose cross angle was narrower than 120 degree.