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

许多弯曲刚构桥正在建设中，以连接几个公路网。弯曲刚构桥的地震反应较直桥复杂，但目前尚未建立弯曲刚构桥的抗震设计方法。本研究的目的是阐明弯曲刚体桥梁的基本地震反应现象。首先，我们对桥梁工程师的问卷回答进行了评估。研究发现，由于三维非弹性地震反应分析的难度和成本仍然很高，如何确定合适的初始截面是摆在桥梁工程师面前的重要问题。然后进行了地震反应分析，研究了弯曲刚构桥的横角对地震反应的影响。模态分析表明，主模态的参与系数随交叉角的减小而减小。梁单元的水平旋转是弯曲刚构桥的特点。在地震反应过程中，由于梁单元的转动，桥墩的位移响应各不相同。另一方面，直桥桥墩的响应几乎相同。因此，对弯曲刚构桥进行模态分析是十分重要的。特别是对于交叉角小于120度的弯曲桥，需要建立三维非弹性模型。

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.