预应力桥梁的竖向振动特性和地震反应分析

Vertical Dynamic Characteristics and Seismic Responses of Prestressed Bridge

摘要:

基于模态摄动法和振型叠加法，建立了预应力桥梁竖向地震反应分析的计算方法。通过2个典型工程实例分析，讨论了桥梁竖向地震反应分析中的几个问题。算例结果表明：①预加力使桥梁的自振频率升高，影响主要体现在低阶自振频率上，随着振型阶序的增加，预加力的影响变小。对于20m和32m跨度的预应力桥梁来说，竖向基频分别升高5.3%和6.3%，而第5阶竖向频率升高只有1%左右；②在地表波作用下预应力梁跨中截面弯矩减小约30%和25%，预加力提高了桥梁的抗震能力；③竖向地震反应中高阶振型的贡献可以忽略；④7度设防烈度下，在预应力桥梁跨中截面弯矩的荷载组合效应中，竖向地震作用效应所占比例分别达24.56％和26.15％，8度设防烈度时所占比例分别为38.93%和41.46%，说明在这类预应力桥梁抗震设计中应考虑竖向地震反应的影响。

Abstract:

Based on the modal perturbation method and the mode superposition method, an approach is established for vertical seismic response analysis of the prestressed bridge. Several problems met in the vertical seismic response analysis of the prestressed bridge are discussed by analyzing two simply-support prestressed bridges. Some conclusions are obtained from the numerical results as follows: ① The natural frequencies increase when the preloading is applied on the bridge. The preloading effect is mainly on the lower natural frequencies and the effect is become smaller when the modal order is higher. The fundament frequency of the prestressed bridges with 20m and 32m span increases about 5.3% and 6.3% respectively and its fifth modal frequency only increases about 1%. ② The moment of middle-span section of the prestressed bridges decreases about 30% and 25% under the excitation of site ground wave. ③ The contributions of high-order modes can be neglected for the vertical seismic responses of the bridges. ④ The ratio factors of the vertical seismic response in the total response of the middle-span section moment of the prestressed bridges are 24.56% and 26.15% when earthquake fortification intensity 7 level and 38.93% and 41.46% when earthquake fortification intensity 8 level respectively. This means that the influence of the vertical responses should be considered in the seismic design of the prestressed bridges.