预应力桥梁竖向振动特性和地震反应分析

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。

Vertical vibration characteristics and seismic response analysis of prestressed Bridges

Based on modal perturbation method and mode superposition method, a calculation method for vertical seismic response analysis of prestressed Bridges is established. Through the analysis of two typical engineering examples, several problems in vertical seismic response analysis of Bridges are discussed. The results show that: (1) The preloading increases the natural vibration frequency of the bridge, and the influence is mainly reflected in the low-order natural vibration frequency. With the increase of the mode order, the influence of the preloading decreases. For prestressed Bridges with 20m and 32m spans, the vertical fundamental frequency increases by 5.3% and 6.3%, respectively, while the fifth vertical frequency increases by only about 1%. (2) The bending moment of the mid-span section of the prestressed beam is reduced by about 30% and 25% under the action of the surface wave, and the earthquake resistance of the bridge is improved by the prestressing force. (3) The contribution of higher order modes in vertical seismic response can be ignored. (4) The vertical seismic effect accounts for 24.56% and 26.15% of the load combination effects of the mid-span bending moment of prestressed Bridges at 7 degrees of fortification intensity, and 38.93% and 41.46% at 8 degrees of fortification intensity, respectively, indicating that the influence of vertical seismic response should be considered in the seismic design of prestressed Bridges.