基于模态分析的Push-over方法在桥梁抗震分析中的应用

采用非线性时程分析是计算结构地震响应较为严格的分析方法,但它存在工作量大、计算复杂等问题。目前土木工程中常采用非线性的静力分析(Push-over分析)来评价在地震作用下结构的抗震性能。均匀分布、倒三角形分布的侧向荷载分布模式,适用于刚度大或第一阶振型为主的结构,为了考虑高阶振型的影响,本文提出了基于模态分析的Push-over方法,并将其应用到桥梁抗震分析中。这种方法需要分析结构的动力特性,尤其是振型贡献率。选出振型贡献率比较高的振型,并以此为基础,依据“侧向荷载分布模式与地震时结构惯性力的分布情况应尽量保持一致”的原则,参考《公路工程抗震设计规范》(JTJ 004—89)可得到对应各振型的侧向荷载,在对主要振型进行组合后,即可获得进行Push-over分析的侧向荷载分布模式。本文采用基于模态分析的Push-over方法对一实桥进行抗震性能分析,结果表明选取主要振型参与计算与采用全部振型计算的结果基本吻合,不仅考虑了高阶振型的影响,又消除了其他次要振型的干扰,因此这种方法应用于桥梁抗震性能评价是可行的。

Mode-based Push-over Method Applied to Aseismatic Analysis of Bridges

Nonlinear time-history analysis is a more rigorous method to estimate seismic response of structure.Because of large workload and complex procedure,at present,Push-over analysis is used widely.Uniform force distribution and triangular force distribution are suitable for the rigid structures or structures whose 1st-mode is main,In order to consider the effects of the high modes,Push-over method based on mode analysis is given in this paper and applied to aseismatic analysis of bridges.This method that put forward in this paper needs to analysis the dynamic characteristics of the structures,especially mode contribution ratio.Based on the main mode shapes that the mode contribution ratios are higher than expected and the principia that distribution of the lateral forces should be in accordance with the inertial distribution in the earthquake as far as possible,the distribution of the lateral load corresponding to the each selected mode shape according to the equation specified in The Highway Engineering Seismic Design Specifications(JTJ 004-89).In this paper,evaluating aseismatic performance of the bridge is done by using mode-based Push-over method.The results indicate that combining modes selected and combining all modes accord with each other.The method that is gotten lateral forces by analyzing the modal contribution ratios to do Push-over analysis not only considers the high modes effect,but also avoids the disturbing of the secondary modes,so it's a available method to estimate the aseismic capacity of the bridges.