摘要
近年来,随着交通事业的飞速发展,我国兴建了大量的大跨度连续梁桥,又因我国是一个多地震的国家,因此研究大跨度连续桥梁在多点激励下地震响应规律,对其的抗震设计和抗震鉴定与加固都有着重要的现实意义。基于此,本文借鉴已建成某桥的工程背景和最新研究成果,对大跨径预应力混凝土连续梁桥进行数值模拟试验研究,得出有益结论,为连续梁桥抗震设计提供参考。
地震动对于类似桥梁的大跨度、空间结构会发生很大变化。这种变化主要由三个因素引起:地震波到达不同位置时发生的时间延迟;地震波在不均匀的土壤介质中不规则的反射折射等原因而导致的各个位置激励之间的部分相干效应和不同位置处场地土的性质不相同而造成的局部场地效应。以上导致结构的各个位置地震动的振幅和相位差差异,而现有的桥梁设计规范采用的反应谱抗震分析方法,只考虑一致地震激励的影响,所以有必要对桥梁结构进行多点激励分析。
本文首先对地震动的特征、影响因素、衰减关系、设计地震动参数的确定和其输入模型等内容做了介绍;其次详细阐述了时间历程分析方法的基本理论,推导了多点激励下大跨度桥梁的基本运动方程并论述了其数值求解方法;最后利用桥梁专用分析软件MIDAS/Civil建立具有代表性的连续梁桥数值模拟分析计算模型,考虑桩-土-结构相互作用,在顺桥向输入地震波的情况下,运用时程分析的方法分析连续梁桥在多点激励作用下随主跨跨径、固定墩纵向抗推刚度、跨数、边中跨比、墩高和支承方式变化的响应规律。在大量的数值分析基础上,得到以下结论:
1增大主跨跨径,增加结构跨数对结构抗震不利;
2减小固定墩纵向抗推刚度或增大墩高对结构抗震有利;
3边中跨比变化对结构抗震利弊兼半;
4对于本文的支承方式,其变化对结构抗震影响不大;
5综合分析各种结构参数,主跨跨径对结构抗震最为敏感。
In the recent years, with the development of traffic, a lot of long span continuous beam bridges have been constructed. In our country, earthquake happens so frequently that it is very important to study the seismic response of the long span continuous beam bridges under multi-support excitation. It is very useful to the aseismatic design and identification and reinforcement. Based on above, the thesis draws lessons from a built bridge and the newest research achievement studying and analysising dynamic parameter design of long span continuous beam bridge, obtains some valuable conclusions which will give some reference for practical aseismatic design of continuous beam bridges.
Seismic ground motions can vary significantly over distances which are of the same order of magnitude as the dimensions of some extended structures, such as bridges. Three phenomena are responsible for these variations: the difference in the arrival times of seismic waves at different stations; the loss of coherency of the motions due to reflections and refractions of the waves in the heterogeneous medium of the ground, as well as due to the difference in the manner of superposition of waves arriving from an extended source at various stations and the difference in the local soil condition at each station. They influence the amplitude and frequency content of the bedrock motion, but the existing bridge criterion use response spectra theory about aseismic analysis considering uniform excitation, so multi-support excitation analysis for bridge structure is very important.
This thesis introduces characteristics and affect factors and attenuation relation of seismic ground motions, as well as confirmation of designing parameters and input model firstly; Secondly the basic theory of time-history analysis are presented minutely. the equations of motion of long-span bridges under multi-support excitation are deduced and numerical solution method is introduced; In the end, a numerical simulation model of continuous beam bridge is built by the bridge special software-MIDAS/Civil. And the seismic response rules of a continuous beam bridge, which is changed a long with main span length, longitudinal stiffness of brake pier, number of bridge spans, ratio of side to main span height of piers and constrain types, are studied with the time-history analysis method considering the interaction of pile-soil-structure system. In all above calculating model only longitudinal excitations are carried out. The following conclusions are given based on a large amount of numerical analyses:
1. Increasing the span length and adding the span number is bad for resisting earthquake;
2. Decreasing the stiffness of brake pier or increasing height of piers is beneficial for resisting the earthquake;
3. Changing the ratio of side to main span can bring advantages and disadvantages for aseismic performance of continuous beam bridges;
4. Changing the constrain types of the continuous beam bridge in this thesis has little effect on aseismic performance;
5. Comprehensive analysis of each structural parameter shows that the length of main span is the most hypersensitive factor for aseismic performance.
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