多年冻土退化对桥墩及其桩基础抗震性能影响的分析研究

发布时间：2018-04-12 22:21

  本文选题：多年冻土 + 桩　； 参考：《兰州交通大学》2017年硕士论文

【摘要】：近年来,全球气候变暖导致多年冻土地区出现了冻土退化的现象。青藏铁路和公路沿线冻土高度发育,而且穿越多处地震带,冻土的退化势必会对铁路桥梁抗震性能产生一定影响。因此研究多年冻土上限退化对桥梁抗震性能的影响具有重要工程适用意义。论文以青藏线上某32m简支梁桥为背景,运用专业分析软件Midas Civil建立桩—承台—桥墩的单墩有限元数值模型,分别采用反应谱法和时程分析法进行了多年冻土上限由1.5m退化至5.5m时,地震荷载作用下桥墩及其基础的自振特性、内力和变位响应分析,探讨了冻土上限退化对桥墩及其桩基础抗震性能影响的变化规律。结论如下:(1)通过反应谱与时程分析法的对数值模型运行分析的结果对比,两种方法得到的分析结论基本一致,说明时程分析法所选的地震波是合理的。(2)通过对单墩及桩基础模型分析,随着多年冻土退化的发展,结构的综合刚度略有下降,桥墩前两阶的自振周期延长,以后各阶变化不明显,对桥墩及其基础抗震性能影响不大。冻土退化对桥墩1、3阶振型的规律影响不大,前三阶振型参与质量达到90%。(3)对于不同含冰量的冻土(饱冰、富冰、多冰、少冰)地基中的桥墩分析,桩身、墩顶和地面处的水平位移均随冻土上限的退化而增大,其中饱冰冻土的变化最大,少冰冻土最小;说明了饱冰冻土对温度变化的敏感性最高,其退化对桥墩抗震性能的影响最不利。(4)针对不同土质(粉土、砂土、碎石土)的均质地基中桥墩的分析,桩身、墩顶和地面处的水平位移随着冻土上限的退化而增大,且以粉土最为敏感,说明粉土地基中的桥墩及其桩基础抗震性能最差。(5)对饱冰、富冰、多冰、少冰四种含冰量冻土中的桥墩及其桩基础进行分析,墩底内力均随着冻土上限的退化而依次增大;而对粉土、砂土、碎石土三种地质条件下的地基中桥墩分析,发现其墩底最大内力随着冻土上限的退化而依次增大,说明多年冻土中,饱冰粉土的退化对桥墩及其基础的抗震影响最大。(6)针对不同含冰量的多土层地基中的桥墩及其桩基础进行分析,得出的结论与均质土层基本一致,即桩身、地面处、墩顶水平位移随冻土上限的退化而增大,墩底内力也随着冻土的退化变大。
[Abstract]:In recent years, global warming has caused permafrost degradation in permafrost regions.The height of permafrost along Qinghai-Tibet railway and highway is developed, and the degradation of frozen soil will affect the seismic performance of railway bridges.Therefore, it is of great significance to study the influence of permafrost upper limit degradation on the seismic performance of bridges.Based on a 32m simply supported beam bridge on Qinghai-Tibet Line, the finite element numerical model of single pier of pile-cap pier is established by using professional analysis software Midas Civil.The natural vibration characteristics, internal forces and displacement responses of piers and their foundations under seismic load are analyzed by using response spectrum method and time history analysis method respectively, when the upper limit of permafrost is reduced from 1.5 m to 5.5 m.The influence of upper limit degradation of permafrost on seismic behavior of pier and pile foundation is discussed.Conclusion as follows: (1) by comparing the results of the operation analysis of the logarithmic model with the response spectrum analysis and the time-history analysis, the results obtained by the two methods are basically the same.It shows that the seismic wave selected by time-history analysis method is reasonable. By analyzing the model of single pier and pile foundation, with the development of permafrost degradation, the comprehensive stiffness of the structure decreases slightly, and the natural vibration period of the first two steps of the bridge pier is prolonged.The change of each step is not obvious, and it has little effect on the seismic performance of pier and foundation.The degradation of permafrost has little influence on the first and third order vibration modes of bridge piers. The first three modes participate in the quality of the bridge piers, and the pile body is analyzed for the pier in the frozen soil with different ice content (saturated, ice-rich, ice-rich, ice-rich, ice-rich and ice-less).The horizontal displacement at the top of the pier and on the ground increases with the degradation of the upper limit of frozen soil, in which the change of saturated frozen soil is the largest, and that of less frozen soil is the least, which indicates that the saturated frozen soil is the most sensitive to temperature change.The impact of degradation on the seismic performance of pier is the most unfavorable. (4) for the analysis of pier in homogeneous foundation of different soil (silt, sand, gravel), the horizontal displacement of pile body, pier top and ground increases with the degradation of the upper limit of frozen soil.And the silty soil is the most sensitive, which shows that the pier and its pile foundation in silty foundation have the worst seismic performance.) the pier and its pile foundation in four kinds of frozen soil with full ice, rich ice, more ice and less ice are analyzed.The maximum internal force of pier bottom increases with the degradation of the upper limit of frozen soil, and the maximum internal force of pier increases with the degradation of the upper limit of frozen soil, and the analysis of bridge pier under three geological conditions of silt, sand and gravel shows that the maximum internal force of pier bottom increases with the degradation of the upper limit of frozen soil.It shows that in permafrost, the degradation of ice-saturated silt has the greatest effect on the seismic resistance of bridge piers and their foundations.) the pier and its pile foundation in multi-soil foundation with different ice content are analyzed, and the conclusion is basically consistent with that of homogeneous soil layer, that is, pile body.On the ground, the horizontal displacement of the pier top increases with the degradation of the upper limit of the frozen soil, and the internal force of the pier bottom increases with the degradation of the frozen soil.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U443;U442.55

【参考文献】

中国期刊全文数据库 前10条

1 刘明浩;孙志忠;牛富俊;武贵龙;，

本文编号：1741688