摘要
在青藏高原多年冻土退化趋势明显及地震活动频发的背景下,为研究多年冻土退化对青藏铁路桥梁桩基础地震易损性的影响,建立了桥梁桩基础-冻土相互作用有限元计算模型,并通过拟静力模型试验验证了模型的合理性。考虑多年冻土退化效应的影响,以桩基础曲率延性比为损伤指标,以地面峰值加速度PGA为地震动强度参数,并选取了符合场地特征的80条地震波,对不同多年冻土活动层厚度和轴压比下的原型桥梁桩基础进行了非线性地震损伤分析。拟静力试验和数值模拟结果表明:地震作用下桥梁桩基础顶部破坏严重,是整个桥墩-桩-土体系的薄弱部位;随着多年冻土活动层厚度的增加(退化程度加剧),周围土体对桩基础的约束减弱,桩身的最大曲率呈减小趋势,从而降低了地震作用下桥梁桩基础的破坏概率,但墩顶位移却有所增大,导致地震过程中落梁风险增加;而随着桥墩轴压比的增大,桩身最大曲率明显增加,多年冻土区桥梁桩基础的地震易损性显著增加。考虑到桥梁桩基础破坏后修复难度较高,因此多年冻土退化背景下青藏铁路桥梁抗震性能评估还需考虑高桥墩轴压比变化对桩基础地震易损性产生的不利影响。
Permafrost degradation induced by global climate warming in Qinghai-Tibet Plateau has drawn great attention of researchers.Meanwhile,the Qinghai-Tibet Plateau is prone to frequent seismic activities in recent years.In order to study the influence of permafrost degradation on the seismic vulnerability of the bridge pile foundation along Qinghai-Tibet Railway,a pile-frozen soil interaction model was established,and its rationality was verified by the quasi-static test.The pile-frozen soil interaction model can simulate the deformation and me⁃chanical behaviors of the bridge pile foundation under lateral loading,and thus it can be used to analyze the seis⁃mic response of bridge pile foundation in permafrost regions.Considering the effect of permafrost degradation,the curvature ductility ratio of the pile foundation was taken as the damage index,the ground peak acceleration(PGA)was taken as the ground vibration intensity parameter,and 80 seismic waves which are consistent with the site characteristics were selected for seismic vulnerability analysis.Nonlinear seismic damage analysis of the bridge pile foundation under different permafrost active layer thickness and axial compression ratio in permafrost region were carried out.The results of quasi-static test and numerical simulation showed that the top of pile foun⁃dation is the weak part of the pier-pile-soil system.It is found that when the active layer thickness increased,the damage probability of the pile foundation under different failure states decreased,especially in the case of severe damage.Specifically,when the PGA is 0.6g,compared with the pile foundation with 1 m active layer thick⁃ness,the damage probability of the pile foundation with the 2 m active layer thickness was reduced by 8.53%and 3.16%under severe damage and collapse states,respectively.The damage probability of the pile foundation with the 3 m active layer thickness was decreased by 13.54%and 4.66%under severe damage and collapse states,respectively.The results showed that the permafrost degradation weakened the soil constraint on pile foundation,then reduced the damage probability of the pile foundation under seismic action,but increased the displacement of the pier top.This will lead to the beam falling failure caused by excessive beam displacement if earthquake occurs.It can be seen that with the increase of axial compression ratio of the bridge pier,the damage probability of the pile foundation under different failure states increased,and the change was more obvious in the case of severe damage and collapse states.Specifically,when the PGA was 0.6g and the axial compression ratio was 4%,5%and 6%,the damage probability of the pile foundation was 10.80%,41.19%and 66.70%,respec⁃tively.Since it is difficult to repair the damaged bridge pile foundation,the seismic performance evaluation of the Qinghai-Tibet Railway bridge under permafrost degradation condition should also consider the adverse effect of the change of the axial compression ratio of the high pier on the seismic vulnerability of the pile foundation.
作者
张益舶
张熙胤
刘有乾
于生生
马华军
王万平
管嘉达
ZHANG Yibo;ZHANG Xiyin;LIU Youqian;YU Shengsheng;MA Huajun;WANG Wanping;GUAN Jiada(School of Civil Engineering,Lanzhou Jiaotong University,Lanzhou 730070,China;China Railway Qinghai-Tibet Group Co.Ltd.,Xining 810000,China)
出处
《冰川冻土》
CSCD
北大核心
2023年第3期953-965,共13页
Journal of Glaciology and Geocryology
基金
国家自然科学基金项目(52068045)
中国国家铁路集团有限公司科技研究开发计划项目(P2021G047)资助。
关键词
多年冻土退化
桥梁桩基础
地震易损性
拟静力试验
有限元分析
permafrost degradation
bridge pile foundation
seismic vulnerability
quasi-static test
finite element analysis
