考虑温度效应下冻土层对桥梁结构地震响应的影响

Influence of frozen soil on the seismic responses of bridge structures considering the effect of temperature

近年来冻土区实际桥梁结构的震害已经表明,冻土的存在会增加桥梁基础的土体侧向刚度,可能会使桥梁结构出现更为严重的地震损伤,然而目前缺乏关于地震作用下冻土桥梁结构的冻土-桩相互作用效应以及相应地震响应规律的研究。基于所提出的高效非线性数值模型来考虑地震作用下的冻土-桩基础相互作用效应,推导了冻土深度与地表温度的关系,给出了冻土层的p-y弹簧非线性数值模拟方法,并选择了多条地震实测记录,研究了地震作用下不同冻土深度对规则桥梁墩柱以及支座地震响应的影响规律。结果表明,本研究所采用的高效非线性数值模型较好地模拟了冻土下桥梁结构的抗震性能,且所建立的冻土p-y弹簧曲线具有很好的准确性。当峰值加速度(PGA)较小时,冻土对于桥墩墩底曲率的增幅达20%,而当PGA较大时,冻土可增加桥墩曲率响应(达185%),使桥墩更易进入屈服。当冻土深度较小(温度等于-5℃)时,支座位移有较大的增加,增加了地震作用下主梁的落梁风险,且冻土可使地震作用下结构体系的最不利部位发生转移。研究结果可为我国冻土桥梁结构的抗震性能与相应的抗震设计方法研究提供必要的理论基础与数据支持,这一基础性工作对于推动我国冻土区桥梁工程防灾减灾的发展与工程应用具有重要意义。

[Objective]Recently,the seismic damage of an actual bridge structure in a frozen soil area has shown that the presence of frozen soil will increase the lateral stiffness of the bridge foundation,which may cause more serious seismic damage to the bridge structure,but there is a lack of research on the frozen soil-pile interaction effect of frozen soil bridge structures under seismic loadings and the corresponding seismic responses.[Methods]The present paper proposed efficient nonlinear numerical models to consider the effect of the frozen soil-pile interaction on the seismic responses of structures.First,the relationship between the depth of frozen soil and surface temperature was constructed.Then,the p-y spring modelling approach was presented to simulate the seismic behavior of frozen soil.Several as-recorded ground motions were selected as the seismic input.The seismic responses of piers and bearings of regular bridges with different depths of frozen soil under seismic loadings were investigated.[Results]The results show that the proposed efficient nonlinear numerical model can be adopted to model the seismic behavior of bridges considering frozen soil.And the proposed p-y curves for frozen soil can accurately predict the p-y relationship from the existing tests.When the PGA is relatively small,the pier curvature increases slightly;by contrast,in the case of large PGA,frozen soil can significantly increase the curvature demands,which can make the pier enter into the inelastic behavior.When the depth of frozen soil is small(the temperature is-5℃),the bearing displacement increases significantly,which increases the probability of unseating under seismic loadings.Moreover,frozen soil can transfer to the adverse locations of structural systems under seismic loadings.[Conclusion]Therefore,the conclusions of this paper can provide the necessary theoretical basis and data support for studying the seismic performance and corresponding seismic design methods of frozen soil bridge structures in China,which is of great significance for promoting the development and engineering application of disaster prevention and mitigation of bridge engineering in frozen soil areas in China.