季节性冻土区和多年冻土区桥梁结构地震反应分析

冻土层的存在，对桥梁结构抗震安全性的影响是一个值得重视的问题。本文利用黏-弹性边界模拟波向无穷远辐射的结构-地基土一体化计算方法，对季节性冻土区和多年冻土区桥梁结构在不同地震波作用下的反应进行计算，分析冻土层的变化对桥梁结构地震反应的影响，总结在地震荷载作用下，不同场地、不同的冻土厚度、不同高度的桥墩和不同基础条件下桥墩应力分布的一般规律。分析结果表明：在Ⅱ类场地上，冻土层对桥墩地震反应的影响十分显著，不同类型冻土场地上桥墩的最大反应差值可达1倍以上；墩高在10～22m时，冻土层对桥墩地震反应的影响最为显著；不同类型的桥墩基础，对冬夏两季桥墩的地震反应的影响不大；在一般情况下，桥墩的地震反应与冻土性质、桥墩的动力特性以及地震波的性质均密切相关，按融土状态进行设计往往是不安全的，需要考虑桥墩与冻土层相互作用的影响。

Study on Seismic Responses of Bridges in Permafrost and Seasonal Frozen Regions

It is worth attaching importance to the problem that the frozen earth layer has influence upon the aseismatic safety of bridges.Using the soil-structure interaction method that can simulate the radiant function of waves by use of the artificial viscidity-elasticity boundary,the responses of bridges under multifarious earthquakes in permafrost and seasonal frozen regions are calculated.The influence of the frozen earth layer change on the seismic responses of bridges is analyzed.The general distributing law of bridge pier stresses under seismic loading is summarized on condition of different sites,different frozen soil layer thicknesses,different heights of bridge piers and different bridge foundations.The analysis results are as follows: on sites type 2,frozen earth layers have marked influence on seismic responses of bridge piers and the maximum stress difference for different types of frozen earth layer sites may reach more than one time;when bridge piers are 10 to 22 m high,frozen earth layers have the most notable effects on pier seismic responses;the types of pier foundations may be neglected when the pier seismic responses are compared between winter and summer;in general,bridge pier seismic responses have close relationship with the frozen earth features,dynamic characteristics of bridge piers and seismic wave features.It needs to consider the interaction between bridge piers and frozen earth layers because it is not safe to apply thawy soil conditions to bridge design.