【作者】 齐文浩；

【导师】 薄景山；

【作者基本信息】 中国地震局工程力学研究所 ， 岩土工程， 2008， 博士

【摘要】 土层非线性地震反应分析方法研究是当前岩土地震工程研究领域的重要内容。土层地震反应分析技术也是当前工程场地地震安全性评价的核心技术之一。早在20世纪初人们就从旧金山大地震的震害中发现场地条件对地震动有一定影响,为合理估计场地条件对地表地震动的影响,人们把场地简化为物理力学模型,提出各种土体动力本构模型,利用解析或数值的方法对场地地震动响应进行求解。当前,工程上应用最为广泛的土层地震反应分析方法依然是等效线性化方法。等效线性化方法把土体非线性问题转化为线性问题近似求解土体动力反应,它在工程应用中存在一些不合理的情况,主要原因是没有恰当的土体动力应力应变关系;此外,历次震害调查表明,特殊场地上烈度异常是地震中经常遇到的现象,特别是软弱场地上震害尤为严重,软土场地震害研究也是当前工程抗震领域中研究的热点问题之一。鉴于此,本文就土层非线性地震反应方法和汶川地震中特殊场地上烈度异常开展了相关的研究工作。主要研究内容如下:1、指出了现行土层地震反应分析方法存在的问题现行土层地震反应分析方法为工程上广泛应用的等效线性化方法。简要介绍了等效线性化方法的基本原理,总结了其优、缺点,简述了其最新进展。通过具体的算例,再现了等效线性化方法在实际工程应用中存在的几个主要问题,即个别离散点个数计算失效、计算软土层时结果异常、地震动输入较大时计算结果不合理、有些情况下出现死循环等。并提出现行土层地震反应方法改进的方向。2、构造了指数形式土体动力本构模型基于指数函数的有界性、函数曲线形状以及构造土体动力本构模型的一般原则,把函数在(-∞,0]区间上的图像进行翻转、平移、放缩,从而构造出土体的动力本构模型的骨架曲线。在卸载和反向加载时,采用与骨架曲线相同的函数形式,并以前一次卸载开始点作为起点,以土体的极限应力水平作为渐近线,构造出土体动力本构模型的滞回曲线。在此基础上构造出适用于非对称循环荷载的指数形式土体动力本构模型(简称UE模型)。UE模型具有四个特点:第一,适用于非对称循环荷载;第二,记忆量小;第三,卸载再加载滞回曲线自动满足Masing准则;第四,模型参数少,物理意义明确,可用常规试验确定。3、利用共振柱试验检验了UE模型推导了UE模型等效剪切模量比的表达式。利用西安阎良区地震小区划工作中若干土样的共振柱试验结果,对所提出的UE模型进行了验证,结果表明UE模型能很好的拟合共振柱的实验结果。同时利用UE模型对剪切模量的推荐值进行了拟合,拟合结果也证明了UE模型的可靠性。4、检验了基于UE模型的土层非线性地震反应分析方法根据UE模型形成了一维土层非线性地震反应分析方法,并编制了相应的计算机程序NDSoilUE-1D。利用响嘡三维台阵的强震记录对NDSoilUE-1D程序进行了检验,地表加速度反应和谱比分析结果表明,新方法较等效线性化能更合理地反映土体非线性特性随输入地震动强度由小到大而由弱变强的趋势。5、初步研究了汶川地震中特殊场地的影响为探究汶川特大地震中汉源县城出现了烈度异常现象的原因,在对地震现场震害、附近地形地貌详细调查的基础上,结合收集到场地资料,根据震害轻重布设了五个地脉动测点,测试结果表明,震害严重区的场地卓越周期较大,并且明显大于震害较轻的场地。初步研究表明汉源县烈度异常是由于场地土软弱造成的。从砂土液化角度指出了背后山滑坡是汉源县城安全的潜在威胁。更多还原

【Abstract】 The study on method of seismic response analysis of nonlinear soil layers is an important content in research domain of geotechnical earthquake engineering now. The technique of soil layers seismic response analysis is also one of core techniques in seismic safety evaluation of engineering sites currently. Early in the beginning of 21th century, site conditions having certain effect on ground motion had been found from seismic damage of The Great 1906 San Francisco Earthquake. In order to estimate reasonably the effection of site conditions on ground motion, researchers predigest sites into mechnics models, suggest all kinds of soil dynamic constitutve models, and estimate sites’response of ground motion by analytical or numerical methods. Currently, the seismic response analysis method of soil layers applied in engineering widely is equivalent linear method all the same. The soil nonlinear problem is translated into linear problem in equivalent linear method when equivalent linear method is used to estimate site’s sesmic response. For having no appropriate dynamic constitutve model, some unreasonable situations have been found from the engineering application of equivalent linear method. Further more, intensity anomaly is a phenomenon fallen across frequently when earthquakes accur. Espelcially, seismic disaster of soft site is more serious. The study on earthquake disaster of soft site is also a hotspot in the research domain of earthquake engineering. In view of these facts, in this paper some research works are made of method of seismic response analysis of nonlinear soil layers and intensity anomaly phenomenon of special site in Wenchuan earthquake. The main works is as blow:1. Some problems of current method of seismic response analysis of soil layers are pointed outCurrent method of response analysis of soil layers is equivalent linear method which is widely applied in ingineering. The basic principle of equivalent linear method is introduced in brief, its merits and shortcomings are summarized, the latest progress of equivalent linear method is also introduced. Engineering examples show some main problems of the method applied in engineering, the problems are as following: the method cannot compute when the acceleration time historys have a certain discrete points, the result is abnormal when site is soft, and it is unreseanable when the input groung motion is strong, the program may occur perpetuating cycle. The way to improve the method is also put forward. 2. Soil dynamic constitutive model with exponential form is constructedBased on boundedness and the form of exponential faction, and also based on general rules for constructing soil dynamic constitutive model, function image of y=ex in interval (-∞,0] is overturned and translated and also magnified or reduced so as to gain the skeleton curve of soil dynamic constitutive model. In the term of unloading and opposite side loading, let the stress-strain curve have the same form of skeleton curve, the curve uses the last unloading point as its starting point, and uses soil’s ultimate stress level as its asymptote. Then the hysteretic curve is constructed. Thus soil dynamic constitutive model which has exponential form is gained, which is suitable for unsymmetrical cyclic loadings. The model is also called UE model. UE model has such traits as flowing: First, UE model is suitable for unsymmetrical cyclic loadings. Secnond, UE model need a less memory. Third, UE model’s hysteretic curves under unloading-reloading follow Masing’s rule automatically. Fourth, UE model has less parameteres, which have clear physical meaning and could be determined by conventional tests.3. UE model is tested by the results of resonance column testFormula of equivalent shear modulus ratio is deduced. UE model is tested by the the results of resonance column tests of the soils, which are obtained from seismic microzontioon work in Yanliang, Xi’an. The results indicate UE model could fit the testing results well. At the same time, the shear moduls ratio values recommended by Yuan Xiaoming are also fitted by UE model, the fitting results also indicate UE model is dependable.4. The method of seismic response analysis of nonlinear soil layers based on UE model is testedOne dimension method of seismic response analysis of nonlinear soil layers is put forward based on UE model. The corresponding computer program NDSoilUE-1D is also compiled. The program is tested by strong ground motion records of Xiangtang three dimension array in Tangshan, the acceleration response at ground surface and analysis resultsof spectral ratio confirme that the new method can reflect the trend more reasonable than equivalent linear method, which soils’nonlinear trait changes from weak to stong when the input ground motion varies from weak to strong.5. Preliminary studies are completed about the effect of special site in Wenchuan earthquakeIn order to study the reason why intensity anomaly phenomenon occurs at Hanyuan county in Wenchuan earthquake, an investigation is taken on seismic damage and the landform and physiognomy of this town. Considering the site data, five sites’microtremor datas are tested according the degree of seismic damage. The testing result is that the predominant periods of the sites with severe damage are larger than the ones of the site with slight damage. The results indicate that the reason why Hanyuan town has severe earthquake damage is that the site is soft. The conclusion based on sand liquefaction point of view points out that the slop of Beihoushan Mountain is a potential threat to Hanyuan town.更多还原