随机地震荷载下黏性土残余应变的半经验计算公式
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摘要
提出一个新的简化半经验计算公式,用于随机地震荷载作用下黏性土残余应变的计算。新公式放弃了目前将不规则地震荷载转换成一定次数等幅正弦波的方式,而采用直接对不规则动应力波进行逐波累计的计算方法,这样可以得到任意随机地震荷载作用下土残余应变的实际发展过程。新公式首先略去地震波频率特性的影响,将一随机地震应力时程保留其有效幅值,筛选成一系列不同幅值的往返荷载;然后,以增量方法逐波累计计算残余应变。对每一动应力循环,以已有等幅荷载经验计算公式对循环次数的偏导构造残余应变的增量模型,并考虑了动压应力对残余应变增长的控制作用。经计算,对于等幅动荷载作用,新公式与现有公式之间误差很小。对于地震荷载输入,采用动三轴试验与新公式进行对比。对比结果表明,提出的公式可以有效地描述不规则地震荷载下黏性土残余变形的增长过程和最终结果,可反映不同类型地震波作用下、CM和EM试验下以及不同波序下土残余变形的发展和差异。
A new semi-empirical formula for evaluating the residual strain of cohesive soils under random earthquake loading is derived by using incremental method and establishing the incremental model.Instead of transforming the irregular seismic loads into the uniform sinusoidal loads with the certain cyclic number, the new formula can attain the real process of the residual strain of soils by directly calculating the irregular dynamic stress. First, the frequency characteristics of the input seismic waves are neglected and the input waves are filtered to form a series of cyclic load with different amplitude.Then, the residual strain is calculated by using the incremental method of the cycle-by-cycle accumulation.For each cyclic dynamic stress, the incremental strain is obtained in terms of the first partial derivative of the known formula for the uniform load with respects to the cyclic number.Also,the dominant effect of the compression stress on the increasing of the residual strain is considered in the formulation of the model.The validity of the formula is verified by the model tests.
A new semi-empirical formula for evaluating the residual strain of cohesive soils under random earthquake loading is derived by using incremental method and establishing the incremental model.Instead of transforming the irregular seismic loads into the uniform sinusoidal loads with the certain cyclic number, the new formula can attain the real process of the residual strain of soils by directly calculating the irregular dynamic stress. First, the frequency characteristics of the input seismic waves are neglected and the input waves are filtered to form a series of cyclic load with different amplitude.Then, the residual strain is calculated by using the incremental method of the cycle-by-cycle accumulation.For each cyclic dynamic stress, the incremental strain is obtained in terms of the first partial derivative of the known formula for the uniform load with respects to the cyclic number.Also,the dominant effect of the compression stress on the increasing of the residual strain is considered in the formulation of the model.The validity of the formula is verified by the model tests.
引文
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[2] NagaseH,IshiharaK.Effectsofloadirregularityonthecyclicbehaviorofsand[J].SoilDynamicsandEarthquake—66—Engineering,1987,6(4):239-248.
[3] 谢定义.土动力学[M].西安:西安交通大学出版社,1988.
[4] YuanXM,SunR,MengSJ.Effectofasymmetryandirregularityofseismicwavesonearthquake induceddifferentialsettlementofbuildingsonnaturalsubsoil[J].SoilDynamicsanEarthquakeEngineering,2003,23(2):107-114.
[5] SendHB,IdrissIM.Simplifiedprocedureforevaluatingsoilliquefactionpotential[J].SoilMechanicsandFoundationsDivision,ASCE,1981,(SM9):1249-1273.
[6] 郁寿松,石兆吉.土壤震陷试验研究[J].岩土工程学报,1989,(4):35-44.
[7] 孟上九.不规则动荷载下土的残余变形及建筑物不均匀震陷研究[D].哈尔滨:中国地震工程力学研究所,2002.
[8] 孟上九,袁晓铭,孙锐.建筑物不均匀震陷机理的振动台实验研究[J].岩土工程学报,2002,(6):747-751.
[9] MartinGR,FinnWDL,SeedHB.Foundamentalsofliquefactionundercyclicloading[J].JournaloftheGeotechnicalEngineeringDivision,ASCE,1975,101(GT5):423-438.
[10] 孙锐,袁晓铭,韩俊伟,赵惠,张尚盈.全自动地震波输入动三轴装置指标和功能测试[J].地震工程与工程振动,2002,(3):100-105.
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