初始剪应力对软土场地震反应的影响
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摘要
实际工程的边坡、斜坡以及挡土结构中的土体都存在一个初始剪应力的作用。在初始剪应力的作用下土体会产生较大的残余应变。然而,原始Iwan模型难以考虑这种因素的影响。因此,将软化模型引入Iwan串联模型中考虑循环软化的影响,同时再串联一理想刚塑性元件,模拟循环过程中产生的残余应变;最后,结合Masing准则对软黏土的动应力-应变关系进行了描述。在此基础上,将修正的Iwan模型用于软土层的一维非线性地震反应分析。通过分析发现,当场地存在初始剪应力且受到强震时,土体模型需考虑这种因素的影响,否则可能低估速度及加速度幅值,也会低估最大剪应变幅值。
Initial shear stress has effect on soils in side slope,sloping ground and retaining wall,etc.Serious residual strain will occur in soft clay under initial shear stress.But,original Iwan's model ignored this effect.In this paper,an empirical degradation model of soft clay has been incorporated into Iwan's series-parallel model to account for cyclic degradation.Simultaneously,an ideal plastic element is paralleled to simulate the development of residual strain.Subsequently,the dynamic stress-strain relationship of each soft clay stratum is described with modified Masing's rules.In this paper,a modified Iwan's model is utilized in one-dimensional seismic response analysis.It's observed that the constitutive model should consider this effect when initial shear stress existed and the earthquake is strong.Otherwise,velocities,accelerations and shear strains may be underestimated.
Initial shear stress has effect on soils in side slope,sloping ground and retaining wall,etc.Serious residual strain will occur in soft clay under initial shear stress.But,original Iwan's model ignored this effect.In this paper,an empirical degradation model of soft clay has been incorporated into Iwan's series-parallel model to account for cyclic degradation.Simultaneously,an ideal plastic element is paralleled to simulate the development of residual strain.Subsequently,the dynamic stress-strain relationship of each soft clay stratum is described with modified Masing's rules.In this paper,a modified Iwan's model is utilized in one-dimensional seismic response analysis.It's observed that the constitutive model should consider this effect when initial shear stress existed and the earthquake is strong.Otherwise,velocities,accelerations and shear strains may be underestimated.
引文
[1]KANAI K.Relation between the nature of surface layer and the amplitudes of earthquake motions[J].Bull.Earthquake Res.Inst.,1952,30:3l-37.
[2]IDRISS I M,SEED H B.Seisemic response of horizontal soil layers[J].Journal of Soil Mechanics and Foundation,1968,94:1003-1031.
[3]JOYNER W T,CHEN A T F.Calculation of nonlinear ground response in earthquakes[J].Bulletin of the Seismological Society of America,1975,65(5):1315-1336.
[4]ALEXANDER Puzrin,SAM Frydman,MARK Talesnick.Effect of degradation on seismic response of Israeli continental slope[J].Journal of Geotechnical and Geoenvironmental Engineering,1997,123(2):85-93.
[5]DIEGO C F Lo Presti,CARLO G Lai,IGNAZIO Puci.ONDA:Computer code for nonlinear seismic response analyses of soil desposits[J].Journal of Geotechnical and Geoenvironmental Engineering,2006,132(2):223-236.
[6]PUZRIN A M,SHIRAN A.Effect of the constitutive relationship on seismic response of soils,partⅡ:The site amplification study[J].Soil Dynamics and Earthquake Engineering,2000,19:319-331.
[7]蔡袁强,柳伟,徐长节,等.基于修正Iwan模型的软粘土动应力-应变关系研究[J].岩土工程学报,2007,29(9):1314-1319.CAI Yuan-qiang,LIU Wei,XU Chang-jie,et al.Study on dynamic stress-strain relationship of soft clay based on modified Iwan’s model under undrained cyclic loading[J].Chinese Journal of Geotechnical Engineering,2007,29(9):1314-1319.
[8]MASING Georg.Eigenspannungen und verfestigung beim messing[C]//Proceedings of Second International Congress of Applied Mechanics.Zurich:[s.n.],1926:332-335.
[9]NARASIMHA S Rao,PANDA A P.Non-linear analysis of undrained cyclic strength of soft marine clay[J].Ocean Engineering,1999,26:241-253.
[10]ALEXANDER Puzrin,FRYDMAN Sam,MARK Talesnick.Normalized nondegrading behavior of soft clay under cyclic simple shear loading[J].Journal of Geotechnical Engineering,1995,121(12):836-843.
[11]蔡袁强,陈静,王军.循环荷载下各向异性软黏土应变-软化模型[J].浙江大学学报(工学版),2008,42(6):1058-1064.CAI Yuan-qiang,CHEN Jing,WANG Jun.Strain-degradation model for antisotropic soft clay under cyclic loading[J].Journal of Zhejiang University(Engineering Science),2008,42(6):1058-1064.
[2]IDRISS I M,SEED H B.Seisemic response of horizontal soil layers[J].Journal of Soil Mechanics and Foundation,1968,94:1003-1031.
[3]JOYNER W T,CHEN A T F.Calculation of nonlinear ground response in earthquakes[J].Bulletin of the Seismological Society of America,1975,65(5):1315-1336.
[4]ALEXANDER Puzrin,SAM Frydman,MARK Talesnick.Effect of degradation on seismic response of Israeli continental slope[J].Journal of Geotechnical and Geoenvironmental Engineering,1997,123(2):85-93.
[5]DIEGO C F Lo Presti,CARLO G Lai,IGNAZIO Puci.ONDA:Computer code for nonlinear seismic response analyses of soil desposits[J].Journal of Geotechnical and Geoenvironmental Engineering,2006,132(2):223-236.
[6]PUZRIN A M,SHIRAN A.Effect of the constitutive relationship on seismic response of soils,partⅡ:The site amplification study[J].Soil Dynamics and Earthquake Engineering,2000,19:319-331.
[7]蔡袁强,柳伟,徐长节,等.基于修正Iwan模型的软粘土动应力-应变关系研究[J].岩土工程学报,2007,29(9):1314-1319.CAI Yuan-qiang,LIU Wei,XU Chang-jie,et al.Study on dynamic stress-strain relationship of soft clay based on modified Iwan’s model under undrained cyclic loading[J].Chinese Journal of Geotechnical Engineering,2007,29(9):1314-1319.
[8]MASING Georg.Eigenspannungen und verfestigung beim messing[C]//Proceedings of Second International Congress of Applied Mechanics.Zurich:[s.n.],1926:332-335.
[9]NARASIMHA S Rao,PANDA A P.Non-linear analysis of undrained cyclic strength of soft marine clay[J].Ocean Engineering,1999,26:241-253.
[10]ALEXANDER Puzrin,FRYDMAN Sam,MARK Talesnick.Normalized nondegrading behavior of soft clay under cyclic simple shear loading[J].Journal of Geotechnical Engineering,1995,121(12):836-843.
[11]蔡袁强,陈静,王军.循环荷载下各向异性软黏土应变-软化模型[J].浙江大学学报(工学版),2008,42(6):1058-1064.CAI Yuan-qiang,CHEN Jing,WANG Jun.Strain-degradation model for antisotropic soft clay under cyclic loading[J].Journal of Zhejiang University(Engineering Science),2008,42(6):1058-1064.
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