竖向地震加速度对堤坝抗震性能影响分析
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摘要
将堤坝地震动力响应的有限元数值分析方法与坝坡地震滑移量的N ewm ark估算方法相结合,通过数值计算探讨了水平与竖向加速度组合作用下堤坝的抗震稳定性.首先以堤坝地震动力响应的二维平面应变有限元分析为基础,按照M akd is i与Seed所建议的计算方法估算堤坝安全系数的变化过程,依此对地震过程中堤坝的瞬态稳定性进行评价.对瞬时安全系数小于1的时段,采用N ewm ark方法估算滑坡体的可能滑移量,进而由此评判堤坝的抗震安全性.最后,针对一座高度为100 m的堤坝,分别采用正弦波和实际E l-C en tro地震加速度记录作为激励,通过具体数值计算讨论了竖向地震加速度对堤坝抗震稳定性的影响.研究表明竖向加速度对堤坝瞬态稳定性及地震滑移量均具有显著影响,在堤坝抗震设计中应合理地予以考虑.
Based on dynamic analyses of seismic response by using plane-strain FEM and evaluation of seismically-induced sliding movement of embankments,the overall effects of simultaneous horizontal and vertical acceleration on aseismic stability of embankments are examined.First,the variation of the safety factor of embankments with time is estimated on the basis of numerical results achieved by finite element analyses and therefore the transient stability performance of embankment can be assessed.When the transient safety factor is below unity for a period of time,a certain permanent movement of potential sliding block will occur and Newmark′s rigid-plastic model is used to evaluate the seismically-induced movement.The overall seismic stability of embankment can be described by the total permanent sliding displacement of the embankment.Based on the proposed method,numerical analyses are made for an example embankment with height of 100 m.Harmonic excitation and acceleration record obtained in El-Centro earthquake are used as the input ground motions.Different combinations of horizontal and vertical components in amplitudes and phase-differences are chosen for comparative analyses.It is shown that the effect of vertical acceleration component will considerably affect both the transient safety factors and overall movements.It seems that the effect of vertical seismic acceleration and its combination with horizontal seismic acceleration can not be overlooked in the earthquake-resistant design of embankment.It should be noted that the conventional understanding on vertical seismic effect is not perfect and sometime will yield a certain non-conservative assessment of earthquake-resistant behaviour of embankment.
Based on dynamic analyses of seismic response by using plane-strain FEM and evaluation of seismically-induced sliding movement of embankments,the overall effects of simultaneous horizontal and vertical acceleration on aseismic stability of embankments are examined.First,the variation of the safety factor of embankments with time is estimated on the basis of numerical results achieved by finite element analyses and therefore the transient stability performance of embankment can be assessed.When the transient safety factor is below unity for a period of time,a certain permanent movement of potential sliding block will occur and Newmark′s rigid-plastic model is used to evaluate the seismically-induced movement.The overall seismic stability of embankment can be described by the total permanent sliding displacement of the embankment.Based on the proposed method,numerical analyses are made for an example embankment with height of 100 m.Harmonic excitation and acceleration record obtained in El-Centro earthquake are used as the input ground motions.Different combinations of horizontal and vertical components in amplitudes and phase-differences are chosen for comparative analyses.It is shown that the effect of vertical acceleration component will considerably affect both the transient safety factors and overall movements.It seems that the effect of vertical seismic acceleration and its combination with horizontal seismic acceleration can not be overlooked in the earthquake-resistant design of embankment.It should be noted that the conventional understanding on vertical seismic effect is not perfect and sometime will yield a certain non-conservative assessment of earthquake-resistant behaviour of embankment.
引文
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[6]CA I Z,BATHURST R J.D eterm in istic slid ing b lockm ethods for estim ating se ism ic d isp lacem en ts ofearth structures[J].So il D yn and E arthquake Eng,1996,15(4):255-268
[7]AL-HOM OUD A S,TAHTAM ON IW.Com parisonbetw een pred ictions us ing d ifferen t s im p lifiedN ewm arks′b lock-on-p lane m ode ls and fie ld va lues ofearthquake induced d isp lacem en t[J].So il D yn andE arthquake Eng,2000,19(1-4):73-90
[8]S IM ONELL I A L,STEFANO P D.E ffects ofvertica l se ism ic acce lerations on slope d isp lacem en ts[C]∥P roceed ings of Fourth In ternationa lCon ference on R ecen t Advance in G eotechn ica lE arthquake Eng ineer ing and So il D ynam ics andSym posium in H onor of P rofessor W.D.L iamF inn.San D iego:[s n],2001
[2]栾茂田,金崇磐,林皋.非均布地震荷载作用下土坡的稳定性[J].水利学报,1990(1):65-72
[3]L ING H I,LESHCH IN SKY D,YO SH IYUK I M.So il slopes under com b ined horizon ta l and vertica lse ism ic acce lerations[J].E arthquake Eng and StructD yn,1997,26(12):1231-1241
[4]NEWM ARK N M.E ffects of earthquakes on dam sand em bankm en ts[J].G eotechn ique,1965,15(2):139-160
[5]M AKD IS I F I,SEED H B.S im p lified procedure forestim ation dam and em bankm en t earthquake induceddeform ations[J].J of G eotech Eng,ACSE,1978,104(GT 7):849-868
[6]CA I Z,BATHURST R J.D eterm in istic slid ing b lockm ethods for estim ating se ism ic d isp lacem en ts ofearth structures[J].So il D yn and E arthquake Eng,1996,15(4):255-268
[7]AL-HOM OUD A S,TAHTAM ON IW.Com parisonbetw een pred ictions us ing d ifferen t s im p lifiedN ewm arks′b lock-on-p lane m ode ls and fie ld va lues ofearthquake induced d isp lacem en t[J].So il D yn andE arthquake Eng,2000,19(1-4):73-90
[8]S IM ONELL I A L,STEFANO P D.E ffects ofvertica l se ism ic acce lerations on slope d isp lacem en ts[C]∥P roceed ings of Fourth In ternationa lCon ference on R ecen t Advance in G eotechn ica lE arthquake Eng ineer ing and So il D ynam ics andSym posium in H onor of P rofessor W.D.L iamF inn.San D iego:[s n],2001
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