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1.
《地震工程与工程振动》2021,41(3)
为研究动荷载作用下饱和砂土发生液化前后斜群桩的动力响应相关问题,利用土工离心机振动台进行了饱和砂土场地条件下的斜群桩物理模型试验。通过试验分别对土层响应、桩身弯矩以及桩顶承台加速度和位移等进行了详细分析,得到了如下结论:不同荷载作用下土层液化范围的改变导致了土层加速度峰值出现了不同程度的放大或缩小现象;砂土液化前后桩身动弯矩和残余弯矩对整个桩身的影响程度发生了显著变化,尤其在砂土大范围液化后残余弯矩相比动弯矩的影响明显减弱;当输入加速度峰值较小时,桩顶承台水平加速度峰值与振动台台面比较出现了明显的放大现象。而随着输入加速度峰值的增加,在振动后期承台水平加速度峰值出现了缩小的现象,同时在振动结束后承台产生了明显的动态残余位移。本研究取得的相关结论为液化土中斜群桩的相关研究以及工程设计提供参考。 相似文献
2.
为研究强震区跨断层桥梁桩基非线性动力相互作用特性,依托海文大桥实体工程,利用MIDAS/GTS有限元软件,建立了桩-土-断层相互作用模型,分析0.20~0.60g地震动强度下断层上下盘桩基加速度响应、桩顶水平位移、桩身弯矩以及桩身剪力响应情况。结果表明:覆盖层土体对桩身加速度放大作用明显,且随着输入地震动强度的增大,放大作用逐渐减弱;覆盖层对地震波的滤波作用显著,随着输入地震动强度的增大,滤波作用逐渐减弱;上盘桩基达到桩顶峰值加速度的时刻滞后于下盘;随着输入地震动强度的增大,上、下盘桩的桩顶产生的永久位移和水平位移峰值逐渐变大,上盘桩顶产生的永久位移和桩顶峰值位移均大于下盘,产生显著的"上盘效应";不同强度地震动作用下,断层上、下盘桩基弯矩均在上部土层界面处达到峰值,剪力均在基岩面处达到峰值,下盘桩基弯矩和剪力峰值大于上盘桩基,呈现出显著的"下盘效应"。在桥梁桩基抗震设计时,应着重考虑断层上、下盘桩基的差异和不同强度地震作用对桩基承载特性的影响。 相似文献
3.
基于u-p有限元公式模拟饱和砂土中水和土颗粒完全耦合效应,建立液化侧向流场地群桩动力反应分析的三维数值模型。模型中,砂土采用多屈服面弹塑性本构模型模拟、黏土采用多屈服面运动塑性模型模拟,群桩在计算过程中保持线弹性状态;采用20节点的六面体单元和考虑孔压效应的20-8节点分别划分黏土层和饱和砂层;选用剪切梁边界处理计算域的人工边界,模拟地震过程中土层的剪切效应;应用瑞利阻尼考虑体系的阻尼效应。随后对比分析2×2群桩中各单桩的地震反应规律,结果表明,各单桩的弯矩、位移时程规律基本一致,峰值弯矩及峰值位移出现时刻滞后于输入加速度峰值时刻,上坡向桩的弯矩和位移峰值大于下坡向的桩的反应值。接着通过改变桩间距研究群桩效应,随着桩间距增加,群桩中各单桩的弯矩最大值均出现在土层分界处,且各单桩的弯矩、桩顶位移逐渐增大。最后给出液化侧向流场地群桩效应的基本原因,得出该类场地群桩抗震设计的基本认识。 相似文献
4.
为研究倾斜场地中桩基的动力响应,以2011年新西兰地震中受损的Dallington桥为原型,设计并完成可液化倾斜场地桥梁桩-土相互作用的振动台模型试验。试验再现了喷砂、冒水、地裂缝、场地流滑等宏观现象。试验结果表明,土层足够的液化势及惯性是造成倾斜场地侧向流滑的必要条件;浅层土相比深层土更易液化,液化层中的加速度由下至上呈现逐渐衰减的趋势,而未液化砂土层却表现为逐渐增大的特征;深部测点的桩侧土压力明显大于浅部测点,且土体的液化会弱化土对结构的压力;结构应变最大值位于上部桥台,而结构弯矩在桩身中部及土层分界面附近出现两个较大值,桩端嵌固及倾斜场地流滑是造成出现两个弯矩较大值的主要原因。 相似文献
5.
基于相同结构不同设计参数的高桩码头建立计算模型,研究两种结构自身动力特性的差异以及在地震作用下抗震性能的差异。研究表明:在相同荷载条件、场地条件、材料用量的前提下六桩码头的刚度要大于八桩码头;天津波作用下六桩码头的桩身加速度响应较大,且两种结构桩身加速度差异值随着震度的增大而增大;在相同峰值的罕遇地震下六桩码头的桩顶位移响应要小于八桩码头,而其残余位移要大于八桩码头;相同荷载条件下八桩码头的延性能力明显强于六桩码头,其极限塑性率是六桩码头极限塑性率的2.28倍;八桩码头在峰值加速度为800gal地震作用下达到极限曲率,六桩码头在峰值加速度为1 150gal的地震作用下达到极限曲率。 相似文献
6.
《地震工程与工程振动》2021,41(5)
基于OpenSees计算软件建立液化微倾场地群桩-土动力相互作用有限元模型,分析液化微倾场地饱和砂土p-y曲线特性,系统研究了场地倾斜角度、桩径、地震作用幅值和基桩位置对饱和砂土动力p-y曲线特性影响。研究表明:土体即将液化时,桩基土反力达到峰值;土体液化后,土体表现出了流体特性;土反力峰值、桩土相对位移峰值和初始刚度随场地倾斜角度增加而增大;桩径越大,液化砂土的耗能效应越明显;随着地震作用幅值的增加,桩土相对位移峰值和土反力峰值也随之增加;液化微倾场地上坡桩受到的土体侧向流动力大于下坡桩。 相似文献
7.
为了研究强震区桥梁跨活动断层时,桩基在地震中的动力响应,以海文大桥为工程背景,利用Midas GTS有限元软件建立其强震区桩-海床岩土体-断层耦合作用的数值模型,研究不同强度(0.20g～0.60g)的50年超越概率为10%的地震波(后文简称5010地震波)作用下,桥梁桩基加速度、位移、弯矩及剪力的动力时程响应特性。结果表明：上部大厚度松散土体对桩身加速度有放大及滤波作用,而基岩对桩身加速度几乎不产生作用;断层上、下盘桩基础的桩顶水平位移随输入地震动强度的增大而增大,但达到振幅的时刻一致;上、下盘桩基础桩顶竖向位移时程响应都在50 s以后产生永久沉降;桩身最大弯矩截面处时程响应均在40 s以后产生永久弯矩;应重点考虑上部覆盖层软硬土体界面和基岩界面的抗弯承载力设计,及桩顶和基岩面附近的抗剪承载力设计;上盘桩基础按桩身加速度、弯矩、桩顶水平位移等动参数控制设计,下盘桩基础按动剪应力控制设计。 相似文献
8.
为研究曲线桥梁在多维地震激励下考虑桩-土动力相互作用的地震响应特性,本文建立了空间桩-土脱离、摩阻和土体压缩非线性理论分析模型。为简化计算将该非线性弹簧模型进行线性化处理,结合有限元ANSYS分析平台建立了黄土场地的曲线桥仿真分析模型,对考虑桩-土相互作用的曲线桥进行了多维多工况数值分析,对比研究了曲线主梁跨中弯矩、墩底剪力和弯矩及桥墩顶位移的地震响应。结果表明:考虑桩-土相互作用的曲线桥梁主梁跨中内力与地震波输入方向密切相关,三维地震作用下主梁内力最大;各工况地震荷载作用下桥墩底部径向剪力响应比切向剪力响应大很多,而桥墩径向弯矩比切向弯矩略小;同一工况下不同桥墩顶切向位移响应大小相当,而径向位移差异较大。在进行非规则曲线桥梁抗震设计时,应充分考虑多维和单维地震激励输入工况。 相似文献
9.
《地震工程与工程振动》2017,(1)
地震作用下的桩基动力响应问题一直是土动力学和岩土工程抗震领域研究的热点。本文基于非液化干砂和饱和砂土中对称双直桩和双斜桩电磁式振动台试验,在试验中输入不同峰值加速度的正弦波和不同的地震波形,对比研究非液化干砂和饱和砂土中斜桩横向动力响应特性的不同,主要包括桩头承台加速度和位移幅值与台面输入时程的对比。研究结果表明:无论是正弦波输入还是地震波输入试验,当饱和砂土发生液化后,桩周土对桩侧支撑反力降低从而导致桩-土之间相互作用力减小,加速度和位移幅值放大效应均发生显著增加,对称双斜桩的动力响应放大程度低于对称双直桩,尤其在饱和砂土液化时更加显著。地震波输入试验中承台加速度和位移量值均明显高于正弦波试验工况,但相对台面输出幅值的动力放大倍数整体水平较低。 相似文献
10.
《地震地磁观测与研究》2016,(5)
基于ABAQUS软件的96CPU显式有限元并行计算集群平台,建立地基土—变截面地铁地下车站结构体系三维非线性地震反应分析有限元模型,数值模拟Kobe地震记录、Mex地震记录和100年超越概率3%的南京人工地震波作用下,软弱地基上变截面地铁地下车站结构地震反应特性。结果表明:地下结构上部土层地表处峰值加速度小于不含地下结构土层表面峰值加速度;地震动作用下模型地基呈现出显著的低频聚集(放大)、高频滤波效应;地震动在穿越地下结构时,出现散射等复杂传播行为。变截面地下结构(上宽下窄型)的下层结构地震响应大于上层结构,下层结构中柱的应力峰值大于楼板和侧墙的应力峰值,侧墙的应力峰值大于楼板的应力峰值。上层结构中柱的应力峰值最大,变截面处侧墙应力峰值次之,楼板应力峰值最小。输入地震动的峰值加速度和频谱特性对地下车站结构的地震反应均有很大影响;地下车站结构的地震反应具有明显的空间效应。 相似文献
11.
Shake table test of soil-pile groups-bridge structure interaction in liquefiable ground 总被引：2，自引：1，他引：1
<正>This paper describes a shake table test study on the seismic response of low-cap pile groups and a bridge structure in liquefiable ground.The soil profile,contained in a large-scale laminar shear box,consisted of a horizontally saturated sand layer overlaid with a silty clay layer,with the simulated low-cap pile groups embedded.The container was excited in three E1 Centra earthquake events of different levels.Test results indicate that excessive pore pressure(EPP) during slight shaking only slightly accumulated,and the accumulation mainly occurred during strong shaking.The EPP was gradually enhanced as the amplitude and duration of the input acceleration increased.The acceleration response of the sand was remarkably influenced by soil liquefaction.As soil liquefaction occurred,the peak sand displacement gradually lagged behind the input acceleration;meanwhile,the sand displacement exhibited an increasing effect on the bending moment of the pile,and acceleration responses of the pile and the sand layer gradually changed from decreasing to increasing in the vertical direction from the bottom to the top.A jump variation of the bending moment on the pile was observed near the soil interface in all three input earthquake events.It is thought that the shake table tests could provide the groundwork for further seismic performance studies of low-cap pile groups used in bridges located on liquefiable groun. 相似文献
12.
Soil liquefaction induced by earthquakes frequently cause costly damage to pile foundations. However, various aspects of the dynamic behavior and failure mechanisms of piles in liquefiable soils still remain unclear. This paper presents a shake-table experiment conducted to investigate the dynamic behavior of a reinforced-concrete (RC) elevated cap pile foundation during (and prior to) soil liquefaction. Particular attention was paid to the failure mechanism of the piles during a strong shaking event. The experimental results indicate that decreasing the frequency and increasing the amplitude of earthquake excitation increased the pile bending moment as well as the speed of the excess pore pressure buildup in the free-field. The critical pile failure mode in the conducted testing configuration was found to be of the bending type, which was also confirmed by a representative nonlinear numerical model of the RC pile. The experimental results of this study can be used to calibrate numerical models and provide insights on seismic pile analysis and design. 相似文献
13.
Observations of pile foundation performance during previous earthquakes have shown that pile failure has been caused by lateral ground movements resulting from soil liquefaction. The recognition that lateral ground movements may play a critical role in pile performance during an earthquake has important implications for design and risk assessment, and requires that analytical models be devised to evaluate these potential problems.In this paper, parametric studies were conducted to estimate the maximum bending moments induced in piles subjected to lateral ground displacement. The results are summarized in charts using dimensionless parameters.The analyses reveal that the existence of a nonliquefiable layer at the ground surface can affect significantly the maximum bending moment of the pile. When a relatively thick nonliquefiable layer exists above a liquefiable layer, neither the material nonlinearity of the soil nor loss of soil stiffness within the liquefiable layer significantly affect the maximum bending moment. When the thickness of the liquefiable soils is greater than about three times that of an overlying intact layer, soil stiffness in the liquefiable layer must be chosen carefully when evaluating the maximum bending moment. 相似文献
14.
R. Uzuoka M. Cubrinovski H. Sugita M. Sato K. Tokimatsu N. Sento M. Kazama F. Zhang A. Yashima F. Oka 《Soil Dynamics and Earthquake Engineering》2008,28(6):436-452
The 1995 Kobe earthquake seriously damaged numerous buildings with pile foundations adjacent to quay walls. The seismic behavior of a pile group is affected by movement of quay walls, pile foundations, and liquefied backfill soil. For such cases, a three-dimensional (3-D) soil–water coupled dynamic analysis is a promising tool to predict overall behavior. We report predictions of large shake table test results to validate 3-D soil–water coupled dynamic analyses, and we discuss liquefaction-induced earth pressure on a pile group during the shaking in the direction perpendicular to ground flow. Numerical analyses predicted the peak displacement of footing and peak bending moment of the group pile. The earth pressure on the pile in the crustal layer is most important for the evaluation of the peak bending moment along the piles. In addition, the larger curvatures in the bending moment distribution along the piles at the water side in the liquefied ground were measured and predicted. 相似文献
15.
To investigate the seismic response of a pile group during liquefaction, shaking table tests on a 1/25 scale model of a 2 × 2 pile group were conducted, which were pilot tests of a test project of a scale-model offshore wind turbine with jacket foundation. A large laminar shear box was utilized as the soil container to prepare a liquefiable sandy ground specimen. The pile group model comprising four slender aluminum piles with their pile heads connected by a rigid frame was designed with similitude considerations focusing on soil–pile interaction. The input motions were 2-Hz sinusoids with various acceleration amplitudes. The excess pore water pressure generation indicated that the upper half of the ground specimen reached initial liquefaction under the 50-gal-amplitude excitation, whereas in the 75-gal-amplitude test, almost entire ground was liquefied. Accelerations in soil, on the movable frames composing the laminar boundary of the shear box, and along the pile showed limited difference at the same elevation before liquefaction. After liquefaction, the soil and the movable-frame accelerations that represented the ground response considerably reduced, whereas both the movable frames and the piles exhibited high-frequency jitters other than 2-Hz sinusoid, and meantime, remarkable phase difference between the responses of the pile group and the ground was observed, all probably due to the substantial degradation of liquefied soil. Axial strains along the pile implied its double-curvature bending behavior, and the accordingly calculated moment declined significantly after liquefaction. These observations demonstrated the interaction between soil and piles during liquefaction. 相似文献
16.
Under the action of Rayleigh waves, pile head is easy to rotate with a concrete pile cap, and pure fixed-head condition is rarely achieved, which is a common phenomenon for it usually occurs on the precast piles with insufficient anchorage. In addition, the propagation characteristics of Rayleigh wave have been changed significantly due to the existence of capillary pressure and the coupling between phases in unsaturated soil, which significantly affects the pile-soil interaction. In order to study the above problems, a coupled vibration model of unsaturated soil–pile system subjected to Rayleigh waves is established on the basis that the pile cap is equivalent to a rigid mass block. Meanwhile, the soil constitution is simplified to linear-elastic and small deformations are assumed to occur during the vibration phase of soil–pile system. Then, the horizontal dynamic response of a homogeneous free-field unsaturated soil caused by propagating Rayleigh waves is obtained by using operator decomposition theory and variable separation method. The dynamic equilibrium equation of a pile is established by using the dynamic Winkler model and the Timoshenko beam theory, and the analytical solutions of the horizontal displacement, rotation angle, bending moment and shear force of pile body are derived according to the boundary conditions of flexible constraint of pile top. Based on the present solutions, the rationality of the proposed model is verified by comparing with the previous research results. Through parametric study, the influence of rotational stiffness and yield bending moment of pile top on the horizontal dynamic characteristics of Rayleigh waves induced pile is investigated in detailed. The analysis results can be utilized for the seismic design of pile foundation under Rayleigh waves. 相似文献