Shake table test of soil-pile groups-bridge structure interaction in liquefiable ground

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 Centro 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.

Study on soil-pile-structure-TMD interaction system by shaking table model test

The success of the tuned mass damper (TMD) in reducing wind-induced structural vibrations has been well established. However, from most of the recent numerical studies, it appears that for a structure situated on very soft soil, soil-structure interaction (SSI) could render a damper on the structure totally ineffective. In order to experimentally verify the SSI effect on the seismic performance of TMD, a series of shaking table model tests have been conducted and the results are presented in this paper. It has been shown that the TMD is not as effective in controlling the seismic responses of structures built on soft soil sites due to the SSI effect. Some test results also show that a TMD device might have a negative impact if the SSI effect is neglected and the structure is built on a soft soil site. For structures constructed on a soil foundation, this research verifies that the SSI effect must be carefully understood before a TMD control system is designed to determine if the control is necessary and if the SSI effect must be considered when choosing the optimal parameters of the TMD device.

Simple Method for Dynamic Responses of Soil-Pile-Isolated Structure Interaction System

To investigate the effect of soil-pile-structure interaction(SPSI effect)on the dynamic response of a baseisolated structure with buried footings on a pile foundation,certain shake table tests are previously conducted.Based on the test results and the existing related studies,an efficient simplified model and a corresponding calculation method are verified for estimating the dynamic characteristics of a base-isolated structure with buried footings on a pile foundation with the SSI effect.In this method,the solutions by Veletsos and co-workers for a non-isolated structure with the SSI effect are verified and advanced for a base-isolated structure,and the solutions by Maravas and co-workers for a non-isolated structure on a pile foundation are introduced to consider the effect of the piles.By comparison with the shake table test,this work proves that the simplified method can efficiently estimate the dynamic responses of a base-isolated structure with buried footings on a pile foundation.Using parameter analysis,this work also shows that the dynamic characteristics of a non-isolated structure are quite similar to those of the base-isolated structure when the soil foundation is sufficiently soft,which means that the isolation layer gradually loses its isolation function as the soil foundation softens.

Evaluation of Dynamic Soil-Structure Interaction and Dynamic Seismic Soil Pressures Acting on It Subjected to Strong Earthquake Motions

In order to clarify the damage mechanism of the subway structure, the dynamic soil-structure interaction and the dynamic forces acting on the structure, a series of shaking table tests and simulation analyses were performed. The seismic response of the structure and the dynamic forces acting on the structure due to sinusoidal and random waves were investigated with special attention to the dynamic soil-structure interaction. The result shows that the compression seismic soil pressures and extension seismic soil pressures simultaneously act on the sidewalls, and big shear stress also acts on the ceiling slab due to horizontal excitation. The seismic soil pressure could be approximated to hyperbola curve, and reached a peak value with increase of the shear strain of the model ground. In addition, a slide and exfoliation phenomenon between the structure and the surrounding ground was simulated, using the nonlinear analyses. The foundation is provided for amending the calculation method of seismic soil pressure and improving the anti-earthquake designing level of underground structure.

Seismic response of underground utility tunnels: shaking table testing and FEM analysis

Underground utility tunnels are widely used in urban areas throughout the world for lifeline networks due to their easy maintenance and environmental protection capabilities. However, knowledge about their seismic performance is still quite limited and seismic design procedures are not included in current design codes. This paper describes a series of shaking table tests the authors performed on a scaled utility tunnel model to explore its performance under earthquake excitation. Details of the experimental setup are first presented focusing on aspects such as the design of the soil container, scaled structural model, sensor array arrangement and test procedure. The main observations from the test program, including structural response, soil response, soil-structure interaction and earth pressure, are summarized and discussed. Further, a finite element model （FEM） of the test utility tunnel is established where the nonlinear soil properties are modeled by the Drucker- Prager constitutive model; the master-slave surface mechanism is employed to simulate the soil-structure dynamic interaction; and the confining effect of the laminar shear box to soil is considered by proper boundary modeling. The results from the numerical model are compared with experiment measurements in terms of displacement, acceleration and amplification factor of the structural model and the soil. The comparison shows that the numerical results match the experimental measurements quite well. The validated numerical model can be adopted for further analysis.

Shaking Table Model Test of Isolated Structure on Soft Site and Analysis on Its Isolation Efficiency

Adopting a soft site model built on soft interlayer soil foundation,a shaking table test for soft interlayer soil-isolated structure interaction is conducted to investigate the seismic response of isolated structure on soft site,and analyze its isolation effect.Test results show that the test can reflect the earthquake response characteristics of isolated structure on soft site.It is on soft site that the dynamic characteristics of isolated structure,acceleration magnification factor(AMF)of isolated structure and isolation efficiency of the isolation layer differ from those on rigid foundation with an soil-structure interaction(SSI)effect,represented by the reduction in fundamental vibration frequency of isolated structure and the increase of damping ratio with changes of the SSI effect.SSI can either increase or decrease AMF of isolated structure on soft site,depending on the characteristics of earthquake motion input.Furthermore,the isolation efficiency of isolation layer on soft site is decreased with the SSI effect,which is related to the peak ground acceleration(PGA)and the characteristics of earthquake motion input.

基于流固耦合的LNG储罐外罐地震响应分析

为研究流固耦合对LNG储罐外罐的地震响应问题,采用振动台试验和数值仿真相结合方法对不同地震波下不同液体高度的LNG储罐进行震动分析。试验结果表明:地震会改变罐体加速度和位移的分布情况,不同地震波和不同液体高度对位移和加速度的放大效应有着不同的影响,在El Centro波、Taft波和SHM2波作用下,流体振荡产生的减震作用和流体压力产生的附加惯性作用能够减小储罐中部的位移,但对加速度有所放大。利用时程分析法对5000m^(3)LNG储罐的位移和环向应力进行地震模拟分析,结果表明:储罐的环向应力呈现出中间大两头小的走势,在罐高的1/4h、1/2h和3/4h上出现极值;位移沿罐高度方向先增加后减少,峰值出现在1/4h、1/3h、1/2h和3/4h处。因此在LNG储罐抗震设计时,应考虑流固耦合效应对结构的影响,在1/4h、1/3h、1/2h和3/4h处的薄弱位置,宜采用增加壁厚、设置阻尼器和钢筋加密等措施增强结构的可靠性和安全性。

考虑土−结构相互作用的地下室层对高层建筑地震反应影响研究

当前建筑抗震设计中往往忽略了地下室层及土−结构相互作用(soil-structure interaction,简称SSI)效应的影响,研究旨在通过振动台试验和数值模拟,研究考虑SSI效应时不同地下室层数的高层建筑在不同地震作用下的地震反应。首先选择相似系数λ(λ=1:50)进行缩尺模型的振动台试验,以模拟真实建筑的地震反应。为了模拟复杂的结构系统,利用PLAXIS 3D对有无SSI效应的缩尺模型和真实模型分别进行了数值模拟。试验和数值模拟的结果取得了很好的精确度并具有良好的一致性,同时也验证了所选相似系数λ=1:50足以反映不同地震作用下建筑的真实情况。通过对试验和数值模拟的结果进行分析,发现SSI效应和地下室对高层建筑的地震反应的影响显著。虽然目前大多数规范都认为SSI效应会减小建筑的剪力,增加相对侧向位移,但研究发现,在某些情况下SSI效应会增加建筑的剪力和相对侧向位移。

桥桩-土-隧道体系动力相互作用的振动台试验研究

为研究地震作用下桥桩-土-隧道体系的动力响应特性,依托某实际工程,设计出8个试验工况,选取3种不同地震波类型及地震强度,开展几何相似比为1/30的振动台模型试验,并从体系的固有频率和加速度响应等方面进行分析。通过对比分析各个工况,结果表明:桥桩的存在会削弱周围土体以及侧穿隧道的加速度响应,而隧道的存在则会放大场地土以及附近桥桩的加速度响应;不同类型的地震波对桥桩-土-隧道体系动力响应的影响不同。试验结论可为类似工程的抗震设计提供一定的理论指导。

隧道-土-桥桩相互作用体系振动台试验与数值模拟研究

以大连实际工程为背景,通过振动台试验研究了双隧道-砂土-桥桩系统在地震作用下的动力相互作用(SSSI),得到结构、场地的动力响应规律,并与ABAQUS数值模拟结果进行对比。数值模型引入Kelvin本构模型子程序,利用等效线性方法处理砂土在计算过程中的非线性问题。将试验结果与数值模拟结果进行对比,验证了数值模拟的可靠性。在此基础上设计了8种工况,通过对比分析研究了体系内各结构之间的相互作用规律。结果表明,隧道会放大桥桩、临近隧道的峰值加速度,而桥桩却会对侧穿隧道的峰值加速度起到减弱作用;隧道与桥桩的存在均会增大彼此的截面剪力与弯矩,其中受影响的区域主要集中在隧道上下拱,桥桩的桩底与桩-土交界面。

穿越非均匀土体综合管廊振动台试验研究

在建设综合管廊的过程中,难以避免地会穿越水平不均匀土体,此场地不利于管廊的抗震。该研究基于振动台试验,对地震作用下水平非均匀土体与综合管廊的动力变形响应及相互作用进行了系统性研究。深入分析了管廊的土压力增量、加速度、位移和应变,包括加速度峰值沿竖向分布情况以及管廊变形的直接影响因素,发现由于地下结构的存在,土体对加速度放大效应发生衰减;在大震时土体与管廊发生了相对滑移,此现象对管廊的变形产生较大影响;随着加速度的增大,土压力增量分布近似呈抛物线形;结构的柔度比越大,变形越大。基于振动台试验研究了管廊穿越非均匀土体的简化计算方法,通过调整变形比来实现土体分界对管廊变形的影响,为管廊的抗震设计提供参考。

桩—土—钢、砼结构动力相互作用试验对比研究

为了分析不同上部结构-桩-土相互作用规律,分别进行了钢框架结构-桩-土模型和混凝土结构-桩-土模型的振动台试验,并对试验模型进行了相应的有限元数值模拟分析。试验采用三维叠层剪切模型箱,土体为均匀粉质黏土,钢结构和混凝土结构模型为简化的3层框架结构,桩基为3×3根群桩,桩径为10 cm,桩长为200 cm,输入为人工地震动时程,按时间相似比压缩1/5。振动台对比试验结果表明,相同几何尺寸的结构试验模型,混凝土结构的整体刚度大于钢结构,因此振动频率大于钢结构;相同地震作用下,钢框架结构模型加速度反应明显大于混凝土结构,桩身加速度放大系数前者为后者1.15~1.2倍,上部结构可达2倍,钢框架结构模型反应谱的卓越周期更长。有限元数值模拟的结果定性地验证了试验结果的合理性。

地震作用下桩板墙-锚索组合支护基覆型边坡的动力响应特性

地震作用下,惯性力方向对组合结构、土体、岩体的平衡状态影响显著。为深入理解桩板墙组合支护结构-基覆型边坡相互作用特性,以西南地区一隧道进口端基覆型高陡边坡为原型,开展一组简谐波加载下组合结构加固边坡的大型振动台模型试验,考虑惯性力方向对桩-土、格构锚索-坡体时程特性展开分析。结果表明:(1)惯性力作用下格构锚索-土体相互作用与桩-土相互作用表现出近似的时程一致性规律,但坡面加固结构惯性力峰值沿高程存在的相位差不可忽视。(2)结构与边坡土体的相互作用大小取决于相对惯性运动,桩-基岩相互作用由悬臂段变形状态决定。(3)惯性力达到临空面峰值,动土压力达到峰值,桩-土位移差达到正向峰值,桩身呈现外倾的主动破坏状态,锚固段前侧受力因外倾而挤压增大,因而悬臂段采用库仑主动土压力进行设计需结合桩土状态进行修正。(4)简谐波作用下,坡体惯性力及变形是组合支挡结构沿高程受力分布特性的关键因素,组合结构设计时需重点关注坡脚应力集中区及坡顶惯性力放大区。本研究可为组合结构抗震加固设计提供理论支撑。

桩-土-结构动力相互作用影响因素分析

为了研究桩-土-结构动力相互作用机理,分析其影响因素,采用振动台试验和数值模拟分析相结合的方法,对不同上部结构质量、不同输入波频率和加速度峰值输入下的桩-土-结构体系的水平动力反应规律进行了分析和讨论。试验地基土体模型为中硬土,剪切波速约为213 m/s;群桩基础由5根长1.35 m、直径0.1 m的基桩“十”字型布置;上部结构模型采用质量块模拟。研究结果表明:桩身的弯矩与剪力在桩-承台连接处最大,并且随深度增加而减小;随着上部结构质量的增加,土体与桩基的加速度反应增大,桩身的弯矩与剪力也增大;随着输入正弦波幅值和频率的增大,桩-土运动相互作用变大,桩身弯矩与剪力变大;最后比较各种影响因素引起的反应发现,上部结构质量的变化对桩-土-结构体系动力相互作用的影响最大,幅值的影响次之,频率的影响最小。

场地土性对核岛隔震结构影响的振动台试验研究

为研究不同地基土的土-结构动力相互作用对基础隔震体系动力反应影响规律,配备了3种不同硬度的地基土,开展土-群桩-核岛体系与土-群桩-隔震支座-核岛体系结构动力相互作用振动台试验,分析了不同场地土之间桩土相互作用、上部结构动力响应特征、桩身内力分布、变形规律以及破坏情况等。结果表明:地基土硬度的变化,对隔震体系桩-土相互作用有明显影响。随着桩土刚度比的增大,基础隔震支座的隔震效率逐渐减小,且土结分离现象更为明显;对于隔震结构,在不同场地土中加入隔震支座后,桩身受弯峰值随着土体刚度增大沿桩身高度逐渐增大;核电工程采用隔震支座时,应考虑不同场地土地基对于桩基础受力分布的改变,做出相应加固措施,以保证其安全性。

基于替代试件模型的振动台迭代控制仿真分析

试件-台面相互作用会显著影响振动台加速度时程复现精度,迭代控制常常成为提高试验数据可靠性的重要手段。然而,砌体、钢筋混凝土等结构易于因开裂而进入非线性力学状态,往往不适合迭代加载。文中开展了基于替代试件模型的振动台迭代控制方法仿真研究,先构建一个与试件动力特性相近的替代试件模型,利用替代试件模型完成振动台迭代加载获得驱动命令后,再开展真实试件的振动台试验。仿真结果表明:基于替代试件模型的振动台迭代控制有效降低了试件-振动台相互作用对系统控制性能的影响,实现了台面加速度时程的高精度复现。

Fundamental Study on Response Properties of Structures Constructed on Lunar Regolith

The Artemis Program, for constructing the lunar base, is in progress. How to design and construct architectural and civil engineering structures in the lunar environment has become an important issue. The lunar surface is covered with soft sand, called regolith, and it is required to protect lunar bases and structures, as well as internal precision equipment, against vibrational disturbances such as moonquakes and meteorite collisions. Therefore, in this study, the static and cyclic triaxial compression tests of the regolith simulant were conducted. The reference strain and equivalent damping factor of the regolith simulant were smaller compared to sandy soil on Earth. In addition, a shaking table test using model specimens was conducted on the response properties of regolith ground alone and structures set on regolith ground. The buried foundation and pile foundation notably suppressed the horizontal response attributed to the rocking component compared to a direct foundation.

考虑桩-土相互作用的深水桥墩地震响应分析

深水桥梁往往为桩基础形式,其地震作用下桩-土相互作用效应显著,掌握桩-土相互作用对深水桥墩地震响应的影响,有助于指导深水桥梁结构的抗震设计。该文通过附加质量方法考虑动水压力作用,采用精细化模型模拟桩-土相互作用,引入动力松弛技术完成初始地应力平衡,建立了考虑桩-土相互作用的深水桥墩地震响应数值模拟方法,并通过离心机振动台试验验证了其正确性。利用已验证的数值模拟方法分析了不同地震强度和不同场地土体强度对深水桥墩地震响应的影响,结果表明:随着场地土体强度提高,桥墩的地震位移响应减小,水体的存在不会改变此规律;软弱土场地的动水压力对桥墩和桩基的地震响应影响较小,最大影响程度在10%左右;中硬土场地的动水压力明显增大桥墩和桩基的地震响应,且地震强度越大,增大效应越明显,因此强震作用下处于硬土场地的动水压力作用在桥梁结构抗震设计中必须予以考虑。

考虑埋深影响的地下LNG罐振动台试验研究

地下LNG罐与地上LNG罐相比,拥有更好的抗震性、更高的安全性等优点,其工程应用是LNG罐结构的发展趋势,目前我国大陆尚无地下LNG罐的应用先例。振动台试验是研究地下LNG罐地震响应的一个重要手段,为考察不同地震动强度、不同液位、不同埋深情况下地下LNG罐的地震响应特性,基于1个结构模型设计并进行了2组层状剪切试验箱的振动台试验。LNG罐模型参照某22万m^(3)LNG罐进行简化,考虑储液与结构、土与结构的动力相互作用关系对储液、结构、土(包括基岩)进行了相似设计。通过试验设计对模型和边界进行了合理的设置,振动台试验考察了不同工况下的地震响应规律,获得了LNG罐结构的动力响应特性。结果表明试验中展现出的储液-结构-土相互作用的部分特征与相近工程实测结果、经典理论具有一致性。

结构-地基动力相互作用体系振动台模型试验研究

本义设计实现了结构－地基动力相互作用体系的振动台试验，通过试验研究了动力相互作用体系的地震动反应的主要规律。由于动力相互作用的影响，软土地基中相互作用体系的频率远小于刚性地基上不考虑结构－地基相互作用的结构频率，而阻尼比则远大于结构材料阻尼比。软土地基对地震动起滤波和隔震作用。由于上部结构的振动反馈，基底地震动与自由场地震动不相同。上部结构柱顶加速度反应主要由基础转动引起的摆动分量组成，平动分量次之，而弹性变形分量很小。桩身应变幅值呈桩顶大、桩尖小的倒三角形分布。桩上接触压力幅值呈桩顶小、桩尖大的三角形分布。试验表明，结构－地基动力相互作用对体系地震反应的影响是很显著的。本试验为验证理论与计算分析的研究成果、改进或提出合理的计算模型和分析方法，提供了丰富的试验数据，为进一步研究奠定了基础。