Seismic performance evaluation of water supply pipes installed in a full-scale RC frame structure based on a shaking table test

As an important part of nonstructural components,the seismic response of indoor water supply pipes deserves much attention.This paper presents shaking table test research on water supply pipes installed in a full-scale reinforced concrete(RC)frame structure.Different material pipes and different methods for penetrating the reinforced concrete floors are combined to evaluate the difference in seismic performance.Floor response spectra and pipe acceleration amplification factors based on test data are discussed and compared with code provisions.A seismic fragility study of displacement demand is conducted based on numerical simulation.The acceleration response and displacement response of different combinations are compared.The results show that the combination of different pipe materials and different passing-through methods can cause obvious differences in the seismic response of indoor riser pipes.

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.

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.

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.

Failure mode and dynamic response of a double-sided slope with high water content of soil

A double-sided slope with high water content in sandy clay was considered under the action of seismic load. Its failure mode and dynamic response were investigated using a hydraulic servo shaking table test. The typical characteristic of failure mode and dynamic responses of the double-sided slope were analyzed. Experimental results show that slope failure undergoes a process of progressive deformation. The slope failure mode can be explained as creep sliding landslide. AFA(Amplification Factor of Acceleration) at the surface and inner parts of the slope shows an increasing trend with the increase of relative elevation. The relationship between AFA and EAA(Excitation Amplitude of Acceleration) is nonlinear. An empirical formula is proposed to describe preferably the relationship between AFA,relative elevation and dimensionless EAA. The AFA at the middle and upper parts of the slope increases apparently with increasing EFA(Excitation Frequency of Acceleration).

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.

Dynamic p-y curves for vertical and batter pile groups in liquefied sand

In this study,centrifuge model tests of vertical and batter pile groups in liquefied sand were conducted on a centrifuge shaking table.The dynamic p-y curves for these pile groups before and during sand liquefaction were obtained from calculations based on test data.The results confirm that liquefaction contributes to a reduction in the energy consumption of pile foundations,with the degradation effect being more pronounced for batter pile groups.At shallow depths,the difference in the backbone gradients of the p-y curves after liquefaction for vertical and batter pile groups indicates that the lateral stiffness of a batter pile group is greater than that of a vertical pile group.As shaking intensity increases,the lateral stiffness of a vertical pile group increases with depth during the late stage of sand liquefaction.However,the lateral stiffness of a batter pile group during liquefaction does not vary with depth.The results of this study provide a reference for the seismic design of vertical and batter pile groups in liquefied soil.

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.

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。

水下振动台竖向动水附加质量特征与机理试验研究

工程结构与水体耦合抗震研究需求越来越大,推动了水下振动台的建设与发展,水下振动台竖向动水附加质量及特征直接影响其设计和自身性能。本文通过试验方法,共设计135个工况,台面负载20 t惯性质量块,分别考虑不同激励量级、不同频率、不同水深,研究水下振动台竖向动水附加质量特征,并试探从机理层面进行解释。试验结果表明:激励量级与动水附加质量之间相关性较为复杂,不同频率之间存在分组现象,水深比(水深/台面直径)可作为水下振动台设计重要参数,不同水下振动台动水附加质量最小值频率拐点不同。试验研究为水下振动台设计以及模型试验可靠性等提供参考。

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。

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。

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。

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。

饱和砂土液化特性的振动台试验研究

基于地震模拟振动台试验,配制3组不同平均粒径和3组不同细粒含量的6个砂土模型,通过埋置于砂土内部的传感器监测模型内部不同位置的超孔隙水压力等指标,分析砂土模型内部的超孔隙水压力时程曲线及孔压比时程曲线,归纳出地震波加载峰值、砂土平均粒径、细粒含量及埋置深度等因素对饱和砂土液化特性的影响规律。试验结果表明:随着地震波加载峰值的增大,砂土模型液化程度逐渐增大,液化势逐渐增大,抗液化强度逐渐减小;随着砂土埋置深度的增加,砂土细粒含量的增加,砂土平均粒径的增加,砂土模型液化程度逐渐减小,液化势逐渐减小,其抗液化强度逐渐增大。同时,试验结果还表明,砂土液化各影响因素对砂土液化的影响程度依次为地震波强度>砂土埋置深度>砂土平均粒径、细粒含量。试验结果可为后续数值模拟的参数选取提供支持,为研究其他因素对砂土液化的影响提供参考。

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。

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。

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。