非一致地震激励地下综合管廊振动台模型试验研究(Ⅰ)——试验方法

针对浅层软土中埋设的矩形截面地下综合管廊进行了非一致地震激励下的振动台模型试验研究。作为首个此种类型结构非一致激励的振动台试验工作,本文主要介绍试验方法,重点包括试验方案设计、开洞试验模型箱与模型结构设计,根据试验的特殊要求而开发的土体滑移传感器和地下结构接头位移测量装置,以及人工合成输入地震波动时程的方法与步骤。上述试验设计方法可供今后类似试验工作参考。试验结果分析及数值模型验证结果将在后续系列论文中介绍。     

非一致地震激励地下综合管廊振动台模型试验研究(Ⅱ)——试验结果

本文以纵向非一致地震激励试验为主,对地下综合管廊振动台模型试验结果进行了分析,包括模型场地的加速度响应、结构的应变响应、结构和场地加速度响应关系、结构应变响应的原因、结构接头位移响应、结构在纵向非一致激励和一致激励下应变响应的区别。结果分析表明,本试验模型场地及模型结构设计合理,从中得到了关于地下综合管廊非一致地震激励作用下响应规律的一些新内容。     

三塔长跨斜拉桥振动台试验研究

多塔长跨斜拉桥受力复杂,采用轻质结合梁时结构地震响应更具特点.本文以某主跨为616m的三塔结合梁斜拉桥为工程背景,制作动力缩尺模型进行三台阵振动台试验.在单向一致激励振动台试验的基础上,进行多维激励、多点激励振动台试验,并与数值分析结果进行比较验证.试验结果表明:此结构的基本振型为中塔纵弯与主梁竖弯的耦合振动.纵向一致地震作用下,主塔及主梁均会有较大的地震响应;横向一致地震激励下,中塔地震响应较边塔更为不利.多点激励振动台试验表明,行波效应使得各构件地震响应不同程度增大;最后,通过多维地震激励下试验结果验证了规范中方向组合计算方法的准确性.     

非一致地震激励地下综合管廊振动台模型试验研究(Ⅲ)——数值模拟

根据非一致地震激励地下综合管廊振动台模型试验结果,以有限元软件ABAQUS为平台,定义了约束方程来考虑层状剪切砂箱的模型箱效应。土体采用线性扩展Drucker-Prager本构模型,并采用主从接触面模型考虑土-结构相互作用,建立了三维有限元模型。对各种试验输入工况下土-综合管廊体系的地震反应进行了数值模拟,并与试验结果进行了对比。结果表明:数值模拟结果与模型试验结果吻合较好。文中所提建模方法合理,可用于后续的分析。     

土工振动台试验连续体模型箱的适用性研究

为更加合理地模拟地下结构多台阵振动台试验中场地的连续性,作者所在课题组研制了用于长线性地下结构振动台试验的连续体模型箱装置,该装置是由端部刚性箱、软连接箱及中间刚性箱组成的空间结构体系.运用有限元软件ABAQUS对其进行三维数值模拟,模态分析论证了可不与模型土发生共振的连续箱体构造的合理性,三维数值试验分析了该连续体模型箱在一致、非一致地震激励作用下的“边界效应”及工作中的稳定性.数值试验结果表明,所设计的连续体模型箱性能良好,为本次试验获得成功打下了坚实的基础.     

非一致地震激励下综合管廊接头响应数值模拟

以横向有接头地下综合管廊非一致激励振动台试验为基础,基于有限元软件ABAQUS,建立了土-地下综合管廊结构数值模型,采用非线性弹簧单元模拟地下综合管廊的接头。分析了模型箱的边界效应、加速度响应、位移响应、以及管廊接头响应,有限元计算结果与试验实测结果进行对比分析,二者对比结果呈一致趋势,非线性弹簧单元可为生命线工程结构接头数值模拟提供了新思路。     

小比例尺地下结构振动台试验模型土的设计与试验研究

基于结构与地基土相似设计相匹配的原则,通过采用卓越周期相似关系来简化锯末混合模型土,进行小比例地下结构振动台模型试验研究。通过对不同配比的锯末混合土进行共振柱试验,在采用等效线性本构模型分析原型土和混合模型土的特性参数(Gmax和G/Gmax-γ)的基础上,进一步确定了混合模型土配合比。对采用本文方法设计的自由场地模型土进行了一致地震激励下的振动台试验。试验结果表明:简化设计模型土满足了小比例地下结构振动台试验主要相似关系,取得了良好的试验效果,为以后进行土-地下结构相互作用的振动台试验奠定了坚实的基础,并且可以为类似试验提供借鉴。     

不同场地条件下非规则截面地铁地下车站结构地震反应特性研究

我国大型城市轨道交通地下结构建设处于蓬勃发展时期,建设场地条件日趋复杂,车站结构形式也复杂多样,呈现不规则特征。近年的地震灾害现象表明,地下结构在强地震作用下可能会出现严重的震害及次生灾害,城市大型地下结构工程的抗震安全性已成为倍受关注的社会问题之一。因此,研究不良地质条件下不规则地下结构的地震安全性具有重要的学术意义与工程应用价值。本文以苏州星海站的不规则(上层五跨下层三跨)地铁地下车站结构和场地条件为原型,分别采用模拟地震振动台试验和数值模拟方法开展研究,探讨饱和砂土地基和软弱粘土地基中非规则截面地铁地下车站结构的地震反应特性及损伤机理。为满足振动台试验中多种类型物理量的有效测试,采用了分布式柔性孔压传感链测试技术,阵列式位移计(SAA)测试技术,并基于机器视觉研发的非接触性动态位移测试技术实现地下结构灾变过程的可视化及数据化。论文的主要工作和成果如下:(1)将阵列式位移计(SAA)首次应用于地基土-地铁车站结构大型振动台系列模型试验中,实现土体变形的测量,并与基于机器视觉研发的非接触性动态位移测试结果相比较,表明采用SAA可较好地测试地震荷载作用下土体的位移响应;研发了分布式柔性孔压传感链测试技术,可以有效解决振动过程中传感器与土体惯性力不同而产生的自身摇摆、移位等问题。形成了地基土-地铁地下结构体系地震损伤与破坏时空演化过程的大型振动台试验可视化及数据化试验技术,可展现非规则截面地下结构的变形模式。(2)将研发的测试技术应用于大型振动台模型试验,开展了可液化地基和软弱粘土地基中非规则截面(上层五跨下层三跨)地铁地下车站结构的地震反应特性研究,给出了模型地基-结构体系加速度、变形、震陷特性,模型地基土与结构接触动土压力反应,模型结构动应变特性以及可液化地基土孔压反应及空间效应等,揭示了不良工程地质条件下地铁车站结构地震灾变特性和破坏机理。(3)对完成的不同场地条件下地铁地下车站结构的振动台系列试验结果进行对比分析,包括地铁车站模型结构周围地基土的加速度反应规律、地表震陷特征,模型地基土与结构接触动土压力反应特性,非规则截面地铁车站模型结构的加速度、侧向位移和动应变的反应规律等,得出了不同场地中非规则截面地铁地下结构地震反应特性的差异性。(4)基于有限元软件ABAQUS计算平台,形成了地基土-地下结构体系成套数值分析流程,开展了软弱场地中非规则截面地铁地下车站结构振动台试验的数值模拟,并与振动台模型试验结果进行了比较,验证了该数值分析方法的可行性和有效性。在此基础上,对复杂环境下足尺非规则截面地铁地下车站结构进行了数值模拟计算,给出了其地震反应特性。     

黄土场地地铁车站振动台试验方案设计与研究

为得到可靠的试验数据,对黄土场地典型断面地铁车站大型振动台试验方案进行设计与研究。根据试验目的和特点,提出黄土场地与地铁车站动力相互作用模型体系相似设计原则,并基于Bockingham的π定理对模型结构进行相似设计;通过室内试验研究模型材料配合比、力学特性及模型制作技术;采用有限元-无限元耦合数值建模方法,分析黄土场地地铁车站地震响应,基于数值模拟结果对振动台试验中的传感器布设方案进行研究;根据西安及周边地区地震环境特点,确定振动台试验输入地震动与加载方案。研究结果表明,试验模型结构宏观震害与数值模拟结果较吻合。本研究可为黄土场地地铁车站、地铁隧道及地下商业街等地下结构振动台试验方案设计与深入研究提供参考。     

埋地管道-场地地震反应振动台试验研究的场地响应

基于多子台台阵系统,北京工业大学于近期开展了多点地震动输入、不同场地条件下埋地管道振动台试验。试验中连续体模型箱固定于3个振动台台面上,相邻台面上的箱体能在水平双方向(纵向、横向)相对运动;3个振动台相互独立,通过分别对3个振动台输入各自的加速度记录实现了多点地震动输入。本文针对其中的横向水平地震激励作用下的场地响应进行研究,分析了一致和非一致地震作用下有无埋地管线时的场地地震响应规律。试验结果表明,非一致激励作用将增大场地土体的相对位移,致使相邻地震动输入点间场地土体受到剪切作用;随着输入地震动强度的增加,场地土体的一阶固有频率持续降低,阻尼比不断增大;非自由场的阻尼比、一阶固有频率等参数略大于自由场。     

Shaking table test of utility tunnel under non-uniform earthquake wave excitation

A series of shaking table tests were conducted on scaled utility tunnel models with and without construction joints under non-uniform input earthquake wave excitation. Details of experimental setup are first presented with particular focuses on: design and fabrication of double-axis laminar shear box with a rectangular hole opened on its side walls; design of two devices for measuring the slippage between the interface of test soil and the structure, and the relative deformation and rotation between joints of the structure model; and procedure for construction of input earthquake wave. The experiments were conducted in three phases. Phase 1 is free-field test. A 2-norm index is suggested to quantify the boundary effect and it is found that the designed laminar box does not impose significant boundary effect. Phases 2 and 3 are model tests in longitudinal and transversal directions, respectively. Test results are discussed in items of shear force–slip relationship at the soil–model structure interaction surface, movement and rotation of the construction joint, and effect of non-uniform earthquake input. The comparison shows that structural response under non-uniform earthquake excitation is larger than that under uniform excitation. The effect of spatial distribution of earthquake excitation should be considered in the seismic design of utility tunnel.     

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.     

沉管隧道穿越纵向非均匀场地振动台试验研究

为了研究穿越纵向非均匀场地的沉管隧道地震反应规律,进行了沉管隧道穿越砂土-黏土场地和均匀砂土场地两种工况的振动台试验。沉管隧道模型材料主要为微粒混凝土和镀锌钢丝,接头材料为橡胶,模型缩尺比为1/30,采用层叠剪切箱装填黏土和砂土构成纵向非均匀场地,输入荷载为不同峰值的El Centro波和Kobe波。采集土层和隧道不同观测点处的加速度和应变等数据并进行分析,研究在不同性质土层中的沉管隧道地震反应的特点,分析纵向非均匀场地对于沉管隧道地震反应的影响。试验结果表明砂土和黏土不同的动力特性会导致沉管隧道地震反应各异:穿越非均匀场地沉管隧道加速度反应、应变反应和管节间相对位移反应明显异于均匀场地沉管隧道,且在输入不同峰值的地震波下呈现不同规律。试验结果可供沉管隧道抗震设计参考。     

简易单向专用地震模拟振动台的研制

振动台实验方法是目前抗震研究中的重要手段之一。作者在碎石桩加固液化地基效果的试验研究中，利用从美国MTS公司引进的电液伺服加载试验系统，建成了一个简易单向专用振动台。主要介绍在振动台设计方面遇到的技术难题及其解决途径。主要包括振动台基础、台面和作动器连接部件、台面支撑系统和侧面导向系统材料的正确选择、设计和制作等。文中所采用的技术措施对试验成功起到了保障作用，研制出的振动台试验系统还可以应用于其它岩土地震问题的试验研究。     

Behaviour of subaqueous tunnels during earthquakes

Three-dimensional models of a subaqueous tunnel were built on a shaking table and vibrated for the purpose of investigating the dynamic behaviour of the tunnel. The material of the soft surface layer was gelatin gel and that of the tunnel was silicon rubber. In addition, earthquake observations at the site of the real subaqueous tunnel have been carried out using accelerometers and strain gauges set on the walls of the tunnel. At the site, micro-tremors were also measured. In these studies, it was noted that non-uniform displacements of the ground along the tunnel axis were caused by variations of the dynamic behaviour of the ground, and that the tunnel deforms correspondingly to the varying deformations of the ground. From these experimental results, a mathematical model of the subaqueous tunnel was formulated for anti-seismic design studies.     

Large scale shaking table model test and analysis on seismic response of utility tunnel in non-homogeneous soil

Underground utility tunnels are the most fundamental and reliable lifeline network in urban cities,and are widely constructed throughout the world.In urban areas,most utility tunnels usually encounter the non-homogeneity of subsoil condition due to various construction effects.Studies have shown that the damage mechanism of shallow underground structures mainly depends on the inhomogeneity of the subsoil conditions.This would become a considerable factor for the stability of the underground utility tunnel structures.However,this type of research still needs to establish the vulnerable seismic design.In this study,a series of shaking table tests were conducted on non-homogenous soils to investigate the performance of seismic interaction between utility tunnels,surrounding soils and interior pipelines.The dynamic responses measured from the test account for the boundary condition of non-homogeneous soils,the internal forces,displacement of tunnel joints,the dynamic characteristics on interior pipelines and the reasonable spring stiffness with damping in the seismically isolated gas pipeline model inside the tunnel.The vulnerability of underground utility tunnel in non-homogeneous soil zone and the mechanism of the stability of interior facilities are the main topics discussed in this paper.     

综合管廊横向振动台试验设计

在基于文献调研及综合考虑试验目的、试验条件、试验经费的基础上对于综合管廊横向振动台试验进行详细设计。首先,对于试验中所需的振动台、模型箱、测试元件等试验设备进行设计与选择。其次,对于试验中两大主要方面:模型相似比和模型配筋进行研究。在相似比设计中依据Bockinghamπ定理以加速度、密度、弹性模量、长度这4个参数为基本量,考虑采用忽略重力模型,从而推导出其余相似比。模型配筋设计中由于无论单层综合管廊还是双层综合管廊原型结构配筋均较为简单同时考虑受力的合理性,本次配筋采用等面积配筋率原则。再次,基于地下结构地震反应特点选用El-Centro波、Kobe波、Taft波,试验加载采用分段逐次加载,并给出详细的加载制度。最后,基于前期二维模型的数值模拟,给出单层及双层综合管廊的测试元件布置图。     

Behaviour of deep immersed tunnel under combined normal fault rupture deformation and subsequent seismic shaking

Immersed tunnels are particularly sensitive to tensile and compressive deformations such as those imposed by a normal seismogenic fault rupturing underneath, and those generated by the dynamic response due to seismic waves. The paper investigates the response of a future 70 m deep immersed tunnel to the consecutive action of a major normal fault rupturing in an earthquake occurring in the basement rock underneath the tunnel, and a subsequent strong excitation from a different large-magnitude seismic event that may occur years later. Non-linear finite elements model the quasi-static fault rupture propagation through the thick soil deposit overlying the bedrock and the ensuing interaction of the rupture with the immersed tunnel. It is shown that despite imposed bedrock offset of 2 m, net tension or excessive compression between tunnel segments could be avoided with a suitable design of the joint gaskets. Then, the already deformed (“injured”) structure is subjected to strong asynchronous seismic shaking. The thick-walled tunnel is modelled as a 3-D massive flexural beam connected to the soil through properly-calibrated nonlinear interaction springs and dashpots, the supports of which are subjected to the free-field acceleration time histories. The latter, obtained with 1-D wave propagation analysis, are then modified to account for wave passage effects. The joints between tunnel segments are modeled with special non-linear hyper-elastic elements, properly accounting for their 7-bar longitudinal hydrostatic pre-stressing. Sliding is captured with special gap elements. The effect of segment length and joint properties is explored parametrically. A fascinating conclusion emerges in all analysed cases for the joints between segments that were differentially deformed after the quasi-static fault rupture: upon subsequent very strong seismic shaking, overstressed joints de-compress and understressed joints re-compress—a “healing” process that leads to a more uniform deformation profile along the tunnel. This is particularly beneficial for the precariously de-compressed joint gaskets. Hence, the safety of the immersed tunnel improves with “subsequent” strong seismic shaking!     

Coordinative similitude law considering fluid‐structure interaction for underwater shaking table tests

Generally, when a model is made of the same material as the prototype in shaking table tests, the equivalent material density of the scaled model is greater than that of the prototype because mass is added to the model to satisfy similitude criteria. When the water environment is modeled in underwater shaking table tests, however, it is difficult to change the density of water. The differences in the density similitude ratios of specimen materials and water can affect the similitude ratios of the hydrodynamic and wave forces with those of other forces. To solve this problem, a coordinative similitude law is proposed for underwater shaking table tests by adjusting the width of the upstream face of the model or the wave height in the model test to match the similitude ratios of hydrodynamic and wave forces with those of other forces. The designs of the similitude relations were investigated for earthquake excitation, wave excitation, and combined earthquake and wave excitation conditions. Series of numerical simulations and underwater shaking table tests were performed to validate the proposed coordinative similitude law through a comparison of coordinative model and conventional model designed based on the coordinative similitude law and traditional artificial mass simulation, respectively. The results show that the relative error was less than 10% for the coordinative model, whereas it reached 80% for the conventional model. The coordinative similitude law can better reproduce the dynamic responses of the prototype, and thus, this similitude law can be used in underwater shaking table tests.