Experimental study of hollow rectangular bridge column performance under vertical and cyclically bilateral loads

To investigate the seismic performance of hollow reinforced concrete(RC) bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending,five specimens were tested.A parametric study is carried out for different axial load ratios,longitudinal reinforcement ratios and lateral reinforcement ratios.The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity,which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns.Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations,and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance.However,the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design.The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations,and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges(JTG/T B02-01-2008).The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns,and it was much less than those specified in the current JTG/T.Thus,the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.     

蜂窝状钢骨混凝土L形柱抗震性能的试验研究

为了考察轴压比对蜂窝状钢骨混凝土L形柱抗震性能的影响,本文进行了3根不同轴压比的蜂窝状钢骨混凝土L形柱的低周往复水平荷载试验,研究了该L形柱的破坏形态、滞回特性、延性、黏滞阻尼系数等抗震性能.研究表明:蜂窝状钢骨能增强钢骨与混凝土间的黏结能力,提高其协同工作与整体受力性能.蜂窝状钢骨的存在,延缓了L形柱的刚度退化,提高了延性,增强了结构的耗能能力及抗震性能.轴压比对该新型构件的破坏形态及抗震性能影响明显.随着轴压比的增大,构件的破坏形态由类似于剪切破坏向轴压破坏形态转变.轴压比越大,构件的极限承载力越大,但延性与黏滞阻尼系数越小,耗能能力越低,抗震性能越差.研究还发现,该新型构件的正、反方向承载力及延性有所差别.     

汶川地震失稳机制的数值模拟研究

考虑断层的软化特性,建立垂直于龙门山断裂带并包含四川盆地和川西高原在内的汶川地震不稳定性地震力学模型.采用有限元方法计算得到了描述整个岩石力学系统稳定性状态和过程的平衡路径曲线.在此基础上,采用稳定性理论研究了汶川地震从孕育到发生的过程,讨论了断层倾角和断层材料参数对地震失稳的影响.数值模拟结果显示,系统只存在稳定的断层无震滑动和不稳定的地震失稳2种状态.断层倾角、初始内摩擦系数、初始黏聚力和强度曲线形状参数的增加会导致系统趋向不稳定的地震失稳状态.而强度曲线胖度参数的增加有助于系统进入稳定的断层缓慢无震滑动状态.地震失稳前,在平衡路径曲线的应力峰值点和失稳点之间,断层错动加速,应变能开始释放并且应力开始减小,是失稳的前兆.最后在失稳点发生应力突跳,地震发生,其间伴随应变能的急剧释放、应力降和断层突然错动.无论是稳定的断层无震滑动还是不稳定的地震失稳,系统重新进入应力和应变能增加状态后,应力和应变能的增速由远场加载速度、岩石力学系统的结构和围岩材料属性决定,与断层软化特性参数无关.

     

长输管道悬索跨越结构抗震性能的试验研究

本文以一实际长输管道悬索桥跨越工程为原型,制作了缩尺比例为1：8的试验模型,对试验模型的模态、抗震性能进行了白噪声和不同强度的El Centro波输入下的试验研究以及有限元分析。试验结果表明：试验模型的自振频率随地震强度的增加而降低,最大降低20％;试验模型的最大地震反应为塔架顶部的纵向振动,加速度达1．75g,折合原型为1．62g,动力放大系数为5．47。管道的地震反应以横向振动为主,最大加速度达1．21g,折合原型结构为1．12g,动力放大系数为2．63。试验过程中,输入的最大横向和竖向地震反应加速度折合原型均超过0．4g,但模型构件未发生破损,结构体系保持稳定,表明悬索跨越结构具有抗御地震烈度9度而保持使用功能的能力。不同强度的地震动作用下,钢索与管道的内力分配改变,钢索具有调节结构体系构件受力的重要机能,有限元分析结果与试验结果比较吻合。     

Experimental research and finite element analysis of bridge piers failed in flexure-shear modes

In recent earthquakes, a large number of reinforced concrete （RC） bridges were severely damaged due to mixed flexure-shear failure modes of the bridge piers. An integrated experimental and finite element （FE） analysis study is described in this paper to study the seismic performance of the bridge piers that failed in flexure-shear modes. In the first part, a nonlinear cyclic loading test on six RC bridge piers with circular cross sections is carried out experimentally. The damage states, ductility and energy dissipation parameters, stiffness degradation and shear strength of the piers are studied and compared with each other. The experimental results suggest that all the piers exhibit stable flexural response at displacement ductilities up to four before exhibiting brittle shear failure. The ultimate performance of the piers is dominated by shear capacity due to significant shear cracking, and in some cases, rupturing of spiral bars. In the second part, modeling approaches describing the hysteretic behavior of the piers are investigated by using ANSYS software. A set of models with different parameters is selected and evaluated through comparison with experimental results. The influences of the shear retention coefficients between concrete cracks, the Bauschinger effect in longitudinal reinforcement, the bond-slip relationship between the longitudinal reinforcement and the concrete and the concrete failure surface on the simulated hysteretic curves are discussed. Then, a modified analysis model is presented and its accuracy is verified by comparing the simulated results with experimental ones. This research uses models available in commercial FE codes and is intended for researchers and engineers interested in using ANSYS software to predict the hysteretic behavior of reinforced concrete structures.     

环境温度对桥梁结构动力特性影响的试验研究

本文以两跨钢-混凝土连续组合梁模型和刚架拱桥的环境振动测试为基础,分析了环境温度变化对桥梁动力特性的影响。结果表明:环境温度变化会引起桥梁动力特性的显著变化,同时温度变化对结构动力特性的影响受到桥梁边界约束条件的很大影响,此类测试和分析对桥梁健康监测与损伤识别具有借鉴意义。     

Forces acting on bridge abutments over liquefied ground

Large earthquake-induced displacements of a bridge abutment can occur, when the bridge is built on a floodplain or reclaimed area, i.e., liquefiable ground, and crosses a water channel. Seismic responses of a bridge abutment on liquefiable ground are the consequence of complex interactions between the abutment and surrounding soils. Therefore identification of the factors dominating the abutment response is important for the development of simplified seismic design methods. This paper presents the results of dynamic three-dimensional finite element analyses of bridge abutments adjacent to a river dike, including the effect of liquefaction of the underlying ground using earthquake motions widely used in Japan. The analysis shows that conventional design methods may underestimate the permanent abutment displacements unless the following two items are considered: (1) softening of the soil beneath the liquefiable layer, due to cyclic shearing of the soil surrounding the piles, and (2) the forces acting on the side faces of the abutment.     

浅部不均匀体对目标体电阻率异常影响的研究

浅部不均匀体能使电阻率测深曲线产生严重的畸变. 为了从根本上消除浅部不均匀体的干扰,本文采用三维有限元数值模拟的方法,计算出浅部不均匀体异常和混合体（目标体+不均匀体）异常,通过一定的校正方法,把不均匀体影响从混合异常中校正掉,从而实现对浅部不均匀体影响的定量校正.     

精细化纤维梁柱单元模拟分析平台FENAP的开发

为精细化模拟桥梁结构的非线性行为,在深入分析纤维梁柱单元模型原理的基础上,本文基于ABAQUS建立了钢筋混凝土精细化纤维梁柱单元模拟平台FENAP,开发了与其相适应的材料模型库FENAP/MAT,涵盖了多种材料本构模型,能够有效考虑构件的刚度退化和强度退化等损伤效应,以及模拟轴力和弯矩的多维耦合效应等复杂非线性动力行为,且可考虑箍筋对混凝土的约束作用等。利用该FENAP平台数值模拟了一个钢筋混凝土矩形截面悬臂梁,进行了Pushover分析,考虑了箍筋对核心混凝土约束效应的影响,并与OpenSEES的计算结果进行对比。结果表明:FENAP平台可有效模拟桥梁构件的多种复杂非线性行为,且具有很好的计算效率和求解精度。     

用于阻尼器结构不锈钢丝金属橡胶元件力学性能试验研究

为研究金属橡胶材料用作土木工程结构消能减震阻尼器的力学性能,本文针对不同成型密度的金属橡胶阻尼元件,分别在静力、动力荷载作用下进行了压缩性能试验,测试加载幅值、循环加载次数、元件成型密度、动力加载频率等因素对金属橡胶元件阻尼耗能的影响规律。研究结果表明,金属橡胶材料有着良好的弹性和阻尼特性,其滞变耗能能力随着成型密度、加载幅值的增加而增大;加载频率和加载次数对金属橡胶滞变性能几乎没有影响。     

Experimental and theoretical study on two types of shape memory alloy devices

This study proposes two types of shape memory alloy (SMA)‐based devices, the tension‐SMA device (TSD) and the scissor‐SMA device (SSD), for the increase of stiffness. Both devices employ superelastic NiTi wires with a diameter of 1.2 mm. Performance tests to study pseudoelastic behavior of NiTi wires find that NiTi wire's pseudoelastic property is insensitive to loading frequency within the meaningful frequency range of most structures in civil engineering. The detailed design of TSD and SSD using NiTi wire is then presented accordingly. Shaking table tests of a scaled 5‐story steel frame incorporated with TSDs and SSDs, respectively, in the first story are carried out. The experimental results indicate that both SMA devices can effectively reduce building seismic response. SSDs achieve greater response reduction than TSDs due to their displacement magnification configuration. The seismic response of the building model with and without SMA devices is numerically simulated and the simulation results demonstrate that they are in good agreement with the experimental results. Finally, it is identified that by using the wavelet transform method the structures incorporated with SMA devices exhibit nonlinear behavior and the time‐dependent characteristics of natural frequency during earthquake excitation. Copyright © 2007 John Wiley & Sons, Ltd.     

钢筋混凝土长肢一字形截面柱抗震性能试验研究

对4个1／2缩尺的长肢一字形截面柱构件进行了低周反复荷载下的抗震性能试验研究,构件截面高厚比分别为4．0、4．5与5．0,分别按柱子配筋与按剪力墙配筋两种配筋方式进行设计。通过试验分析了长肢一字形截面柱的承载力、刚度、延性、耗能、滞回特性等,并提出了抗震设计建议。     

新型钢柱脚抗震性能分析

为研究在普通露出型钢柱脚上安装楔块装置的新型钢柱脚的抗震性能,采用通用有限元软件ANSYS建立了该柱脚两种常用形式下的三维实体模型,在低周反复加载作用下对其进行了抗震性能分析。根据有限元分析所得该柱脚的M-θ滞回曲线,及M-θ骨架曲线,对新型柱脚耗能能力和延性性质做了相关研究。同时,对比分析了不同轴压和不同形式柱脚的力学性能。结果表明:新型钢柱脚的恢复力特性为非滑移型,其M-θ滞回曲线饱满,并有较好耗能和延性性能,显示出良好的抗震性能。研究结果对新型柱脚的设计和应用提供了相关参考。     

较小剪跨比带暗柱T形柱抗震性能试验研究

提出了带暗柱Ｔ形柱,进行了４根较小剪跨比的Ｔ形柱抗震性能试验,分析了轴压比对承载力,刚度,片断生的影响以及设暗柱对提高Ｔ表柱抗震能力的作用。最后进行了理论计算,计算值与实测值符合较好。     

国家体育场柱脚锚固性能试验研究

大跨结构柱脚锚固性能是抗震设计的关键之一。国家体育场柱脚为钢柱脚,该钢柱脚锚固于钢筋混凝土承台中,其受力复杂,以往国内外类似的试验很少。笔者共进行了4个钢筋混凝土承台-钢柱脚试件锚固性能的试验研究,本文介绍其中2个几何尺寸较大的钢筋混凝土承台-钢柱脚试件锚固性能的试验研究概况,1个试件为混凝土承台中配置抗拔钢筋的试件,1个为混凝土承台中未配置抗拔钢筋的试件。通过单向重复加载下的钢柱脚锚固性能试验,对试件的锚固承载力、延性、合理配筋型式等进行了研究。试验结果表明,混凝土承台中配置抗拔钢筋的试件与未配置抗拔钢筋的试件相比其锚固承载力和延性显著提高。在试验基础上,建立了柱脚锚固承载力计算的桁架模型,计算结果与实测结果符合较好。     

较小剪跨比带暗柱十字形柱抗震性能试验研究

提出了带暗柱十字形柱,进行了４根较小剪跨比的十字形柱抗震性能试验,分析了轴压比对承载力,刚度,延性的影响,以及设暗柱对提高十字形柱抗震能力的作用,最后进行了理论计算,计算值与实测值符合较好。     

Damping/global energy balance in FE model of bridge foundation lateral response

A global energy analysis is presented of three static unloading–reloading foundation lateral loading cycles, calculated using the nonlinear finite element (FE) program DYNAFLOW. This simulates seismic action on an offshore pier foundation in the Rion-Antirion Bridge in Greece, located in deep-sea water (65 m). A cyclic horizontal force is applied at a height of 30 m to a rigid raft 78 m in width placed on the surface of an idealized 2-layer soil profile consisting of a 3.5 m man-made gravel layer over soft deep natural clay, with elastic vertical steel inclusions reinforcing the soil. Results of the two-dimensional FE run are used for the energy analysis. It is verified that for the three cycles, the sum of energies associated with the external forces and moments, mostly dissipated through hysteresis loops, is about equal to the sum of the total internal energies dissipated or stored in the system. For the smaller loops almost all energy is dissipated in the soil, while for the largest loop about half of the energy is dissipated by horizontal sliding at the raft-soil interface. Global damping ratios obtained from the areas of the horizontal and rocking moment hysteresis loops are about double of those computed from the corresponding static backbone curves using the Masing criterion.     

Experimental study of the seismic behavior of partially concrete‐filled steel bridge piers under bidirectional dynamic loading

The seismic behavior of steel bridge piers partially filled with concrete under actual earthquake conditions was investigated by using 20 square section specimens subjected to static cyclic loading tests and single‐directional and bidirectional hybrid loading tests. Acceleration records of two horizontal NS and EW directional components for hard (GT1), medium (GT2), and soft grounds (GT3), obtained during the 1995 Kobe earthquake, were adopted in dynamic tests. Experimental results clearly showed that maximum and residual displacements under actual earthquake conditions cannot be accurately estimated by conventional single‐directional loading tests, especially for GT2 and GT3. A modified admissible displacement was proposed on the basis of bidirectional loading test results. The concrete fill can effectively improve the seismic resistance performance if the concrete inside the steel bridge piers is sufficiently high in quantity. Copyright © 2013 John Wiley & Sons, Ltd.     

主动变刚度-阻尼系统预测最优控制的理论与试验研究

介绍了一种具有自主知识产权的新型开关控制型半主动控制系统——主动变刚度.阻尼(AVS.D)系统的减振控制机理,建立了AVS.D结构振动控制体系的运动方程。为了合理补偿AVS.D系统实时控制过程中不可避免地存在着的控制时滞,本文提出一种预测最优控制算法,推导了其开关控制律。为了检验AVS.D系统的减震控制效果及预测最优控制算法的有效性,我们设计研制出AVS.D装置,编制了AVS.D系统预测最优控制的实时控制软件,在某单层钢框架模型上进行了AVS.D系统的模拟地震振动台试验,比较了不同控制方式时的减震效果。研究结果表明,本文所提出的预测最优控制算法是非常有效的,可推广应用于所有开关控制型半主动控制系统。AVS.D系统具有反应放大功能,经济可靠、安全有效,可望有较好的工程应用前景。     

装配式圆钢管柱-钢梁节点抗震性能试验研究

为验证新型装配式圆钢管柱-钢梁节点的破坏模式及抗震性能,进行了3个十字形节点的低周反复循环加载试验。研究了不同试件节点的破坏模式、滞回性能、延性及耗能性能等。试验结果表明:试件的位移延性系数为3.38~3.44,能量耗散系数为1.72~2.25,节点具有良好的滞回性能、延性及耗能能力,满足现行规范设计要求。建议在采用新型装配式节点时,梁柱连接处可同时采用加强型连接或骨式连接,以获得良好的抗震性能。