整体式桥台研究综述EI北大核心CSCD

整体式桥的桥身与桥台之间没有设置支座和伸缩缝,而是刚性连接为一体,从而能极大地节省桥梁全寿命周期的维护与维修费用。但是由于季节性温度波动导致桥身长度变化,桥台后土体随之受到水平方向循环加载作用。桥台后土压力的发展变化,成为整体式桥研究的重点。另外,对整体式桥台在地震作用下的动力反应还缺乏认识。该文首先系统总结了关于整体式桥台后土压力的相关研究成果,包括现场监测、缩尺模型实验、土单元应力路径实验、以及数值模拟等,揭示出在这种特殊循环作用下桥台后土压力的变化规律,并对土压力累积机理进行了探讨。然后,该文总结了整体式桥台在地震作用下动力响应的相关研究成果,指出由于桥台与桥身的刚性连接,桥身惯性力对桥台与土动力相互作用产生很大影响。     

加筋土整体式桥地震反应研究

加筋土整体式桥结合了整体式桥和加筋土的优点,是一种新型的桥梁形式,但目前对加筋土整体式桥的动力响应还很缺乏认识。该文对典型的单跨加筋土整体式桥的地震反应进行数值模拟,分析了地震峰值加速度对桥台弯矩、位移、筋材拉力的影响,并对比了另外3种桥型(整体式桥、加筋土简支梁桥、简支梁桥)在地震作用下桥台弯矩、位移和筋材拉力分布的区别。研究结果表明,地震作用下,简支梁桥台水平位移很大,有发生“落梁”的危险,整体式桥的水平位移更小,且加筋土整体式桥相比其他3种桥型抗震稳定性最高;地震时桥台弯矩和筋材拉力均显著增大;静力时每层筋材的最大拉力一般在筋材端部,而地震时是在筋材内部回填土滑移面附近。     

桩-土动力相互作用对连续梁桥半主动控制的影响研究

建立刚性地基和桩土相互作用两种模式的整体桥梁有限元模型，在桥梁支座部位设置线性粘滞阻尼器，计算桥梁在地震动作用下未施加控制和半主动控制的地震反应，探讨了桩土动力相互作用对连续梁桥地震反应半主动控制的影响以及半主动控制的减震效果。结果表明，桩土动力相互作用使连续梁桥自振周期增大，半主动控制的减震效果也相应增大，而最终的桥梁最大位移反应数值比较接近，最大内力数值更加减小，桩土动力相互作用对连续梁桥半主动控制系统减震效果的不利影响非常小，充分显示了半主动控制的优越性。     

斜交简支梁桥纵向地震碰撞反应精细化研究

为精细化分析简支斜交桥地震碰撞反应,首先基于Hertzdamp碰撞理论,采用开放式地震模拟软件OpenSees建立能够考虑碰撞过程中摩擦作用的简支斜交桥精细化计算模型;然后从动力特性、动力反应层面验证模型的可靠性;最后采用三维精细化计算模型分析斜度、摩擦对斜交简支梁桥纵向地震碰撞反应的影响。结果表明：梁体与桥台间最大碰撞力的产生位置随着斜度的变化而改变;最大碰撞力的大小不仅与斜度有关,而且与斜交桥梁端与桥台间摩擦系数也存在一定关系;摩擦作用削弱了斜度对梁端锐角处纵向最大位移的影响,大幅度减少上部结构峰值转角,使峰值转角最大值滞后在较大斜度时出现;不考虑摩擦作用会高估锐角处梁端纵向最大位移反应。     

挡土墙地震土压力的拟动力分析

基于均匀土层剪切梁理论建立了边坡水平地震动力运动方程,得到了边坡坡后土体的水平位移和加速度响应。将水平加速度应用到挡土墙地震土压力拟动力分析中,对坡体刚性假定和加速度沿坡高恒定的不足进行了改进,推导出主动、被动土压力的计算公式。结合实际工程分析了墙后填土面倾角、填土内摩擦角、挡墙与填土界面摩擦角对于总土压力大小的影响,并与传统的拟静力法和拟动力法进行了比较,结果表明:地震土压力随着时间呈一种类似正弦或者余弦状波动;随着墙后填土面倾角增大挡土墙地震总主、被土压力的也呈逐渐上升趋势;随填土内摩擦角、以及挡土墙与填土界面摩擦角的增大挡土墙地震总主动土压力逐渐减小,而被动土压力则随之增大;传统的计算方法由于计算值偏小而不安全。     

地震荷载下双腹板-顶底角钢连接半刚接钢框架的动力特性研究

利用大型有限元分析软件ANSYS对双腹板、顶底角钢半刚性连接的钢框架进行了三维弹塑性动力有限元分析。该分析采用了有限元实体建模,考虑了钢框架连接节点的非线性、几何非线性以及材料非线性等因素。通过有限元数值模拟分析得出了在地震荷载作用下,半刚性节点刚度的变化对钢框架的基本自振周期、楼层剪力、楼层位移、楼层加速度和节点的弯矩-转角关系的影响规律,并将部分数值模拟分析结果与拟动力试验结果进行对比,发现这两种研究方法所得结果基本一致。通过该文的分析,得出了节点刚度的变化对结构动力特性影响的一般规律,为今后高层钢结构设计和钢结构规范的修改提供了一定的理论依据。     

多向地震作用下土-框筒结构动力响应试验研究与数值模拟

为研究土—框筒结构动力相互作用体系在多向地震作用下的动力响应,对20层框筒结构的土—结构动力相互作用(SSI)模型和刚性基础(FB)模型分别进行了多向地震作用的振动台试验。通过试验数据的模态识别,分析了SSI和FB两种模型在不同工况下的固有频率、阻尼比和振型的差别。将不同烈度地震作用下SSI模型上部结构水平方向的峰值加速度、最大层间位移、最大层间位移角以及最大动应变进行对比,分析了单向水平和多向地震作用下SSI模型水平方向动力响应的差别;通过对比SSI和FB两种模型在多向地震作用下上部结构的竖向峰值加速度和层间位移,分析了土对结构竖直方向动力响应的影响;采用有限元软件ANSYS对试验模型和工况进行数值模拟,验证了试验结果的可靠性。研究成果可为框筒结构高层建筑的抗震性能研究提供参考。     

考虑土-桥台-上部结构相互作用的曲线桥抗震性能研究

对国内外历次地震中桥台震害进行了梳理。介绍了简化桥台模型、弹簧桥台模型、弹性梁单元桥台模型等几种针对城市桥梁桥台的典型数值模拟方法;以某立交G匝道曲线梁桥梁为工程背景,建立考虑土-桥台-上部结构相互作用的不同精细化程度的数值模型,开展人工地震动条件下的非线性动力时程反应分析,对比分析不同数值模型的计算误差;在此基础上选取合理数值模型,对桥梁曲率半径进行变参数研究,探讨墩底内力、墩梁相对位移以及台梁相对位移的变化规律。研究发现:提高土-桥台-上部结构相互作用的模拟精细化程度可以更准确地反映桥梁边墩的地震响应,特别是弹性梁单元桥台模型可综合考虑桥台的动力响应,值得推荐;考虑土-桥台-上部结构相互作用条件下,曲率半径越小,各桥墩横向内力及位移差异越明显,建议在进行曲线桥梁抗震设计中应予以重视。     

砂土中刚性挡墙不同主动变位模式任意位移土压力计算

已有模型实验及现场实测表明,刚性挡墙随着变位模式和位移量的变化,主动土压力合力和分布均发生改变,有时甚至与经典理论的线性分布有很大不同。采用中间状态系数定义非极限状态,提出了砂土中刚性挡墙不同主动位移模式下非极限状态土压力合力系数的计算公式;将墙后土体简化为连续非线性弹簧和刚塑性体的组合体作用在挡墙上,得到了不同位移模式任意位移的土压力分布和合力作用点高度。与已有理论方法和实验结果对比表明,该文方法在三种典型位移模式下与实验数据吻合更好。研究还发现,平动模式土压力呈线性分布,其合力随挡墙位移量的增大易趋于稳定并到达极限状态;绕墙底和绕墙顶转动模式下土压力合力随着位移增大只能接近极限状态且呈非线性分布。绕底转动时,土压力分布曲线逐渐向上凹,合力作用点高度趋于降低;绕顶转动时,分布曲线则逐渐向上凸,合力作用点高度趋于升高,墙顶附近表现出明显的土拱效应。     

动水压下减震连续梁桥随机优化及减震性能研究

地震作用下,跨海桥梁桥墩和周围水体的动力相互作用将对桥梁结构的动力响应产生较大影响。建立了考虑动水压力的2自由度连续梁桥简化分析模型,推导了其组合刚度和附加质量;提出了以墩顶位移方差最小为目标的黏滞阻尼器参数随机优化的Lyapunov方法。在此基础上,通过对设置黏滞阻尼器的某跨海连续梁桥简化模型进行了阻尼器参数优化,研究了动水压力和地震耦合作用下连续梁桥的减震性能。研究结果表明:动水压力增大了桥梁的地震反应,对桥梁的动力响应特性有较大影响。采用黏滞阻尼器可有效减小跨海连续梁桥的地震反应,改善桥梁结构抗震安全性能。     

Discrete element model study into effects of particle shape on backfill response to cyclic loading behind an integral bridge abutment

The discrete element method, implemented in a modular GPU based framework that supports polyhedral shaped particles (Blaze-DEM), was used to investigate effects of particle shape on backfill response behind integral bridge abutments during temperature-induced displacement cycles. The rate and magnitude of horizontal stress build-up were found to be strongly related to particle sphericity. The stress build-up in particles of high sphericity was gradual and related to densification extending relatively far from the abutment. With increasing angularities, densification was localised near the abutment, but larger and more rapid stress build-up occurred, supported by particle reorientation and interlock developing further away.     

桩柱式桥台土-结构相互作用抗震性能研究

为研究桩柱式桥台在地震过程中的结构响应规律。分析了现有研究的不足;以某立交G匝道曲线梁桥的桥台为工程背景,开展了基于实体的地震反应研究,并对地震过程中桥台背墙自底部向上各位置的位移时程曲线进行监测。在此基础上,对桥台高度、土体剪胀角度、土体与桥台接触条件三个因素对桥台地震响应的影响开展了研究。研究发现:随着桥台高度的增加,台背最大位移的放大系数逐渐变大;在该研究范围内,土体剪胀角对桥台地震位移响应影响不大;当不考虑桥台与土体分离效应时桥台顶部地震响应比考虑桥台与土体分离时的地震响应小,建议在进行桥台抗震设计中应准确模拟土体与桥台的接触界面状态。研究成果可为桥台结构的地震响应研究提供参考依据。     

Prediction Model of Abutment Pressure Affected by Far-Field Hard Stratum Based on Elastic Foundation Theory

In view of the three-dimensional dynamic abutment pressure, the influence of the far-field hard stratum (FHS) in deep, thick coal seams is indeterminant. Based on elastic foundation theory, a three-dimensional dynamic prediction model of the abutment pressure was established. Using this model, the dynamic change in the coal seam abutment pressure caused by the movement of the FHS was studied, and a method for determining the dynamic change range of the abutment pressure was developed. The results of the new prediction model of the abutment pressure are slightly higher than the measured values, with an error of 0.51%, which avoids the shortcomings of the results because the Winkler foundation model results are lower than the measured values and have an error of 9.98%. As time progresses, the abutment pressure and its distribution range are affected by the FHS movement, which has the characteristics of gradually increasing dynamic change until the FHS fractures. The peak value of the abutment pressure increases linearly with time, and the influence range increases with time following a power function with an exponent of less than 1. The influence range of the FHS movement on the abutment pressure ahead of the working face, behind the working face, and along the working face is 10 times, 25 times, and 17 times the mining thickness, respectively. According to the actual geological parameters, the dynamic change range of the coal seam abutment pressure was determined by drawing an additional stress curve and by determining the threshold value. These research results are of great significance to the partition optimization of the roadway support design of deep, thick coal seams.     

Time-wise variation of scouring at bridge abutments

Accurate estimation of the maximum possible depth of scour at bridge abutments is important in decision-making for the safe depth of burial of footings. Besides, investigation of the geometric features of scour holes around abutments provides useful information for the degree of scour counter-measure to be implemented against excessive scouring. Experiments have been performed to investigate time-dependent characteristics of scour holes around vertical wall abutments under clear water conditions with uniform bed materials. Temporal variations of scour depth and scour contours were measured. Using this information, an empirical relation was developed for temporal variation of scour depth. Additional relations were also derived for time-dependent volume and surface area of the scour holes around abutments. The findings of this study may provide useful information for preliminary design of abutment footings and placement details of armoring counter-measures, such as riprap.     

桥面铺装病害检测技术研究

在桥梁的全生命周期中,桥面板是最容易出现病害的部分。桥面铺装层常常由于施工方法选择不当、混凝土老化、钢筋锈蚀等原因产生各种病害,这对桥梁结构、使用性能都会造成不利影响,因此有必要对相关病害进行检测,并对桥面质量做出相关评价。本文介绍了国内外四种主要无损检测方法(半电池电位法、探地雷达法、冲击回波法、红外热成像法)的工作原理以及相应的检测设备,利用其中一种或几种方法能准确评估桥面板的恶化情况,对桥面板状况进行快速、无损检测,为实现桥面铺装的准确检测提供技术支持,从而减少结构病害,延长桥梁的使用寿命。     

Velocity and turbulence at a wing-wall abutment

Experimental investigation of the 3D turbulent flow field around a 45‡ wing-wall abutment, resting on a rough rigid bed, is reported. The experiment was conducted in a laboratory flume using the Acoustic Doppler Velocimeter (ADV). Profiles of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy and Reynolds stresses at different azimuthal planes are presented. Vector plots of flow fields at azimuthal and horizontal planes show the presence of a primary vortex associated with the downflow in the upstream side of the abutment and a wake vortex on the downstream side. The shear stresses acting on the bed around the abutment are estimated from the Reynolds stresses and velocity gradients. The data presented in this study would be useful to researchers for future development and comparison of theoretical models of flow fields around bridge abutments.     

Field and laboratory performance of a rectangular shaped glass fiber reinforced polymer deck

Fiber reinforced polymer (FRP) composites have been favorably noticed as state-of-the art construction materials, but sufficient material and structural data about FRP applications are not available. This study was intended to evaluate the applications and safety of FRP deck systems, which are developed by laboratory testing (static and fatigue tests), field application and testing of glass fiber reinforced polymer (GFRP) deck systems made of glass fiber and vinyl ester resin. The results show that the developed FRP deck systems have the expected strength and stiffness to replace the existing systems. FRP deck systems can effectively shorten the construction time and reduce the equipment required. In addition, it is determined that there is a need to evaluate the long-term structural behavior and durability of FRP deck systems in order to obtain comprehensive data for preparing the future design, manufacturing and construction materials.     

Time-dependent behaviour of widened reinforced concrete under-bridge

The paper reports on data acquired during 700 days of monitoring a widened reinforced concrete underbridge. The deck was monitored before, during and after widening and both portions of the deck, existing and new, were instrumented. Concrete strains were monitored by means of embedment and surface Vibrating Wire strain Gauges (VWG). Predicted creep, shrinkage, thermal and settlement strains were evaluated by means of a finite element analysis. The creep and shrinkage factors used were those from the simplified form of the B3 model [1]. Good agreement between calculated and measured longterm strains was observed at almost all gauge positions. From the analysis carried out, it was found that the stresses from the time dependent phenomena of creep, shrinkage and temperature, combined with those from the settlement of abutments, were greater than the magnitude of stresses obtained from the design live load.