某斜拉桥车辆荷载动力响应分析

利用空间有限元软件以某斜拉桥为实例,建立了空间分析模型,并在此基础上进行了车辆荷载作用下桥梁结构动力时程响应分析研究。根据车辆过桥动力响应分析的结果求得不同车速、不同截面上的冲击系数,并与规范方法计算的冲击系数进行对比。其结论不仅为该桥车辆荷载冲击系数的取值提供了重要的依据,同时也可为同类桥梁冲击系数的取值提供参考。     

宽幅钢箱梁桥冲击系数研究

合理的冲击系数取值对桥梁的安全性具有重要的意义。该文以某城市宽幅钢箱梁高架桥为背景,采用与设计荷载等效的车队,研究了此类桥梁冲击系数取值规律,分析了车速、行车位置、阻尼比和路面不平度对桥梁冲击系数的影响。研究结果表明:车辆对此类桥梁的冲击作用在横桥向存在显著的不均匀性,数值模拟得到的冲击系数超过规范取值26%,阻尼比、路面不平度、车速与车辆作用位置的耦合效应对冲击系数有显著影响。     

曲线连续梁桥在车辆制动作用下的动力响应

以某一匝道公路曲线连续箱梁桥为例,分析了该类桥梁的空间车桥耦合振动问题。用ANSYS软件模拟梁桥,选用典型的三轴空间车辆模型,采用模态综合法编制公路曲线车桥耦合振动响应MATLAB程序,获得了车辆制动作用下曲线连续梁桥的动力响应及冲击系数,研究了初速度、制动位置、制动力上升时间、桥面平整度等参数对冲击系数的影响。结果表明:车辆制动时,主梁最大挠度、挠度和内力冲击系数没有随初速度的增大而单调递增或递减,但均明显大于车辆以相同初速度匀速行驶时的结果,且可能超过规范值。在桥前半跨内制动时,挠度和跨中剪力冲击系数大于在后半跨度内制动情况,同时,当车辆制动位置大于半跨且越靠近支点时,车辆制动时挠度和内力冲击系数越接近匀速时的结果。随着曲率半径的增大,桥梁的挠度、弯矩和扭矩冲击系数逐渐减小,而剪力冲击系数逐渐增大;弯桥的挠度、弯矩和扭矩冲击系数大于直线桥结果,紧急制动易于加剧桥梁的振动。     

重型车辆与桥梁耦合振动及桥梁冲击系数的数值模拟研究

为了更合理地评估桥梁在重型车辆作用下的耦合动力响应,在有限元软件LS-DYNA的平台上,根据车桥振动实验数据,建立了具有11个自由度的3轴重型车辆和桥梁上部结构的车桥耦合系统有限元模型。对桥梁模型进行了模态分析,并对车桥耦合振动的三个工况进行了数值模拟,所得结果与实测数据一致,验证了有限元模型的合理性、可靠性。进一步利用该有限元模型进行车桥耦合体系参数分析,选择了车辆运行速度,桥梁桥台搭板的沉降以及桥梁跨度进行桥梁冲击系数的参数敏感性研究。参数分析结果表明:冲击系数整体上随车辆速度的增大而增大,同时有局部极大值的存在;冲击系数随桥台搭板沉降量的增大而增大;冲击系数呈现随桥梁跨度的增大而增大的趋势。     

简支梁桥在车辆荷载谱作用下的动力分析

编制程序VLS(Vehicle Load Spectrum)构造随机车辆荷载谱,利用有限元方法将不同运行状态下的随机车辆荷载谱加载于简支T型钢筋混凝土梁桥上,模拟桥梁在车辆荷载通过时的动力响应,得出了桥梁的位移时间历程曲线,同时分析了车速对桥梁冲击系数的影响。分析表明:车辆荷载谱作用下桥梁偏载作用明显;车流方向对桥梁振动的影响不大;密集运营状态下桥梁挠度是一般运营状态下的1.35倍左右;车速对桥梁冲击系数的影响非常复杂,冲击系数曲线在车辆高速和低速时均有峰值出现,总体上呈波动上升趋势。     

多层桥梁不同结构体系冲击系数特性分析

依据现行《公路桥梁通用规范》(2004年版)对车辆荷载冲击系数的计算公式,考虑桩土结构相互作用的影响,在4种结构体系动力基频计算基础上,将不同层的基频模态形式分为7种工况,分别计算出对应工况的汽车荷载冲击系数,并与相同体系单层桥的基频及冲击系数作比较,评价不同结构刚度优劣,总结了桩土结构相互作用及不同结构体系的多层桥梁的冲击系数的基本规律;论文对多层立交桥梁动力特性及活载动力冲击系数的研究成果可供此类桥梁设计参考,也可为同类桥梁的进一步研究提供经验技术支持和理论依据。     

大跨度钢管混凝土拱桥的动力冲击系数分析

在桥梁设计中,考虑车桥耦合振动的影响,精确确定结构受到的冲击效应是非常必要的。以茅草街钢管混凝土拱桥和常见的三轴货车为例,分别利用有限元法和动力平衡原理建立了结构分析模型和车辆的多刚体动力学模型。考虑桥面不平顺的影响,利用车桥系统的协调条件,用Newmark-β法求解振动微分方程,计算桥梁结构动力响应,分析桥梁冲击系数。结果表明:考虑车桥耦合振动的影响,冲击系数通常大于按规范计算的结果;冲击系数随路面不平度的增加而快速增大;车速对冲击系数的影响具有一定的随机性,通常存在某一车速使冲击效应最明显;吊杆截面面积的增加使冲击系数大致呈减小趋势,但具有不确定性。     

桥面不平整度对桥梁冲击系数的影响研究

采用有限元方法,研究了桥面不平整度对不同跨度及宽度简支梁桥冲击系数的影响,结果表明,桥面不平整对桥梁冲击系数影响显著,且与桥梁的宽跨比有关;当宽跨比小于1.0,桥面不平整时冲击系数随着桥梁宽跨比变化明显,而当宽跨比在2.0~3.0之间时,冲击系数的变化趋势减缓,相对稳定,宽跨比的影响可以忽略。     

载重汽车桥梁伸缩缝跳车动力荷载计算方法与影响因素分析

为分析载重汽车在桥梁伸缩缝处跳车时的动力荷载,提出一种基于分布式弹簧-阻尼单元的计算方法,该方法考虑了车辆-路面的接触长度和车轮的动力特性。车轮通过伸缩缝的过程分3个阶段来模拟,分别为下伸缩缝、跨伸缩缝、上伸缩缝,结合车辆有限元动力学分析,实现对车轮经过伸缩缝时的竖向动荷载的定量研究。对载重汽车经过单缝式伸缩缝的实例分析表明:①由分布式弹簧-阻尼单元计算得到的轮底位移比以往文献中的假设值小得多,动力荷载也将减小;②载重汽车伸缩缝跳车时的轮载冲击系数可能超过中国、欧洲桥梁规范的设计值,需要引起重视;③跳车最大轮载与伸缩缝宽度成正比,可以用减小伸缩缝宽度的方法降低冲击系数;④降低车速并不一定能降低冲击系数,轮载最大冲击系数往往发生在中等车速时;⑤伸缩缝跳车的最大冲击荷载主要分布在伸缩缝旁,因此只需要对伸缩缝附近的局部结构进行加强。     

双层变高钢桁连续梁桥车辆荷载效应研究

为了研究双层变高钢桁连续梁桥的车辆荷载效应,以福州市道庆洲大桥为工程背景,采用ANSYS软件建立桥梁有限元模型,考虑多种加载模式及工况并对模型加载,研究此种桥型关键位置和关键杆件的车辆冲击作用。结果表明：在上下层单独加载和上下层同时加载工况中,计算所得的挠度冲击系数均符合现行规范规定;在上下层同时加载时,变高度段的关键杆件相比于等高度段,轴力计算值更大,而轴力冲击系数更小;在单、双线轻轨加载工况的结果对比中可以发现,偏载对关键杆件轴力冲击作用较为明显。上下层同时加载计算值不能简单等效为上层和下层单独加载的线性叠加,前者普遍小于后者。     

公路桥梁汽车冲击系数对比研究

通过对比各国公路桥梁规范关于汽车冲击系数的计算公式,分析了各种冲击系数计算方法的差异,并就几座实际桥梁进行了对比研究,可以为公路桥梁结构设计提供参考,同时提出了公路桥梁汽车冲击系数研究的重点。     

Design criteria for impact factors based on dynamic on-site data in railway bridges

To evaluate the dynamic behaviours of bridges, many researchers have analysed interactions between vehicles and bridges with numerical methods instead of field loading tests. However, conventional numerical methods take too much time and cost to evaluate the impact factor of bridges in design and maintenance practice. The objective of this study was to propose improved design criteria by using impact factors based on natural frequency rather than span length of railway bridges using dynamic field load-carrying capacity test database. The improved design criteria use a different methodology than that outlined in the International Union of Railway specifications Code. Statistical regressions are applied to more easily estimate the natural frequency of a bridge with a span length of 20?m or longer with steel plate girder or truss superstructures. Calculated impact factors were compared to impact factors obtained from field measurements. Results indicated that the improved method could provide a very reliable estimation for actual impact factors. Since the suggested impact factor criteria are conservative, the proposed method can be used in design and management stages to consider dynamic effects of railway bridges in a more intuitive manner.     

简支梁桥位移与内力动力系数差异研究

动力系数是桥梁结构设计和检定中一个基本而关键的参数,其可以用位移放大系数来表示,也可以用内力(弯矩、剪力)放大系数来表示,而在桥梁的设计、检定工作中,并未注意到它们量值之间的区别.文中理论探讨了移动荷载列过桥模型的位移、内力放大系数的异同,以及不同动力系数沿简支梁桥跨长的变化规律,为区分制定桥梁动力系数的合理表达形式提供理论依据.并计算分析了车桥耦合模型与移动荷载列过桥模型的桥梁动力系数计算值的差异,结果表明应用移动荷载列模型计算简支梁桥动力系数可以得到安全可靠的结果,即可应用该模型解析解分析动力系数的主要影响因素.     

Application of a self-adaptive Kalman filter approach in alignment control for an extra long span rail transit cable-stayed bridge

Extra long span rail transit bridges are generally slender and sensitive to excitations, and alignment control of the bridges should be conducted during construction. In this paper, the self-adaptive Kalman Filter (SKF) method was applied to the alignment control of the second longest rail transit bridge in the world. Each influential factor of the bridge alignment was firstly introduced. Then, the finite-element analysis and field tests of the bridge were carried out to obtain the influential factors that induced bridge cambers quantitatively. Combining with the cambers, the SKF method was applied to the alignment control of the bridge. Comparisons of the SFK-predicted alignment with the target alignment or the field measured alignment were carried out. Results show the SKF for alignment control of bridges is feasible and reliable.     

桥梁吸力式沉箱基础承载特性试验研究

吸力式沉箱基础是跨海桥梁基础的一个新选择。基于桥梁基础的受荷特点,考虑不同的荷载作用方式,通过一系列模型试验研究了砂土中吸力式沉箱基础的承载特性。试验结果表明:沉箱的长度越长,吸力式沉箱基础的竖向承载力越大,侧壁摩阻力的贡献越大,而沉箱端部阻力可忽略不计;沉箱的长度越长,吸力式沉箱基础的水平承载力也越高,但相对于竖向承载力而言,基础的水平承载力很小,一般不超过其竖向承载力的5%。预加一定的竖向荷载,可显著提高吸力式沉箱基础的水平承载力,且预加的竖向荷载越大,基础的水平承载力越高,由于桥梁工程中基础承受的竖向荷载很大,所以有必要考虑这一因素对基础水平承载力的提高。     

现有铁路钢桥的评估

对现有铁路钢桥进行一系列的动力试验、加速度测量、评估、有限元模拟和安全指数计算。采用专门列车进行动力试验,并获取动力参数。这些参数还可用于建立桥梁的有限元模型。如果模型能够反映实际工况,就能用于计算每种工况下桥梁结构的安全指数。这些安全指数可用于计算杆件的破坏可能性,因此可采用本模型评估桥梁的可靠性。通过了解现有桥梁结构的实际工况,本研究可为新的货运列车重级荷载研究提供可靠依据。     

Assessment of existing steel railway bridges

A series of dynamic tests, acceleration measurements, evaluation, finite element model simulations and safety index calculations were performed on existing steel railway bridges giving service on railway network. Dynamic tests were fulfilled by using a special test train on these bridges to obtain the dynamic parameters and these parameters were then used to refine the finite element models of the bridges. Once the models have been updated to represent the actual condition, safety indices were calculated for structural components of the bridges for each proposed loading condition. These safety indices were used to calculate failure probabilities of structural members. As the final step, system reliability of the bridges was evaluated based on proposed system models of the bridges. It is believed that this study will provide a reliable background for proposed heavier axle loads resulting from new freight trains by realizing the current condition of bridge structures.     

厦漳跨海大桥风速测量与研究

随着桥梁建设的不断发展,桥梁的跨径越来越大。桥梁所受到的自然灾害也越来越多。风作用下桥梁结构的安全性已成为人们极为关注的重要问题,同时也给桥梁风工程研究带来更大的机遇和挑战。21世纪的跨海大桥工程中出现了许多超大跨度的斜拉桥和悬索桥,在台风多发的海域建造柔性的超大跨度桥梁,抗风安全将是最重要的控制因素。本文采用FY-W2风速风向仪对福建厦漳跨海大桥进行风速测量,为后期桥梁风雨振的研究提供数值依据。     

Critical issues,condition assessment and monitoring of heavy movable structures: emphasis on movable bridges

In this paper, a relatively less studied class of structures is presented based on the research conducted on Florida's movable bridges over the last several years. Movable bridges consist of complex structural, mechanical and electrical systems that provide versatility to these bridges, but at the same time, create intermittent operational and maintenance challenges. Movable bridges have been designed and constructed for some time; however, there are fewer studies in the literature on movable bridges as compared to other bridge types. In addition, none of these studies provide a comprehensive documentation of issues related to the condition of movable bridge populations in conjunction with possible monitoring applications specific to these bridges. This paper characterises and documents these issues related to movable bridges considering both the mechanical and structural components. Considerations for designing a monitoring system for movable bridges are also presented based on inspection reports and expert opinions. The design and implementation of a monitoring system for a representative bascule bridge are presented along with long-term monitoring data. Various movable bridge characteristics such as opening/closing torque, bridge balance and friction are shown since these are critical for maintenance applications on mechanical components. Finally, the impact of environmental effects (such as wind and temperature) on bridge mechanical characteristics is demonstrated by analysing monitoring data for more than 1000 opening/closing events.     

Typical diseases of a long-span concrete-filled steel tubular arch bridge and their effects on vehicle-induced dynamic response

A long-span concrete-filled steel tubular (CFST) arch bridge suffers severe vehicle-induced dynamic responses during its service life. However, few quantitative studies have been reported on the typical diseases suffered by such bridges and their effects on vehicle-induced dynamic response. Thus, a series of field tests and theoretical analyses were conducted to study the effects of typical diseases on the vehicle-induced dynamic response of a typical CFST arch bridge. The results show that a support void results in a height difference between both sides of the expansion joint, thus increasing the effect of vehicle impact on the main girder and suspenders. The impact factor of the displacement response of the main girder exceeds the design value. The variation of the suspender force is significant, and the diseases are found to have a greater effect on a shorter suspender. The theoretical analysis results also show that the support void causes an obvious longitudinal displacement of the main girder that is almost as large as the vertical displacement. The support void can also cause significant changes in the vehicle-induced acceleration response, particularly when the supports and steel box girder continue to collide with each other under the vehicle load.