Framework of vehicle–bridge–wind dynamic analysis

This paper presents a framework of dynamic analysis of coupled three-dimensional vehicle–bridge system under strong winds. A general formulation of this system is introduced to simulate a series of vehicles consisting of different numbers and different types of vehicles running on bridges under hurricane-induced strong winds. Each vehicle is modeled as a combination of several rigid bodies, axle mass blocks, springs, and dampers, considering wind and road roughness loads. With this vehicle–bridge model, coupled dynamic analysis of vehicles running on bridges is conducted with a numerical example. Effects of driving speeds on the dynamic performance of the vehicles as well as the bridge are discussed. It is found that the driving speeds mainly affect the vehicle's vertical relative response while they have insignificant effect on the rolling response of vehicles. Vehicle's absolute response is dominated by the bridge response when wind speed is high, while it is dominated by road roughness when the wind speed is low. Detailed accident analysis of vehicles on bridges under strong winds will be reported in an accompanying paper.     

风-汽车-桥梁系统空间耦合振动研究

为了考虑侧风引起的车轮相对于桥面的侧向相对滑动,在车轮与桥面之间引入了一个特殊阻尼器,这个阻尼器的阻尼系数依赖于车辆与桥梁的竖向耦合运动。在综合考虑路面粗糙度、车辆悬挂系统以及车轮相对于桥面侧向相对滑动的基础上,提出能够考虑桥梁的静风响应、抖振响应、汽车-桥梁耦合振动、系统的时变特性以及结构几何非线性和气动荷载非线性影响的风-汽车-桥梁系统空间耦合振动分析模型,编制了相应的分析程序。该程序既可以预测不同路面粗糙度,车速以及干、湿、雪、冰路面状况下行驶于桥梁上车辆的行车安全性,也可以评价低风速下车辆驾驶舒适度以及侧风和车辆移动荷载对桥梁振动的影响。     

Dynamics of wind-rail vehicle-bridge systems

An analytical model for dynamics of wind-vehicle-bridge (WVB) systems is presented in this paper in the time domain with wind, rail vehicles and bridge modeled as a coupled vibration system. The analytical model considers many special issues in a WVB system, which include fluid-solid interaction between wind and bridge, solid contact between vehicles and bridge, stochastic wind excitation on vehicles and bridge, time dependence of the system due to vehicle movement, and effect of bridge deck on vehicle wind load and vice versa. The models of wind, vehicles and bridge are presented with wind velocity fluctuations simulated using the simplified spectral representation method, with vehicles modeled as mass-spring-damper systems, and with bridge represented by a finite element model. The interactions between wind and bridge are similar to those considered in conventional buffeting analysis for long span bridges. In considering difficulties in measuring aerodynamic coefficients of moving vehicles on bridge deck, the cosine rule is adopted for the aerodynamic coefficients of moving vehicles to consider yaw angle effect, and expressions of wind forces on moving vehicles are then derived for engineering application. To include mutual effects of wind loads, aerodynamic parameters of vehicles and bridge deck are measured, respectively, using a composite section model test and a specially designed test device. The dynamic interaction between vehicle and bridge depends on both geometric and mechanical relationships between wheels of vehicles and rails on the bridge deck. The equations of motion of the coupled WVB system are derived and solved with a nonlinear iterative procedure. A cable-stayed bridge in China is finally selected as a numerical example to demonstrate dynamic interaction of the WVB system. The results show the validity of the present model as well as wind effects on the rail vehicles and the bridge.     

侧风作用下静动态车-桥系统气动特性数值模拟研究

我国现阶段正处于轨道交通建设的高峰时期,线路中桥梁占有相当大的比重,车辆在桥梁上运行时构成车-桥系统共同承受侧向风的作用,车辆和桥梁间存在着显著的相互气动影响。基于数值模拟方法,对侧向风作用下车-桥体系的空气绕流场进行静动态模拟分析,将静态数值模拟气动力系数与风洞试验结果进行对比,基于动态气动统流特性,提出将桥面上方流场分为6个特征区域,并进一步分析风速和车速对车-桥系统气动特性的影响。分析表明,体系绕流状态具有三维特性,气动力随着车速和风速变化显著。研究结论对车-桥系统绕流及静动态气动荷载的确定具有一定的参考价值。     

Iterative Equation Solver for Bridge Analysis Using Neural Networks

A technique for enhancing finite-element analysis equation solvers for particular problem domains, i.e., particular classes of structures such as highway bridges, is presented. The technique involves merging artificial neural networks, used as a domain knowledge-encoding mechanism, together with a preconditioned conjugate gradient iterative equation-solving algorithm. In the algorithm, neural networks are used to seed the initial solution vector and to precondition the matrix system using customizable and trainable neural networks. A case study is presented in which the technique is applied to the particular domain of flat-slab highway bridge analysis. In the case study, neural networks are trained to encode the load-displacement relationships for concrete flat-slab highway bridges. Analytical load-displacement data are generated using finite-element analyses and subsequently used to train neural networks. Acting collectively, the neural networks predict approximate displacement patterns for flat-slab bridges under arbitrary loading conditions.     

连续刚构桥墩动力性能分析研究

以高速公路上1座连续刚构桥为例,分别采用等截面、变截面箱墩研究其动力性能。通过有限元程序对其进行动力特性和反应谱分析后结果表明：箱型薄壁墩自身刚度大;桥梁以桥面系振动为主;变截面高桥墩能增加连续刚构桥的稳定性;在高烈度地区采用变截面高桥墩可减弱地震响应。     

Reliability based analysis of the crosswind stability of railway vehicles

The computational models used to assess the crosswind stability of railway vehicles by multibody simulation (MBS) are affected by large uncertainties. Especially, the aerodynamic loads acting on the vehicle are difficult to model and the respective parameters cannot be easily acquired. Such uncertainties are usually neglected in the safety norms even though their effects on the risk assessment can be very large. In this paper the problem is tackled by modelling the most influential but uncertain parameters as stochastic variables. The resulting task can be efficiently managed by reliability techniques, mainly inherited from structural mechanics. This finally leads to the substitution of the conventional characteristic wind curve (CWC) by the probabilistic characteristic wind curve (PCWC). The proposed approach is referred to the most recent European norms for crosswind stability and exemplified on the test case of a German high speed train (ICE2).     

Bridge dynamics and aerodynamics: design and practical requirements for high structural performance and safety

Abstract

Bridge dynamics and aerodynamics have been in many cases overlooked in the design stages and consequent low behaviour performance and safety margin have been not rarely observed and detected by means of structural monitoring of the bridge soon after it is brought into full service. In this paper, a selection of important issues regarding design and practical requirements for a high structural performance of main components of conventional and cable-stayed bridges are pointed out and discussed briefly. The paper encompasses sections describing some relevant aspects regarding the numerical and physical modelling of the structural system and the mathematical modelling of the dynamic and aerodynamic loads. Special attention is given to the dynamic interaction between vehicles and structures of roadways and railway bridges and also to the aeroelastic analyses of bridges′ behaviour and their consequent implications on the structural performance of a bridge during its service life. Case examples of actual bridges subjected to dynamic forces produced by the traffic of heavy vehicles and by the wind action are explored to depict the main sources of problems which in some cases caused structural misbehaviour. Some practical measures to improve the behaviour and performance of bridge structures are outlined.     

Effect of approach span condition on vehicle-induced dynamic response of slab-on-girder road bridges

The present study investigates the effect of approach span conditions on a bridge’s dynamic response induced by moving vehicles. After developing a 3D bridge–vehicle interaction model for numerical prediction, a dynamic test on a full scale slab-on-girder bridge is conducted with dump trucks to validate the developed numerical methodology. A wooden plank is used to simulate the large faulting between the bridge deck and the approach slab. With consideration of the road surface profile and approach span condition, the predicted dynamic response of the bridge is compared to the experimental results, and they show a satisfactory agreement. The numerical model is also applied to investigate the effect of the approach span condition on the dynamic behavior of the bridge induced by the AASHTO HS20 truck. A parametric study is eventually conducted by changing the road surface condition and the faulting value. The faulting condition of the approach span is found to cause significant dynamic responses for the slab-on-girder bridges and to have a considerable effect on the distribution of impact factors along the transverse and longitudinal directions. Furthermore, impact factors obtained from the numerical analyses are compared with those values specified in the AASHTO codes.     

Effects of bridge motion and crosswind on ride comfort of road vehicles

Ride comfort of road vehicles running on the ground has been extensively investigated as one of the main criteria in the design of road vehicles. The information on the ride comfort of road vehicles running on a long span cable-supported bridge under crosswind is, however, very limited. This paper presents an evaluation of ride comfort of road vehicles running on a long span cable-stayed bridge under crosswind. The ride comfort criteria for road vehicles are briefly reviewed first. The principle of mathematical modeling and the equation of motion of a coupled road vehicle–bridge system under crosswind are then introduced. The framework proposed is finally applied to a group of high-sided road vehicles running on a real cable-stayed bridge under crosswind as a case study. Ride comfort of the high-sided road vehicle under various conditions of road roughness, vehicle speed, and crosswind speed is investigated for the vehicle running on either the ground or the cable-stayed bridge with and without crosswind. The results show that the crosswind influences the ride comfort of the vehicle in the lateral direction while the bridge motion affects the ride comfort of the vehicle in the vertical direction.     

移动车辆荷载作用下钢管混凝土拱桥振动的舒适性分析

以某主跨110 m的自锚式钢管混凝土中承桁架拱桥为对象,分析了该桥的自由振动特性和车辆荷载作用下主跨桥面系振动的特性,并依据人行桥的舒适度指标评价了振动的舒适性.     

风环境对行车安全影响和对策初步研究

本文讲述侧向风对汽车行驶的安全和稳定会产生不良影响。桥梁风障是解决桥面行车安全和舒适性问题的主要手段,尤其是在强侧风作用下,风障对保证轻型车辆行驶安全可能是必需的。     

车辆荷载及盾构施工对既有快速路基坑三维数值模拟

以杭富城际铁路盾构下穿既有快速路基坑为研究背景,利用PLAXIS 3D对地面车辆动荷载及盾构施工下穿既有快速路基坑进行三维数值模拟,分析对既有快速路基坑力学性状的影响.研究表明,车辆动荷载和盾构施工对既有基坑的影响主要体现在对周围土体的扰动上,盾构施工主要影响基坑底板,使基坑底部隆起变形,车辆荷载主要影响基坑上部,车辆...     

Improvement effects of bottom lateral bracings on dynamic performance of curved steel twin I-girder bridges under running vehicles

The torsional stiffness of curved twin I-girder bridges is very low, which may lead to a vulnerability to eccentric dynamic loads. This study is intended to investigate the improvement effect of bottom lateral bracings on dynamic performance of curved twin I-girder bridges under running vehicles, using a developed numerical approach. In this approach, to conduct the running vehicle-bridge interaction analysis, finite element method is used to create the detailed models of both the curved bridge and the running vehicle. Parametric studies are carried out using these numerical models to investigate the effect of bottom lateral bracings on the dynamic performance of the curved bridge under running vehicles. The numerical results indicate that the proposed bottom lateral bracing systems can increase the torsional stiffness of the bridge, whose increasing rate depends on the type of bracing configuration. The bottom lateral bracings can also distribute dynamic loads smoothly between the two main girders, which leads to a more stable structure.     

应用碳纤维缆索的大跨度悬索桥抗风稳定性研究

为了探讨碳纤维复合材料缆索在大跨度悬索桥中应用的可能性,以主缆等轴向刚度为原则,拟定了一座主跨为1490m的碳纤维复合材料主缆悬索桥,并运用三维非线性计算理论进行了空气静力和动力稳定性分析。通过与同跨度钢主缆悬索桥的比较,讨论了不同主缆材料对大跨度悬索桥抗风稳定性的影响。分析结果表明:大跨度悬索桥采用碳纤维复合材料主缆后,静风作用下结构的变形增大,但其静风稳定性却与钢主缆悬索桥基本接近;由于结构自振频率特别是扭转频率有显著的提高,使得其空气动力稳定性要比钢主缆悬索桥好。因此从抗风稳定性角度而言,大跨度悬索桥采用碳纤维复合材料主缆是可行的,但是主缆截面尺寸的确定应采用等轴向刚度的准则。     

Reliability-based design of medium mast lighting structural supports

Rural intersections and interchanges often require lighting for driver safety. Although high mast lighting supports, sometimes as tall as 50 m have been installed in many locations, it is becoming apparent that light pollution to nearby residences is an issue. As a response to this problem, the Colorado Department of Transportation is moving towards the use of medium mast lights which are typically 15–20 m in height. This article presents the results of a numerical investigation to develop reliability-based design charts as a function of several key design variables and the mean wind velocity at a site. These medium-mast structures are less than 1 m in diameter at the base and are quite flexible relative to many civil engineering structures. The limit state function is formulated in terms of fatigue life and is computed based on the moments at the base that are produced during multi-mode dynamic excitation as a result of the wind loading. Morison's equation, which provides relative force for slender bodies as a function of flow velocity, was applied within a dynamic finite element framework in order to account for the relative motion between the wind and the motion of the structure. Then, a well-known random vibrations approach was coupled with Miner's rule to estimate the fatigue life of the structural support. Reliability-based design charts for several different design variables such as wall thickness and outside diameter are presented.     

基于神经网络的大跨空间结构脉动风荷载的随机模拟

研究了大跨空间结构脉动风荷载的随机模拟技术,基于神经网络进行了风速时程的随机模拟。将该数值模拟技术应用于南京奥林匹克体育中心体育场的随机风荷载模拟,计算结果表明了该方法的有效性。     

Accident assessment of vehicles on long-span bridges in windy environments

Currently, there are very few systematic analyses of vehicle performance on bridges in windy environments. There are thus no scientific data to support bridge management in this regard, such as when to close traffic on bridges. This paper presents a framework of vehicle accident analysis model on long-span bridges in windy environments. In the accompanying paper, a three-dimensional analysis of the coupled bridge-vehicle-wind system is developed. Each vehicle is modeled as a combination of several rigid bodies, axle mass blocks, springs, and dampers. Dynamic interaction analysis is then conducted on the vehicle-bridge system to predict the “global” bridge and vehicle dynamic responses without considering accident occurrences. The results of the global bridge-vehicle vibrations serve as the basis for the present accident analysis of the “local” vehicle vibrations. With the global vibrations as inputs of the accident model, the lateral response, yaw response of the vehicle, and the reaction forces of each individual wheel are obtained and the stability condition of the vehicles are analyzed. The vehicle accidents on long-span bridges are then identified with given accident criteria. The developed framework can be used in not only analyzing the vehicle performance on highways and on bridges, but also in predicting useful information for emergency preparedness agencies in developing evacuation plans.     

新建地铁隧道内活塞风温度变化理论分析

列车在地铁隧道中运行时,会产生大量的热,一部分被隧道内岩土层吸收,其它部分散失在空气中,随列车活塞风带入站台。本文假设在新建单线隧道,一列车行驶周期内,对隧道内活塞风温度变化规律进行理论分析。隧道内列车散热假设为移动热源,将隧道区间内的空气流动简化成一维管流,活塞风与隧道壁面发生对流换热,根据隧道内空气的热平衡,建立简单的流固耦合模型。简化后得到新建地铁区间隧道活塞风温度变化数学模型,并给出其数值计算方法,借鉴上海某地铁的参数,利用MATLAB软件计算并绘出整个过程中隧道内活塞风温度变化曲线,隧道内活塞风温度下降约1.9 ℃。分析发现隧道内的岩土层温度、隧道长度和列车速度等影响隧道内温度分布和温度变化幅度。     

辅助结构对悬索桥的颤振稳定性的影响

随着悬索桥跨度不断增加,风荷载引起的稳定性问题在悬索桥的设计过程中的地位越来越重要,探求具有优异结构性能的悬索桥结构形式成为一项极有意义的工作,本文旨在研究在传统悬索桥基础上增加辅助结构之后悬索桥自振特性的变化,并寻求提高悬索桥颤振临界风速的有效措施。