A practical multi-lane factor model of bridges based on multi-truck presence considering lane load disparities

Many bridge design specifications consider multi-lane factors (MLFs) a critical component of the traffic load model. Measured multi-lane traffic data generally exhibit significant lane disparities in traffic loads over multiple lanes. However, these disparities are not considered in current specifications. To address this drawback, a multi-coefficient MLF model was developed based on an improved probabilistic statistical approach that considers the presence of multiple trucks. The proposed MLF model and approach were calibrated and demonstrated through an example site. The model sensitivity analysis demonstrated the significant influence of lane disparity of truck traffic volume and truck weight distribution on the MLF. Using the proposed approach, the experimental site study yielded MLFs comparable with those directly calculated using traffic load effects. The exclusion of overloaded trucks caused the proposed approach, existing design specifications, and conventional approach of ignoring lane load disparity to generate comparable MLFs, while the MLFs based on the proposed approach were the most comprehensive. The inclusion of overloaded trucks caused the conventional approach and design specifications to overestimate the MLFs significantly. Finally, the benefits of the research results to bridge practitioners were discussed.     

A pseudo-microsimulation approach for modelling congested traffic loading on long-span bridges

This paper investigates congested traffic loading on long-span bridges through the use of traffic microsimulation. Six months of Weigh-In-Motion free-flow traffic data (including cars) are used as input for the microsimulation of congested traffic. Key parameters that affect traffic loading are identified in the output of the microsimulation, and these parameters form the basis for a more computationally efficient ‘pseudo-microsimulation of congested traffic’ (PMCT) model. This PMCT model is shown to replicate the traffic loading from full microsimulation accurately and allows long-run simulations, equivalent to 1000 years of congested traffic, to be performed with an acceptably short duration. This reduces the significant uncertainties associated with extrapolating short-run simulation results to long return periods. The 1000-year simulated results from the PMCT are compared with the extrapolated results from full microsimulation, and with the traffic loading from some design codes, for different bridge lengths. Both types of microsimulation are also applied to calculate maximum lifetime loading for two typical long-span bridges – one cable-stayed and one suspension bridge – using influence lines determined from finite-element models.     

Increasing Signalized Intersection Capacity with Unconventional Use of Special Width Approach Lanes

Heavy traffic volume coupled with insufficient capacity due to limited space cause most of traffic congestion at urban signalized intersections. This article presents an innovative design to increase the capacity of heavily congested intersections by using the special width approach lane (SWAL), which consists of two narrow approach lanes that are dynamically utilized by either two passenger cars or a heavy vehicle (e.g., buses or trucks) depending on the composition of traffic. The impact of the SWAL on the saturation flow rate is quantified and validated, followed by an optimization model for best geometric layout and signal timing design with the presence of the SWAL. The optimization model is formulated as a mixed‐integer‐linear‐program for intersection capacity maximization which can be efficiently solved by the standard branch‐and‐bound technique. Results of extensive numerical analyses and case studies show the effectiveness of SWAL to increase intersection capacity, indicating its promising application at intersections with very limited space that prevents the addition of separate lanes.     

Fatigue stress monitoring and analyses for steel box girder of Runyang Suspension Bridge

The monitoring of fatigue stress of steel bridge is a key issue of bridge health monitoring and safety assessment. This paper aims to find out the strain history features of the girder components of Runyang Suspension Bridge (RYSB) under vehicle and environmental loading during its first year of service based on the strain-history data recorded by structural health monitoring system installed in the bridge. The fatigue stress spectrums of steel box girders under normal traffic load, heavy trucks and typhoon loads were studied as well as the correlation between varying strain and temperature based on real-time monitoring of temperature histories. The results show that, monitoring on local strain in health monitoring systems of RYSB can effectively provide the information on fatigue stresses. The range of the equivalent fatigue stress on the monitoring location of the bridge is currently low, mainly due to varying traffic loading and temperature. There exists significant correlation between varying temperature and mean value of fatigue stress. Effect of the passing of heavy trucks on bridge fatigue is quite significant since the value of the cumulative fatigue damage generated by heavy trucks is 10 to 100 times larger than that by normal traffic. Therefore, the effect on fatigue cumulative damage due to heavy trucks or overloaded vehicles needs to be monitored and paid much attention to.     

Eulerian-Lagrangian model for traffic dynamics and its impact on operational ventilation of road tunnels

This contribution deals with a computational Eulerian-Lagrangian model that simulates movement of cars inside a road tunnel and its impact on operational ventilation. The model simulates moving cars as discrete objects that “fly” through the tunnel. The objects are treated with a Lagrangian momentum equation and their velocity is solved along their trajectories that are determined by the shape of the roadway. The flow of the ambient air is solved with a commercial CFD code StarCD. Due to drag force, the cars virtually change their velocity, but the latter is continuously re-set to its original value. The momentum equation for the continuous phase contains an additional source term that results from the net efflux of momentum of cars when they enter and leave a particular control volume of the solution domain. The model by Jicha et al. (Int. J. Environ. Monit. Asses. 65 (2000) 343) can simulate cars moving at different speeds and traffic rates in individual traffic lanes. As a result we obtain flow rate generated by moving vehicles as a function of traffic speed and traffic rates. Turbulence was modelled using standard k-ε model with three different formulas for extra sources of the kinetic energy of turbulence that account for additional turbulence generated by moving vehicles. The traffic-induced turbulence shows a non-negligible effect on the total flow rate inside the tunnel. The model was validated with experimental data from Chen et al. (Int. J. Wind Eng. Ind. Aerod. 73 (1998) 99), where the small-scale tunnel 1:20 was investigated. The experiments were carried out with a moving belt carrying small car-like objects. The tunnel length was 20 m, the height 36.5 cm and the tunnel had two parallel lanes. Several traffic densities and speeds were simulated, namely 10,000, 20,000 and 30,000 cars/h per lane with speeds of 20 km/h and 40 km/h.     

高速公路钢桥在地震荷载下的疲劳评估

在概率论的前提下,运用线弹性断裂力学的方法研究高速公路桥钢梁在地震荷载作用下的疲劳特性。第一部分介绍的疲劳破坏是由经过桥面的重型卡车的车辆荷载引起;第二部分介绍的疲劳破坏由地震荷载引起。两种类型的破坏都使用线弹性断裂力学方法进行分析,并计算了最初裂缝发展的时间。考虑到在桥梁的使用年限里通常不同时考虑疲劳效应和地震效应,提出的方法能更好地理解桥梁由疲劳引起的逐渐破坏现象,并对如何延长地震区众多钢桥梁的疲劳寿命提出一些建议。     

Characteristic dynamic traffic load effects in bridges

When formulating an approach to assess bridge traffic loading with allowance for Vehicle-Bridge Interaction (VBI), a trade-off is necessary between the limited accuracy and computational demands of numerical models and the limited time periods for which experimental data is available. Numerical modelling can simulate sufficient numbers of loading scenarios to determine characteristic total load effects, including an allowance for VBI. However, simulating VBI for years of traffic is computationally expensive, often excessively so. Furthermore, there are a great many uncertainties associated with numerical models such as the road surface profile and the model parameter values (e.g., spring stiffnesses) for the heavy vehicle fleet. On site measurement of total load effect, including the influence of VBI, overcomes many of these uncertainties as measurements are the result of actual loading scenarios as they occur on the bridge. However, it is often impractical to monitor bridges for extended periods of time which raises questions about the accuracy of calculated characteristic load effects.Soft Load Testing, as opposed to Proof Load or Diagnostic Load Testing, is the direct measurement of load effects on bridges subject to random traffic. This paper considers the influence of measurement periods on the accuracy of soft load testing predictions of characteristic load effects, including VBI, for bridges with two lanes of opposing traffic. It concludes that, even for relatively short time periods, the estimates are reasonably accurate and tend to be conservative. Provided the data is representative, Soft Load Testing is shown to be a useful tool for calculating characteristic total load effect.     

Damage due to heavy traffic on three RC road bridges

An investigation of the damage caused by road traffic on three reinforced concrete bridges was performed. This study was performed with a focus on the determination of the damage induced by heavy vehicles in relation to the damage caused by average everyday traffic. A damage model based on fatigue of reinforcement bars was employed. The stress cycles in the reinforcement bars were determined using measurements of the crack widths under traffic loading. Stress cycles were analyzed using the Rainflow Method and Miner’s Rule was employed to gain a measurement for the damage. Monitoring systems were installed on each of the three bridges and operated for several weeks continuously to collect input data for the damage model. Computer software was developed to process the monitoring data in the sense of the damage model. The described methodology was developed and used for the first time in the described project.Heavy traffic was shown to cause a disproportionate high portion of the overall damage on all three bridges. The obtained results indicated that the damage caused by singular events, such as the passage of a heavy vehicle, in relation to the damaging effects of every-day traffic differed significantly between the considered bridges. For one of the bridges the greatest damage from singular traffic events was computed for passages of special transport vehicles. The same bridge was also found to display the highest damage by a single passage in relation to average everyday traffic. Passages of short and heavy trucks with four and five axles were identified as the most detrimental traffic events on the other two bridges.     

Modelling the spatial distribution of heavy vehicle loads on long-span bridges based on undirected graphical model

Abstract

Vehicle load modelling is highly important for bridge design and safety evaluation. Conventional modelling approaches for vehicle loads have limitations in characterizing the spatial distribution of vehicles. This article presents a probabilistic method for modelling the spatial distribution of heavy vehicle loads on long-span bridges by using the undirected graphical model (UGM). The bridge deck is divided into grid cells, a UGM with each node corresponding to each cell is employed to model the location distribution of heavy vehicles, by which probabilities of heavy-vehicle distribution patterns can be efficiently calculated through applying the junction tree algorithm. A Bayesian inference method is also developed for updating the location model in consideration of the non-stationarity of traffic process. Gross weights of heavy vehicles are modelled by incorporating additional random variables to the vehicle-location UGM, corresponding probability distributions are constructed conditioned on ignoring correlation and considering correlation, respectively. Case studies using simulated data as well as field monitoring data have been conducted to examine the method. Compared with previous studies involving vehicle load modelling, the presented method can implement probabilistic analysis for all spatial distribution patterns of heavy vehicles on the entire bridge deck.     

A filtering-based bridge weigh-in-motion system on a continuous multi-girder bridge considering the influence lines of different lanes

A real-time vehicle monitoring is crucial for effective bridge maintenance and traffic management because overloaded vehicles can cause damage to bridges, and in some extreme cases, it will directly lead to a bridge failure. Bridge weigh-in-motion (BWIM) system as a high performance and cost-effective technology has been extensively used to monitor vehicle speed and weight on highways. However, the dynamic effect and data noise may have an adverse impact on the bridge responses during and immediately following the vehicles pass the bridge. The fast Fourier transform (FFT) method, which can significantly purify the collected structural responses (dynamic strains) received from sensors or transducers, was used in axle counting, detection, and axle weighing technology in this study. To further improve the accuracy of the BWIM system, the field-calibrated influence lines (ILs) of a continuous multi-girder bridge were regarded as a reference to identify the vehicle weight based on the modified Moses algorithm and the least squares method. In situ experimental results indicated that the signals treated with FFT filter were far better than the original ones, the efficiency and the accuracy of axle detection were significantly improved by introducing the FFT method to the BWIM system. Moreover, the lateral load distribution effect on bridges should be considered by using the calculated average ILs of the specific lane individually for vehicle weight calculation of this lane.     

Structural adequacy assessment of a disused flat bottom rail wagon as road bridge deck

This paper presents half of a full scale experimental testing technique for assessing the structural adequacy of a disused flat bottom rail wagon (FBW) for low volume, heavy axle load road bridge applications. The aim of this ongoing research project is to develop sufficient knowledge required for achieving significant economy and safety of the heavy axle transportation system in regional government council roads. In the absence of such knowledge, the viability of replacing/rehabilitating the ageing bridges could not be economically justified, mainly due to low volume traffic and the costs of alternate solutions using new materials for heavy axle load demands.This study describes a comprehensive laboratory testing of half of a single lane, single span bridge deck and an associated three dimensional finite element modeling. The novel idea in the paper is to enforce the transverse continuity conditions along the longitudinal edge of the half of full scale bridge so that the single FBW tested will mimic the behaviour of a double FBW deck for a single lane road bridge under heavy axle design loads. Several serviceability and ultimate load tests, conforming to the Australian bridge design traffic loads applied at critical locations of the FBW system are reported in the paper. The test results demonstrate that the FBW possesses sufficient structural strength and can service the required design traffic loads.     

Fatigue stress monitoring and analyses for steel box girder of Runyang Suspension Bridge

The monitoring of fatigue stress of steel bridge is a key issue of bridge health monitoring and safety assessment. This paper aims to find out the strain history features of the girder components of Runyang Suspension Bridge (RYSB) under vehicle and environmental loading during its first year of service based on the strain-history data recorded by structural health monitoring system installed in the bridge. The fatigue stress spectrums of steel box girders under normal traffic load, heavy trucks and typhoon loads were studied as well as the correlation between varying strain and temperature based on real-time monitoring of temperature histories. The results show that, monitoring on local strain in health monitoring systems of RYSB can effectively provide the information on fatigue stresses. The range of the equivalent fatigue stress on the monitoring location of the bridge is currently low, mainly due to varying traffic loading and temperature. There exists significant correlation between varying temperature and mean value of fatigue stress. Effect of the passing of heavy trucks on bridge fatigue is quite significant since the value of the cumulative fatigue damage generated by heavy trucks is 10 to 100 times larger than that by normal traffic. Therefore, the effect on fatigue cumulative damage due to heavy trucks or overloaded vehicles needs to be monitored and paid much attention to. __________ Translated from Journal of Southeast University (Natural Science Edition), 2007, 37(2): 280–286 [译自: 东南大学学报(自然科学版)]     

Die Wupper‐Talbrücke Oehde – eine moderne Verbundbrücke

The Wupper River valley bridge – a state‐of‐the‐art composite bridge. The German motorway Autobahn A 1 is one of the nation's most important and frequently traveled highways, connecting the country's northern and southern regions. The road currently has two lanes in each direction, which do not provide enough capacity to carry the traffic volume without daily traffic jams and heavy delays. Therefore, the federal government and the Northrhine‐Westfalia Department of Transportation decided to ease the situation by adding one lane in each direction. This total of 6 lanes fits into the master plan of widening major highways around the Ruhr River region. North of Cologne, the Autobahn A 1 crosses mountainous terrain, so several bridges with total lengths between 240 and 420 meters have had to be widened, replaced, or, most commonly, supplemented by a new bridge. Such supplementation was used on the Wupper River Valley Bridge, called Oehde, close to the city of Wuppertal. The bridge illustrates an example of modern composite bridges adopting new methods in construction and design, and also marks an outstanding example of current composite structures in Germany.     

基于WIM的典型城市桥梁车辆荷载状况分析

基于安装在杭州石祥路留石高架上的动态称重系统（WIM）采集的交通流和车辆荷载数据,通过对交通流量、车辆构成、轴重、车辆总重等进行分析,获取了其概率统计特性及分布规律,建立了轴载谱和车辆总重谱,并与相关文献、规范进行了比较。结果表明：一天中各时段的交通流量具有很强的潮汐规律性;2.86%的车辆轴重超过了10 t的超载标准,最大的单轴重量达39.5 t,最大车辆总重达115 t,后半夜车辆恶性超载严重;2轴车车辆总重表现为单峰分布,3轴以上车辆的总重均表现为多峰分布,5轴车和6轴车的总重表现为3峰分布;轴重大的车辆主要是超载的2轴、3轴车辆,这部分车辆对桥梁等基础设施的危害较大。这些车辆荷载特征的获取有助于区域既有桥梁安全性的合理评估,为超重车辆治理和桥梁安全管理提供帮助。     

城市道路桥梁的疲劳荷载谱

我国针对公路及城市道路桥梁疲劳设计的车辆荷载谱还是个空白,本文以上海市内环线中山路3号桥地面道路桥梁为例,对城市道路桥梁的疲劳荷载作了研讨.在1994年和1995年两次交通调查的基础上,得到了由18类日常典型的运营车辆组成的荷载频值谱.依据等效的疲劳损伤原理,将实测的车辆荷载频值谱简化成由6类模型车辆组成的具有实用性的荷载频值谱.所建立的模型车辆荷载频值谱,对于日常车辆交通构成与本文状况相类似的其它城市道路桥梁的疲劳损伤度验算,可作为参考.     

Spatial time-dependent reliability analysis of reinforced concrete slab bridges subject to realistic traffic loading

Resistance and loads are often correlated in time and space. The paper assesses the influence of these correlations on structural reliability/probability of failure for a typical two-lane reinforced concrete (RC) slab bridge under realistic traffic loading. Spatial variables for structural resistance are cover and concrete compressive strength, which in turn affect the strength and chloride-induced corrosion of RC elements. Random variables include pit depth and model error. Correlation of weights between trucks in adjacent lanes and inter-vehicle gaps are also included and are calibrated against weigh-in-motion data. Reliability analysis of deteriorating bridges needs to incorporate uncertainties associated with parameters governing the deterioration process and loading. One of the major unanswered questions in the work carried out to date is the influence of spatial variability of load and resistance on failure probability. Spatial variability research carried out to date has been mainly focused on predicting the remaining lifetime of a corroding structure and spatial variability of material, dimensional and environmental properties. A major shortcoming in the work carried out to date is the lack of an allowance for the spatial variability of applied traffic loads. In this article, a two-dimensional (2D) random field is developed where load effects and time-dependent structural resistance are calculated for each segment in the field. The 2D spatial time-dependent reliability analysis of an RC slab bridge found that a spatially correlated resistance results in only a small increase in probability of failure. Despite the fact that load effect at points along the length of a bridge is strongly correlated, the combined influence of correlation in load and resistance on probability of failure is small.     

Fatigue assessment of highway steel bridges in presence of seismic loading

In this study a LEFM (Linear Elastic Fracture Mechanics) approach is used in a probabilistic context to evaluate the fatigue reliability of steel girder highway bridges in the presence of seismic loading. In the first part the fatigue damage is related to the traffic load produced by heavy trucks crossing the bridge; the second part deals with the fatigue damage related to seismic loading. Both damage typologies are analyzed using linear elastic fracture mechanics principles, and the time required for an initial crack propagation is calculated. Taking into account that the correlation between fatigue effects and seismic actions is not usually considered in the literature, this method could enable a better understanding of progressive damage phenomena due to fatigue related problems, and could give some new insights for increasing the remaining fatigue life of a large number of steel bridges in seismic zones.     

Monte Carlo simulation of extreme traffic loading on short and medium span bridges

The accurate estimation of site-specific lifetime extreme traffic load effects is an important element in the cost-effective assessment of bridges. A common approach is to use statistical distributions derived from weigh-in-motion measurements as the basis for Monte Carlo simulation of traffic loading. However, results are highly sensitive to the assumptions made, not just with regard to vehicle weights but also to axle configurations and gaps between vehicles. This paper presents a comprehensive model for Monte Carlo simulation of bridge loading for free-flowing traffic and shows how the model matches results from measurements on five European highways. The model has been optimised to allow the simulation of many years of traffic and this greatly reduces the variance in calculating estimates for lifetime loading from the model. The approach described here does not remove the uncertainty inherent in estimating lifetime maximum loading from data collected over relatively short time periods.     

某公路大桥车辆荷载调查与局部疲劳分析

近年来,随着公路交通流量的不断增加,公路桥梁的疲劳问题变得越来越显著。对于公路桥梁的疲劳问题,国内外已做了大量研究,并形成了相关规范。但是,对于局部疲劳问题,尚存在着两个问题需要解决:一是局部疲劳应力与车辆荷载位置的关系因桥而异,目前还没有统一的处理方法;二是需要在现有的疲劳评估方法基础上进一步考虑车辆荷载、疲劳应力以及疲劳寿命的不确定性。以某公路大桥为例,对其过去11年的车辆荷载进行统计分析,得到车辆荷载的概率模型,并利用Monte Carlo方法模拟出桥面板的局部承载历史,分析计算出等效疲劳荷载及相应的等效循环次数。在模拟过程中考虑了车辆荷载的不确定性,同时提出车辆荷载局部折减系数以考虑车轮横向位置对局部应力的影响。模拟结果表明:分析得出的等效循环次数,在AASHTO规范规定的出现疲劳破坏的疲劳应力循环次数的合理范围内,与该大桥出现疲劳裂缝的现状相符。     

大跨度悬索桥梁端竖向折角对列车走行性的影响研究

大跨度桥梁较为柔性,易产生梁端竖向折角,过大的梁端竖向折角会影响列车的安全性和舒适性。有代表性地选取较为柔性的大跨度公轨两用悬索桥作为工程背景,基于车-桥耦合动力仿真数值计算方法,采用自主研发的桥梁科研分析软件BANSYS(Bridge ANalysis SYStem),分析列车进桥及出桥全过程中车辆和桥梁的响应,对比不同车辆运行方式、不同车速、不同车载状态下的响应,讨论大跨度悬索桥梁端竖向折角对列车走行性的影响,进一步提出减小梁端竖向折角的措施。研究结论对大跨度轨道交通桥梁的运营安全具有指导意义。