规划航道桥梁抗撞性能研究

为了评估规划航道提升等级后桥梁的抗撞性能是否具备抵抗船舶撞击的能力,文章以白沙大桥为依托工程,明确桥梁抗撞性能分析流程,采用Madis Civil软件建立桥梁有限元模型计算其弯矩及剪力效应值,通过对弯矩及剪力效应值进行强度验算以评估桥梁的抗撞性能。结果表明：当规划航道的等级远高于桥梁所处的原航道等级时,船舶对桥墩的撞击损坏面位于中下部位;白沙大桥在规划Ⅱ级航道等级中受到2 000 t的船舶撞击时,其抗撞性能较差,抗剪效应值几乎高出抗弯承载力两倍,无法抵抗船舶撞击时所产生的抗剪效应,对桥墩造成抗剪破坏。     

高速铁路桥墩沉降对行车的动力响应分析

高速铁路产生墩台位移后,会造成钢轨变形,对列车安全性、平稳性和舒适性产生不利影响。为探寻桥墩沉降对车辆动力响应的作用规律,本文通过分析车辆在不同桥墩位移和行车速度下的动力响应,分析得到相应的影响程度,为今后的高速铁路养护维修提供可借鉴的成果。     

桥墩位移与钢轨变形的映射关系

准确模拟轮轨之间的动力相互作用是仿真求解并科学评估车辆真实安全、舒适动力响应指标的基础和关键。因此有必要对轮轨不平顺进行有效模拟。桥墩发生沉降后,与沉降桥墩相邻的两跨梁桥受到重力作用而产生垂直方向位移,轨道等构件也随着桥梁位移发生相应变形~([1])。为确定桥墩沉降下不同行车速度对车辆动力响应的作用规律,需首先确定桥墩沉降与钢轨变形的映射关系~([2]),得出桥墩沉降所引发的钢轨变形~([3])。本文基于所建立的钢轨—无砟轨道—桥梁精细化静力分析模型~([4]),通过对桥墩施加给定的位移荷载,得到了桥墩沉降以及横移条件下钢轨变形曲线,获得了桥墩位移与钢轨变形的映射关系。     

框架锚索结构加固市政公路桥梁边坡效果分析研究

针对目前由于山区城市地形的限制使得部分被布置在高边坡上的桥墩其自身受力情况及防治措施的问题,本文以贵州省大兴至思南高速公路某特大桥为工程实例,采用数值模拟方法,在充分考虑边坡和桥墩的相互作用的条件下,对框架锚索加固市政公路桥梁边坡的效果进行分析。研究结果表明:在饱和工况条件下,桥墩顶部水平向位移超过规范要求限值且桥墩的桩身最大弯矩值远大于桥墩的抗弯强度,并导致桥墩产生一定的倾斜度,为防止桥墩倾斜的进一步加大,设计单位对该段边坡采取了框架锚索加固的治理措施。经过加固后边坡处于稳定状态且桥墩顶部位移值和桩身最大弯矩均满足要求,显示出了框架锚索结构加固市政公路桥梁边坡的有效性。     

基于车载测试的CNG汽车微观排放特性研究

为了分析CNG汽车道路排放的微观特性,采用车载排放测试系统,并选取市区主要道路为试验路段进行了实车道路试验。通过试验获取典型车辆的排放数据及行驶状态,分析车辆在实际行驶中的排放特性,为预测不同交通状态下CNG汽车的排放特性和区域排放清单建立提供参考。     

桥墩变位对预应力混凝土刚构连续T梁桥受力性能的影响分析

结合环境振动测试和精细有限元模型,对一座桥墩变位的3×40m预应力混凝土刚构连续T梁桥的受力性能进行了分析。首先,介绍了该桥概况以及由于施工导致的桥墩变位情况。其次,在环境振动测试的基础上,建立能反映当前状况的基准有限元模型。最后,对该桥的正常使用性能进行了评估,并分析了桥墩偏位发展对桥梁受力性能的影响。结果表明,当前状态下桥梁能够满足正常使用性能,但当扭转偏位达到0.2°时,将引起主梁开裂。     

高墩大跨连续刚构桥P-△效应分析

高墩在纵向水平地震力作用下产生水平变位,从而使作用在墩顶上的上部结构的重力荷载以及墩身自身的重力荷载产生了偏心,在桥墩内将引起二次内力和变形(称P-△效应)。本文分别采用对比的方法及不同的桥墩参数,对桥墩的P-△特性进行比较研究,得出一些有意义的结论,为抗震设计和计算提供一些参考和借鉴。     

高墩柱桥梁的施工难点及控制要点

桥墩是支撑桥跨结构,是将恒定荷载、车辆等荷载传递到地基的重要结构物。伴随着我国公路桥梁工程项目的日益增多,以及线形规模的不断扩大,难免需要跨越大量的河流、深谷,而在跨越河流和深谷的桥梁工程中,为使桥梁更加经济、合理,经常设计高墩柱作为桥墩结构。结合工程实例,从高墩柱桥梁的施工方案及施工难点出发,就施工过程中的相关控制要点进行了分析与探讨,以有效降低和避免工程中可能出现的质量问题与安全隐患,确保工程质量与工程工期的顺利实现。     

基于信息融合技术的车辆主动防御系统研究

文章设计开发了基于信息融合技术的车辆主动防御系统,以期在测试车辆起步及正常行驶状态下,实时监控前方障碍物的相对距离,在设定的不同危险级别下执行报警、缓减速、急减速至停车的动作。装车试验证明,该系统采集信息、判断距离、执行相应命令的准确率较高,具有一定的实用价值。     

高速公路养护维修中旧桥实体碳纤维板加固技术

建成的各类桥梁由于设计缺陷、施工控制、运营车辆长期严重超载等原因,加之桥梁的技术状态得不到及时有效地监测,以及受洪水冲刷、车船撞击等外因作用,使得为数众多的桥梁发生了各种不同程度的病害,如桥面破损、栏杆断裂、梁板裂缝、钢筋钢索锈蚀、钢结构裂纹锈烂、墩台断裂位移等,破坏了桥梁的正常功能状态。本文介绍旧桥碳纤维板加固技术对高速公路养护中危桥原有功能进行恢复,以提高旧桥的承载能力。     

基于GPS和GSM的清管器智能跟踪系统

为了在清管施工中实时跟踪清管器,设计一种基于GPS系统和GSM通信系统的智能清管器跟踪系统,系统包括发射机、中继器和监控系统。发射机搭载在清管器上持续发射电磁信号和静磁信号,中继器预先埋设在设定的跟踪点接收和转发通过信息;清管器通过跟踪点时,中继器接收发射机发出的信号,精确识别出清管器并将通过时间和跟踪点GPS位置信息通过GSM网络发送至监控系统;监控系统接收到信息后,在监控界面地图上实时显示通过位置和通过时间。清管器卡堵时,系统可及时在地图上指示卡堵区间和到达卡堵现场路径。现场应用表明:该系统实现了清管器智能跟踪,通过时间和通过位置记录精确,降低清管施工中安全风险,节约成本。     

西部交通基础设施影响评价指标体系研究

文章以交通基础设施为研究主体,以西部地区社会经济为研究对象,结合国内外基础设施评价的理论基础和西部地区的实际情况,分析主体和研究对象之间的影响因素,并在此基础上构建了交通基础设施评价指标体系,从区域经济影响、社会环境、自然环境3个方面评估交通基础设施对西部地区的影响,通过模糊综合评价模型的计算,得到分项评价结果和总体评价结果,并作出评价分析。     

A new approach for modeling of Fundamental Diagrams

According to the intra-vehicle interaction, a traffic flow can generally be divided into three homogeneous states (1) that of free driving, (2) that of bunched driving, and (3) that of standing. The parameter describing the state of free driving is the desired speed, for the state of bunching it is the intra-vehicle gaps (time headway) within the convoy and the mean speed of the convoy, and for the state of standing it is the maximum jam density. These are the most essential parameters which do not depend on the actual traffic situation.This paper introduces a new model which considers the Fundamental Diagram (equilibrium speed–flow–density relationship) as a function of the homogeneous states. All traffic situations in reality can be considered as combinations of the homogeneous states and therefore can be described by the essential parameters mentioned above. The non-congested (fluid) traffic is a combination (superposition) of the states of free driving and bunched driving, the congested (jam, stop, and go) traffic is a combination of the states of bunched driving (go) and standing (stop). The contribution of the traffic states within the differently congested traffic situations can then be easily obtained from the queuing and probability theory. As a result, Fundamental Diagram in all equilibrium traffic situations is derived as simple functions of the essential parameters.According to the new model the capacity of freeways and rural highways can be determined by measuring the essential parameters. This is much easier than measuring the capacity directly.Furthermore, the probabilities of the various traffic states can be obtained from the new model. This leads to new possibilities in real-time controlling and telematics.The new model is verified by comprehensive measurements carried out on freeways and rural highways in Germany.     

Factors affecting the use of bus and rail services in a deregulated environment

In 1987, the NSW Government commenced deregulation of the long-distance bus industry in NSW. This immediately led to greater inter-modal competition and contestability within the context of changing passenger markets.This study utilises categorical data analysis methods to examine the emerging passenger markets of inter-modal competitors (bus and rail) and to assess the relative importance of socioeconomic and travel related variables which affect the use of bus and rail services along the high volume Sydney-Canberra and Sydney-North Coast corridors.Conclusions from the study indicate varied passenger markets within a relatively new contestable environment which are mode and corridor specific. Results are indicative of the need for competitors to develop marketing strategies conducive to the demands of the travelling public in order to enhance viability and commercial opportunities.     

Vulnerability and resilience of transport systems – A discussion of recent research

The transport system is critical to the welfare of modern societies. This article provides an overview of recent research on vulnerability and resilience of transport systems. Definitions of vulnerability and resilience are formulated and discussed together with related concepts. In the increasing and extensive literature of transport vulnerability studies, two distinct traditions are identified. One tradition with roots in graph theory studies the vulnerability of transport networks based on their topological properties. The other tradition also represents the demand and supply side of the transport systems to allow for a more complete assessment of the consequences of disruptions or disasters for the users and society. The merits and drawbacks of the approaches are discussed. The concept of resilience offers a broader socio-technical perspective on the transport system’s capacity to maintain or quickly recover its function after a disruption or a disaster. The transport resilience literature is less abundant, especially concerning the post-disaster phases of response and recovery. The research on transport system vulnerability and resilience is now a mature field with a developed methodology and a large amount of research findings with large potential practical usefulness. The authors argue that more cross-disciplinary collaborations between authorities, operators and researchers would be desirable to transform this knowledge into practical strategies to strengthen the resilience of the transport system.     

A cost and CO2 comparison of using trains and higher capacity trucks when UK FMCG companies collaborate

Companies working in a collaboration are able to achieve higher vehicle capacity utilisation and reduced empty running, resulting in lower costs and improved sustainability through reduced emissions and congestion. Collaboration produces higher volumes of goods to be moved than individual companies which means that further efficiencies may be possible by relaxing the freight mode constraints and considering rail and higher capacity vehicles. This paper explains how real world data has been used in a model to quantify the economic and environmental benefits in the FMCG sector delivered through collaboration utilising road and rail freight modes. Data for one month was provided by 10 FMCG companies and included freight transport flows between depots and customers, inter depot movements, and supplier collections. Detailed road and rail costs and operating characteristics were obtained and, with the transport flows, applied to a network design model which was used to validate the company data sets. A strategy examining the potential use of alternative higher capacity vehicles and rail for the flows between nine regional consolidation centres showed cost and CO₂ savings. Just under half the inter-regional flows benefited from double deck trailers, longer heavier vehicles for 30% of the flows and rail with different wagon configurations for the rest. In summary there was a 23% reduction in cost with 58% fewer road kilometres and a 46% reduction in CO₂ emissions. The ability to backhaul the same mode of transport between most of the regional centres was one of the strengths of this strategy.     

Walking,cycling and the urban form: A Heckman selection model of active travel mode and distance by young adolescents

Physical inactivity of children and adolescents is a major public health challenge of the modern era but, when adequately promoted and nurtured, active travel offers immediate health benefits and forms future sustainable and healthy travel habits. This study explores jointly the choice and the extent of active travel of young adolescents while considering walking and cycling as distinct travel forms, controlling for objective urban form measures, and taking both a “street-buffer” looking at the immediate home surroundings and a “transport-zone” looking at wider neighborhoods. A Heckman selection model represents the distance covered while cycling (walking) given the mode choice being bicycle (walk) for a representative sample of 10–15 year-olds from the Capital Region of Denmark extracted from the Danish national travel survey. Results illustrate the necessity of different urban environments for walking and cycling, as the former relates to “street-buffer” urban form measures and the latter also to “transport-zone ” ones. Results also show that lessening the amount and the density of car traffic, diminishing the movement of heavy vehicles in local streets, reducing the conflict points with the density of intersections, and intervening on crash frequency and severity, would increase the probability and the amount of active travel by young adolescents. Last, results indicate that zones in rural areas and at a higher percentage of immigrants are likely to have lower probability and amount of active travel by young adolescents.     

Stockholm congestion charging: an assessment with METROPOLIS and SILVESTER

This paper reviews and compares the performance of two dynamic transportation models – METROPOLIS and SILVESTER – which are used to predict the impacts of congestion charging for Stockholm. Both are mesoscopic dynamic models treating accumulation and dissipation of traffic queues, route choice, modal split and departure time choice. The models are calibrated independently for the baseline situation without charges and applied to forecast the effects of congestion charging. The results obtained from the two models are mutually compared and validated against the actual outcome of the Stockholm congestion charging scheme. Both models successfully predict the outcomes of the congestion charging trial at both aggregate and disaggregate levels. Results of welfare analysis, however, differ substantially due to differences in model specification.     

A century of evolution of the accessibility concept

The concept of accessibility has acquired numerous meanings along multiple dimensions during the century of its evolution. This essay argues for the salience of two dimensions: application-based and definition-based. In its application, accessibility has incorporated positive and normative dimensions which have varied in prominence over time. In its definition, accessibility has varied between a mode of evaluation incorporating measured mobility and proximity, on the one hand, and a predefined market basket of urbanist improvements to transportation and land use systems, on the other. Advocates of the accessibility shift should emphasize both the measured approach to accessibility and accessibility’s normative side.