混凝土梁式桥抗震设计应注意的几个问题

依据桥梁结构的抗震理论,分析了国内外历次地震造成混凝土梁式桥毁损的主要原因,提出了桥梁在抗震结构设计中应充分注意的问题,以及为提高抗震能力而采取的设防构造措施.     

桥梁抗震性能评价及抗震加固技术研究

《桥梁抗震性能评价及抗震加固技术研究》项目结合我国西部地区桥梁结构的具体特点,将调查研究、理论分析与试验方法相结合,开展适合西部地区特点、并具有在全国其他地区推广前景的桥梁结构抗震性能评价及抗震加固技术研究。本篇对该项目研究的内容、成果及创新性技术进行推介,为桥梁工程的抗震性能评价与加固提供方法借鉴。     

桥梁抗震性能评估及加固方法研究

桥梁由于受到结构以及基础尺寸的影响,很容易发生地震破坏。桥梁结构一旦出现地震破坏,不仅会造成交通运输的中断,同时也有可能造成严重的人员伤亡以及财产损失事故。因此,桥梁抗震设计非常重要,以桥梁工程中最为常见的混凝土桥梁为例,首先分析了现行相关规范中对于桥梁抗震设计的相关要求,进而系统地论述了桥梁抗震性能的评估方法,并提出了提高桥梁抗震性能加固措施,可以为桥梁工程检测与加固工作的实施提供合理的参考。     

横系梁对双柱式高墩桥梁抗震性能的影响分析

以具体高墩桥梁工程为例,进行了横系梁数量、设置位置及刚度等对双柱式高墩桥梁抗震性能影响的分析。结果表明,桥梁结构中的桥墩主要发挥上部荷载顺利传递至地基基础的作用,是较为重要的受力性构件;在双柱式高墩桥梁墩柱间增设横系梁能有效改变桥梁下部结构受力状态,且在地震影响下双柱式高墩桥梁结构的内力分配会因横系梁设置数量、设置位置的不同而不同,应通过横系梁结构的合理设计以充分发挥该结构消耗地震能量的作用,并确保高墩桥梁下部结构内力合理分配,提升高墩桥梁结构的抗震性能。     

桥梁结构减隔震设计研究

传统的桥梁结构抗震设计方法存在诸多弊端,一种新的抗震技术桥梁减隔震技术应运而生。针对减隔震设计展开研究,探讨了桥梁减隔震装置的布置方案和设计参数,通过力学计算分析了减震装置对桥梁结构的减震效果,结果表明采用减隔震设计能够有效减小桥梁结构所受地震力,改善抗震性能。     

浅谈模数式桥梁伸缩装置的选型及改进

在桥梁设计中,桥梁伸缩装置的选型是否得当对桥梁运营影响很大。文章分析了几种典型结构的模数式伸缩装置的优缺点和适应性,提出了模数式伸缩装置选型应注意的几个问题,以及对现有模数式伸缩装置进行细部改进的思路。     

基于Midas Civil建模对大跨连续刚构桥的抗震分析

市政工程中大跨径桥梁抗震分析很重要。文章以某连续刚构桥为例,利用桥梁软件Midas Civil建立桥梁结构的空间三维动力计算模型,并使用线性反应谱方法对桥梁的抗震性能进行计算分析。计算结果满足相关规范要求,结构安全可靠,可为今后大跨连续刚构桥的设计提供参考。     

高低塔斜拉桥抗震设计分析

高低塔斜拉桥由于结构不对称,使其受力特性也体现出不对称性,因此对此类桥梁的抗震分析显得尤为重要。文章以广西某特大桥为工程实例,建立空间有限元模型进行抗震分析,对设置阻尼器提高桥梁抗震性能提供了可靠的理论依据,并介绍了有限元分析的详细过程,可为今后同类桥梁的抗震设计提供参考。     

公路桥梁结构抗震设计要点分析

作为公路桥梁工程设计的重要环节,抗震设计质量将对工程使用年限等造成极大的影响。鉴于此,在介绍我国桥梁结构抗震体系及震害特点的基础上,阐述公路桥梁抗震设计的要点,并探讨抗震设计中应注意的事项,为相关工程抗震设计提供参考。     

铅芯橡胶支座在桥梁隔震中的应用研究

国外隔震技术在桥梁上的应用已比较广泛,一些采用隔震技术的桥梁在地震中也已表现出良好的抗震性能.阐述了铅芯橡胶支座的构造特点、力学性质、控制参数、计算模型及运动方程,为铅芯橡胶支座的设计提供依据.     

Survey of R&D in PRT systems

A survey of research and development in advanced transit has been made by Chalmers University of Technology in Gothenburg in cooperation with Trans21 in Boston. Summary findings are reported for fourteen academic research programs and ten development programs for PRT. An earlier version of this paper was presented at the International Conference of PRT and other Emerging Systems held in Minneapolis in 1996.     

Optimization of bus stop locations for improving transit accessibility

A mathematical model is developed in this paper to improve the accessibility of a bus service. To formulate the optimization model, a segment of a bus route is given, on which a number of demand entry points are distributed realistically. The objective total cost function (i.e. the sum of supplier and user costs) is minimized by optimizing the number and locations of stops, subject to non‐additive users' value of time. A numerical example is designed to demonstrate the effectiveness of the method thus developed to optimize the bus stop location problem. The sensitivity of the total cost to various parameters (e.g. value of users' time, access speed, and demand density) and the effect of the parameters on the optimal stop locations are analyzed and discussed.     

Productive efficiency and ownership of urban bus services

The established ownership mix of urban bus operations in Australia provides a unique opportunity to investigate the productivity differences between public and private bus service supply. Using duality theory in economics which links economic indices of factor productivity to the cost structure of a firm, we develop empirical measures of total and partial productivity of inputs, and adjust the differences for the effects of ownership status and operating environment. The evidence supports the notion that private supply of public passenger transport in general has performed more efficiently in the past than public supply, although the differences in productivity need not continue in the future.     

管道风险分析指数评分法中分值调整初探

管道风险分析指数评分法中重要步骤之一就是确定影响管道事故因素的权重,各个管道风险因素在整个管道事故中所占的权重是不相同的。针对目前管道风险分析指数评分法基本假设之一（各因素的分值范围都是0～100分）,为了更加客观、准确、合理地反映各个风险因素对于管道事故的影响程度,提出并论述了依据层次分析法的数学逻辑性进行综合计算得出管道风险因素的权重,然后对评分法中各个因素的最高分值,根据其权重不同进行相应调整,从而增强评价者对风险因素的认识和评判能力,提高管道风险评价结果的准确性。     

Determinants of modal choice in freight transport

In the next few years, exciting developments in the field of freight transport are likely to occur. The Channel Tunnel will be perceived as giving railways much greater distance of operation, compared to the current train ferry to/from Great Britain. The further development of swap-body technology will allow easier modal transfer and the creation, in 1992, of a single market in Europe will transform the pattern of trade. All of these are likely to have significant impacts on modal choice, and hence modal split, in freight transport. Reappraisal by many firms of the modes of transport used is likely but will it result in a net transfer of freight from road to rail and, if so, to what extent? To answer such questions, an accurate and reliable method of predicting modal split is required. Research in the past has concentrated on the development of modal split models based on generalised costs. These fail to explain adequately the prevalence of road freight in the UK. From surveys of freight managers within industry, it is clear that models to date rely too heavily on the economic cost factor and too little on behavioural factors (Jeffs 1985). This paper derives from a recent study of freight transport modal choice from the standpoint of the transport decision-maker within the firm. It attempts to shed light on the actual parameters which should be incorporated into a modal split model. Many variables appear to exert an influence on modal choice decision-making process. However, it is possible to categorise them into six main groups, namely: customer-requirements; product-characteristics; company structure/organisation; government interventions; available transport facilities; and perceptions of the decision-maker him/herself. It is the interactions and inter-relationships between these which ultimately determine freight modal split. This study has shown that the relationship between the outcome of the transport decision process and the values of particular determinants of modal split is not straight-forward, due to the complexity and variety of interactions involved. Perhaps one of the main reasons for researchers' failure hitherto to develop a successful modal-split model has been the preoccupation with techniques that rely on the development of common metric (e.g. generalised cost), which has led to the exclusion of some important explanatory variables along quite different dimensions. Another important issue concerns the appropriate level of aggregation. In order not to reduce the explanatory power of the key variables, it is important to work at a disaggregate level, although this does make substantial demands on data. The use of factor analysis enables both the aggregation of information without loss of behavioural reality and the specification of variables in terms of a common metric. In conclusion, freight transport has usually been examined within too narrow a framework. It must be placed firmly within the context of the total industrial process. The demand for freight transport is directly influenced by the level, composition and geographical distribution of production and consumption activities. Freight flows are complex and so it is highly unlikely that a universal mode-choice model can ever be developed. Future research should, therefore, be directed towards developing partial models in response to specific needs of those involved in decision-taking in the freight sector.     

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.     

Governing autonomous vehicles: emerging responses for safety,liability, privacy,cybersecurity, and industry risks

ABSTRACT

The benefits of autonomous vehicles (AVs) are widely acknowledged, but there are concerns about the extent of these benefits and AV risks and unintended consequences. In this article, we first examine AVs and different categories of the technological risks associated with them. We then explore strategies that can be adopted to address these risks, and explore emerging responses by governments for addressing AV risks. Our analyses reveal that, thus far, governments have in most instances avoided stringent measures in order to promote AV developments and the majority of responses are non-binding and focus on creating councils or working groups to better explore AV implications. The US has been active in introducing legislations to address issues related to privacy and cybersecurity. The UK and Germany, in particular, have enacted laws to address liability issues; other countries mostly acknowledge these issues, but have yet to implement specific strategies. To address privacy and cybersecurity risks strategies ranging from introduction or amendment of non-AV specific legislation to creating working groups have been adopted. Much less attention has been paid to issues such as environmental and employment risks, although a few governments have begun programmes to retrain workers who might be negatively affected.     

Real-world gaseous and particle emissions of a Bi-fuel gasoline/CNG Euro 6 passenger car

The objective of the present study is the assessment of the environmental impact of a bivalent (bi-fuel) vehicle, running either on gasoline or compressed natural gas (CNG). To that aim, a Euro 6 passenger car was tested under various real-world driving conditions. In order to cover the full range of conventional powertrains currently in the market, the tests were also repeated on a Euro 6 diesel passenger car. Both cars were driven in two routes, the first complying with the regulation limits and the second going beyond them. Carbon monoxide (CO), nitrogen oxides (NO_x) and particle number (PN) emissions were recorded using a Portable Emissions Measurement System (PEMS). Apart from the aggregated emission levels, in g/km, the exact emission location along the route was also assessed. Natural gas proved beneficial for CO and PN emissions, the level of which always remained below the respective legislation limits. On the other hand, under the dynamic driving conditions with gasoline, the relevant limits were exceeded. Cold start, occurring at the beginning of the urban part, and motorway driving were identified as major contributors to total emissions, especially in gasoline mode. However, the application of natural gas was associated with a penalty in NO_x emissions, which were significantly increased as compared to gasoline. Local peaks within the urban part were identified in CNG mode. In any case, the diesel vehicle was by far the highest NO_x emitter.