冲击弹性波无损检测预应力管道注浆质量的研究

预应力混凝土结构桥梁管道注浆不密实是影响桥梁梁体强度和寿命的最主要因素,直接影响到桥梁结构的承载能力和耐久性。本文通过对实际工程中预制跨径为40、30、20m T梁预应力管道进行注浆质量冲击弹性波无损检测,对定性检测结果整理对比分析,发现了预应力管道长度与测试结果的关系,为预应力管道注浆质量冲击弹性波无损检测提供评定指导依据。     

超声波在混凝土桩基础无损检测中的应用

文章介绍了超声波无损检测相比于其他检测方法在混凝土桩基础质量检测中的优越性,并基于超声波无损检测的工作原理,进行了相关的试验验证。结果表明,运用超声波无损检测技术可以有效地检测出混凝土桩基础存在的质量问题。     

碎裂岩质高边坡锚杆应力的监测分析

高边坡的现场监测是一个系统工程,文章以西攀高速公路为例,结合高边坡施工期监测锚杆的应力状态和受力原因,建立锚杆应力测值统计模型,分析了开挖、温度、时效变形这三种因素对锚杆应力影响的规律,并对锚固效果和边坡稳定性进行了评价。     

基于Rayleigh波法的浅埋混凝土基础无损检测方法研究

由于基础缺陷引起的事故日益增多,基础的安全性已经逐渐引起了相关部门的重视。然而,对于已有浅埋混凝土基础,常规的检测方法不但会对结构产生二次伤害,而且效率极低,不利于大规模的检测。文章提出了基于Rayleigh波法的浅埋混凝土基础无损检测技术,阐述了Rayleigh波法检测浅埋混凝土基础尺寸的原理,介绍了Rayleigh波法检测浅埋混凝土基础尺寸的流程,并通过对一浅埋混凝土基础模型进行检测试验,验证了该方法的有效性。     

船舶焊接质量无损检测存在的问题及对策

文章分析了当前广西船舶焊接质量无损检测中存在的主要问题,从加强对第三方检测机构的监督管理方面,针对验船师、无损检测机构及船厂的无损检测工作提出了相应的对策。     

无损检测技术在道路桥梁试验检测中的应用分析

由于道路桥梁工程传统检测技术存在一些不足之处,在很大程度上制约了无损检测技术的应用。为了保障道路桥梁工程建设施工质量,分析无损检测技术的含义及特点,着重研究无损检测技术在道路桥梁试验检测中的应用措施,并针对无损检测技术在道路桥梁试验检测中应用时存在的问题,提出相应的解决方案,以期为相关工作人员提供参考。     

路面基层注浆加固质量评价的无损检测方法应用研究

文章以科研项目路面基层注浆加固试验路为依托,采用3种无损检测手段对注浆加固前后的基层进行检测评价,并取芯验证。结果表明:注浆前后,2D地质雷达同轴图像、高频弹性波反射波法的主频幅值和瞬态面波法的剪切波速度等的变化明显,其中地质雷达法可以实现对路面注浆加固效果的定性描述,后两者可作为半定量评价,而瞬态面波法的剪切波波速对路面结构技术状况变化更敏感。     

路堑高边坡静力荷载下支护前后数值模拟分析

为研究边坡开挖及支护后的稳定性,对开挖及支护后边坡进行FLAC3D数值模拟分析,从水平位移、应力和垂直位移、应力云图等方面对其稳定性进行分析。结果表明:(1)边坡开挖后其稳定性系数较低,不能达到规范要求,其潜在破坏模式为沿岩层分界面滑移破坏,坡脚部位为受应力最大区域。(2)进行锚杆支护后,边坡位移量明显降低,水平方向较之于垂直方向更为明显,且稳定性系数达到规范要求。(3)从应力云图中可得,锚杆锚固段明显受到剪应力作用,锚杆将不同风化程度的岩层连接在一起,使其处于相对稳定状态。     

非接触磁应力在管道焊缝评价中的应用

管道建设期焊缝遗留问题影响管道安全运行,因此应对在役管道焊缝复核检查.文中介绍了磁应力检测技术原理,并以做过内检测以及焊缝开挖无损检测的管道作为目标管段,通过现场对这部分管道采取非接触磁应力检测,验证了该技术具备焊缝识别定位以及焊缝异常识别的能力,但在焊缝异常评价精度上有欠缺.     

基于数值分析的隧道衬砌病害检测技术研究

在高速公路隧道质量控制中,隧道衬砌质量常常因其隐蔽性,而难以做到直观有效的检测。现阶段,关于隧道衬砌质量检测技术的研究主要集中在地质雷达探测、声波探测、回弹检测等无损检测方法的应用方面,而关于检测中发现的衬砌质量缺陷对结构稳定性影响方面的研究较少。文章依托工程实践,通过地质雷达探测的病害分布信息,采用MIDAS GTS NX有限元数值模拟手段,建立荷载-结构法的二维平面模型,研究不同脱空位置对衬砌结构受力的影响,发现隧道衬砌结构受力对拱腰部位的衬砌脱空最敏感,当脱空尺寸达0.2m(高)×1m(长)时,衬砌结构最大von Mises应力位置发生变化,应力增幅达58%,从而为有效指导工程实践提供了数据支撑。通过探索雷达检测与数值分析相结合的手段在公路隧道衬砌质量检测中的应用,可为类似检测工程提供参考借鉴。     

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.