箱梁悬臂施工考虑剪力滞效应的应力测试影响分析

随着箱形梁桥向长悬臂板、大肋间距的简洁型单箱单室截面发展,其剪力滞效应日益受到关注。文章采用Midas Civil软件建立单梁施工阶段模型,采用Midas FEA软件建立实体施工阶段模型,通过两种模型数据的比较,分析箱梁剪力滞效应的分布情况,并通过研究几个典型施工阶段的剪力滞系数分布规律,完善了箱梁剪力滞效应对应变测试影响分析的方法。     

单箱多室斜交箱梁剪力滞效应分析

文章结合具体工程实例,介绍了单箱多室斜交箱梁的剪力滞分析思路,并通过建立三维实体有限元模型,对比分析了正交桥与斜交桥剪力滞效应的差异,探讨了宽高比、斜交角等结构参数对单箱多室斜交桥剪力滞效应的影响。研究发现,单箱多室斜交箱梁桥的剪力滞效应与正交桥相比有很大差异,同时其参数敏感性也更加显著。     

弯曲连续刚构桥剪力滞效应初探

箱梁的剪力滞后效应是大跨径连续刚构桥梁设计分析中较为复杂的内容之一,影响着桥梁结构设计的合理性。文章介绍了曲线箱梁的剪力滞计算方法,并结合泥溪沟2号大桥工程实例,通过建立三维实体有限元模型,对不同曲率的桥梁结构进行线性静力分析,得出曲线连续钢构桥任-截面剪力滞的分布规律。     

弯曲宽箱梁受力性能分析

曲线梁桥由于其结构自身存在着弯扭耦合问题,因此其设计、施工及研究的难度比直线桥大得多。文章以某弯曲宽箱梁为依托工程,运用有限元软件AN-SYS建立简支曲线钢箱梁模型,对其空间受力性能进行分析,得出了其在自重作用下的应力状态和支座处剪力滞效应规律。     

钢-混组合梁负剪力滞有限元分析

负剪力滞现象普遍存在。剪力流是产生负剪力滞的关键,而在简支梁的跨中,因截面无法自由翘曲必然产生剪力滞效应。文章结合港珠澳大桥工程实例,运用Midas/FEA建立组合梁简支状态有限元模型,模拟组合梁在海上临时架设施工工况,探讨钢-混组合梁在简支状态下施加区域均布荷载前后,负剪力滞的分布规律。     

浅谈现浇连续箱梁施工方案

本文根据紫洞特大桥引桥连续箱梁结构及实际地形情况,介绍了现浇连续箱梁施工方案和施工要点。     

现浇预应力混凝土连续箱梁施工技术探讨

文章分析了预应力混凝土连续箱梁的特点,介绍了几种常见的现浇预应力混凝土连续箱梁施工技术,并结合具体工程案例探讨了该技术的施工方法。     

船岭岽特大桥连续箱梁合龙段施工技术

中跨合龙段施工是连续箱梁桥施工过程中的关键施工阶段,此阶段施工实现了桥梁从悬臂梁转换为连续梁。本文结合船岭岽特大桥预应力连续箱梁左幅中跨合龙施工过程控制,阐述了合龙段施工几个技术要点。     

滨博高速公路分离式立交桥支撑体系的设计与施工

支撑体系是保证现浇连续箱梁外观质量符合设计要求的支架与模板施工方案.所述的支撑体系方案较好的解决了实际工程中遇到的现浇连续箱梁支撑体系这一技术问题,保证了现浇连续箱梁的工程质量.     

分离式桥现浇连续箱梁钢管支架施工方案

文章以陈家田分离式桥现浇连续箱梁满堂钢管支架施工为例，介绍了在山区软质地基上进行现浇预应力连续箱梁满堂钢管支架施工的总体布置方案，并通过支架力学检算验证了施工方案的可行性，同时阐述了支架地基处理、支架装拆及加载预压等施工过程。     

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.     

Inland waterways—their role and significance in European transport

Summary

1) Western Europe has a navigable waterways‐network of about 19,000 kms. For the coming decades, however, about 40 percent of the length of these waterways has a very limited relevance, because of the small capacity of the barges that can pass along them.

2) Of the different types of barges the majority are the self‐propelled type. The importance of the pull‐towed barges is declining quickly, whereas the push‐towed barges are on the upswing.

3) The relative importance of inland shipping in comparison with rail transport is far from uniform. In The Netherlands inland shipping is dominant. On the other hand, in France, this mode of transport has only 30 percent of the total number of tons transported by inland shipping and railways together.

4) May the relative importance defer, there is a strong resemblance between the types of goods that are transported via the waterways with crude and manufactured minerals as well as building materials ranking high. In general, inland shipping is primarily involved in the transport of basic products and is of vital importance to the functioning of the West‐European economy.

5) The rather complicated legal regime of the waterways in Western Europe is certainly not the only reason why the integration in the transportation sector of the European Communities hardly moves on.

A fundamental discussion about the basic conceptions of the transport policy in the Common Market is unavoidable before real progress can be made. The entrance of the United Kingdom into the European Community may give an opening on this point.

6) Life goes on, with or without transport‐integration. Inland shipping moves forward too, paying for the use of infrastructure or not.

The general trends in transport support the expectation that the relative importance of inland shipping will increase in the coming decades. The increase in size of shipments and transport distances works in favour of this mode of transport. Besides this, inland shipping still has many possibilities to improve its productivity.

7) The future of inland shipping will be found in bulk transport and the transport of general cargo that has a volume per destination that goes far beyond the quantities for which the container or comparable types of transport units are better suited.     

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。     

Induced traffic: what do transportation models tell us?

Mathematical models of transportation systems have played a prominent role in transportation planning throughout the world since the 1960s. These models are hypotheses of how people use transport systems. They provide a means of extrapolating the necessarily limited empirical evidence of how road users respond to changes in the road system. However, it needs to be recognised that these extrapolations rely for their validity on the realism of the underlying theories; transportation models can only tell us about the relationships actually built into them.This paper reviews the limited number of studies undertaken mainly in the UK in which calibrated transportation models have been used in a systematic way to give some insight into the relative importance of the various components of induced traffic. These studies include analyses of the effects of road schemes using: a theoretical single link model; conventional four-stage transportation models of Cardiff and Belfast; elasticity models in Cardiff, Belfast, West London and Norwich; land-use interaction models in Leeds, Bilbao, Dortmund; and a model of land-use effects in Norwich. The results tell us two things: (a) the scale of the various elements of induced traffic, and (b) the implications for the economic benefits of road schemes.     

Transport emissions and travel behaviour: A critical review of recent European Union and UK policy initiatives

There are clear signs of a shift in the UK transport policy in response to concerns about the environmental impacts of road transport and anxieties about the implications of the projected future growth in demand.Much of the framework of UK transport policy is now determined at the overall European Union level. To date most European legislation and policy proposals have been concerned with reducing the specific externalities associated with the transport sector, with none of the measures involved likely to have more than a marginal impact on the growth in demand. The emerging research evidence suggests however that the private costs of car use in Europe may fall substantially short of its total social costs and there is an important emerging policy debate about how this gap might be closed.The UK has introduced a policy package designed to reduce the growth of car travel and its environmental impact, within which land-use planning measures feature prominently. The land-use policies, which to some extent represent a reassertion of many traditional UK planning policies, include: an emphasis on focussing new development in urban areas, increasing residential densities, strengthening the role of existing centres and improving provision for walking and cycling.A number of factors will constrain the effectiveness of the package in practice. There are also concerns about its impact on key environmental objectives, including air quality. There are important questions too about the welfare effects of increasing densities and about the wider impacts of the package on economic efficiency.     

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.     

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.     

The quality of survey data: Telephone versus face-to-face interviews

Those designing surveys and producing data have always been concerned about its quality. The increasing stringency of the financial constraints which affect public authorities and the increased scope of involvement in the regulation of urban travel has led us to pay even greater attention to the quality of data. This issue is frequently covered in the literature on survey methods. However, comparisons between different survey methods are more rarely conducted. The decision to conduct such an analysis is partly the result of the development of telephone use to the detriment of other survey modes in many countries and also the development of Computer-Aided Telephone Interviewing (CATI) which facilitates the running and monitoring of the survey.This paper examines several aspects of this question in order to compare the performance of telephone and face-to-face interviews. The first aspect is the representativeness of the sample, and therefore relates mainly to the issue of nonresponses and the choice of a sample base. The second concerns the accuracy of the information and involves the choice of a survey area and the recording of all trips, including short-distance travel. Finally, the quality of data is obviously determined by the quality of the responses given by those interviewed.The answers we give frequently depend on the objective of the surveys, which leads us to put forward a table which summarizes the performance of telephone and face-to-face interviews on the basis of the main objective of the survey. Broadly, the telephone seems to be the favoured tool for surveys in the area of transport planning and surveys which aim to provide data for forecasting models, mostly on the grounds of cost. However, face-to-face techniques are often preferred for surveys which aim to discover and analyze the factors which explain individual travel behaviour.     

Immobility in travel diary surveys

The share of immobile persons, i.e. persons not leaving their homes on a given reporting day, is both a central result and a prime quality indicator of a travel diary survey. The wide range of values for the share of immobiles reported in travel diary and time budget survey literature has motivated this in-depth analysis of the reasons for these disparities. This paper collates available evidence on the share of immobiles in travel diary surveys. The share of these non-travellers (UK), or no-trippers (US), varies greatly between otherwise similar surveys. After analysing both disaggregate and aggregate information, this paper concludes that the share of immobiles should be in the range of 8%–12% for the standard one-day, weekday-only travel diary. The analysis suggests that a substantial share of respondents refuse to participate in a soft way, i.e. by claiming not to have left the house. In its conclusions, the paper sketches new ways to reduce the share of such soft refusers during the interview and to identify them during the analysis.