钦江特大桥钢管拱肋安装施工方案

文章针对钦江特大桥桥位处的具体地形状况及其拱肋安装施工特点,提出了钢管拱肋加工制作场地布置方案,介绍了大桥钢管拱肋缆索安装系统构成,阐述了大桥钢管拱肋安装施工的工艺流程及要点。     

钢管混凝土单圆拱肋压弯屈曲的有限元方法

文章结合实例对钢管混凝土拱桥拱肋的极限承载力进行研究,通过利用大型有限元分析软件ANSYS建立钢管混凝土拱肋模型,施加平面内不对称荷载,分析钢管混凝土拱肋的极限承载力和抗弯性能,并和传统的弹性理论方法计算所得的拱肋的压弯屈曲性能进行比较,得出拱肋压弯屈曲的有限元方法。     

马滩红水河大桥钢管焊接质量无损检测与监控分析

大跨度钢管混凝土拱桥的拱肋加工与焊接直接影响到施工质量,文章以马滩红水河特大桥为例,介绍了钢管拱肋加工过程中,拱肋加工焊接无损检测技术的应用方法,并分析了无损检测监理要点,供类似钢管混凝土拱桥施工参考。     

钢管拱桥单肋安装单肋合龙施工技术

钢管拱桥拱肋安装施工一般采用双肋平行对称安装工艺,曹娥江袍江大桥主桥钢管拱肋安装过程中,采用了国内首创的单肋安装、单肋合龙施工工艺,使拱肋节段安装进度大大加快,文章对该施工技术进行总结,为今后类似工程提供借鉴。     

钢管拱肋加工制作工艺

文章结合银川绕城高速公路大西湖特大桥工程实例，从钢管拱肋管节划分方法、制作加工精度要求、拱肋加工工艺流程、制作方法等方面介绍了钢管拱肋的加工制作工艺，并提出了工艺制作中的注意事项。     

鸿福路跨河钢管拱桥墩式支架法安装拱肋施工技术

钢管拱肋安装是钢管混凝土拱桥施工的关键技术。本文论述了鸿福路跨河钢管拱桥钢管拱肋采用墩式支架法安装的施工方法，施工工艺，以及机具设备等施工技术。     

铁路钢管混凝土简支拱桥拱肋施工关键技术研究

为提高铁路钢管混凝土简支拱桥拱肋施工质量,结合蒙华铁路杨家沟跨延延高速公路大桥,从支架搭设、吊机上下桥、拱节段吊装、拱节段焊接、支架拆除、混凝土浇筑、钢管拱涂装等方面对钢管混凝土简支拱桥拱肋施工关键技术进行研究,旨在为相关施工单位提供技术指导,提升拱桥拱肋施工质量,为铁路施工建设贡献力量。     

合江长江一桥钢管拱肋高空焊接质量控制分析

文章以合江长江一桥为例,介绍了其钢管拱肋安装过程中,拱肋空中接头的焊接工艺及质量控制方法,供类似钢管混凝土拱桥施工参考。     

合江长江一桥200t级钢管拱肋节段拼装工艺

文章结合世界最大跨径钢管混凝土拱桥——主跨530m合江长江一桥的200t级钢管拱肋节段拼装工程实例,介绍了卧拼和立拼两种钢管拱肋节段拼装工艺方法,指出两种工艺都是可行的,立拼工艺更接近拱肋安装施工的正式状态,而卧拼工艺可以大大提高施工的效率、经济性和安全性。通过立拼检验证明,当控制轴线偏位在±3mm以内时,卧拼工艺可以达到规范规定的精度,200t级钢管拱肋节段拼装推荐采用卧拼方法。     

光照作用下的钢管拱肋变形研究

为探究拱肋在日照下的表面温度场及其对拱肋变形的影响,文章运用傅里叶定律推导空钢管拱肋在日照下的表面温度变化规律,并建立拱肋截面平均温度解析式,通过对某未灌浆的大跨径四肢桁架钢管拱桥的温度和变形进行实地测量,将测量值与Midas Civil有限元软件模拟结果作对比,验证了该理论在计算拱肋合龙后的竖向位移方面具有较高准确性,并对拱肋的横向位移做出了初步分析,为拱桥的合龙及合龙后的变形计算提供了参考依据。     

Cost and time damping: evidence from aggregate rail direct demand models

There is a significant body of evidence from both disaggregate choice modelling literature and practical travel demand forecasting that the responsiveness to cost and possibly to time diminishes with journey length. This has, in Britain at least, been termed ‘Cost Damping’, and is recognised in guidance issued by the UK Department for Transport. However, the consistency of the effect across modes and data types has not been established. Cost damping, if it exists, affects both the forecasting of demand and our understanding of behaviour. This paper aims to investigate the evidence for cost and time damping in rail demand using aggregate rail ticket sales data. The rail ticket sales data in Britain has, for many years, formed the basis of analysis of a wide range of impacts of rail demand. It records the number of tickets sold between station pairs, and it is generally felt to provide a reasonably accurate reflection of travel demand. However, the consistency of these direct demand models with choice modelling and highway demand model structures has not been investigated. Rail direct demand models estimated by ticket sales data indicate only slight variation in the fare elasticity with distance, as is evidenced in the largest meta-analysis of price elasticities conducted to date (Wardman in J Transp Econ Policy 48(3):367–384, 2014). This study of UK elasticities shows strong variation between urban and inter-urban trips, presumably a segmentation at least in part by purpose, but less remaining variation by trip length. A lack of variation by length supports the hypothesis of cost damping, because constant cost sensitivity would imply that fare elasticity would increase strongly with distance, because of the increasing impact of higher fares at longer distances. In this paper we indicate that rail direct demand models have some consistency of behavioural paradigm with utility based choice models used in highway planning. We go on to use rail demand data to estimate time and fare elasticities in the context of various cost damping functions. Our empirical contribution is to estimate time elasticities on a basis directly comparable with cost elasticities and to show that the phenomenon of cost damping is strongly present in ticket sales data. This finding implies that cost damping should be included in models intended for multimodal analysis, which may otherwise give incorrect predictions.     

Optimal subwork zone operational strategy for short‐term work zone projects in four‐lane two‐way freeways

Roadside trees in Singapore are regularly trimmed for the purpose of traffic safety and roadside tree‐trimming project is one typical type of short‐term work zone projects. To implement such a short‐term work zone project, contractors usually divide an entire work zone into multiple subwork zones with the uniform length. This paper aims to determine an optimal subwork zone strategy for the short‐term work zone projects in four‐lane two‐way freeways with time window and uniform subwork zone length constraints. The deterministic queuing model is employed to estimate total user delay caused by the work zone project by taking into account variable traffic speeds. Based on the user delay estimations, this paper proceeds to build a minimization model subject to time window and uniform length constraints for the optimal subwork zone strategy problem. This paper also presents a variation of the minimization model to examine the impact of unequal subwork zone length constraint. Since these minimization models belong to the mixed‐integer non‐differentiable optimization problems, an iterative algorithm embedding with the genetic simulated annealing method is thus proposed to solve these models. Finally, a numerical example is carried out to investigate the effectiveness of the proposed models. Copyright © 2010 John Wiley & Sons, Ltd.     

Consumers' responses to fuel-efficient vehicles: a critical review of econometric studies

In an effort to conserve fuel, Congress required that automobile manufacturers increase the average fuel efficiency of the vehicles which they sell. The extent to which this policy is successful in conserving fuel depends on how consumers respond to the more fuel-efficient vehicles. The present paper reviews previous economic research on automobile demand and examines what this research can tell us about how consumers will respond to fuel-efficient vehicles. Three categories of research are reviewed, namely aggregate econometric studies, disaggregate econometric studies, and hedonic price analyses. It is shown that insufficient variation and too large covariation among automobile characteristics (such as price, weight and length) are problems which hinder the usefulness of each type of analysis. Two methods to alleviate these problems are proposed for future research.     

Ridership drivers of bus rapid transit systems

We have collected information on 46 bus rapid transit (BRT) systems throughout the world to investigate the potential patronage drivers. From a large number of candidate explanatory variables (quantitative and qualitative), 11 sources of systematic variation are identified which have a statistically significant impact on daily passenger-trip numbers. These sources are fare, headway, the length of the BRT network, the number of corridors, average distance between stations; whether there is: an integrated network of routes and corridors, modal integration at BRT stations, pre-board fare collection and fare verification, quality control oversight from an independent agency, at-level boarding and alighting, as well as the location of BRT. The findings of this paper offer important insights into features of BRT systems that are positive contributors to growing patronage and hence should be taken into account in designing and planning BRT systems.     

浅谈如何更好地规范公路建设设计变更行为

文章针对目前我国公路建设设计变更领域存在的一些问题,从设计变更内容、设计变更种类分析产生问题的原因,就如何更好地规范公路建设设计变更行为,提出了相关建议。     

Analysis of vehicle ownership evolution in Montreal,Canada using pseudo panel analysis

This paper employs a pseudo-panel approach to study vehicle ownership evolution in Montreal region, Canada using cross-sectional origin–destination survey datasets of 1998, 2003 and 2008. Econometric modeling approaches that simultaneously accommodate the influence of observed and unobserved attributes on the vehicle ownership decision framework are implemented. Specifically, we estimate generalized versions of the ordered response model—including the generalized, scaled- and mixed-generalized ordered logit models. Socio-demographic variables that impact household’s decision to own multiple cars include number of full and part-time working adults, license holders, middle aged adults, retirees, male householders, and presence of children. Increased number of bus stops, longer bus and metro lengths within the household residential location buffer area decrease vehicle fleet size of households. The observed results also varied across years as manifested by the significance of the interaction terms of some of the variables with the time elapsed since 1998 variable. Moreover, variation due to unobserved factors are captured for part-time working adults, number of bus stops, and length of metro lines. In terms of the effect of location of households, we found that some neighborhoods exhibited distinct car ownership temporal dynamics over the years.     

宽浅变迁性河段桥长计算公式比较分析

文章以新疆宽浅变迁性河段现行桥长计算公式为基础,通过建立桥长模型公式与实桥的比较分析,选出适用于新疆宽浅变迁河段水流泥沙运动特性的桥长计算公式。     

高压燃气管道储气能力分析

高压燃气管道储气能力与两端压力和管长有着密切的联系.为了得到高压管道的储气量与压力和管长的关系,利用稳态仿真模型,采用四阶龙格-库塔法对模型进行求解,对求出的沿线压力进行线性拟合,得到沿线压力变化公式.结合储气定义推导出储气量与管长的关系式,并得到实例验证.从关系式来看,当管长等于最优管长时储气量最大.     

Collision avoidance analysis for transition taper length

Transition taper length plays a vitally important role in work zone safety operations because too short a transition taper length will result in higher accident risks and too long a transition taper length could increase traffic delay. This paper evaluates transition taper length under various traffic conditions and road geometries using collision avoidance analysis. The longitudinal distances for lane changing and emergency stopping manoeuvres are respectively calculated using collision avoidance analysis. The higher value between the longitudinal lane changing distance and emergency stopping distance is considered as the expected transition taper length. The comparison of transition taper lengths from the collision avoidance analysis and current empirical transition taper formulae shows that the collision avoidance analysis has the capability of evaluating transition taper lengths. This paper also contributes to providing theoretical supports for these empirical formulae.     

Improved vehicle classification from dual-loop detectors in congested traffic

Vehicle classification is an important traffic parameter for transportation planning and infrastructure management. Length-based vehicle classification from dual loop detectors is among the lowest cost technologies commonly used for collecting these data. Like many vehicle classification technologies, the dual loop approach works well in free flow traffic. Effective vehicle lengths are measured from the quotient of the detector dwell time and vehicle traversal time between the paired loops. This approach implicitly assumes that vehicle acceleration is negligible, but unfortunately at low speeds this assumption is invalid and length-based classification performance degrades in congestion.To addresses this problem, we seek a solution that relies strictly on the measured effective vehicle length and measured speed. We analytically evaluate the feasible range of true effective vehicle lengths that could underlie a given combination of measured effective vehicle length, measured speed, and unobserved acceleration at a dual loop detector. From this analysis we find that there are small uncertainty zones where the measured length class can differ from the true length class, depending on the unobserved acceleration. In other words, a given combination of measured speed and measured effective vehicle length falling in the uncertainty zones could arise from vehicles with different true length classes. Outside of the uncertainty zones, any error in the measured effective vehicle length due to acceleration will not lead to an error in the measured length class. Thus, by mapping these uncertainty zones, most vehicles can be accurately sorted to a single length class, while the few vehicles that fall within the uncertainty zones are assigned to two or more classes. We find that these uncertainty zones remain small down to about 10 mph and then grow exponentially as speeds drop further.Using empirical data from stop-and-go traffic at a well-tuned loop detector station the best conventional approach does surprisingly well; however, our new approach does even better, reducing the classification error rate due to acceleration by at least a factor of four relative to the best conventional method. Meanwhile, our approach still assigns over 98% of the vehicles to a single class.