沥青混合料骨架结构抗剪强度特性的试验研究

采用悬浮密实结构AC-20I、骨架空隙结构AM-20及骨架密实结构SMA-20试样,对三种典型结构的沥青混合料抗剪强度进行了对比试验研究.试验采用粗骨料大型直剪仪,探讨了球形和椭球形集料对抗剪强度的影响.结果表明:从集料级配看,骨架结构形成的抗剪强度明显大于悬浮结构形成的抗剪强度;从集料形状看,椭球体集料构成结构的内摩擦角大于球形体集料构成结构的内摩擦角,而且,骨架密实结构对集料形状最为敏感.     

Has heavy vehicle tolling in Europe been effective in reducing road freight transport and promoting modal shift?

Transportation - During the last few decades, the European Union has promoted distance-based charges on heavy goods vehicles for the use of main roads as a means of funding the infrastructure and...     

Towards an enriched framework of service evaluation for pedestrian and bicyclist infrastructure: acknowledging the power of users’ perceptions

Transportation - More and more cities worldwide are striving for sustainability and livability. Measuring the service or performance of local-scale spaces for pedestrians and bicyclists to better...     

A Step Zero Analysis of the Galapagos Marine Reserve

Contrary to common perceptions, the creation of protected areas does not start when they are officially declared but generally follows a long process. For instance, the Galapagos Marine Reserve (GMR) was not “born” when it was formally announced on March 18^th 1998, but several decades before that. Through document analysis and key informant interviews, we applied the “step zero” approach to examine what happened prior to the implementation of the GMR. This study reveals that the GMR did not arise from a social and political vacuum; rather, events took place in the distant past, even centuries ago, influenced the reserve's creation and current status. Its establishment was driven by complex geopolitical, economic, social, and environmental factors from both within and outside Galapagos. Additionally, the process of creating the GMR was convoluted, marked by hidden interests and conflictive political agendas that triggered controversies between users. The making of the GMR was also influenced by the interest in promoting “nature-based” tourism, and the regulations that followed had disadvantaged small-scale fishers. This knowledge about the reserve's pre-implementation phase enables a broader understanding of the current challenges facing the performance of the GMR and points to possible governance interventions needed to enhance its sustainability.     

Nature or nurture: why do railroads carry greater freight share in the United States than in Europe?

During the 1950s, the share of freight carried by railroads was similar and declining in both the United States and Europe. By 2000, the railroads’ share of freight (measured in ton–kilometers) had reached 38% in the United States while falling to 8% in Europe. This paper examines the reasons for the difference in rail’s share of freight in Europe and the United States. We find that almost 83% of the gap in 2000 is probably due to natural or inherent differences, principally geography, shipment distance, and commodity mix. However, 17% of the gap cannot be explained by these inherent differences and is presumably due to public policies including priority of passenger service, lack of interoperability at borders, service quality and rates, and incentives of the rail operators. We estimate that if that policy gap were closed, railroads’ share of freight in Europe would increase from 8% to 13%.

New appraisal values of travel time saving and reliability in Great Britain

Transportation - This paper provides an overview of the study ‘Provision of market research for value of time savings and reliability’ undertaken by the Arup/ITS Leeds/Accent consortium...     

Port competitiveness in container traffic from an internal point of view: the experience of the Port of Algeciras Bay

The objective of this article is to analyse the factors that affect port competitiveness from the perspective of the agents and companies that operate in one of the Mediterranean ports most active in container traffic: the Port of Algeciras Bay (PAB). It is essential to understand the perspective of the suppliers of port services, in order to apply the necessary judgment when formulating policies to strengthen the competitive position of a port. The model selected to meet the objective outlined is based on the 'extended diamond' of Porter. The universe for the study comprises all the institutions and companies involved in the containerization process in the Port of Algeciras Bay. Within this methodology, two procedures are utilised. First, from the quantitative perspective, a survey has been conducted to obtain responses to two groups of questions, one dealing with situation and the other with perceptions. Second, and from a qualitative perspective, several open interviews have been conducted to corroborate the responses obtained to the questionnaire. From the data obtained in the survey, a model has been estimated that minimises the sum of the residuals in absolute value, utilizing the L1 regression; this model enables the competitive advantages and disadvantages of the PAB, from the point of view of the port operators, to be determined by an analysis of residuals. This analysis demonstrates that the variables representing greater competitive advantages are associated with trans-shipment, and with the maritime accessibility of the Port to vessels, whereas those generating greater disadvantages are associated with rail transport (which, according to those surveyed, has resulted in the diversion of significant volumes of traffic to other Spanish or European ports with better communications, particularly Valencia, Barcelona and Gioia-Tauro, and with the state of competition in container trans-shipment activities.     

Surface intersection in geometric modeling of ship hulls

In this work a methodology is presented for the computation of the intersection of parametric surfaces, namely Non Uniform Rational B-Splines (NURBS), with special attention to some specific requirements for applications to ship hull modeling. The algorithm adopted and the steps of the proposed method are described, namely checking whether the surfaces intersect, preprocessing of linear surfaces with strong discontinuities, computation of starting points, marching along intersection curves, and approximation of the intersections with NURBS curves. Finally, the results of some intersection tests are presented and discussed. The results are validated by comparison with results of commercial codes.     

Fatigue life prediction of welded ship details

Ship structures are submitted to variable cyclic loading during navigation. The cyclic motion of waves induces variable and complex loadings in the structure, which could generate fatigue damage. Moreover, most of these metallic structures are welded assemblies. This technique generates local stress concentrations at the weld toe, which becomes a critical area regarding fatigue. In previous works, a methodology to predict fatigue life was developed and tested on butt-welded and cruciform joints. The present work focuses on other welded assemblies in order to extend fatigue crack initiation life evaluation to a wider range of ship details. The strategy could be split into two steps. First, a finite element calculation is performed under constant or variable amplitude loadings, in order to analyze the elastic shakedown of the structure. To characterize the material heterogeneity of the welded joint, experimental tests together with micro-hardness measurements, are performed on a simulated heat-affected zone. If there is a shakedown in the structure, a post-treatment is applied to predict the fatigue crack initiation. It is based on a two-scale damage model, initially developed by Lemaitre et al. and again includes the heterogeneity of fatigue properties. To validate this methodology, some experimental tests have been performed on welded assemblies which are typical of shipbuilding applications, using a fatigue machine. These comparisons between experimental and numerical fatigue lives are encouraging.     

马德里:城市地下公路与铁路基础设施安全高效发展的全球典范

马德里已经成为城市地下公路与铁路基础设施安全高效发展的一个全球典范.作为改善城市交通系统与公共运输网络的有效投资典范,文章详细介绍了过去12年中地铁网络的发展以及目前M-30环线改建项目情况,分析总结了马德里获得成功的关键因素.