苏拉马都跨海大桥主桥桥面板设计及板、梁连接分析

苏拉马都跨海大桥主桥采用预应力钢-混凝土组合梁结构,介绍了组合梁的桥面板设计,对主梁通过实体模型分析,研究主梁与混凝土桥面板之间作用力传递的途径和方式,定量分析钢主梁、横梁及小纵梁上剪力钉沿桥纵向及水平方向分担力的状况与大小.     

统计学在近代中国的演变——从社会统计到数理统计

从19世纪末期至20世纪初期,统计学在中国完成了从传入到发展的第一个进程.在近半个世纪的时间里,中国统计学的发展浓缩了西方统计学近两百年的发展历程,较之其他的西学知识在近代中国的传播和发展,统计学的历史则表现出了其自身的独特性,这种发展受到当时的社会政治、经济、文化等方面的影响甚大.这是由当时中国的社会背景以及统计学这门学科知识的特殊性质所决定的.     

Approximations to the magic formula

Pacejka’s tire model is widely used and well-known by the automotive engineering community. The magic formula describes the brake force, side force and self-aligning torque in terms of the longitudinal slip and slip angle, plus several corrections. This paper uses approximation theory to obtain different types of approximations to the magic formula: rational functions (RA) resulting from the Remez algorithm, expansions in a series of Chebyshev polynomials (ACh), a series of Chebyshev rational polynomials (ARChPs), a series of rational orthogonal functions (ORF) and a series of ARChPs that result from grade-1 ORFs. The last expansion shows the fastest convergence and most effective computation. Jacobi rational polynomials can also be obtained to complement this expansion and facilitate fine-tuning in specific areas of the error curve. This work is complemented by obtaining the original rational approximations to the inverse tangent function, which take advantage of the curve symmetry to reduce the computation load and provide models that include the influence of the vertical load. The convergence properties of the development in series and the error values resulting from numeric examples for the three types of stress are shown. The proposed final ARChP expressions show very low error (1%) compared to the original magic formula. They can be computed 20 times faster; they can be evaluated, derived and integrated analytically easily; and their coefficients can be obtained from tests using common least-squares algorithms.     

沥青混合料级配曲线研究进展

级配曲线是由富勒模型中最大粒径和形状系数两个参数来确定的,富勒模型能够很好地拟合使用性能良好的级配.级配曲线图是由形状系数和最大粒径组成的直角坐标系,它可以表示出级配范围、砂石比和相关的性能参数.该文分析了Superpave沥青混合料力学和水稳性能的试验结果,提出了根据级配曲线推荐的集料设计出满足路面各项性能的自由设计理念.     

基于监测数据的悬索桥加固技术及其应用

为了确定悬索桥吊拉组合体系加固结构中斜拉索的合理张拉力,根据已有理论提出一种基于监测数据的悬索桥加固技术.以某悬索桥加固为背景,对该悬索桥的主缆温度位移、荷载位移以及桥塔荷载位移进行监测,基于监测数据建立斜拉索索力预测模型,采用该模型得出斜拉索的合理张拉力.该悬索桥加固完成后,通过斜拉索索力实测表明:基于监测数据的悬索桥加固技术具有较高的可靠性,该技术能够较准确地反映既有悬索桥的实际受力状态.     

Numerical prediction of the modal response of flexible cylinders in cross-flow with a current dependent form of damping

A quadratic eigenvalue problem (QEP) was posed in order to study the dynamics of flexible cylinders in cross-flow, simulating slender offshore structures such as risers, catenaries or tendons. The Euler–Bernoulli equation was used to model the structure assuming a fluid loading model, and yielding a quadratic eigenvalue problem that included a form of damping dependent not only on the structural damping itself, but also on the free stream velocity and the fluid force coefficients. We solved the QEP using the finite element method. We also derived a simplified analytical solution in this work for comparison with the QEP, however this solution does not consider changes in tension along the length of the cylinder as the QEP does. In our study, the QEP solutions were first validated against the simplified analytical solution, and also against a well-known experimental dataset obtained in 2003, in which a flexible circular cylinder model was used to model the dynamics of a riser undergoing multi-mode vortex-induced vibrations.     

Actors and Their Representations in Shipping Policy: Developing the European Maritime Safety Agency

This paper discusses the European Maritime Safety Agency (EMSA). Through a chronological reconstruction, the study looks at the events that lead to the official birth of the Agency in 2003 and how it developed to its current state. The conceptual framework draws from cognitive policy analysis, a French political science perspective related to new institutionalisms. This approach emphasizes the role of the actors' own representations of their sector and the ways they fit within the socioeconomic system as a whole. This highlights the evolution of the stakeholders' positions and influence throughout the development process. Findings suggest that although considerable discrepancies between European representatives and those of the shipping industry were present in the context leading to EMSA's creation, the Agency has now established a working consensus confirming a greater implication of European authorities in the regulation of international shipping. The work also suggests that a greater attention to plays of power among stakeholders and how they translate in their representations could be pertinent to strengthen research in shipping policy.     

Are Longer and Heavier Vehicles (LHVs) Beneficial for Society? A Cost Benefit Analysis to Evaluate their Potential Implementation in Spain

Abstract

In this paper we carry out a thorough review of the current research related to the benefits and costs arising from the implementation of longer and heavier vehicles (LHVs). From this review we concluded that despite the many studies available, little has been said about the sensitivity of the benefits and costs to the ultimate performance of the key variables related to the evolution of the economy, road transport performance, safety, and so on. In order to fill this gap, we have designed a sensitivity approach based on a cost benefit analysis tool to determine which variables demonstrate the greatest influence on the benefits and costs stemming from the implementation of LHVs. In order to test the methodology, we have used it in an analysis of the Spanish trunk network. The results show that the benefits of LHVs for society are significant. Even in the least favorable scenario, the economic benefits are greater than €3500 million over 15 years, and the environment enhanced as well, for CO₂ emissions are reduced by 2 Million tonnes. Overall we noted how the results are not very sensitive to the evolution of key variables in determining the final outcome. However, we found that the variables that have the greatest affect on the final benefit, such as traffic growth and social discount rate, depend basically on the performance of the overall economy. Moreover, the private cost for haulers seems to be more important in determining the final benefit than externality costs.     

Incentives in Bus Concession Contracts: A Review of Several Experiences in Latin America

Abstract

This paper reviews the incentive structure of concession contracts in several Latin American transit reforms. It also presents a conceptual analysis of the optimal design of concession contracts. The conceptual discussion and case studies reviewed indicate that payment to operators should be linked to operational variables and that some demand risk should optimally be transferred to operators. Performance standards linked to fines and penalties are not sufficient to guarantee good quality of service, particularly in citywide reforms and where institutional capacity ― in terms of size, experience and expertise of staff ― is lacking and regulatory processes are slow, bureaucratic and cumbersome. This review may be useful for policy-makers designing transit reforms in other countries. The policy lessons of the paper are particularly relevant to cities in the developing world but they are also important for reforms in other countries.     

The economic impact of logistics infrastructure: the case of PLAZA – the Zaragoza Logistics Platform

Abstract

The economics literature offers many examples of studies of the economic impact of transportation infrastructure such as highways, ports, and airports; however, little attention has been paid to other types of infrastructure such as logistics platforms. This article is a first assessment of the economic effects of the largest logistics platform in Europe – PLAZA, the Zaragoza Logistics Platform – located in Spain. More precisely, this paper analyzes the economic significance of PLAZA on the economy of the Aragon region where it is located. The methodology is based on the application of input–output analysis to the final demand of logistics platform-based companies in a manner that is similar to well-established studies of the economic impacts of tourism on tourist expenditure. This makes it possible to quantify the various levels of economic effects (direct, indirect, and induced) in terms of jobs, salaries, and wages, turnover, gross operating surplus (GOS), and gross value added (GVA). The conclusions reveal the economic importance PLAZA has for the regional economy of Aragon, representing just over 2% of total GVA and 3% of turnover.