限位装置对斜拉索风雨激振的减振研究

由于拉索风雨激振问题的复杂性,有效的减振方法有待于进一步的探索。文章在Den Hartog驰振机理的基础上,通过对在拉索端部附近安装限位装置来抑制风雨激振的措施进行研究,用有限元方法模拟了斜拉索风雨激振现象,分析了安装限位装置后拉索的振动,解明了安装限位装置前后拉索的振动特性。经比较得知,限位装置能够有效地抑制拉索发生大幅风雨激振。并详细讨论了施加限位装置后,各相关参数对减振效果的影响规律,为今后桥梁工程设计提供理论依据。     

Mitigating environmental impacts in advance: Evidence of cost and time savings for transportation projects

The traditional model for mitigating a transportation project’s environmental impacts typically operates project-by-project and delivers the mitigation just-in-time. In contrast, the newer practice of advance mitigation comprehensively assesses and mitigates impacts from one or multiple transportation projects before or during project planning, sometimes long before project construction begins. The practice has gained adherents for its potential to improve ecological outcomes, by better aligning mitigation and conservation goals. Advance mitigation also stands to reduce mitigation costs, an important secondary benefit for transportation agencies with constrained resources. Evidence of cost savings, however, has been piecemeal and anecdotal. This paper advances knowledge of advance mitigation’s financial impacts in two ways. First, it critically assesses the evidence about cost savings realized through advance mitigation, both through avoided up-front costs and reduced project delay. Second, it directly estimates the project time savings that might accrue with advance mitigation of state highway projects in California. Overall, the balance of evidence is encouraging for transportation agencies that would introduce the practice, and general agreement exists on its financial benefits. Considering project delays related only to the environmental process, we estimate advance mitigation could reduce delivery times by 1.3–5.0 months per project. Still, we also identify factors limiting comprehensive analysis. Transportation agencies adopting advance mitigation practices into their operations could use a pilot approach that includes rigorous environmental and mitigation cost accounting; such pilots would build needed empirical evidence of advance mitigation’s financial and ecological outcomes.     

Evolving Narratives of Low-Carbon Futures in Transportation

Scenarios of low-carbon transport demonstrate that a vast range of different outcomes is possible and contingent on policy, technology and cultural developments. But a closer look indicates that different schools of thought suggest possible pathways diverging in their fine structure. This perspective reveals how three different scientific communities — integrated assessment modelers, transport-sector modelers, and place-based modelers — emphasize distinct solution domains. While integrated assessment models focus on fuel composition, transport-sector models put slightly higher emphasis on efficiency measures; in turn place-based research specifies idiosyncratic behavioral and infrastructural mitigation options that are likely to be beneficial in realizing local co-benefits. These specific local approaches could mitigate urban transport emissions by 20–50%, higher than that revealed in aggregate global models. We discuss differences in approach, possibilities for reconciliation, and the implications of normative assumptions. Targeted three-directional interactions would foster comprehensive understanding of possible low-carbon transportation futures.     

基于摩擦摆支座的城市大跨连续梁桥减震性能研究

为研究摩擦摆支座在提高城市大跨连续梁桥抗震性能上的适用性,以位于8度区的（90＋170＋90） m某城市大跨连续梁桥为研究对象,对该桥摩擦摆支座进行设计,并采用非线性时程反应分析法研究摩擦摆支座的减震效果。结果表明：摩擦摆支座对城市大跨连续梁桥下部结构的纵、横向内力减震效果显著;从自复位能力的角度,摩擦摆支座的摩擦系数取值不宜过大,应根据非线性时程反应分析获得的支座最大位移量验算摩擦摆支座的自复位能力;由于该桥上部结构恒载较大,摩擦摆固定支座的静摩擦力远大于全桥的制动力,因此在不设置剪力键的条件下,也能满足桥梁的正常使用功能。     

Atmospheric Emissions from Shipping: The Need for Regulation and Approaches to Compliance

Shipping has traditionally been viewed as the least environmentally damaging mode of freight transport. Recent studies have increasingly questioned this perception, as attention has focused on both the greenhouse gas emissions (mainly CO₂) and the emission of health-damaging pollutants (such as sulphur, nitrogen oxides and particulates) by ships. This paper reviews the available evidence on the atmospheric emissions of shipping. It proposes that the profit objective has prompted the pursuit of greater fuel efficiency within the sector, but that reliance on market forces alone is insufficient to deliver on the environmental imperative. The paper outlines the current and planned regulatory regime for the atmospheric emissions from ships and posits that greater, and more diverse, market regulation is required. Alternative general approaches to regulatory compliance are categorised as ‘alternative sources of energy’ or ‘abatement technologies’ and the characteristics of a range of specific options are analysed. The paper concludes that although the shipping industry has been slow to improve its environmental credentials, a combination of regulation and technological innovation provides it with significant potential to dramatically reduce its environmental impact.     

基于节段模型试验的悬索桥涡振抑振措施

为研究大跨度悬索桥涡激振动性能,并提出有效的涡振抑振措施,以某大跨度钢箱梁悬索桥为工程背景,通过1∶20大尺度节段模型风洞试验,在低阻尼下研究了人行道栏杆、检修轨道、导流板对主梁涡激振动性能的影响;通过在检修轨道内侧设置导流板抑制主梁的涡激振动,并基于试验现象探讨了涡激振动发生的机理.研究表明,在检修轨道内侧设置导流板抑制主梁涡激振动的措施使桥梁断面的气动外形更合理,抑振效果好,且结构形式简单,便于工程应用.     

大跨度中承式钢箱桁架拱桥抗震体系研究

为研究大跨度中承式钢箱桁架拱桥合理抗震体系,以某主跨519 m的中承式钢箱桁架拱桥为背景,采用MIDAS软件建立全桥有限元模型,分析桥梁自振特性、非线性时程地震响应,对比采用拉索减震支座前、后2种抗震支承体系下的桥梁地震响应,并对拉索减震支座的自由程进行参数分析。结果表明:对于大跨度中承式拱桥,抗震体系设计应重点关注桥梁支座反力;由于主梁从主拱肋间穿过,降低了桥梁的抗扭刚度;采用拉索减震支座前、后,拱脚内力变化不大,桥梁支座横向水平力最大值由3 027 kN降至915 kN,桥梁顺、横桥向位移响应也得到明显改善;该桥合理拉索自由程为5 cm。     

The influence of tyres on the use of the CPX method for evaluating the effectiveness of a noise mitigation action based on low-noise road surfaces

The usage of low-noise road surface can be an important and effective noise mitigation action and, in many cases, it might represent the only viable solution. After the laying of a low-noise road surface, it is necessary to verify if the planned objectives have been actually obtained: the Close Proximity Method (CPX) could be a possible method to achieve this result.The current release of the ISO 11819 draft regarding CPX redirects to a future third part for all details about the reference tyre to be used, while the previous one gave indications on dimensions, kind of tread pattern and maintenance conditions. As well known, tyre dimensions and tread pattern are the main sources of variability of rolling noise. Even though many tyres available on the market comply with all ISO requirements, the choice of a brand or a model rather than another one could nevertheless influence results of measurements.In this work, results obtained in several measurement sessions, repeated using different tyres, are compared, aiming to analyse the influence of the tyre choice in assessing the acoustic performance of a low-noise road surface. Limitations and advantages of the CPX method in regards to the evaluation of the effectiveness of a noise mitigation action are reported, and new perspectives are suggested, in order to improve the relationship with the noise level reduction at the receiver.     

小半径曲线侵入有效站台曲线 超高设计研究

在城市轨道交通车辆扩编、站台加长的既有线改造项目中,为克服小半径曲线侵入有效站台较多带来的 车辆限速问题,借鉴公路曲线超高的设计思路,提出将曲线超高过渡段设置在缓和曲线局部区段,全超高断面设 置在缓圆点或圆缓点处,通过缓和曲线分段顺坡的设计思路,并以北京地铁 13 号线扩能提升改造工程知春路站 车站加长为案例,进行缓和曲线分段顺坡的应用实践。研究结果表明,方案最大限度匹配进出站速度,节省了运 营时间。     

Environmental assessment of electrification of road transport in Norway: Scenarios and impacts

The study develops scenarios regarding the introduction of electric vehicles to the passenger vehicle fleet of Norway to reach the 2020 Norwegian greenhouse gas reduction target and a more extreme target to limit global temperature increase to two degrees. A process-based life cycle assessment approach is integrated with a temporally variable inventory model to evaluate the environmental impacts of these scenarios. We find that greenhouse gases in the reference scenario increase by 10% in 2020 in comparison to 2012; while for the more intensive improvements in conventional vehicles, this increase is reduced to 2%. For electric vehicles deployment scenarios, although the fleet share will reduce the tailpipe greenhouse gas emissions by 8–26%, with the upper end representing the two-degree reduction target, emissions reductions over the entire life cycle are only 3–15%. Electric vehicles also reduce emissions of NO_x, SO₂ and particulates reducing acidification, smog formation and particulate formation impacts, however, with addition of large numbers of electric vehicles significant trade-offs in toxicity impacts are found.