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251.
《铁道标准设计通讯》2017,(7):84-88
箱涵刚域效应是指结构在节点处,由于构件相交而存在的性质特殊的区域,该区域的相对抗弯刚度趋近无限大,呈现出不可变形的特性,从而对结构受力和变形产生影响的现象。为研究刚域效应对箱涵结构的影响,对箱涵进行受力和变形的特性分析,确定刚域及其判定方法。以箱涵的基本参数和加腋特征参数为变量,分析箱涵结构刚域效应的规律。并对比分析考虑刚域效应后结构变形和内力结果,经分析确定出顶板和侧墙的刚域范围与结构尺寸之间的比例关系,以及加腋构造的最优坡度。考虑刚域效应后的变形和内力值较小,可以减小钢筋用量,降低工程造价。 相似文献
252.
Land border crossings in North America, such as those between Canada and U.S.A., are expected to experience severe imbalance of travel demand and capacity of processors. During peak travel periods, this is already the case at high traffic locations. The land border crossing authorities have to address problems of congestion, national security and environmental impacts in the operation of the existing systems and to continue to address these problems as a part of infrastructure expansion plans. There is a need to adapt the crossing system management in order to accommodate efficiency and productivity‐oriented priority crossing measures. From a methodological perspective, it is a challenge to evaluate the role of priority crossing measures within the complex border crossing system. This paper reports research on modelling priority crossing initiatives. A microsimulation approach was used to model and analyse integrated processors of the Peace Bridge crossing system between Fort Erie (Ontario) and Buffalo (New York) under different scenarios of travel demand, customs processing times, priority crossing and queue jump lanes for automobile and truck traffic. Findings show the extent to which a border crossing system with priority crossing and queue jump lanes is more efficient and productive than one without these innovations. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
253.
In this paper we examine two questions; what is it that makes some cases of airlines within airlines apparently successful while in many other cases it is just the opposite? And second, why would a carrier attempt such a strategy, is there a common set of circumstances or is each case unique? In the US, Canada and Europe a number of legacy carriers have sought to respond to LCC entry by creating an LCC within the legacy carriers; most have failed but some have succeeded, most notably in Australia and Germany. We first examine the evolution of the LCC business model and illustrate the different forms it takes today. Following this we provide a discussion of the underlying sources of cost advantage of the LCC and assess which sources are sustainable in the longer term. Finally we examine the conditions under which these apparent successes have occurred and look for common threads. We find market dominance, judicious network planning and co-ordination are necessary conditions for success. 相似文献
254.
Vehicle headway modeling and its inferences in macroscopic/microscopic traffic flow theory: A survey
Vehicle headway distribution models are widely used in traffic engineering fields, since they reflect the fundamental uncertainty in drivers' car-following maneuvers and meanwhile provide a concise way to describe the stochastic feature of traffic flows. This paper presents a systematic review of vehicle headway distribution studies in the last few decades. Since it is impossible to enumerate the merits and drawbacks of all of existing distribution models, we emphasize four advances of headway distribution modeling in this paper. First, we highlight the chronicle of key assumptions on the existing distribution models and explain why this evolution occurs. Second, we show that departure headways measured for interrupted flows on urban streets and headways measured for uninterrupted flows on freeways have common features and can be simulated by a unified microscopic car-following model. The interesting finding helps gather two kinds of headway distribution models under one umbrella. Third, we review different approaches that aim to link microscopic car-following models and mesoscopic vehicle headway distribution models. Fourth, we show that both the point scattering on the density-flow plot and the shape of traffic flow breakdown curve implicitly depend on the vehicular headway distribution. These findings reveal pervasive connections between macroscopic traffic flow models and mesoscopic headway distribution. All these new insights bring new vigor into vehicle headway studies and open research frontiers in this field. 相似文献
255.
考虑总人口是非常数的SIRS传染病模型,在不考虑空间扩散和考虑空间扩散两种情形时,分别构建了Liapunov函数并讨论了其模型的常数平衡点的稳定性. 相似文献
256.
《铁道标准设计通讯》2017,(6):111-115
基于各行业规范中没有明确提及圆形竖井设计方法的现状,在进行相关规范解读分析的基础上,对比分析竖井侧压力、国内外规范中提到的圆形水平径向荷载的计算方法,并采用3种结构计算方法对实例进行分析论证,得出合理的结论。结果表明:竖井侧压力采用朗肯土压力计算公式;圆形水平径向荷载引入折减系数,该值为25%;荷载结构法采用主动荷载+被动荷载模式,推荐采用二维荷载结构法设计为主,三维荷载结构法及三维连续介质有限元法设计为辅的设计方法。 相似文献
257.
结构参数对鼓式制动器高频噪声的影响 总被引:4,自引:1,他引:4
本文在建立鼓式制动器高频噪声问题的结构闭环耦合计算模型的基础上,对某国产车的高频噪声问题进行了计算。分析中所用的制动底板,鼓和蹄的结构参数均取自实际结构。计算分析的结果表明:制动器所有部件的结构参数对制动高频噪声均有重要影响,过去仅把产生高频器材怕的原因归结为蹄与鼓间的参数匹配是不正确的。对计算结果的归纳表明:对制动器高频噪声起决定作用的是鼓子结构和包含有底板,蹄,分泵及油路操纵系统在内的PSPO 相似文献
258.
David A. Hensher 《Transportation》1994,21(2):107-133
Stated preference (SP) methods are widely used in travel behaviour research and practice to identify behavioural responses to choice situations which are not revealed in the market, and where the attribute levels offered by existing choices are modified to such an extent that the reliability of revealed preference models as predictors of response is brought into question. This paper reviews recent developments in the application of SP models which add to their growing relevance in demand modelling and prediction. The main themes addressed include a comparative assessment of choice models and preference models, the importance of scaling when pooling different types of data, especially the appeal of SP data as an enriching strategy in the context of revealed preference models, hierarchical designs when the number of attributes make single experiments too complex for the respondent, and ways of accommodating dynamics (i.e. serial correlation and state dependence) in SP modelling.An earlier modified version was presented as the keynote address to the 1993 National Conference on Tourism Research, held at the University of Sydney, 19 March 1993. The comments of Jordan Louviere, Lester Johnson, Paul Hooper, W.G. Waters II and Mark Bradley are appreciated. 相似文献
259.
结构性能检测和评价是沥青路面养护管理过程中的一项重要内容,据此可以判断路面结构的完好程度及其损坏发展的速率,并确定是否需要采取改建措施。本文对目前常用的弯沉检测技术和设备进行了汇总比较;对我国规范中的路面结构承载能力评价方法和评价指标进行了分析,提出了改进的计算方法;建立了指标值域转换模型,并推荐了相应指标的分级评价标准。 相似文献
260.