桥面混凝土铺装层对主梁承载能力的影响分析

在桥梁结构设计与桥梁荷载试验计算中,铺装层往往被保守地当作恒载来处理,未考虑其对主梁受力影响,而桥面铺装层对主梁的影响主要取决于铺装层与主梁的结合形式。文中以某普通钢筋混凝土梁为研究对象,针对桥面铺装结构和主梁的强、弱2种不同结合形式,在不同铺装层厚度下进行有限元模拟计算和结构静载试验;通过对比分析计算结果与试验结果,指出混凝土铺装层是桥梁结构承力构件的一部分,与主梁共同参与受力,从而提出桥梁结构计算模型中混凝土铺装层与主梁的合理的结合形式。     

The role of anticipated time pressure in activity scheduling

In the present article we focus on the cost or disutility of engaging in activities arising from the time pressure people frequently experience when they have committed themselves to perform too many activities in a limited amount of time. Specifically, we propose that anticipated time pressure increases the likelihood of two types of planning, one short-term and the other long-term encompassing different strategies for eliminating or deferring activities. In addition, we discuss several behaviorally realistic such strategies. It is assumed that strategies differ depending on whether an activity satisfies physiological needs, is performed because of institutional requirements or social obligations, or is performed because of psychological or social motives. Strategies are also assumed to differ depending on the degree to which planning is feasible. Computer simulations of available activity data are presented to illustrate consequences of the different strategies on time pressure and activity agendas.     

Travel to work and household responsibility: new evidence

A persistent empirical finding in the research on travel patterns is that women tend to engage in shorter work commutes than men. Research evaluating the degree to which this gender differential in commuting may be explained by the division of labor in the household has produced decidedly mixed findings. This paper presents a critical review of the methods and results of recent research on the gender differential in commuting along with the associated implications for the household responsibility hypothesis (HRH). While all of the articles reviewed are informative and unique, not all conclusions are well supported. The paper then tests the HRH using the 1990 NPTS travel data. The new evidence confirms that women continue to exhibit shorter commute times and distances than men and provides support for the HRH. The paper concludes with a summary of findings and recommendations for further research.     

Temporal disaggregation of travel demand for high resolution emissions inventories

The commonly used photochemical air quality model, the Urban Airshed Model (UAM), requires emission estimates with grid-based, hourly resolution. In contrast, travel demand models, used to simulate the travel activity model inputs for the transportation-related emissions estimation, typically only provide traffic volumes for a specific travel period (e.g. the a.m. and p.m. peak periods). A few transportation agencies have developed procedures to allocate period-based travel demand data into hourly emission inventories for regional grid cells. Because there was no theoretical framework for disaggregating period-based volumes to hourly volumes, application of these procedures frequently relied upon a single hypothetical hourly distribution of travel volumes. This study presents a new theoretical modeling framework that integrates traffic count data and travel demand model link volume estimates to derive intra-period hourly volume estimates by trip purpose. We propose a new interpretation of the model coefficients and define hourly allocation factors by trip purpose. These allocation factors can be used to disaggregate the travel demand model ‘period-based’ simulation volumes into hourly resolution, thereby improving grid-based, hourly emission estimates in the UAM.     

双横臂前独立悬架转向梯形断开点的确定

与独立悬架相适应的转向梯形机构一定是断开式梯形，其断开点位置正确与否直接影响汽车的操纵稳定性，给出了求解双横臂式独立悬架结构梯形断开点的方法，并通过计算实例说明了断开点最佳位置的确定。为汽车设计和结构分析提供了简便有效的方法。     

Stated adaptation surveys and choice process: Some methodological issues

The "Stated Adaptation" survey is an interactive technique which allows us to obtain a clearer picture of the attitudes and behaviours of individuals when confronted with hypothetical situations, in particular inexperienced travel conditions. This method makes use of a simulation game whose purpose is to explore on small samples individuals' choice processes when selecting between the different transport alternatives which are available to them. This paper describes how gaming-simulation is designed, with reference to the issues tackled by two surveys which have recently been carried out in France (reactions to urban road pricing and perception of electric vehicles). It describes the benefits of this experimental approach which allows stated behaviours to be checked to a considerable degree. The limits and potential developments of this survey technique are also discussed.     

突发事件下路网运行时间可靠性研究

对突发事件下的路网运行时间可靠性进行分析,从路段通行能力与运行时间关系的角度,对交通流量与运行时间关系进行讨论。在研究运行时间的均值、标准差等特征值在突发事件下变化的基础上,利用机会约束模型,建立异常状态下路网容量分析的非线性规划模型。实例分析结果表明,突发事件出现时路网运行时间可靠性与其承担的交通流量有直接的关系。     

二灰碎石混合料抗冲刷性能试验研究

利用冲刷试验仪进行了不同材料、不同级配二灰碎石混合料的冲刷试验研究,并通过试验确定了二灰碎石混合料的预冲刷时间,提出了在扣除预冲刷时间对试验结果的影响后,可利用7min内的单位时间冲刷率,作为评价二灰碎石混合料抗冲刷性能的指标。试验结果表明,影响二灰碎石混合料抗冲刷性能的主要因素是集料的级配状况,结合料的影响较小。     

基于居民出行时耗与出行比例关系的OD矩阵估算新方法

建立了基于居民出行时耗与出行比例关系的OD矩阵估算新方法，该方法依据出行时耗分布规律进行，将小区出行量离散为不同出行时耗区间的出行量，并根据出行时耗区间所覆盖的交通吸引小区的面积及吸引量进行交通分布，方法运用中还可根据城市不同区域交通特征调整区域居民出行时耗分布，从而克服了重力模型OD估算结果与出行时耗特征不一致及模型参数全局不变等缺点。实例证明了该方法优于重力模型OD矩阵估算精度。     

智能公交电子站牌显示时间预测方法研究

公共交通智能化调度系统是利用先进的技术手段，动态地获取实时公共交通信息，实现对公交车辆的实时监控和调度，这是公交调度的新模式。公交站点间运行时间预测是城市公共交通智能化调度最重要的工作。研究了基于智能化调度系统的公交电子站牌显示时间的预测理论、模型和方法，旨在为推进我国智能公交系统的快速发展奠定基础。