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立交匝道桥由于其结构受力与直线桥存在差异,特别是由于弯扭耦合作用,其转矩通常比直线箱梁桥大。介绍了鹦鹉洲接线工程立交匝道桥的计算方法和特殊构造细节,如箱梁横隔板、抗扭钢筋、伸缩缝及支座选用布置等设计要点。 相似文献
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The well-known feedback ramp metering algorithm ALINEA can be applied for local ramp metering or included as a key component in a coordinated ramp metering system. ALINEA uses real-time occupancy measurements from the ramp flow merging area that may be at most a few hundred meters downstream of the metered on-ramp nose. In many practical cases, however, bottlenecks with smaller capacities than the merging area may exist further downstream, which suggests using measurements from those downstream bottlenecks. Recent theoretical and simulation studies indicate that ALINEA may lead to poorly damped closed-loop behavior in this case, but PI-ALINEA, a suitable Proportional-Integral (PI) extension of ALINEA, can lead to satisfactory control performance. This paper addresses the same local ramp-metering problem in the presence of far-downstream bottlenecks, with a particular focus on the employment of PI-ALINEA to tackle three distinct cases of bottleneck that may often be encountered in practice: (1) an uphill case; (2) a lane-drop case; and (3) an un-controlled downstream on-ramp case. Extensive simulation studies are conducted on the basis of a macroscopic traffic flow model to show that ALINEA is not capable of carrying out ramp metering in these bottleneck cases, while PI-ALINEA operates satisfactorily in all cases. A field application example of PI-ALINEA is also reported with regard to a real case of far downstream bottlenecks. With its control parameters appropriately tuned beforehand, PI-ALINEA is found to be universally applicable, with little fine-tuning required for field applications. 相似文献
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In a connected vehicle environment, vehicles are able to communicate and exchange detailed information such as speed, acceleration, and position in real time. Such information exchange is important for improving traffic safety and mobility. This allows vehicles to collaborate with each other, which can significantly improve traffic operations particularly at intersections and freeway ramps. To assess the potential safety and mobility benefits of collaborative driving enabled by connected vehicle technologies, this study developed an optimization-based ramp control strategy and a simulation evaluation platform using VISSIM, MATLAB, and the Car2X module in VISSIM. The ramp control strategy is formulated as a constrained nonlinear optimization problem and solved by the MATLAB optimization toolbox. The optimization model provides individual vehicles with step-by-step control instructions in the ramp merging area. In addition to the optimization-based ramp control strategy, an empirical gradual speed limit control strategy is also formulated. These strategies are evaluated using the developed simulation platform in terms of average speed, average delay time, and throughput and are compared with a benchmark case with no control. The study results indicate that the proposed optimal control strategy can effectively coordinate merging vehicles at freeway on-ramps and substantially improve safety and mobility, especially when the freeway traffic is not oversaturated. The ramp control strategy can be further extended to improve traffic operations at bottlenecks caused by incidents, which cause approximately 25% of traffic congestion in the United States. 相似文献
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介绍从舷侧门技术参数、组成、建造精度要求及布置出发,分析其建造和安装难点,通过同胎架建造技术研究、焊接变形控制技术研究、以及铰链眼板轴孔同心度控制技术研究,制定舷侧门建造工艺流程,达到提升舷侧门建造效率和质量,减少坞内高空作业风险,提高舷侧门安装后与复杂线型船体外板的吻合度,从而确保船体外板的水密性能和船体美观。 相似文献
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为了优化山区公路避险车道参数设计方案,基于离散元基本理论与方法,建立轮胎与避险车道集料颗粒流模型。利用自主研发的轮胎性能测试系统对货车轮胎垂直特性进行了室内台架试验研究,通过检测不同输入条件下的响应,标定了轮胎颗粒流模型细观参数。采用漏斗法测量了避险车道集料休止角,结合离散元颗粒流仿真方法,对集料颗粒流模型表面摩擦因数进行了标定。基于所建立的轮胎与避险车道的集料颗粒流模型,仿真分析了轮胎在避险车道中的行驶过程,模拟了车辆在运行过程中的行驶距离、行驶速度与轮胎转速的变化趋势。在甘肃S308省道K209+400处避险车道进行了实车道路试验,试验结果验证了该仿真方法的正确性。通过所建立的轮胎-颗粒流模型对比分析了不同铺设厚度,不同集料大小下的仿真结果。综合考虑减速效果和施工成本,确立了避险车道铺设厚度、铺设长度、颗粒材料等设计技术参数。研究结果表明:离散元法能够很好地模拟车辆在避险车道中的行驶过程;考虑到颗粒固结等因素,建议避险车道铺设厚度不小于0.8 m;针对行驶速度大于90 km·h-1的载货汽车,避险车道设计长度建议大于130 m;避险车道集料方面,建议选用粒径为1~3 cm且圆度较高的砾石作为路床材料。 相似文献
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结合地形条件及交通分析,对宜昌市东城大道南延线进行了路线方案比选。根据东城大道南延线和港窑路节点的交通量预测、地形地貌,提出了不同的立交节点方案,从功能、安全和造价等方面进行比选,最终确定节点方案。最后,总结了山区城市道路选线和立交选型的要点。 相似文献