Effect of temperature- and frequency-dependent dynamic properties of rail pads on high-speed vehicle–track coupled vibrations

The soft under baseplate pad of WJ-8 rail fastener frequently used in China’s high-speed railways was taken as the study subject, and a laboratory test was performed to measure its temperature and frequency-dependent dynamic performance at 0.3?Hz and at ?60°C to 20°C with intervals of 2.5°C. Its higher frequency-dependent results at different temperatures were then further predicted based on the time–temperature superposition (TTS) and Williams–Landel–Ferry (WLF) formula. The fractional derivative Kelvin–Voigt (FDKV) model was used to represent the temperature- and frequency-dependent dynamic properties of the tested rail pad. By means of the FDKV model for rail pads and vehicle–track coupled dynamic theory, high-speed vehicle–track coupled vibrations due to temperature- and frequency-dependent dynamic properties of rail pads was investigated. Finally, further combining with the measured frequency-dependent dynamic performance of vehicle’s rubber primary suspension, the high-speed vehicle–track coupled vibration responses were discussed. It is found that the storage stiffness and loss factor of the tested rail pad are sensitive to low temperatures or high frequencies. The proposed FDKV model for the frequency-dependent storage stiffness and loss factors of the tested rail pad can basically meet the fitting precision, especially at ordinary temperatures. The numerical simulation results indicate that the vertical vibration levels of high-speed vehicle–track coupled systems calculated with the FDKV model for rail pads in time domain are higher than those calculated with the ordinary Kelvin–Voigt (KV) model for rail pads. Additionally, the temperature- and frequency-dependent dynamic properties of the tested rail pads would alter the vertical vibration acceleration levels (VALs) of the car body and bogie in 1/3 octave frequencies above 31.5?Hz, especially enlarge the vertical VALs of the wheel set and rail in 1/3 octave frequencies of 31.5–100?Hz and above 315?Hz, which are the dominant frequencies of ground vibration acceleration and rolling noise (or bridge noise) caused by high-speed railways respectively. Since the fractional derivative value of the adopted rubber primary suspension, unlike the tested rail pad, is very close to 1, its frequency-dependent dynamic performance has little effect on high-speed vehicle–track coupled vibration responses.     

The cost of convenience; Air pollution and noise on freeway and arterial light rail station platforms in Los Angeles

Light rail transit (LRT) systems constitute one of the most sustainable public transportation modes and transit agencies have increasingly constructed LRT lines along the median of roadways to reduce land acquisition costs and traffic conflicts. Despite these conveniences, few studies have examined the air pollution and noise exposures for passengers on LRT station platforms within freeway or arterial medians. In response, we monitored particle number count (PNC) concentrations and noise levels on 17 station platforms in the Los Angeles metro system in summer 2012 and assessed differences between freeway and arterial platforms. We visited each station on average 7 times for approximately 19 min with two teams carrying a full set of instruments. As expected, impacts were higher on green line platforms in the center of a grade-separated freeway compared to blue line platforms in the center of an arterial due to being in close proximity to greater traffic volumes. Overall, freeway-arterial platform differences were 35,100 versus 20,000 particles/cm³ for PNC and 83 versus 62 dBA for noise. This average noise intensity on green line platforms was four times that on blue line stations. We also found that PNC concentrations were significantly higher at open air monitoring platform positions compared to standing under a shade canopy (about 2000 particles/cm³ higher), but that noise levels were significantly lower at open air positions compared to under canopy positions (about 3.2 dBA lower). Results identify important factors for transport planners to consider when locating and designing in-roadway LRT platforms.     

我国城市轨道交通发展条件指标

针对目前我国城市轨道交通发展条件与实际情况不相适应的状态,提出2个方案:一是从需求、可能性和建设能力3方面对指标进行分析和筛选;二是从需求和可能性的复合性指标进行分析。经比选后推荐方案1作为我国城市轨道交通发展条件的基本指标。在此基础上,综合考虑各方面因素及与现行有关政策的衔接,提出适应我国城市轨道交通健康持续发展的发展条件指标,并对有关问题提出建议。     

地铁车辆段最小曲线半径研究与分析

我国不同时期地铁规范中关于车辆段最小曲线半径取值随着时间推移不断加大,并逐渐稳定。为证实规范合理可行,在收集国内外有关资料的基础上,从地铁车辆段最小曲线半径出发,剖析最小曲线半径的影响因素,并以工程实例分析最小曲线半径选取的标准,论述最小曲线半径对工程实施和运营的影响。建议在现行车辆条件下应尽量遵守现行地铁规范要求,改善运营条件。同时尽快投入力量研究能适应较小曲线半径的车辆及轮轨。     

先张法U形梁快速施工与机械设备配套技术

为满足合同工期紧迫的要求,使1232片U形梁达到快速预制、运输和架设的目的,从施工方案和资源配置着手,紧紧围绕快速施工,介绍梁场的选址、梁场的布置、张拉台座的布置、模板设计、混凝土浇筑、运梁车配备以及大吨位吊车配备等技术研究等内容,采用上述技术方案,在10个月内成功完成了1232片U形梁的预制和架设施工任务,确保了合同工期。     

吉隆坡安邦轻轨轨道工程施工技术与装备研究

吉隆坡安邦轻轨延伸线轨道工程技术条件复杂,曲线多、半径小,应用城市轨道交通130 m小半径曲线无砟轨道施工技术与装备,解决无枕式130 m小半径曲线无砟轨道施工技术难题,总结小半径曲线轨排的组装工艺,实现复杂断面多规格道床模板的架设,高精度、高质量、高效率地完成安邦线轨道工程施工。     

基于SE-DEA的城市轨道交通线网规划方案优选

城市轨道交通线网规划初始方案的选择是城市规划者与建设者应予以重视的关键问题。针对已有研究方法中所存在的不足,提出一种基于超效率数据包络分析(SE-DEA)的轨道交通线网方案比选方法,构建城市轨道交通线网方案的综合评价指标体系并有效筛选出决策单元的输入输出指标。结合某市轨道交通线网规划方案进行实证研究,模型所测结果与该市主推线网方案一致,验证方法的可行性与有效性。所提出的方法依据方案间的相对效率,对预选方案进行优劣性排序,可为城市管理者提供决策依据。     

跨座式单轨交通的认识误区分析及发展展望

跨座式单轨是一种优良的中运量轨道交通系统制式,具有环保性能好、景观效果好、地形适应能力强、投资低、建设周期短、占地少等优点,也存在冰雪天气适应能力差、牵引能耗高的缺点,部分人士对跨座式单轨在橡胶粉尘、疏散救援、运营安全、运营成本、适应范围、景观影响和土地开发等方面存在认识误区。对上述缺点及认识误区一一进行释疑,并分析跨座式单轨未获广泛推广的原因,进一步针对我国城市轨道交通发展现状、存在问题、国家政策导向进行分析,提出随着城市轨道交通发展阶段的转变,应消除对跨座式单轨的认识误区,在其适应范围内大力推广,促进我国城市轨道交通的可持续发展。     

一种改进的十字交叉轨道扣件定位方法

针对传统的十字交叉定位法对轨道扣件区域定位不准确,对图像要求较高,需要特定角度的光照采集才能实现扣件定位,定位过程较慢等问题,提出一种改进的十字交叉定位法对其进行定位。通过对其图像中扣件的初步位置判断定位,然后用中值滤波的图像增强,Canny算子的边缘提取,灰度投影的判断来提高定位准确性,加快定位速率,通过实验表明,改进的定位方法能够很好解决光照采集角度、快速有效的定位和判断出扣件,实现对扣件区域的初定位。     

基于模式预测法的城市轨道噪声影响研究

为研究城市轨道交通高架线两侧噪声传播特点与规律,探索声环境敏感点的降噪防治措施,以拟建成都地铁5号线工程为研究对象,选取适合的预测模式,确定出各个技术参数并模拟计算出噪声预测结果,通过类似既有上海轨道5号线工程的大量实测数据有效验证了预测结果的正确性和可靠性。在此基础上的研究结果表明:水平方向上桥梁两侧声影区内,噪声级随着距离增加而增强;而在声照区内,噪声级则随距离的增加而减弱。垂直方向上高架线噪声影响最严重区域为周边建筑物5层楼附近,因此要特别关注并加强该区域的降噪治理工作。