龙卷风作用下高速列车的运行安全性评估

随着我国铁路线网密度的加大以及龙卷风等极端天气出现的频次增多,列车遭受龙卷风袭击的风险不断增加。利用物理模拟器对列车进行测压试验,通过试验得到的气动力对龙卷风作用下高速列车的运行安全性进行评估。结果表明：受龙卷风气压降和水平风速的共同影响,列车距龙卷风中心不同相对位置时,所受风荷载作用机制明显不同;迎风侧轮轨横向力主要由侧力产生,风速较大时,升力和侧滚力矩对轮轨垂向力的贡献增大;横向力、脱轨系数、轮重减载率等列车运行安全性指标随径向距离的增大先增大后减小;列车运行安全性指标随风速、车速的增大而增大,列车安全运行的龙卷风临界风速值随车速的增大而急剧减小,其中,当车速为350km/h 时,轮对横向力对应的临界风速仅为11.06m/s。     

水泥土搅拌桩复合地基承载力设计公式的可靠性分析

通过水泥土搅拌桩复合地基的承载力设计公式,建立试计比的极限状态方程,利用各随机变量的概率分布及统计参数,计算被统计复合地基的平均可靠度指标,分析设计公式的可靠性。     

Ⅲ型重载混凝土轨枕的设计与试验研究

由于重载列车速度的提高和运量的增加,轨道结构伤损破坏加速、线路设备病害发生和发展速度加快。目前,我国尚无27 t及以上重载铁路专用轨枕,为有效解决线路用枕需求,采用预应力混凝土轨枕设计方法,对设计荷载分析、结构型式尺寸及结构强度计算进行了设计,并完善了27 t轴重重载轨枕的制造工艺,通过试验和检测,满足重载轨枕的质量要求。     

Vibration of subgrade and evaluation of derailment coefficient of train under combined earthquake- moving train load

Vibration response of track and foundation subjected to dynamic loading is one of the key issues to solve on-track safety of high-speed train. The previous pioneering works commonly only considered the train moving load, however, in reality, trains are likely to be on track when an earthquake occurs due to the high frequency and widespread distribution of earthquake activities. Hence, a three-dimensional FEM of track-subgrade- foundation interaction system with bidirectional seismic and moving loads is established for investigating the differences and relations of vibration responses of subgrade in such two immensely disparate loads: train moving load and earthquake-moving load. As a case study, the vibration characteristics of the Beijing-Shanghai High-speed Railway of the China, excited by moving load and seismic-moving composite load are analyzed respectively, with various velocity (v = 50 m/s, 70 m/s, 100 m/s, 130 m/s). On the other hand, the increases in operational train speeds mean that critical velocity effects are becoming more common on high speed rail lines. If unaddressed, critical velocity issues can cause safety concerns and elevated maintenance costs. Based on the derailment coefficient and lateral deformation of the rail, the critical speed of the model is discussed, which is a reasonable improvement to the derailment mechanism of the train.     

Passive and Adaptive Damping Systems for Vibration Mitigation and Increased Fatigue Service Life of a Tied Arch Railway Bridge

In this article, the use of external damping systems for vibration mitigation of railway bridge dynamics is studied. For a presented case study bridge, the performance of different tuned mass damper systems (TMDs) is studied. During train passage, the change in dynamic characteristics of the bridge may produce a significant detune to a passive TMD. Therefore, routines for a variable stiffness TMD using incremental frequency estimates are developed. Based on numerical simulations, the cumulative fatigue damage is calculated for different damper systems. Due to resonant behavior, the results are found to highly depend on the train speed. Based on an assumed probability density function for the train speed, fragility curves are produced to express the probability of fatigue failure as a function of the number of train passages.     

Experimental study on dynamic load magnification factor for ballastless track-subgrade of high-speed railway

The magnitude of dynamic load produced by high-speed trains depends on many factors, of which train speed is the most critical one. However, it is quite difficult to determine the effect of train speed on dynamic load using the theoretical methods due to the complexity of the interaction between vehicle and track-subgrade. Thus large-scale model test has gradually become an important approach for studying dynamic responses of ballastless track-subgrade of high-speed railway. In this study, a full-scale model of ballastless track-subgrade was constructed in accordance with the design and construction standards for Shanghai–Nanjing intercity high-speed railway line firstly. Then, the dynamic strain of slab and the dynamic earth pressure of subgrade were measured by conducting single wheel axle excitation test. In addition, the relationship between the dynamic load magnification factor (DLF) and the train speed was obtained. Finally, the DLF of track-subgrade under different train speeds was proposed, similar to that given by German Railway Standard.     

重载列车作用下桥墩-桩基竖向动荷载特性试验研究

为探明大轴重、长编组和高密度重载列车作用下桥墩和桩基承台顶的动荷载特性，开展不同车速和轴重条件下的桥墩-桩基体系竖向动荷载响应现场试验。分析桥墩动荷载曲线的时域、频域特征，采用Kolmogorov法对动荷载幅值进行正态性检验，建立列车参数与动荷载频域特征的联系；基于3σ原则对不同敞车作用下的动荷载特征值(均值、均幅值和均峰值)进行统计，结合实测数据建立重载列车作用下的墩顶动力系数计算公式，并提出墩顶和桩基承台顶的荷载谱公式及其参数取值。结果表明：动荷载响应在时域上可分为快速增加，周期波动和快速衰减3个阶段，在频域上服从倍频规律和幅值调制效应，0~5Hz频段激振对动荷载起控制作用；动荷载幅值服从正态分布，动荷载均峰值和振动能量沿墩身衰减明显，动荷载均值和均峰值随轴重增大而增大，均幅值随轴重的增加而减小；建议采用φ=1+0.0045v计算墩顶动力系数，采用三角级数式拟合桥墩荷载谱效果显著。研究成果可为重载列车作用下桩基的长期承载变形性状及环境振动评估的研究提供关键参数和可靠检验样本。     

高速铁路路基动力响应计算中列车荷载的模拟

高速铁路列车荷载是一个比较复杂的问题,同时涉及列车轴重、悬挂体系、行车速度、轨道组成、线路平顺等因素。在试验区段测试的基础上,考虑了轴重、速度、轨道不平顺等影响因素,采用正弦激励函数模拟列车荷载,以期为高速列车动荷载的确定和路基动力响应分析提供借鉴和参考。     

整体驱动桥的可靠性设计

本文重点介绍了整体驱动桥的可靠性设计方法。     

Estimating uncertainty in terrestrial critical loads and their exceedances at four sites in the UK

Critical loads are the basis for policies controlling emissions of acidic substances in Europe and elsewhere. They are assessed by several elaborate and ingenious models, each of which requires many parameters, and have to be applied on a spatially-distributed basis. Often the values of the input parameters are poorly known, calling into question the validity of the calculated critical loads. This paper attempts to quantify the uncertainty in the critical loads due to this "parameter uncertainty", using examples from the UK. Models used for calculating critical loads for deposition of acidity and nitrogen in forest and heathland ecosystems were tested at four contrasting sites. Uncertainty was assessed by Monte Carlo methods. Each input parameter or variable was assigned a value, range and distribution in an objective a fashion as possible. Each model was run 5000 times at each site using parameters sampled from these input distributions. Output distributions of various critical load parameters were calculated. The results were surprising. Confidence limits of the calculated critical loads were typically considerably narrower than those of most of the input parameters. This may be due to a "compensation of errors" mechanism. The range of possible critical load values at a given site is however rather wide, and the tails of the distributions are typically long. The deposition reductions required for a high level of confidence that the critical load is not exceeded are thus likely to be large. The implication for pollutant regulation is that requiring a high probability of non-exceedance is likely to carry high costs. The relative contribution of the input variables to critical load uncertainty varied from site to site: any input variable could be important, and thus it was not possible to identify variables as likely targets for research into narrowing uncertainties. Sites where a number of good measurements of input parameters were available had lower uncertainties, so use of in situ measurement could be a valuable way of reducing critical load uncertainty at particularly valuable or disputed sites. From a restricted number of samples, uncertainties in heathland critical loads appear comparable to those of coniferous forest, and nutrient nitrogen critical loads to those of acidity. It was important to include correlations between input variables in the Monte Carlo analysis, but choice of statistical distribution type was of lesser importance. Overall, the analysis provided objective support for the continued use of critical loads in policy development.     

基于2.5维有限元方法分析列车荷载产生的地基波动

开发一种2．5维有限单元结合薄层单元的高效数值方法来研究铁路轨道和周围地基在列车运动荷载作用下的振动响应以及应力波在三维地基中的传播问题。其中轨道被简化成铺设在无限半空间上的欧拉梁，具有复杂构造和地质条件的路基近场区域则采用有限单元来模拟，并且利用动力薄层单元构建透射边界来模拟波在远场土体中的传播。通过沿轨道方向的波数变换将三维问题降维成每个节点有3个自由度的平面应变问题，对求解得到的结果进行波数扩展，获得轨道和地基在移动荷载作用下的三维动力学问题的解。考虑单一移动荷载和列车多轮重荷载两种情况下轨道的振动以及周围地基中的响应波场，并用瑞典X2000高速列车运行的现场测试数据对计算结果进行验证，分析列车荷载作用下地基的响应特性和在特定场地上运行高速列车时临界速度的确定。     

参数化分析列车运行产生的路堤–地基振动

 为预测和分析高速列车运行产生的轨道和路堤振动及波动在沿线周围地基中的传播，利用2.5维有限元方法建立了轨道、路堤和下卧层地基在移动荷载作用下的动力耦合分析模型及无路堤情况下的轨道地基模型，求解三维地基的动力响应。对高速或低速运行的列车多轮重荷载产生的路堤和地基振动进行对比分析。通过参数化分析明确轨道刚度、路堤高度、地基土的剪切波速及阻尼系数、列车速度和振动频率等参数对地基振动和传播特性的影响。给出的方法和结论可用于分析软土地基上运行高速列车时的稳定性问题和评估列车运行对周围环境的振动影响。     

Remaining fatigue life of steel railway bridges under enhanced axle loads

In this study, various fatigue damage models proposed by researchers have been briefly discussed and found that the models are problem specific and their efficacy needs to be checked for high cyclic fatigue cases such as in railway bridges. Towards this, field studies were conducted to obtain the strain responses from a steel bridge during the passage of scheduled trains and test train formation with enhanced axle loading. Instrumentation was carried out at critical locations to obtain the responses from the girder. Three different scenarios have been considered to avoid the influence of noise. Further, numerical simulation of the bridge subjected to train loading at different speeds was carried out using ANSYS to obtain synthetic data of strain response from the validated finite element model. Analysis was carried out for normal as well as for futuristic speed of the trains. Responses obtained from field measurements as well as from numerical investigations were used to calculate the damage indices. Based on the damage indices, remaining fatigue life of the bridge was evaluated. The present study can be helpful in assessing the health condition of the railway bridges and to check the suitability of further increase in axle load or speed of trains.     

Assessment of existing steel railway bridges

A series of dynamic tests, acceleration measurements, evaluation, finite element model simulations and safety index calculations were performed on existing steel railway bridges giving service on railway network. Dynamic tests were fulfilled by using a special test train on these bridges to obtain the dynamic parameters and these parameters were then used to refine the finite element models of the bridges. Once the models have been updated to represent the actual condition, safety indices were calculated for structural components of the bridges for each proposed loading condition. These safety indices were used to calculate failure probabilities of structural members. As the final step, system reliability of the bridges was evaluated based on proposed system models of the bridges. It is believed that this study will provide a reliable background for proposed heavier axle loads resulting from new freight trains by realizing the current condition of bridge structures.     

现有铁路钢桥的评估

对现有铁路钢桥进行一系列的动力试验、加速度测量、评估、有限元模拟和安全指数计算。采用专门列车进行动力试验,并获取动力参数。这些参数还可用于建立桥梁的有限元模型。如果模型能够反映实际工况,就能用于计算每种工况下桥梁结构的安全指数。这些安全指数可用于计算杆件的破坏可能性,因此可采用本模型评估桥梁的可靠性。通过了解现有桥梁结构的实际工况,本研究可为新的货运列车重级荷载研究提供可靠依据。     

Determination of the critical loading conditions for bridges under crossing trains

A procedure based on experimental and theoretical analyses to identify critical loading conditions on existing metallic railway bridges is presented. This method requires knowledge of the principal modal frequencies, and for this reason, a consolidated and simple procedure to study the bridge dynamics is herein explained. This consists of: preliminary studies; material and dynamic tests; and identification techniques to identify modal parameters and eventual non-linear behaviours. Generally the information collected can be used both to calibrate the bridge model and to obtain the refined frequency response function. In order to avoid high computational effort due to long time-history dynamic analyses by using the bridge model subjected to a series of train crossings, a new frequency domain approach for the identification of critical loading conditions is proposed. Evidence of the influence of the axle spacing and velocity of the vehicle on the dynamic magnification due to the train crossing is shown. The method is based on the construction of an excitation spectrum related to the train axle spacing and the velocity, given the weight of the vehicle. Comparison of the excitation spectrum with the frequency response function allows identification of the load patterns that bring the bridge to resonance conditions and might threaten bridge stability, bearing in mind continual changes in train technology.     

Full-scale model testing on the dynamic behaviour of weathered red mudstone subgrade under railway cyclic loading

Although weathered red mudstone (WRM) is widely distributed in the southwest of China, its suitability as a fill material for the subgrade bed of a high-speed railway (HSR) has not been comprehensively investigated. This paper presents the results of a field full-scale model testing of the cyclic loading and response of a railway track-subgrade system for the Dazhou-Chengdu Railway, where some WRM has been used in a newly designed subgrade structure. A control section of the HSR was also built using a traditional subgrade bed (Group A&B material) to compare the performances of the different sections. To better understand the dynamic characteristics and cumulative deformation of the two types of subgrade, the dynamic actions of different axle loads and different train speeds were simulated using specifically designed track-cyclic-loading equipment. The transverse and vertical distributions of the dynamic stress, dynamic displacement and acceleration of the track-subgrade system were measured and evaluated. The influence of the wheel axle load on the growth factor of the dynamic parameters, the vertical attenuation coefficient of the dynamic stress, and the effect of using WRM in the subgrade on the post-construction settlements were investigated. The tests enabled the development of cumulative settlement laws with railway loading for the two types of subgrade. Although the dynamic parameters and cumulative settlement of the WRM subgrade are always greater than those of better-quality material (Group A&B subgrade), they comply with HSR regulations. In conclusion, the results demonstrated that weathered red mudstone can be used as a filling material in the newly designed subgrade structure for HSRs.     

Impact of train speed on the mechanical behaviours of track-bed materials

For the 30,000 km long French conventional railway lines(94% of the whole network),the train speed is currently limited to 220 km/h,whilst the speed is 320 km/h for the 1800 km long high-speed lines.Nowadays,there is a growing need to improve the services by increasing the speed limit for the conventional lines.This paper aims at studying the influence of train speed on the mechanical behaviours of track-bed materials based on field monitoring data.Emphasis is put on the behaviours of interlayer and subgrade soils.The selected experimental site is located in Vierzon,France.Several sensors including accelerometers and soil pressure gauges were installed at different depths.The vertical strains of different layers can be obtained by integrating the records of accelerometers installed at different trackbed depths.The experimentation was carried out using an intercity test train running at different speeds from 60 km/h to 200 km/h.This test train was composed of a locomotive(22.5 Mg/axle) and 7 "Corail"coaches(10.5 Mg/axle).It was observed that when the train speed was raised,the loadings transmitted to the track-bed increased.Moreover,the response of the track-bed materials was amplified by the speed rise at different depths:the vertical dynamic stress was increased by about 10% when the train speed was raised from 60 km/h to 200 km/h for the locomotive loading,and the vertical strains doubled their quasistatic values in the shallow layers.Moreover,the stressestrain paths were estimated using the vertical stress and strain for each train speed.These loading paths allowed the resilient modulus Mrto be determined.It was found that the resilient modulus(M_r) was decreased by about 10% when the train speed was increased from 100 km/h to 200 km/h.However,the damping ratio(D_r) kept stable in the range of speeds explored.     

同时考虑速度和轴跨比影响时铁路钢桥的影响因子的确定

传统桥梁设计方法中,把交通荷载处理为静载乘以影响因子。依据现行规范,该因子仅是跨度或一阶自振频率的函数。分析各种参数对钢桥动力响应的影响,包括:速度、火车轴距、车轴数、桥跨度,并研究影响因子。计算了火车速度100～400km/h,轴距13～20m,桥跨度10,15,20,25m情况下的动力响应和影响因子。动力分析表明,大多数情况下,算得的影响因子高于相关规范中的值。影响因子随火车速度、火车轴距和桥跨度之比而变化,而车轴数仅在共振时产生影响。给出了速度、车轴距、桥跨度与影响因子的关系。     

基于Beta分布的改进的一次可靠度法研究

为了提高一次可靠度方法的计算精度和计算效率,文章利用Beta分布拟合了功能函数中的随机变量的概率分布,利用VBA语言给出了将Beta分布和对数正态分布转化为标准正态分布的方法,采用蒙特卡洛模拟法比较了采用不同概率分布的一次可靠度计算精度。算例分析表明:当功能函数中随机变量服从对数正态分布时,失效概率被高估;当随机变量服从正态分布时失效概率被低估。利用本文提出的Beta分布拟合随机变量的概率不仅大大提高了计算精度,而且在保证迭代收敛的前提下提高了计算效率。