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.

Accumulative deformation in railway track induced by high-speed traffic loading of the trains

Prediction and control of the permanent settlement of a track caused by traffic loading from trains is crucial to high-speed railway design and maintenance. In this study, a unified prediction model of accumulative deformation of geomaterials used in railway construction subjected to cyclic loadings is introduced and calibrated using physical model testing. Based on this versatile model, a calculation approach to determine the track structure settlement under repeated loadings caused by the movement of the wheel axle of the train is proposed. Regression analysis on the physical model testing is adopted to determine the parameters involved in the computational approach. Comparison of model test data and computed results shows that the parameters obtained from the back-analysis are consistent throughout the various testing conditions, and the proposed calculation approach is capable of satisfactorily predicting the accumulative settlement of the railway roadbed and subgrade soil for various axle loads and loading cycles. A case study of a high-speed railway is performed to demonstrate the feasibility of the proposed approach in realistic engineering applications. The computation results from the settlement development of a roadbed and subgrade soil are presented and discussed.

Model tests on XCC-piled embankment under dynamic train load of high-speed railways

Piled embankments,which offer many advantages,are increasingly popular in construction of high-speed railways in China.Although the performance of piled embankment under static loading is well-known,the behavior under the dynamic train load of a high-speed railway is not yet understood.In light of this,a heavily instrumented piled embankment model was set up,and a model test was carried out,in which a servo-hydraulic actuator outputting M-shaped waves was adopted to simulate the process of a running train.Earth pressure,settlement,strain in the geogrid and pile and excess pore water pressure were measured.The results show that the soil arching height under the dynamic train load of a high-speed railway is shorter than under static loading.The growth trend for accumulated settlement slowed down after long-term vibration although there was still a tendency for it to increase.Accumulated geogrid strain has an increasing tendency after long-term vibration.The closer the embankment edge,the greater the geogrid strain over the subsoil.Strains in the pile were smaller under dynamic train loads,and their distribution was different from that under static loading.At the same elevation,excess pore water pressure under the track slab was greater than that under the embankment shoulder.

Theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains

One of the major problems in structural fatigue life analysis is establishing structural load spectra under actual operating conditions.This study conducts theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains.The quasistatic load series that corresponds to quasi-static deformation modes are identified according to the structural form and bearing conditions of high-speed train bogie frames.Moreover,a force-measuring frame is designed and manufactured based on the quasi-static load series.The load decoupling model of the quasi-static load series is then established via calibration tests.Quasi-static load–time histories,together with online tests and decoupling analysis,are obtained for the intermediate range of the Beijing—Shanghai dedicated passenger line.The damage consistency calibration of the quasi-static discrete load spectra is performed according to a damage consistency criterion and a genetic algorithm.The calibrated damage that corresponds with the quasi-static discrete load spectra satisfies the safety requirements of bogie frames.

Study on the subgrade deformation under high-speed train loading and water–soil interaction

It is important to study the subgrade characteristics of high-speed railways in consideration of the water–soil coupling dynamic problem,especially when high-speed trains operate in rainy regions.This study develops a nonlinear water–soil interaction dynamic model of slab track coupling with subgrade under high-speed train loading based on vehicle–track coupling dynamics.By using this model,the basic dynamic characteristics,including water–soil interaction and without water induced by the high-speed train loading,are studied.The main factors-the permeability coefficien and the porosity-influencin the subgrade deformation are investigated.The developed model can characterize the soil dynamic behaviour more realistically,especially when considering the influenc of water-rich soil.

Soldiers' load carriage performance in high mountains: a physiological study

Background: The present study was designed to evaluate load carriage performance at extremely high altitudes with different loads and walking speeds in terms of physiological evaluation. The degree of maximum oxygen consumption changes at high altitudes was also examined.Methods: Twelve Indian Army soldiers were acclimatized at altitudes of 3,505 m and 4,300 m. They walked for 10 minutes on a motorized treadmill at 2.5km/h and 3.5km/h speeds during carrying no loads and three magnitudes of load(10.7kg, 21.4kg, 30kg) at both altitudes. Physiological parameters such as oxygen consumption, energy expenditure, heart rate, and ventilation were recorded for each breath using a gas analyzer. The rating of perceived exertion was also noted after each load carriage session. Maximal oxygen consumption(VO2max) was measured at sea level and the two high altitudes, and respective relative workloads(% of VO2max) were calculated from oxygen consumption. Repeated measure ANOVA was applied to reveal the significant effects of the independent variables.Results: The participants had significant reductions in VO2 max with rising altitude. Marked increases in almost all physiological parameters were observed with increasing load, altitude, and speed. The soldiers expressed heavy perceived exertion levels with higher loads at 3.5km/h at the two high altitudes.Conclusions: Considering the physiological responses, expressions of perceived exertion and changes in relative work load at both of the high altitudes. Indian soldiers are advised to walk slowly with adequate rest in between their schedules and to carry not more than 32% of their body weight.

Research on dynamic characteristics of high speed milling force based on discontinuous functions

This paper begins with a consideration of the influence of feed per revolution upon the depth of a cut and the impact of the machining method on the direction of tool pressure average and subsequent description of efficient cutting directions and the methods for load cell orientation. The paper goes further into the key conclusions concerning the dependences of the cutting depth at high-speed milling as in the case of discontinuous functions. It ends with recommendations offered for positioning of load cells for cut-up milling and cut-down milling.

Research of inverse mathematical model to high-speed trains

Operation safety and stability of the train mainly depend on the interaction between the wheel and rail.Knowledge of wheel/rail contact force is important for vehicle control systems that aim to enhance vehicle stability and passenger safety.Since wheel/rail contact forces of high-speed train are very difficult to measure directly,a new estimation process for wheel/rail contact forces was introduced in this work.Based on the state space equation,dynamic programming methods and the Bellman principle of optimality,the main theoretical derivation of the inversion mathematical model was given.The new method overcomes the weakness of large fluctuations which exist in current inverse techniques.High-speed vehicle was chosen as the research object,accelerations of axle box as input conditions,10 degrees of freedom vertical vibration model and 17 degrees of freedom lateral vibration model were established,respectively.Under 250 km/h,the vertical and lateral wheel/rail forces were identified.From the time domain and frequency domain,the comparison of the results between inverse and SIMPACK models were given.The results show that the inverse mathematical model has high precision for inversing the wheel/rail contact forces of an operation high-speed vehicle.

Investigation of insulation layer dynamic characteristics for high-speed railway

Dynamic performance of insulation is one of the key parameters during the insulation application for high-speed railway subgrade. This paper conducted laboratory and field tests for the materials and dynamic load, especially for thermal performance, elastic deformation, and accumulated deformation of insulation materials. Experiment results show that mechanical properties of insulation layer structure are stable, which satisfies the requirements of the high speed railway.

Structural analysis and design of frost resistance function for subgrade of high-speed railway ballasted track in cold regions

According to the technical characteristics of short fixed wheelbase of a high-speed carriage, a subgrade-track integrated space mechanical response analysis model is proposed for trains under the action ofbiaxial load after the comparison of the stress distribution characteristics of the ballast track subgrade bed structures for high-speed railway under the action of uniaxial load and biaxial load. The loading threshold value （high-cycle long-term dynamic strength） under the circum- stance where the cumulative deformation of subgrade structure gradually develops and finally reaches the convergent state, and its relationship with the foundation coefficient K30 were deduced, based on the characteristics of cumulative defor- mation evolution obtained from the unit structure filling model test under the action of cyclic loading. In view of structure stability and frost resistance requirements of the railway subgrade in cold regions, technical conditions to maintain good service performance of subgrade structure of high-speed railway ballasted track are discussed and analyzed. Study results show that the additive effect manifests itself obviously for railway train bogies under the action of biaxial load than uni- axial load, which has a significant dynamic effect on the subgrade bed bottom and a slight effect on the surface layer. Thus, the adoption of a biaxial load model in the design of a high-speed railway subgrade accurately reflects the vehicle load. Pursuant to the structure design principle, the design method of the subgrade structure of high-speed railway ballasted track is proposed to meet the technical requirements such as structural strength, bearing stiffness and high-cyclic and long-term stability. Technical indicators are obtained for the variation of thickness of the surface layer of reinforced sub- grade bed in the double-layer subgrade mode along with the change of K30 at the subgrade bed bottom. The double-layer structure mode of ＂closure on the upper layer and drainage on the lower layer＂ was proposed in order to meet the water- proofing and drainage requirements of the upper layer of the subgrade bed in cold regions. A dense-framework graded gravel filler with weak water permeability at a coefficient of 10 4 cm/s is used on the upper layer and the void-framework graded gravel filler at the water permeability coefficient of 10 2 cm/s is adopted on the lower layer.

OPTIMUM DESIGN OF HIGH-SPEED RAILWAY LOCOMOTIVE TRACTION GEAR

On the basis of deep investigation of locomotive traction gears manufactured at home and abroad , a variety of measures are putted forward to improve the driving load-bearing capacity and working life of our country's high-speed locomotive traction gears. The measures include the fol- lowing five aspects : optimally selecting the material and heat treatment process , optimally designing the tooth profile . reasonably choosing the manufacture accuracy and technique , optimally choosing the lubricant and the way of lubrication and seal , improving the dynamic feature of the gearing. In the respect of the tooth profile , a hob with optimal cutter angles is designed to make root thickness on the dangerous section as large as possible and the stress concentration as small as possible. Ad- dendum modification coefficient is optimized to minimize the maximum flash temperature in the course of meshing. Finally . finite element analysis method is used to calculate the deformation and the stress of teeth accurately. And on this basis , optimal profile correction and axial modification have been designed with regard to the start , continuious running and high speed travel of the loco- motive .

高速注采储气库井套管螺纹密封性研究

套管螺纹密封性是影响周期性高速注采作业的储库气井安全性的关键因素,因此保证储气库井的密封性完整极其重要。需要重点研究储气库井注采过程中对其套管柱密封性的影响,特别是循环注采过程中产生的交变载荷对储气库套管柱特殊螺纹接头密封结构性能的影响。基于有限元法理论,针对中国北部某储气库井所选用的特殊螺纹接头,结合储气库井实际工况和现场数据,建立套管接头螺纹有限元计算模型,研究了循环注采条件下,温度、注采压力、轴向载荷及点蚀对储气库套管螺纹密封状态的影响。结果表明,温度对套管螺纹接头的结构完整性和密封完整性影响较小,注采压力、轴向载荷和点蚀对其影响较大,需控制在一个较低值。研究可为储气库井套管柱密封失效判定及其套管柱设计提供参考。

地震和高铁共同作用下桩网复合地基振动特性

为研究地震和高铁列车荷载共同作用下桩网复合地基振动特性,通过建立轨道-路堤-桩网复合地基三维有限元计算模型,分别与实测数据和一维波动理论对比验证模型的正确性。通过对比不同荷载工况下地面位移和加速度时频振动曲线,分析地震和高铁两动载共同作用时不同车速下桩网复合地基时频振动特性,研究桩体模量对桩网复合地基减震效果的影响。研究表明,Hollister地震荷载和高铁荷载共同作用下,距轨道中心1 m处地面振动位移由地震荷载主导,地面振动加速度由列车荷载主导;20 Hz以下地面低频振动由高铁和地震荷载共同控制,地面高频振动主要由列车荷载控制。Lytle Creek地震荷载和高铁荷载共同作用下,桩网复合地基地面振动位移和加速度峰值均大于高铁荷载单独作用下的值;增加桩体模量对高铁荷载单独作用和两动载共同作用下桩网复合地基地面振动均有减振效果,但两动载共同作用下增加桩体模量对地面减振效果比高铁荷载单独作用下弱。

千万吨级主井高速大载重提升技术研究与应用

以千万吨级“双超”矿山——思山岭铁矿主井提升系统建设为背景,从主井提升系统方案、竖井提升运行安全间隙研究、大型化提升技术装备应用、大型主井井塔布置等方面综合论述了主井提升系统参数确定所开展的研究工作以及设计建设采用的新技术、新装备。思山岭铁矿主井提升系统的建设将对我国类似矿山竖井高速大载重提升系统的建设实施具有较强的标杆示范意义。

考虑风速纵、横分量的列车气动载荷变化特性

为探索侧向环境风作用下列车气动载荷变化特性,对任意风向角下随车移动点处的风速纵、横分量进行建模,研究考虑风速纵、横分量的列车气动载荷计算方法,并分析在列车速度200~400 km/h、平均风速10~35 m/s及风向角30°~150°时的列车气动载荷特性.研究发现:在不同风向角下,考虑风速横向分量后,高速列车气动载荷波动变大,作用于列车上的瞬时气动载荷极值增大;风速横向分量主要影响列车气动载荷的标准差,且影响程度与风向角有关;随着风向角接近临界风向角,风速横向分量对列车气动载荷标准差的影响逐渐变小,随着风向角远离临界风向角,风速横向分量对列车气动载荷标准差的影响逐渐变大;列车气动载荷的标准差/均值主要与侧偏角有关,且在风向角为30°及150°时较大,其次是风向角60°和120°,而在风向角90°时则较小.

风向角对高速列车驶出隧道过程中气动效应的影响

为研究风向角对驶出隧道过程中高速列车气动效应的影响,以某型高速动车组列车为研究对象,采用数值模拟方法对隧道内气动压力、列车风风速、流场分布及列车气动荷载进行分析。通过与动模型试验结果进出对比,验证数值模拟方法的准确性。研究结果表明:隧道壁面气动压力峰值及变化幅值最大值出现在隧道内部,且出现位置到隧道出口距离与风向角有关;背风侧气动压力受风向角影响更大,气动压力变化幅值随风向角增大呈现先减小后增大再减小的趋势;出口处列车风风速随风向角增大基本呈现先增大后减小的趋势,30°风向角时列车风风速最大,但迎、背风侧列车风风速峰值出现时刻不同;随着风向角增大,流场分布不对称性增强,列车绕流特性由流线型绕流逐渐过渡到钝体绕流,流动分离点到头车鼻尖的距离呈现先增大后减小最后再增大的变化规律,隧道内流动结构愈加复杂;气动横向力、升力变化幅值随风向角增加呈现先增后减趋势,头车横向力系数最大变化幅值分别是中车、尾车的2.4倍和2.6倍,升力系数最大变化幅值分别是中车、尾车的1.1倍和1.5倍,故保证头车安全是控制整车运行安全的关键;侧风下高速列车驶出隧道情形下的最不利风向角为30°,此时头车发生列车事故风险最高。

高铁列车荷载作用下桩-土复合地基及近接地铁隧道的动力响应模拟研究

[目的]作为典型的振动荷载,高铁列车运行引起的振动荷载会诱发桩-土地基及附近结构产生动力响应,有必要对桩-土复合地基及近接隧道的动力响应特性进行研究。[方法]基于西安地铁14号线下穿大西高速铁路特大桥工程,采用模型试验和数值模拟相结合的方法,以峰值振动加速度、峰值振动速度和峰值振动位移作为动力响应评价指标,研究了列车移动荷载作用下桩-土复合地基及近接隧道的动力响应特性。[结果及结论]研究结果表明,当施加列车荷载时,地基内部的动力响应指标均随着埋深的增加而衰减,但存在近接隧道时,动力响应指标值显著增加,且在隧道埋深处衰减明显。随着距桩基中心距离的增加,隧道埋深处的桩-隧之间地基的各动力响应指标从“波浪形”分布变为单调递减分布。根据峰值振动速度的控制阈值,近接隧道埋深处距桩基础中心水平3.6 m范围内的地基处于危险影响区,必须采用减振措施;3.6~11.4 m范围内的地基处于强影响区,建议采取减振措施;11.4 m以外的地基处于弱影响区,视结构的重要性决定是否需要采取减振措施。

高速跨介质入水多相流动与流固耦合特性研究综述

高速跨介质入水问题广泛存在于海洋工程、航空航天等领域,入水多相流动与流固耦合作用机理是该领域的研究热点,对于跨介质航行器的载荷预报、弹道稳定性评估、结构强度校核以及安全性设计等具有重要意义。本文围绕高速跨介质入水所涉及的基础关键力学问题,重点论述了高速跨介质多相流动与空泡演化、冲击载荷与降载方法、运动稳定性与流固耦合响应、流固耦合数值研究方法等方面的研究现状,并针对目前仍存在的问题提出了建议,旨在为高速跨介质入水的相关研究与设计等提供参考。

轨道不平顺条件下列车运行引起的饱和地基振动响应

为研究轨道不平顺条件下列车运行引起的饱和地基振动响应,进一步完善饱和地基的振动传播和衰减规律,将轨道不平顺引入饱和地基2.5D有限元,通过Fourier变换得到频域-波数域表达式,对比分析准静态荷载与不平顺条件下高铁列车运行对饱和地基加速度、位移和孔隙水压力的影响规律。研究结果表明:列车速度较低时,2种条件下列车引起的饱和地基振动相差不大,随着列车速度提高,轨道不平顺使饱和地基的加速度幅值和位移幅值显著增大,且在时程曲线规律上呈现更强的波动性;轨道不平顺对轨道中心加速度频谱影响较小,列车在低速和高速运行时,2种荷载的频谱规律均基本一致,主频分布也基本相同,轨道不平顺条件下仅各频段加速度大小略有增加;轨道不平顺会大幅增加高速列车运行引起的饱和地基孔隙水压力,且随着深度增加孔压迅速衰减。

静风荷载下大跨斜拉桥上无缝线路受力与变形

大跨度斜拉桥在自然风场中易因自身柔度特性发生位移变形。为研究静风荷载作用下大跨斜拉桥上CRTS(China Railway Track System)双块式无砟轨道无缝线路桥梁及轨道结构在空间三向的力学性能分布规律,参照某一四线预应力混凝土斜拉桥工程实例,基于有限元法建立了大跨斜拉桥上无缝线路精细化空间耦合模型,分析了横桥向静风荷载作用下桥梁体系及桥上轨道结构的力学性能。分析结果表明:桥梁及桥上轨道结构三向(应)力最大值基本分布在斜拉桥跨中及边墩附近;各结构三向(应)力中,底座板、桥梁结构纵向应力峰值最大,约为横向应力峰值的8倍,约为竖向应力峰值的7倍、15倍,轨道板结构表现为横向应力峰值最大,且与其余两向应力峰值之间差距较小;各结构三向位移中,横向、竖向位移均在跨中及附近达到最大值,纵向位移在斜拉桥边墩附近达到最大值,其中,横向位移峰值是其余两向位移峰值的20余倍;桥梁两侧构件竖向、纵向位移方向相反,即桥梁表现为静风作用下的倾覆、弯曲倾向。研究成果可为风环境中大跨斜拉桥上线路设计、维护检修以及健康监测提供理论依据。