Prediction and mitigation analysis of ground vibration caused by running high-speed trains on rigid-frame viaducts

In this study a 3D numerical analysis approach is developed to predict the ground vibration around rigid-frame viaducts induced by running high-speed trains. The train-bridge-ground interaction system is divided into two subsystems： the train-bridge interaction and the soil-structure interaction. First, the analytical program to simulate bridge vibration with consideration of train-bridge interaction is developed to obtain the vibration reaction forces at the pier bottoms. The high- speed train is described by a multi-DOFs vibration system and the rigid-frame viaduct is modeled with 3D beam elements. Second, applying these vibration reaction forces as input external excitations, the ground vibration is simulated by using a general-purpose program that includes soil-structure interaction effects. The validity of the analytical procedure is confirmed by comparing analytical and experimental results. The characteristics of high-speed train-induced vibrations, including the location of predominant vibration, are clarified. Based on this information a proposed vibration countermeasure using steel strut and new barrier is found effective in reducing train-induced vibrations and it satisfies environmental vibration requirements. The vibration screening efficiency is evaluated by reduction VAL based on 1/3 octave band spectral analysis.

Experimental study on aerodynamic characteristics of a high-speed train on viaducts in turbulent crosswinds

In this study, experiments were carried out to investigate aerodynamic characteristics of a high-speed train on viaducts in turbulent crosswinds using a 1:25 scaled sectional model wind-tunnel testing. Pressure measurements of two typical sections, one train-head section and one train-body section, at the windward and leeward tracks were conducted under the smooth and turbulence flows with wind attack angles between-6° and 6°, and the corresponding aerodynamic force coefficients were also calculated using the integral method. The experimental results indicate that the track position affects the mean aerodynamic characteristics of the vehicle, especially for the train-body section. The fluctuating pressure coefficients at the leeward track are more significantly affected by the bridge interference compared to those at the windward track. The effect of turbulence on the train-head section is less than that on the train-body section. Additionally, the mean aerodynamic force coefficients are almost negatively correlated to wind attack angles, which is more prominent for vehicles at the leeward track. Moreover, the lateral force plays a critical role in determining the corresponding overturning moment, especially on the train-body section.

Propagation characteristics of wideband high-speed railway channel in viaduct scenario at 2.35 GHz

In order to obtain accurate characteristics of wireless channels in the viaduct area of China, a channel meas- urement was taken in a railway viaduct scenario of the Zhengzhou-Xi＇an passenger dedicated line with a bandwidth of 50 MHz at 2.35 GHz. The single-slope log-distance model is used to analyze the path-loss （PL）, and the distribution of shadow fading （SF） is obtained by statistical methods, which shows that the normal distribution fits the samples well. Ricean K-factor is analyzed by the method of moments, and the variation of K-factor is given along the measured route. Small scale such as delay spread and Doppler behavior are parameterized. Based on empirical channel measurement, this paper provides parameters for the evaluation and simulation work on viaduct scenarios of high-speed railway.

Key technologies of precision demolition blasting of ultra-long urban viaduct in complicated surroundings

The key technologies of precision blasting were put forward based on the characteristics of urban via- duct blasting demolition in complicated surroundings. Initial bending instability mechanics model of reinforcing steel bar frame of blasting fragmented pier and sequenced collapsed dynamic model were established for quanti- tative blasting design. Technologies of water pressure blasting were applied in multi-cell box girder fragmenta- tion. The detonating network of non-electric duplication crossover was adopted for the safety and reliability of ultra-long delay. The rationality of blasting scheme and parameters were validated by physical model test. Harm- ful effects were forecasted and controlled by integrated protective technologies. Specialization, cooperation, pre- cision, execution （SCPE） project management method was put forward for precision management. The key tech- nologies of precision demolition blasting can provide reference for similar proiects.

Engineering Characteristics of Ground Vibration Caused by Blasting Demolition of Urban Viaducts

Ground vibration accelerations caused by the collapse of blasting demolition of urban viaducts was recorded in ordered to analyze the engineering characteristics and effects on the surrounding buildings. Through the analysis of peak ground acceleration,peak frequency,duration and response spectra of the recorded vibrations in different acceleration arrays,some conclusions are drawn: the peak ground acceleration decreases with increasing distance, and the amplitude of vertical component is higher than that of the horizontal components,especially in near source region. The peak frequency of ground acceleration decreases with distance,and in near source region,it is larger than the natural frequency of the surrounding buildings,and thus it will not have much effect on the buildings. The duration of ground acceleration caused by collapse is longer than that caused by blasting itself. The vertical response spectrum is the largest of the three components,and it decreases rapidly in the near source region of about 30 m,but beyond that the distance decreases slowly.The horizontal components are smaller than the local seismic design spectrum,while the vertical component for natural period under 0.15 s exceeds the seismic design spectrum,but the natural periods of general buildings are usually beyond that domain,so this will not have much effect on the nearby buildings.

A substructure approach for analyzing pile foundation and soil vibrations due to train running over viaduct and its validation

An efficient computational approach based on substructure methodology is proposed to analyze the viaduct-pile foundation-soil dynamic interaction under train loads.Thetrain-viaductsubsystemissolvedusingthe dynamic stiffness integration method,and its accuracy is verified by the existing analytical solution for a moving vehicle on a simply supported beam.For the pile foundation-soil subsystem,the geometric and material properties of piles and soils are assumed to be invariable along the azimuth direction.By introducing the equivalent stiffness of grouped piles,the governing equations of pile foundation-soil interaction are simplified based on Fourier decomposition method,so the three-dimensional problem is decomposedintoseveraltwo-dimensionalaxisymmetricfinite element models.The pile foundation-soil interaction model is verified by field measurements due to shaker loading at pile foundation top.In addition,these two substructures are coupled with the displacement compatibility condition at interface of pier bottom and pile foundation top.Finally,the proposed train-viaduct-pile foundation-soil interaction model was validated by field tests.The results show that the proposed model can predict vibrations of pile foundation and soil accurately,thereby providing a basis for the prediction of pile-soil foundation settlement.The frequency spectra of the vibration in Beijing-Tianjin high-speed railway demonstrated that the main frequencies of the pier top and ground surface are below 100 and 30 Hz,respectively.

Discrete-Event Simulation of Viaduct Construction Methods in Riyadh Metro

The Riyadh metro project is one of the current megaprojects that aim to improve the transit systems in Saudi Arabia.It consists of several metro lines with a total length of 176 km and 85 stations.The viaducts are considered as one of the main construction elements in the metro lines.Four methods for viaducts construction have been used in the Riyadh metro project:precast beam,full span launching method,cast on-site,and segment method(precast segment method and BCM(balanced cantilever method)).The viaducts work consumes a large portion of a project’s time and cost.Furthermore,the competitive nature of the construction industry increases the need to improve the efficiency of construction performance.Accordingly,this paper takes the initial steps toward increasing the efficiency of viaduct construction methods through simulation.Simulation of construction processes provides a systematic tool that can be used for determining the resources,time,and cost of these processes.The simulation processes should focus on the main activities affecting this element’s execution for viaducts construction,such as segment storage,handling,transporting,and installation.This study highlights the viaducts construction methods and develops general discrete-event simulation models for the most commonly used viaducts construction methods in the Riyadh metro using AnyLogic simulation software.The simulation models visualize and capture the interaction between the different activities and resources in a viaduct construction.Consequently,the construction drawbacks can be identified.Furthermore,the simulation model can be manipulated by adding assumptions to develop more efficient construction methods in terms of time and cost in such projects.

竖向地震引起的城市高架桥的车‒桥耦合作用

建立了典型城市高架桥的车‒桥耦合作用简化模型,利用非线性接触单元模拟桥面和车辆之间的耦合,并选取不同频谱特性的竖向地震动作为激励,研究汽车质量、频率、地震动频谱特性和峰值加速度等多个参数对车‒桥耦合系统动力响应的影响。结果表明,车辆质量和车辆振动频率以及地震动频谱特性均对车桥耦合系统有较大的影响,在共计1866个工况中有221个工况出现了车桥分离的现象;车桥分离对桥梁竖向位移响应多表现为不利,同时还大幅增加了车辆对桥面的碰撞力;在统计意义上,车桥分离的峰值加速度的平均值随着汽车质量的增加而增加,随着汽车频率的增加而减小,随着地震动平均周期的增大而减小。

公路明挖隧道近接穿越地铁高架桥跨段稳定性分析

结合无锡至太仓高速公路惠山新城隧道工程穿越无锡地铁1号线高架桥工程设计,研究公路明挖隧道近接穿越地铁高架桥跨时对高架稳定性的影响,结合相关工程资料进行分析,在此基础上对基坑围护进行设计,并根据基坑所处地理位置及工程地质情况,利用Midas GTSNX建立三维模型进行模拟,分析其位移及整体稳定性。

盾构隧道近距离侧穿立交桥桩基的变形影响分析

[目的]盾构掘进会引起附近桥梁基础发生位移变形,降低桥梁基础承载能力,为此结合某工程实例对盾构隧道近距离侧穿桥梁桩基的变形影响进行研究。[方法]依托合肥地铁5号线盾构侧穿立交桥桩基工程,建立三维数值模型,分析盾构施工引起的桩基横向水平位移、纵向水平位移以及桩基沉降规律。[结果及结论]研究结果表明,桩底横向水平位移呈现“离开—靠近—离开”隧道的动态变化,桩身横向水平位移近似“C”形扰曲曲线,位移沿桩深呈先增大后减小的变化趋势,极值位于桩深9~10 m处。桩底纵向(平行隧道轴向)水平位移表现为“双峰”形曲线,盾构通过桩基后,桩身发生与掘进方向相反的纵向位移,在盾构通过桩基12 m后桩身纵向水平位移出现回弹变化,表明盾构掘进对桩基的纵向变形影响一定程度上是可逆的。桩基沉降变化呈陡峭趋势,同侧桩基距离隧道越近沉降越大,且远侧隧道开挖会引起桩端二次沉降,最大沉降值发生在4号桩基桩底处,沉降值为4.94 mm。

沿海液化天然气接收站工程高架式排水方案设计

针对目前我国沿海液化天然气接收站海水排水通常采用的海管暗埋方式会破坏现有自然海岸线的问题,提出新型高架式排水方案。开展物理模型试验对高架式排水过程中产生的泡沫问题、排水过程中对排水头内部结构的冲击问题和排水头内部的壅水问题进行研究论证,分析了高架式排水方案中的平面及竖向高程布置和排水管道应力补偿方式。结果表明,采用高架式排水方案是可行的,该方案可避免对现有海岸和海床的开挖,较大程度保护海岸线,减少对海域的影响,在某些对海岸线保护要求高的液化天然气接收站工程中可考虑采用。

山地城市轨道交通高架段列车引起环境振动实测研究

对作为典型山地城市的重庆市轨道交通1号线、9号线和10号线高架段列车运行所引起周围地面振动进行实测,将测得的地面垂向振动加速度数据在时域和频域内进行了分析。结果表明:同一线路高架段列车运行引起的振动主要频率分布区域基本一致,1号线主要频率分布在52 Hz附近,9号线主要频率分布在25 Hz附近,10号线主要频率分布在37 Hz附近;随着距离的增加,高频振动衰减速度大于低频振动;高架段列车所引起地面振动的衰减规律总体趋势是随着距离的增大逐渐减小,振动在近场衰减较快,在距离桥梁中心线15 m范围外,振动衰减逐渐平缓,9号线在距离中心线12 m位置出现一定程度的振动放大现象,10号线在距离中心线25 m位置出现振动放大的现象,与平原地区相比,山地城市轨道交通引起的振动衰减趋势有所不同;不同线路高架段引起振动大小存在较大差异,1号线振动源强为74.9 dB,9号线振动源强为53.6 dB,10号线振动源强为59.3 dB,1号线高架段列车运行引起地面振动大于10号线,由于车速较低且采取了梯形轨枕减振措施,9号线引起的振动最小。

Modeling the impact of the viaduct on particles dispersion from vehicle exhaust in street canyons

In this paper, the impact of the viaduct on flow and traffic exhausting particles dispersion within urban street canyons was numerically simulated using a computational fluid dynamics （CFD） model. Two-dimensional flow and dispersion of particles from traffic exhausts were modeled using the standard k-e turbulence model. The street canyons with a viaduct at different widths and different heights above the ground are simulated. The results show that the airflow in street canyon is evidently in- fluenced by the viaduct： The position of the main vortex center is changed, especially there are two strong vortexes when the viaduct is placed at 10 m height above the ground. It is found based on the study of the particles number concentrations （PNCs） that the viaduct may mitigate the pollution level in the street canyon sometimes. The impact of the viaduct width on PNCs is stronger than that of the height. The study of PNDs reveals that the mean PNCs at the wall of upwind building increase when a viaduct is placed in street canyon. In addition, it is found based on the study of mean particles residence time （PRT） that the removal of the particles strongly correlates to the mean PNCs. The results indicate that the viaduct is an important factor to influence the flow patterns and particles dispersion in street canyons.

Numerical simulation of the aerodynamic characteristics of heavy-duty trucks through viaduct in crosswind

In our numerical simulation the hybrid mesh and the SST k-ω turbulence model are adopted to investigate the variations of the aerodynamic loads and the flow field of heavy-duty trucks while crossing a viaduct with 1.1 m high fences in a crosswind at a velocity of 20 m/s. The results show that, with the protection of a fence, the side force is weakened, and the rolling and yaw moments are strengthened while the truck is crossing the viaduct, which relatively reduces the roll-over safety and the driving stability of the truck. Meanwhile, the direction of the side force changes when the truck enters the viaduct, which makes the roll-over safety and the driving stability the lowest during the process.

苏虞张市域(郊)铁路高架区间标准桥梁初步研究

市域(郊)铁路桥梁占比大,但行业内尚无统一的桥梁建设标准。项目前期研究冗繁,差异大,标准化、科学化水平有待提高。本文以苏虞张线(苏州—常熟—张家港)为例,从结构体系、梁跨选择、下部结构设计等方面,对标准跨度桥梁进行初步研究。结果表明:能适应梁场整孔预制、架桥机架设工法的标准跨度简支梁,是市域(郊)铁路桥梁选择的方向;双线大箱梁为市域(郊)铁路优选梁型;35 m为市域(郊)铁路标准桥梁的最优跨径;35 m梁设计可采用薄腹板、大型号钢束,结构尺寸较优。桥墩纵向尺寸可以优化,高度10 m及以下的桥墩,纵向尺寸可减小至1.2 m,全桥动力性能满足规范要求。打入桩最经济,但受限条件多;预钻根植桩和后压浆桩受压浆质量难以检测或判断影响,可以少量试验应用;常规钻孔灌注桩仍是市域(郊)铁路桥梁主要采用的桩基形式。

复合地层盾构机连续下穿高架桥梁施工技术研究

以南京地铁某区间连续侧穿、下穿高架桥和高架桥路基段为基础,建立高架桥及周边土体的三维数值模型,在不同的施工参数下对盾构机下穿风险源期间情况进行模拟,根据模拟结果对施工进行指导,并将施工过程中的监测情况和数值模拟情况进行对比、分析,验证数值模拟结果的可靠性。施工过程中盾构机优化掘进参数,隧道内部进行二次注浆和深孔注浆可以有效减小桥梁及路面的变形量,并降低桥桩之间的差异沉降值;通过合理设置盾构施工参数可将桥梁及路面的变形控制在允许范围之内,减小桥梁及路面的变形量,为类似工程提供参考依据和经验。

双层离港高架桥梁抗震体系对比研究

双层高架桥是城市桥梁建设中常用的一种桥梁形式,可合理利用空间,减少交通拥堵。随着北京某机场的建成,“双层出发,双层到达”的设计理念使得双层离港高架桥得到快速发展,但在设计过程中,航站楼建筑物与桥梁结构组合时,桥梁结构体系选择显得尤为重要。本文以北京某机场双层离港高架桥为研究对象,根据相关工程情况设计了墩梁固结、上层支座和双层支座3种典型结构体系,建立线弹性分析模型,对常遇地震下结构地震反应进行对比研究,分析表明墩梁固结体系地震位移和内力较小,具有良好的抗震性能;随后对3种体系考虑墩柱塑性铰损伤行为的力学性能开展了罕遇地震下非线性时程反应分析,研究表明上层支座随着弯矩反弯点的变化,墩柱转角需求最小,同时三者的纵横向墩柱转动能力均满足抗震需要。综合对比分析在本文探讨的地震情况下,3种结构体系,墩梁固结体系由于整体刚度大、地震参与质量小进而导致内力位移响应小,具有良好的抗震性能优势。同时本文研究成果可为同类桥梁提供技术支持。

地铁高架线环境振动和噪声特点及其传播规律研究

为研究城市轨道交通高架桥线路环境振动与环境噪声特点及其传播规律,选取穿越居民区域典型高架桥线路段为研究对象,通过测试列车运行经过此线路段时车内振动和噪声、沿线地面振动和周边环境噪声及沿线建筑物外环境噪声等,系统地研究了列车通过高架桥沿线,车内车外环境振动和环境噪声的频谱特性及其分布,使用函数回归拟合进一步研究其振动和噪声的衰减规律。研究结果表明:车内噪声、沿线周边环境噪声和沿线建筑物外环境噪声主要频率分布区间分别为:200~1250Hz、20~1000Hz和500~1600Hz,列车轮轨滚动噪声及桥梁振动辐射噪声为主要噪声源;车内振动主要频率范围在1000Hz以下,低频结构振动对车内噪声的贡献不可忽视;高架桥沿线地面振动和周边环境噪声随距离的增加而呈指数衰减。研究结果对城市轨道交通高架桥线路的分析和测试评价及减振降噪具有一定的借鉴意义。

慈溪市长溪村高架桥下空间更新与利用

针对当前多数乡村高架桥下空间闲置或不当利用现状,以慈溪市长溪村高架桥下空间项目为例,从满足人群需求、修复乡村环境、串联区域功能、促进乡村发展目标出发,探讨乡村高架桥下空间更新与利用的设计路径,将这些具有潜力且不被关注的剩余空间进行合理且可持续地提升,为当代乡村桥下空间更新设计提供有益思路。

Numerical study of reactive pollutants diffusion in urban street canyons with a viaduct

In this paper,the influences of the ambient wind speed and the height and width of a viaduct in a 2-dimensional street canyon on the diffusion of reactive pollutants emitted by motor vehicles were investigated using computational fluid dynamics(CFD)method.Pollutants were treated as reactive by including a NO-NO_(2)-O_(3) photochemical reaction mechanism in the simulation.The Reynolds-averaged Navier-Stokes(RANS)k-ε turbulence model and the discrete phase model were used to simulate the airflow movement and the concentration distribution,respectively,of the reactive pollutants in the street canyon.Three indices,i.e.,the chemical reaction contribution of NO(CRC_(NO)),the chemical reaction contribution of NO_(2)(CRC_(NO_(2))),and the O_(3) depletion rate,were used to evaluate the relative importance of the photochemical reactions.It was found that the presence of a viaduct changed the flow field structure in the street canyon.The CRC_(NO) and CRC_(NO_(2))decreased from the windward side to the leeward side of the canyon.The maximum values of the CRC_(NO) and CRC_(NO_(2)) were observed at the pollution source(x=245 m)due to the influence of a clockwise vortex in the street canyon.As the height and width of the viaduct increased,concentration of the ground pollutants and the O_(3) depletion rate increased.The O_(3) depletion rate was much higher on the leeward side(90%)than on the windward side.The pollutant concentrations after the reaction were twice as high with the viaduct as without the viaduct when the viaduct height was the same as the building height.The viaduct had a significantly larger influence on the concentration of the reactive pollutants than the chemical reactions.The O_(3) depletion rate in the canyon and the pollutant concentrations decreased as the ambient wind speed increased,whereas the CRC_(NO_(2)) increased.