Experimental and semi-analytical studies on the aerodynamic forces acting on a vehicle passing through the wake of a bridge tower in cross wind

In a strong cross wind, sudden change of wind velocity in the wake of a bridge tower causes rapid change of the aerodynamic forces acting on a passing vehicle, which may result in an accident due to driver’s miss-steering. This paper discusses and clarifies the transient characteristics of the aerodynamic forces acting on a ground vehicle in high cross winds when the vehicle is passing through the wake of a bridge tower using a scale model in a wind tunnel experiment. Various parameters, such as wind speed and direction, type of vehicle and tower, were considered in the study.The side force and yawing moment acting on the vehicle model were measured using strain gauges on the model-supporting system that was designed as two cantilever beams with high stiffness. Characteristics of the aerodynamic forces acting on the vehicle model were described and the prediction methods that considered the wind non-uniformity acting on the vehicle were proposed and their applicability was studied.For the side force, the quasi-steady forces based on the relative wind velocity acting at the c.g. of the vehicle model generally agreed with the measured results. Changes in side force were found to be more or less proportional to the wind speed distribution. For the yawing moment, however, the quasi-steady prediction did not agree well with the measured results due to the wind non-uniformity. Therefore, a modified prediction method was proposed that included the effects of wind non-uniformity in a simple manner. Depending on the case, the agreement of prediction and measured results was still not good quantitatively, but from the qualitative point of view, the proposed prediction method could reproduce the yawing moment peak that was similar to the experimental results.     

Strengthening of a steel railway bridge and its impact on the dynamic response to passing trains

Two different strengthening methods for a through-girder steel railway bridge are investigated. The studied structure is the Söderström Bridge, located in the city of Stockholm, Sweden. Due to fatigue problems, it is in need of assessment and strengthening. In one of the methods, arches are added under the bridge modifying the structural system and lowering the stress ranges for all structural members. The other method consists of prestressing the floor beams. This increases their stiffness and transforms the mean stress in the lower flanges from tension to compression. A 3D finite element model is created and verified with measurements. The different strengthening methods are tested in the model by dynamic analysis with moving train loads. The strengthening methods show some positive effect concerning the fatigue life. Changes in vertical bridge deck acceleration for high speed traffic are also presented. A comparison between the European code and the Swedish code regarding vertical bridge deck acceleration levels for high speed traffic shows large differences for the bridge.     

On the aerodynamic and aeroelastic response of a bridge tower

This work is concerned with the aerodynamic characterization of a cable-stayed bridge tower in free-standing configuration; experimental tests were performed at Politecnico di Milano Wind Tunnel under smooth and turbulent flow conditions. The aerodynamic behavior of the tower was investigated through static and dynamic tests on a 1:30 scale sectional model; the whole structure response has been studied using a 1:100 scale full aeroelastic model in stand-alone configuration. Aim of this paper is to compare wind tunnel test results obtained on the two models for different wind exposures, discussing the problems related to scale effects in scale model testing. Some inconsistencies found during the experimental campaign confirm that scale effects in wind tunnel testing represent a serious issue especially for bluff body structures whose vortex shedding response is strongly affected by Reynolds number.     

Extracting the bridge frequencies indirectly from a passing vehicle: Parametric study

Previous studies on the extraction of the bridge frequencies indirectly from the dynamic response of a passing vehicle were focused primarily on the feasibility of the technique. Few investigations have been conducted to study the effects of key dynamic parameters of the system on the vertical response of the passing vehicle. To fill such a gap, the key parameters will be studied not only for evaluating their relative influence, but for increasing the probability of successfully identifying the bridge frequencies of concern. Various amplitude ratios will be defined and expressed in terms of the key parameters, serving as useful indicators for evaluating the probability of successful identification of the bridge frequencies from the passing vehicle. For the two cases studied, in which either one or two bridge frequencies are to be identified, it was shown that the initial amplitude ratio plays a role that is more important than the others in successful identification of the bridge frequencies. Suggestions are made for application of the technique in the field.     

矮塔斜拉桥交叉抗滑键技术的研究

矮塔斜拉桥一般采用环氧握裹式对拉索整体抗滑,但该装置无法实现单根钢绞线抗滑和单根换索,提出采用交叉抗滑键抗滑装置,研究该装置在矮塔斜拉桥中的应用。通过有限元分析、抗滑力试验、疲劳寿命、布置形式研究可知,抗滑键能够可靠地握裹住钢绞线、具有足够的抗滑能力及良好的抗疲劳性,采用交叉布置形式,解决了单根钢绞线抗滑和单根换索难题。根据交叉抗滑键模拟张拉工艺试验总结、完善其张拉工艺,并在山西临汾汾河桥中成功应用。     

释能法在大件通过桥梁时的加固运用

以安龙新桥为例,结合工程现状及大件的相关资料,提出了加固方案,进行了结构计算,并给予了实践检验.实践证明"释能法"在大件通过桥梁时的加固运用效果显著,为超限运输的桥梁加固提供了参考,具有重要的现实意义.     

基于地震荷载作用下的风力发电塔的地震响应分析

基于地震荷载的作用,应用大型有限元软件FINAL,研究不同结构参数的风力发电塔在地震荷载作用下的地震响应,以及比较它们之间的差异,进而得出改变风力发电塔的结构参数对于地震响应的影响规律.以二维风力发电塔模型为例,建立4个不同参数的模型,首先进行模态分析,计算出每个模型的固有频率,通过比较固有频率得出结论,并对其进行比较分析.然后对4个模型施加1993年北海道西南海面桥地震波形,分析比较它们在此地震波形作用下的地震响应值,进而得出不同的结构参数对地震响应的影响规律.     

车速对铁路桥梁动力响应的影响分析

针对桥梁结构对移动列车动力响应的复杂性,通过有限元分析软件ANSYS分析石太铁路一简支梁桥在不同车速下的动力响应,得出了铁路筒支梁桥在高速列车作用下的一些动力响应特性,从而为铁路简支梁桥的合理设计提供科学依据。     

考虑脉动风影响的风电塔风致动力响应数值分析与现场监测比较

本文基于"风轮-机舱-塔体"三维仿真模型,进行风电塔在暴风荷载作用下的风致动力响应分析,并基于规范中的风荷载计算方法与动力分析方法对风电塔的应力、位移和内力进行计算分析,同时研究风电塔风轮受不利风向影响时的力学特性变化规律,并对风电塔在常规风荷载作用下的应力和位移进行现场监测比较研究。结果表明,基于规范计算的风电塔的应力、位移及内力要比动力分析的计算值偏小;脉动风时程激励下,风电塔的最大应力值低于结构的最小许用应力值,但结构顶部的水平位移超过结构的位移限值,在风电塔设计中应予以注意。风电塔受不利方向的暴风影响会产生很大的内力,塔底最大剪力和弯矩增大了91%和106%,在风电塔设计过程中应该重点考虑;基于常规风荷载作用下的应力和位移的数值仿真结果与监测结果吻合较好。     

龙江特大桥主塔下横梁施工关键技术及应用

本文以龙江特大桥为例,阐述了其桥梁主塔横梁的关键施工,根据其地理位置、工作进度等,提供相关的材料还有施工方法,为后续工程提供参考价值.     

Dynamic response of a long span suspension bridge and running safety of a train under wind action

A dynamic analysis model of a wind-train-bridge system is established. The wind excitations of the system are the buffeting and self-excited forces simulated in time domain using measured aerodynamic coefficients and flutter derivatives. The proposed formulations are then applied to a long rail-cum-road suspension bridge. The dynamic responses of the bridge and the train under wind action are analyzed. The results show that the lateral and rotational displacements of the bridge are dominated by wind, while the vertical by the gravity loading of the moving train. The running safeties of the train vehicles are much affected by wind. Under wind conditions of 30–40 m/s, the offload factors, derail factors and overturn factors of the train vehicles exceed the safety allowances, to which great attention should be paid. Translated from Engineering Mechanics, 2006, 23(2): 103–110 [译自: 工程力学]     

Measurements of the cross wind forces on trains

The results of full-scale and wind tunnel experiments to measure the cross wind time averaged and unsteady forces and moments on trains are presented. The results demonstrate good agreement between the two sets of experiments but also illustrate the need for care in simulating local roughness effects in the wind tunnel simulation. It is also shown that quasi-steady effects need to be taken into account when calculating force and moment aerodynamic admittances.     

超载车辆作用下桥梁的评定和加固与管理

介绍了超载车辆的管理措施,探讨了超载车辆过桥的安全评定、承载力评价、加固措施及管理系统,提出为保证超载车辆安全过桥,公路管理部门应加大超载车辆的治理力度。     

台风作用下输电塔塔周风场与动力响应实测分析

通过安装于台风中心的输电塔监测装置获取的实测结果,分析了台风“海马”经过期间塔身所处位置的风场特性及其动力响应特征。测试和分析结果表明：台风登陆前后,处于风眼区域的塔身位置处风向相反,登陆时刻的风速明显减小。台风经过期间湍流度和阵风因子均随风速增大呈现明显的非线性减小。10min平均风速大于10m/s后,顺风向湍流度稳定在20%~40%之间,阵风因子小于2.0。塔身位置处的顺风向脉动风速谱相较von Karman经验谱,其低频段吻合较好,高频区域能量明显偏低。不同风速下的塔线体系频率和阻尼相对稳定,对于1阶弯曲,横、顺跨线向阻尼比均约为2.5%,其较一般钢结构的偏高。输电线和塔身的耦合共振不明显。实测塔头加速度频谱分析表明塔身横、顺跨线向的1阶整体弯曲模态振动显著,但其模态位移在塔头总振动位移中占比不到10%,表明塔身动位移是以背景分量为主。     

厢式货车在桥塔区域的气动力特征研究

以曼牌16.170F货车及象山港大桥为背景,加工制作了曼牌货车和象山港大桥的1∶25缩尺模型,在TJ-3风洞,使用六分量测力天平对货车模型进行了测力试验,通过试验得到了货车在双向四车道,五个风偏角,相对于桥塔的五个不同位置以及无桥塔状态时的气动力系数。     

A computational study of the aerodynamic forces acting on a tractor-trailer vehicle on a bridge in cross-wind

This paper examines the effect of truck speed on the aerodynamic forces acting on a standard sized, North American transport truck travelling across a bridge under conditions of cross-wind. The objective is to establish a relationship between wind speed, truck speed and propensity for truck rollover that may be used to devise strategies for accident avoidance. Conditions of a moving truck travelling in both windward and leeward lanes were considered with a cross-wind speed of 120 km/h and truck speeds of 0-120 km/h. Using the calculated pressure distributions on the surface of the truck; the aerodynamic lift, drag and moment coefficients were determined for relative wind directions. The results show that the aerodynamic moment tending to overturn a truck in the windward lane of the bridge rises from approximately 120 kN m at low speeds (0-40 km/h) to 217 kN m at a truck speed of 120 km/h. For a truck in the leeward lane, the corresponding moments are substantially less, at 82 and 154 kN m, respectively. The 1.1 m barrier wall along the side of the bridge is a contributing factor to the aerodynamic difference between windward and leeward lanes.     

陆上风力发电机机组用塔架结构综述

介绍了国内外风力发电的发展历程,国内风力发电现状以及风机的种类与组成,论述了当前国际上常见陆上风力发电机塔架的几种形式及其结构特点,总结了每种塔架的优势和不足,并对未来风机塔筒的发展做了展望,指出减轻重量和降低材料成本对于促进风机塔筒的发展至关重要。