Influence of the ballasted track on the dynamic properties of a truss railway bridge

This article presents numerical and experimental analyses of a steel truss railway bridge. The main feature of this work is that dynamic experiments have been performed before and after the ballasted track was placed on the bridge. Consequently, it has been possible to quantify the effect of the ballast and the rails on the dynamic properties of the bridge. For that, two finite element models, with and without the ballasted track, have been implemented and calibrated using the experimental results. It appears that the ballast gives an additional stiffness of about 25–30% for the lowest three eigenmodes. This additional stiffness can be only partly explained by the stiffness of the ballast. In fact, it seems that this additional stiffness is also due to a change in the support conditions.     

基于动载试验的某双曲拱桥动力性能评价

为了延长桥梁的使用寿命,需要对桥梁做相应的评估,并采取对应的措施。本文就是在某双曲拱桥加固后,根据需要进行了动载试验,并将动载试验的结果与建立的有限元模型的计算结果相对比发现。该双曲拱桥加固后的自振频率、冲击系数和阻尼比等动力性能参数均符合要求,可为同类双曲拱桥的动力性能测试提供借鉴。     

某市双层钢结构特大桥消防设计研究

通过对某市双层钢结构特大桥过往运输车辆的分析,列举了该桥发生火灾的种类,同时结合规范要求,提出了两种设计方案并进行了比选,得出防火涂料加消火栓系统的方案为最佳方案,为类似工程提供了参考依据。     

桥墩沉降下纵连板式轨道与桥面间动态#br# 接触行为及其对列车动态特性的影响

桥墩沉降在高速铁路运营过程中不可避免,其会导致纵连板式轨道与桥面之间的变形不协调,进而引起底座与桥面之间的动态接触行为,恶化轨道力学性能并最终影响列车正常运行。这对这一问题,文章首先研究该动态接触过程的产生机制,并基于列车-轨道-桥梁动力相互作用理论提出纵连板式轨道和桥面间动态接触行为的研究方法;借助该方法从静态与动态两个角度研究桥墩沉降下轨道-桥梁动态接触行为;在此基础上探讨列车通过时的动态特性。结果表明：桥墩沉降和列车荷载会导致底座与桥面出现三处明显的动态接触区域;桥墩沉降导致的相邻桥墩处梁体上拱位移远小于沉降桥墩处的梁体下沉,但是沉降对上拱区域力学特性的影响却不可忽略;轨道的纵向连接特性可以在一定程度上缓解高速列车通过沉降区域时的振动;轨道随机不平顺不能完全掩盖桥墩沉降对系统动态特性的影响,表明沉降对系统的影响是不可忽视的。     

沿竖向运动的水中截断圆柱体辐射波浪问题的解析解答

根据线性势波理论,分析了水中截断圆柱体作竖向简谐运动时结构周围的辐射波浪.利用分离变量法,分别得到了含有未知常数的3个流体子域速度势的简谐表达形式,并采用一个较为简单的匹配方法,使其在流体子域的共同边界上满足压力和法向速度的连续条件,于是求解得到速度势,进而可得到由等效附加质量和附加阻尼表示的柱体上、下表面的动水力.本文方法不仅能考虑自由表面波对动水压力的影响,也适用于位于任意水深处的截断圆柱体.算例结果证明了该方法的正确性.     

A new approach to estimate the wind speed probability distribution along a railway track based on international standards

The plan to establish a European market for railway services and equipment requires technical regulations for interoperability. One topic to be regulated is the safety of railway operation under crosswind conditions. For this a method is necessary for categorising high-speed tracks with respect to their wind exposure. This method has to be simple and robust, and it has to be applicable to all European countries. The method presented here is based on available and reviewed wind data and on procedures described in the Eurocode and other standards. The new approach is compared to the well-established German method which has been used in the past for all high-speed lines in Germany.     

Experimental studies on natural smoke filling in atrium due to a shop fire

How smoke spilling out of a shop fire would fill up an atrium has been studied experimentally in this paper. Full-scale burning tests were carried out in the PolyU/USTC Atrium constructed in Hefei, China. Since balcony spill plume expressions appeared in the literature might not be applicable for a shop fire with finite width, two plume models for smoke spilling out of a shop fire inside an atrium were proposed and assessed. An equation on studying the smoke layer interface height with a two-layer approach was derived.     

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.     

Human-induced landslide on a high cut slope: a case of repeated failures due to multi-excavation

The paper attempts to represent a case of repeated failures on a high cut slope due to multi-excavation. The characteristics of each failure induced by excavation are analyzed through geological investigation, and then a geological model at different failure stages is proposed. The geological analysis shows that the excavation-induced repeated failures are related to the exposure of the weak bedding plane and the toe unloading of the cut slope. Numerical modeling is conducted based on a sequential method, taking into account the main failure stages of cut slope. The simulation results fairly coincide with the practical phenomena observed in field. It is shown that the decrease in normal stress of displaced mass on cut slope will induce the increase in shear stress in bedding planes and that at the toe of the cut slope. The released stress leads to repeated gravitational instabilities of cut slope due to the decrease in normal stress and the increase in shear stress along the bedding planes of mudstone.     

Dynamic contact problem for an absolutely rigid plate joined to a rigid slab on an elastic half space

The dynamic contact problem is solved by a method based on use of static determination of the stresses beneath a plate and additional slab. The static mixed edge problem is reduced to the solution of integral equations, and then to determination of the normal stresses on the contact boundary. A sample calculation confirms the effectiveness of reducting vibration by joining slabs to the basic foundation. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 2–6, September–October, 1995.     

A note on the prediction of bod profile due to a source of effluent discharged in a uniformly flowing stream

The concentration profile downstream from a source of decaying effluent is described by a solution of the diffusion equation with a source of finite width at the origin. It is shown that neither the point source model nor the plug flow model can give satisfactory approximation to the concentration until the effluent has been diluted to an insignificant value. Conditions under which the plug flow model may be used are discussed and a set of curves is given for estimating the distance required for lateral mixing from sources of different widths.