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随着时间的推移,桥梁两端外的轨道(桥头引线)常常发生下陷(如图1所示)。桥梁两端外轨道下陷,亦称冲击,是经常造成列车走行不平稳的地方,与其他位置的轨道相比,更需要经常进行轨道找平作业。人们普遍认为,轨道下陷是由于车轮通过桥梁上轨道与桥梁两端外轨道之间刚度急剧变化处所产生的动态车轮作用力所致。图2显示的是铺碴桥面桥梁上的轨道与该桥梁两端外轨道间轨道刚度(或称轨道模量)差。通过减少轨道刚度差,或使刚度过渡更为渐进,以此来消除桥头引线轨道下陷,为此虽然经过了多次尝试,但都收效甚微。由此引发了对轨道刚度差理论的研究,以期发现以往努力未成功的原因。为评估轨道刚度差造成桥头引线下沉,及其影响列车走行质量的程度,采用五种了不同的方法。其中包括技术上最复杂的方法和最基本的方法。五种方法的结果得到的结论相同:桥梁端头轨道刚度的变化对桥梁引线处的轨道下沉或列车走行质量未造成实质上的影响。
As time goes by, bridges (bridgehead leads) outside the bridge often sag (as shown in Figure 1). The subsidence of outer rails at both ends of the bridge, also known as impact, is often caused by the unstable running of trains. Compared with the tracks at other locations, it is even more necessary to track leveling work. It is generally accepted that the orbital sag is due to the dynamic wheel forces that occur when the wheel passes through a sharp change in the stiffness of the track on the bridge and the outer orbit at both ends of the bridge. Figure 2 shows the difference in track stiffness (or orbital modulus) between the track on the ballast bridge deck and the outer track at the two ends of the bridge. By reducing the track stiffness difference, or the stiffness of the transition is more gradual, in order to eliminate bridge subduction of the lead track, although after many attempts, but with little success. This led to a study of the theory of orbital stiffness difference with a view to discovering the reasons why previous efforts were unsuccessful. To assess the difference in rail stiffness caused by the bridge lead sink, and the extent of its impact on the quality of train travel, using five different methods. These include the most technically complex methods and the most basic ones. The results obtained by the five methods have the same conclusion: the change of the stiffness of the bridge ends has no substantial effect on the track sinking or the quality of the train running at the bridge leads.