1、路 基 中 的 过 渡 段 Transition regions,Another set of dynamic problems occurs at locations where a railway track exhibits abrupt changes in the vertical stiffness. They usually take place at abutments of open-deck bridges, at the ends of a tunnel, at grade crossings with a highway or a railway, and at loc
2、ations where “rigid“ culverts are placed close to the tie bottoms. 桥路、桥涵、隧路、无碴有碴,Transition regions of this type require frequent maintenance. When neglected, they deteriorateat an accelerated rate (compared to a regular track). This may lead to pumping ballast, hanging cross-ties, permanent rail de
3、formations, worn fastener components, and loss of surface and gauge.,主要存在方面问题： 受到列车荷载影响较大的范围内(基床以上部分)线路结构抵抗变形能力差异，即轨道综合模量(刚度)平顺过渡的问题(舒适度问题）； 刚性桥台与土工结构的柔性路基间工后沉降差引起轨面弯折的限值问题,Fig. VIII.23. Schematic dynamic wheel force distribution in transition zone,At a transition point, because of the abrupt change
4、 in the vertical track stiffness, a moving wheel experiences a rapid change in elevation (either up or down). This, in mm, causes vertical accelerations of the moving car. According to Newtons laws, this leads to vertical wheel force changes caused by the vertical dynamics of the moving car. The mag
5、nitude of these force variations depends on the elevation difference (relative rail deflections) between each side of the transition, how k varies in the transition zone, on the speed of the moving train, and on the suspension characteristics and the masses of the car components. The distribution of
6、 the vertical force that a moving wheel exerts on the rail, depends also on the direction of the moving train.,In Case A, the train is moving toward the bridge. The increased dynamic wheel force that the rail is subjected to is caused by the lifting of the wheel (and car) up onto the rigid abutment
7、in a very short period of time (a second or less). The region of increased dynamic wheel loads is located at the abutment, as shown. The resulting damage may be battered rails and plate-cut wood ties on top of the abutment near the transition. These impact forces may also cause damage to the abutmen
8、t.,In Case B, the wheel is moving off the bridge and onto the softer ballasted track. Because the track-in-ballast deflects much more than the track on the abutment, the wheels drop off the abutment, imparting increased vertical forces to the rails. The location of the largest wheel force depends on
9、 the train speed; the larger the speed, the farther away from the abutment is the maximum vertical wheel force. Since it takes less force to disturb the ballast and the subgrade than it takes to cause rail batter 冲击and tie damage, these wheel loads cause fouled 脏污 ballast, hanging cross-ties, perman
10、ent rail deformations, and the well-known “dip“ in the track at the end of the bridge.,Similar situations may occur at the ends of a tunnel, especially where the ties in the tunnel rest on a hard base. Or, they may occur at both ends of a road crossing, where the track is stiffened by tile crossing
11、structure as well as by the ballast-subgrade base that has been well compacted by the moving auto traffic.,Problems of this type may also occur at the transitions between wood- and concrete-tie tracks where the track moduli k differ substantially . In these cases, the generated dynamic wheel forces
12、of the cars that move toward the concrete-tie section may crack the first few concrete ties that adjoin the transition point and soften the “stiff“ side. The result is a “zipper effect“ that creates its own transition to the stiffer concrete-tie section.,二 过渡段设置目的,1 使线路刚度逐渐变化，将台阶式跳跃沉降变为连续的斜坡式沉降，以达到降
13、低列车与线路的振动，减缓线路结构的变形，保证列车安全、舒适、高效运行的目的。 2 过渡段长度、刚度如何匹配等国内外均没明确的结论，过渡段长度从060米不等。,产生这种现象的主要原因有以下几个方面： 地基条件原因 桥台后路堤填料的原因 设计及施工的原因 重桥轻路的意识 路基与桥台结构的差异,影响线路运行质量的因素还有:桥上轨道技术状态和种类。 路桥过渡区段轨道技术状态和种类。 机车车辆的类型，运行速度和技术状况。,二高速列车与路桥过渡段相互作用力学分析模型,1.机车车辆模型：车辆模拟成一个以速度V运行于线路上的多刚体动力系统，各刚体分别为：车体、前转向架、后转向架、第一轮对、第二轮对、第三轮对、
14、第四轮对。,路桥过渡段动力分析模型,2.道线路模型：依据“钢轨是靠各个轨枕延纵向支承于道床和路基” 的事实，将轨道结构用连续弹性点Euler支承梁和三层(钢轨一轨枕一道床)离散的线性振子相连接来模拟轨道线路，钢轨被当作连续点支承的无限长梁，在X=Xi处与三层线性谐振子相连，相临支撑点距离即轨枕间距，连接关系如图所示。,轨道结构连接关系,车辆系统的动力学方程由DAlembert原理获得，轨道系统的动力学方程中需要将钢轨四阶偏微分方程转化成普通二阶常微分方程组。最后，可将列车一轨道系统的动力学方程写成如下标准形式：MX+CX+KX=F为了高效快速求解这一大型振动系统响应，这里采用快速数值积分方法，
15、从而在普通微机上实现了列车一路桥过渡段系统的动力学仿真分析.,路桥过渡段动力学性能计算方案,在研究轨道过渡段动力特性时，考虑下列因素变化的影响: 由地基(或填土)沉降引起的轨道变形； 沉降差(A)取5cm, 10cm, 15cm； 行车速度(V)取80, 160, 200km/h ； 行车方向考虑从低刚度到高刚度轨道和从高刚度到低刚度轨道两种； 过渡段长(L)取10 m,2 0 m,30m。,为了完整分析和评价列车通过轨道过渡段时系统的动力学性能，特选取下列评价内容: 1) 轮轨垂向力Fwr (k N) 2) 钢轨支点压力Fr (k N) 3) 路基基床表面应力 ( Mpa) 4) 钢轨加速度
16、ar (m/s2) 5) 轨枕加速度as (m/s2) 6) 道床加速度ab (m/s2) 7) 车体加速度av (m/s2) 8) 车轮悬浮量yw (mm),轨道过渡段动力学性能计算方案,沉降差5 cm,沉降差引起的钢轨变形曲线 (沉降差5 cm),钢轨变形曲线分析,行车方向对轮轨力的影响 (沉降差5cm，无过渡段),行车方向对车轮悬浮量的影响 (沉降差5cm，无过渡段),行车方向影响分析,行车方向为从高刚度轨道到低刚度轨道，过渡段长度为20 m，行车速度分别取80、160、200 km/h三档。,行车速度影响分析,过渡段长度对轮轨力的影响 (沉降差5 cm),过渡段长度对车体心盘处加速度的
17、影响 (沉降差5 cm),过渡段长度的确定,三 路隧过渡的动力学分析,轨道刚度差,不平顺越严重，动力性能越差,初始不平顺,速度影响,路基面应力增加，其它均减小,四 Remedies at Track Transitions,Over the past several decades a variety of measures have been developed by railroads for reducing the damage that takes place near transition points. They all aim at decreasing the vertica
18、l acceleration of the wheels and cars as the train moves through the transition zone. These remedies may be grouped in three categories:(I) The smoothing of the k-distribution on the “soft“ track side of the transition(II) The smoothing of the transition by increasing the bending stiffness of the ra
19、il-tie structure on the “soft“ track side, in the close vicinity of the transition point(III) The reduction of the vertical track stiffness on the “hard“ side of the transition,1) Longer Ties When considering Category (I), it appears that the most well-known remedy adopted by North American railroad
20、s is the one that uses progressively increasing wood-tie lengths in the track transition region (Fig. VIII.24). These longer ties create a gradual increase of the vertical track stiffness by engaging a larger section of the ballast. This method requires a sufficiently wide ballast section in the vic
21、inity of the transition, unlike the one shown in Fig. VIII.25.,Category I（增加轨道刚度）,Fig. VIII.24. Track transition remedies using ties of varying lengths,2) Decreased Tie Spacing Another approach uses regular size ties throughout, but, in order to create the stiffening effect, the tie spacings are dec
22、reased gradually when approaching the stiffer structure. This method, used years ago, was phased out in recent decades after the introduction of mechanical tampers that work more efficiently when the tie spacing is constant.,Fig. VIII.25. Insufficient ballast section near bridge abutment,reinforcing
23、 layers utilize reinforcing geotextile layers,layers of Hot Mix Asphalt (HMA), a cantilevered slab（悬臂板） whose one end is supported by the “rigid“ structure and the other is free floating.,Category （增加路基刚度）,Use of geotextiles,Use of Hot Mix Asphalt,Use of cantilevered slab,A method belonging to Categ
24、ory (II) creates a transition section by increasing the bending stiffness of the rail-tie structure on the “soft“ track side. It was developed by the German railways (DB) for the ICE high-speed lines where the slab section inside the tunnel changes outside to a concrete cross-tie track in ballast. A
25、ccording to Schrewe (1987), the transition section is formed by four 30 m long (lOO ft) rails attached to the ties near the tunnel end (two inside and two outside the running rails).The use of tie pads belongs to Category (III). The aim is to reduce the stiffness of the track on the “hard“ side of t
26、he transition point. Ideally, the pads should be sufficiently compressible, so that the vertical stiffness of the track on both sides is the same. This is necessary in order to assure that the wheels of a moving train cause the same vertical deflection and thus do not generate excessive dynamic forc
27、es by the moving cars.,四.路桥过渡段的工程措施,工程上常用的措施:1.在轨道刚度较小一侧增大路基基床的垂向刚度，以减少路基的沉降。2.在轨道刚度较小一侧增大轨道的垂向刚度。3.在轨道刚度较大一侧降低轨道的垂向刚度。4.改进桥头路面结构。,日本新干线的路桥过渡段设置措施,德国高速铁路的路桥过渡措施,国外常用的方法,1加筋土法,2 碎石类优质材料填筑法,日本 德国,使用力学性能较好的轻型材料（如EPS，人工气泡混凝土等） 填筑过渡段是近年国内外研究开发和应用的一种减轻结构物自 重的工艺方法。该法可显著减少台背填料自身的压缩变形，降 低对地基竖向加载作用及对桥台结构的水平土压
28、力，使地基变 形减小，并可与地基处理进行综合考虑，降低地基处理费用， 减小地基处理范围和缩短施工工期。,3过渡板法,注意：由于列车荷载更大，速度更快，过渡段将更长更厚，这对过渡板的受力非常不利，一旦破损，更换将及其困难。该处理方法对轨道刚度均匀过渡有利，但不能减少路堤及地基沉降，必须配以其他处理措施才能有效控制由此引起的轨面弯折变形，,我国过渡段的处理措施,1 路桥过渡段,图244 普通铁路过渡段,200公里客货共线铁路过渡段,200250公里新建客运专线过渡段,2 路堤与横向结构物的过渡段,客货共线铁路路堤与横向结构物过渡段,客运专线铁路路堤与横向结构物过渡段,3路堤与路堑连接处的过渡段,硬质岩石堤堑过渡方式,软质岩石或土质堤堑过渡方式,秦沈高速铁路涵洞过渡段动态试验,动应力测试结果,
