Bridge and Alignment
Formerly, the bridge indicates the alignment of the road. If possible, the bridge was built at right angles to the river or railroad, even when the road had then to be linked up with curves. In elevation too, steep ramps were chosen with a small radius of summit. Nowadays, the alignment of the road governs the design of the bridge and the bridge engineer is well advised to accept this subordination, provided that the alignment is good. This change of attitude has arisen as a result of the requirement of high speed driving and by the challenge to achieve a steady, good looking road in the landscape.
To design a good alignment for a road nowadays has become a great requiring the consideration of many factors. One has learned, for example, that long straight sections may lull drivers to sleep and are therefore dangerous .One has learned that curves in plan must be seen in space in combination with curves and slopes in elevation. Easement curve was introduced ,whereby curvature changes steadily from a straight line to the desired radius. The integration of a planned alignment into the environment is usually checked by perspective computer drawings as seen from different sight points.
Bridge are a part of the alignment and it is evident these days that the bridge must be adapted to it. This means that bridges often lie within plan curvature and that they follow the slopes or curvature in elevation. The radii of curvature are generally large in order to achieve adequate range of vision. Such Elevation and vertical alignment.
For overpass bridge over motorways in flat country the vertical curve should be extended into the approach ramps. For bridges crossing rivers in plains it is desirable to extend the curve over the total length of the bridge, even when a very large radius results(Fit.18.1).For bridge across the River Rhine with main spans of 200m and more, the bridge looks better if the curvature continues over the central span, rather than having a central horizontal section between curves over the side spans.
For bridge crossing valleys, the vertical alignment along the bridge depends upon further alignment of the road; does it continue without much slope, or does the road descend from higher ground and asend again after crossing the valley? An example of first situation is sulzbach viaduct of the autobahn seutuart-Ulm which was one of the first viaducts for the autobahn system(1934). It was designed with greet care and the spans of the continuous beam decrease with the slope . For the view from the valley a slight summit curvature looks better than a stiff straight line, and thus the bridge was built with the profile shown in Fig.18.2. S soon as the autobahn was finished, the“hump”of the bridge, as the car-driver sees it, was criticized and the bridge-destroyed in the war-was later rebuilt without the“hump”but with a straight steady upper line of the bean as shown in Fig.18.3.
求此土木工程专业英语译文
第1个回答 2013-11-13
桥和对准以前，桥梁表示公路线形。如果可能的话，大桥建成直角向河流或铁路，即使路便是与曲线。在海拔太陡峭的斜坡，选择了同一个小半径的首脑会议。如今，道路的线形控制的桥梁和桥梁工程师都应该接受这种从属关系的设计，只要对准是好的。这种态度的转变，出现了由于高速行车的要求和所面临的挑战，实现稳定，良好的展望道风景。设计一个良好的路线，一路如今已成为一个伟大的需要考虑的因素很多。一个了解，例如，长直路段会给司机的睡眠，因此危险。一个了解，曲线图，要看在太空与海拔高度的曲线和斜坡相结合。介绍了缓和曲线，即曲率变化，逐步从直线到所需的半径。一个整合计划对准到环境通常是由透视计算机图从不同的观光点看到检查。桥的线形的一部分，这些天，桥必须适应它很明显。这意味着桥梁经常趴在平面曲率和他们遵循的斜坡或曲率在海拔。的曲率半径一般都是大，以达到足够的视线范围。这样的高度和垂直对齐。立交桥高速公路平面国竖曲线应延伸到方法舷梯。桥梁跨越河流的平原上，它是理想的扩展曲线在桥梁的总长度，即使在一个非常大的半径结果（配合。18.1）。对于跨河大桥莱茵200米以上主跨，桥看起来更好，如果在中央跨度曲率继续，而不是中央横截面曲线之间在边跨。桥梁跨越峡谷，沿桥纵向排列取决于路的进一步调整；它继续没有倾斜，还是一路下降更高的地面和扬升后再次穿过峡谷？第一种情况的一个例子是-苏尔茨巴赫高架高速公路seutuart乌尔姆是为高速公路系统的第一个高架桥（1934）。它被设计成与问候关怀和带坡度的连续梁的间距减少。为视图从谷轻微的山顶曲率看起来比硬直的线，因此桥是显示在fig.18.2剖面的建立。就高速公路被完成了，“驼峰”的桥梁，为汽车司机看见它，批评和桥梁毁于战争以后被重建了没有“驼峰”但一直稳定的上线，如fig.18.3所示
