【正文】 expanding and potential buckling when in service, welded rail is laid when temperatures are high (or is artificially heated). Rail anchors clipped on at the ties keep the rail from getting shorter as it contracts with falling temperatures. Thus constrained, it shrinks in cross section (height and width), but not in length. Because it39。s wheel would shear them all off, causing the rails to part. Transition between rails of two different weights is achieved with special angle bars. In territory where the rails serve as conductors for signal systems, bond wires must be used at the joints to maintain the circuit. Welded rail The troublesome nature of rail joints prompted the most easily recognized advance in rail technology: the adoption of continuous welded rail (CWR).From its early use on a handful of roads in the 194039。s 155lb. section, used for a time after World War II, was the heaviest used in the .) Jointed rail segments The length of standard rails has historically been related to the length of the cars used to transport them. From an early range of 1520 feet, rail length increased with car size until a standard of 39 feet (easily acmodated by the oncemon 40foot car) was reached. Even with the advent of today39。蘭州交通大學畢業(yè)設(shè)計（論文）China HighSpeed RailwayAs the economic grow, intercity travel demand has increased dramatically in the Greater China Area. Traditional railways can hardly satisfy the passenger and freight travel demand, high speed rail is hence proposed and constructed after 1990s. This study aims to integrate current development of both railbased and Maglev high speed trains in this area. From 1997, Taiwan kickedoff its high speed rail construction by importing the technology of Japanese Shinkansen. The Taiwan High Speed Rail is a 15billion US dollars project. To save the cost of construction and management, the BOT model was applied. Though not totally satisfied, this project is still successful and ready to operate in the 4th quarter of 2007. China is preparing its high speed rail services by upgrading current networks. The capacity and operating speed are all increased after 5times system upgrade. The 6th upgrade will be initiated in 2006. By then, trains will run at a speed of 200km/h in a total distance of 1,400km in 7 different routes. From the white paper published by the Ministry of Railway in China, there will be totally 8 railbased High Speed Train services. Four of them are NorthSouth bound, and four of them are EastWest bound. 5 of the 8 High Speed Rails are now under construction, the first line will be finished in 2009, and the 2nd one will be in 2010. By 2020, there will be totally 12,000 kilometers high speed rail services in China. The 250 billion US dollars construction cost still leaves some uncertainties for all these projects. Finally, the future of the Maglev system in China is not so bright as railbased. Shanghai airport line could be the first, also the last Maglev project in China if the approved ShanghaiHangzhou line cannot raise enough billion dollars to build it.Steel rail position Steel rail is posed of iron, carbon, manganese, and silicon, and contains impurities such as phosphorous, sulphur, gases, and slag. The proportions of these substances may be altered to achieve different properties, such as increased resistance to wear on curves. The standard configuration for North American rail resembles an upside down T. The three parts of Trail are called the base, web, and head. The flat base enabled such rail to be spiked directly to wooden crossties。 later, rail was placed on the nowstandard steel tie plate. While the proportions and precise shape of rail are subject to constant analysis and refinement, the basic Tsection has been standard since the mid19th century. Weight The most mon way of describing rail is in terms of its weight per linear yard (the historic British unit of length), which is a function of its cross section. In the late 19th century, rail was produced in a range of sections weighing between 40 and 80 lbs. per yard. Weights increased over time, s