道路畢業(yè)設(shè)計(jì)外文翻譯---交通系統(tǒng)-交通線路-全文預(yù)覽
【正文】 level to assure proper bonding. Anther method is to pour the entire thickness of concrete and then force the steel mesh down i nto it to a predetermined level. A group of machines collectively callled a concrete train usually perform these operations at a rate of about threefourths of a meter per minute. A single new machine called a slipform pawer can perform all the different jobs of a concrete train excep laying the reinforcing mesh. However, a technique has been worked out in which the mesh is held in place before the machine passes over it and pours concrete aroung it . The slipform paver can operate at a rate of about two meters per minute. The construction of airport runways follows similar procedures, except that the slabs in a runway are much wider then those in a highway. Airport runways must also be designed to carry the heavy load of the big modern jumbo jets, as well as to withstanf enormous blastes of heat from the engines of heat form the engines of the impact fatcor is also greater with airplanes than with automobiles. Highways differ form airport runways, however, insize and strength rather than design and construction methods. If huge concrete freeways are the transportation phenomenon of hort this century, then the railroads were the transportation phenomenon of the nieenth century . Transportation by rail was not unkonw before the invention of steam lootive in 1892, but rail lines had been limited to the short distances over which horses or other draft animals pulled the load. Most of the lines were bugreat ilt in conjunction with mining operations. After the steam lootive became a practical machine, a surge of railroad construction rapidly spread a work of railroads across the face of the word. By 1920 the age of railroad building generally seemed to be over. As automobiles came into increasingly wider use, the emphasis shifted to highway consruction. Except for few improvements such as electrification, railroads were n
環(huán)評公示相關(guān)推薦
鄂ICP備17016276號-1