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A trestle (sometimes tressel) is a rigid frame used as a support, historically a tripod used both as stools and to support tables at banquets, and in contemporary usage usually referring to a bridge composed of a number of short spans supported by such frames. In the context of trestle bridges, each supporting frame is generally referred to as a bent. Timber and iron trestles were extensively used in the 19th century, the former making up from 1 to 3% of the total length of the average railroad.〔Walter Loring Webb, (Railroad Construction -- Theory and Practice, 6th Ed. ), Wiley, New York, 1917; Chapter IV -- Trestles, pages 194-226.〕 In the 21st century, steel and sometimes concrete trestles are commonly used to bridge particularly deep valleys while timber trestles remain common in certain areas. The historical trestle is sometimes seen as a charge in heraldry. Many timber trestles were built in the 19th and early 20th centuries with the expectation that they would be temporary. Timber trestles were used to get the railroad to its destination. Once the railroad was running, it was used to transport the material to replace trestles with more permanent works, transporting and dumping fill around some trestles and transporting stone or steel to replace others with more permanent bridges.〔Charles Lee Crandall and Fred Asa Barnes, (Railroad Construction ), McGraw-Hill, New York, 1913; Section 96 -- Wooden Trestles, pages 212-213.〕 In the later 20th century, tools such as the earthmover made it cheaper to construct a high fill directly instead of first constructing a trestle from which to dump the fill. Timber trestles remain common in some applications, most notably for bridge approaches crossing floodways, where earth fill would dangerously obstruct floodwater. For the purposes of discharging material below, a coal trestle carried a dead-end track, rather than a bridge. ==Timber trestles== One of the longest trestle spans created was for railroad traffic crossing the Great Salt Lake on the Lucin Cutoff in Utah. It was replaced by a fill causeway in the 1960s, and is now being salvaged for its timber. Many wooden roller coasters are built using design details similar to trestle bridges because it is so easy to make the roller coaster very high. Since loads are well distributed through large portions of the structure it is also resilient to the stresses imposed. The structure also naturally leads to a certain redundancy (provided that economic considerations are not overly dominant). Such wooden coasters, while limited in their path (not supporting loops), possess a certain ride character (owing to structural response) that is appreciated by fans of the type. The Camas Prairie Railroad in northern Idaho utilized many timber trestles across the rolling Camas Prairie and in the major grade, Lapwai Canyon. The viaduct across Lawyers Canyon was the exception, constructed of steel and in height.〔(【引用サイトリンク】publisher=Camas Prairie Rails )〕 The floodway of the Bonnet Carré Spillway in St. Charles Parish, Louisiana, is crossed by three wooden trestles each over 1.5 miles in length. The trestles are owned by the Canadian National Railway (two trestles) and the Kansas City Southern Railroad. The trestles were completed in 1936, after construction of the Spillway. The trestles may be the longest wooden railroad trestles remaining in regular use in North America. File:Wooden trestle bridge approach.JPG|A classic wood trestle using logs and beams File:Aerial_view_of_Trestle_Bridge_over_Kinzua_Creek_Valley_-_01.jpg|Kinzua Creek, Pennsylvania. File:Interurban train on completed temporary trestle.jpg|Interurban train completed trestle after 1915 Galveston Hurricane File:Interurban train with passengers crossing temporary trestle.jpg|Interurban train with passengers crossing temporary trestle after 1915 Galveston Hurricane 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Trestle」の詳細全文を読む スポンサード リンク
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