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In structural engineering, a trestle support (or simply trestle) is a structural element with rigid beams forming the equal sides of two parallel isosceles triangles, joined at their apices by a plank or beam. Sometimes additional rungs are stretched between the two beams. A pair of trestle legs can support one or several boards or planks, forming a trestle table or trestle desk. A network of trestle supports can serve as the framework for a trestle bridge, and a trestle of appropriate size to hold wood for sawing is known as a sawhorse.
Trestle legs come in two kinds:
In the United States, a table or desk supported by X-shaped trestles is usually called a sawbuck table.
Timber and iron trestles (i.e. bridges) were extensively used in the 19th century, particularly for railroads.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 occasionally used to bridge particularly deep valleys, while timber trestles remain common in certain areas. Timber trestles remain common in some applications, most notably for bridge approaches crossing floodways, where earth fill would dangerously obstruct floodwater.
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.
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