Trestle
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| Trestle | |
|---|---|
 |
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| Trestles are useful as approaches to bridges over marshes and shallows | |
| Ancestor: | Beam bridge, clapper bridge |
| Related: | None |
| Descendant: | Viaduct |
| Carries: | Heavy rail |
| Span range: | Short |
| Material: | Timber, iron, steel, reinforced concrete, prestressed concrete |
| Movable: | No |
| Design effort: | low |
| Falsework required: | No |
A trestle is a bridge that consists of a number of short spans, supported by splayed vertical elements and is usually for railroad use. Timber trestles were extensively used in the nineteenth century in mountainous areas and to traverse floodplains adjacent to rivers as approaches to bridges. These were typically constructed using peeled logs preserved with creosote as vertical elements and with bolted and spiked sawn timbers for bracing.
Twentieth century construction eliminated much of the need for trestles by using far more extensive grading and tunneling. In many parts of Australia, trestle bridges were replaced with earth-fill over corrugated iron pipe culverts.
The steel trestle shown below (to the left) is a modern structure with a long expected lifetime compared to a wooden trestle. Being fire resistant in this brushy location is also an advantage.
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.
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