Truss arch bridge
From Wikipedia, the free encyclopedia
| Truss arch bridge | |
|---|---|
 |
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| Viaduc de Garabit, a thrust arch type employing a catenary shape | |
| Ancestor | Truss bridge, arch bridge |
| Related | None |
| Descendant | Compression arch suspended-deck bridge |
| Carries | Pedestrians, vehicles, light rail, heavy rail |
| Span range | Medium |
| Material | Steel |
| Movable | No |
| Design effort | Medium |
| Falsework required | Sometimes, but long spans are often built using temporary cantilevers |
A truss arch bridge combines elements of a truss and an arch. The actual resolution of stresses will depend upon the design. If no horizontal thrusting forces are generated this becomes an arch shaped truss, essentially a bent beam - see Moon bridge for an example. If horizontal thrust is generated but the apex of the arc is a pin joint, this is structurally an A frame composed of two bents - see The Iron Bridge for an example. If the stresses in the arch are along the path of the arc then it is a true arch or thrust arch.
In the Iron Bridge shown below, the structure of each frame emulates the kind of structure that previously had been made of wood. Such a wood structure uses closely fitted beams pinned together, so the members within the frames are not free to move relative to one another, as they are in a pin-jointed truss structure that allows rotation at the pin joint. Such rigid structures (which impose bending stresses upon the elements) were further developed in the 20th century as the Vierendeel truss.
[edit] Some bridges of this type
- Navajo Bridge An older (1929) and newer (1995) bridge of the same general construction, each built as unsupported cantilevers joined with a central pin.
- The Iron Bridge (1791), the first metal bridge of any kind, still standing.
