A cantilever bridge is a form of bridge where the structure is supported using the technique of cantilevers. Unlike suspension bridges where the load is supported at either end of the bridge, the strength of a cantilever bridge comes from a structure or structures positioned towards the middle of the bridge.
 the Forth Bridge (Firth of Forth rail bridge) with its three double cantilevers | |
| Ancestor | Truss bridge |
|---|---|
| Related | None |
| Descendant | Cantilever spar cable-stayed bridge |
| Carries | Pedestrians, automobiles, trucks, light rail, heavy rail |
| Span range | Short to medium |
| Material | Iron, steel |
| Movable | No |
| Design effort | Medium |
| Falsework required | No |
The bridge usually consists of three spans, with the ground or footing supports at either end of the bridge providing additional anchorage for the two outer spans, and the central cantilevers, positioned over the channel that is being crossed, providing the support for a central span. This span may be lifted into place or may be constructed using special traveling supports which are themselves also cantilevers. Usually the bridge's cantilevers are in identical pairs, but this is not required, provided that they are either balanced or supported until attached to appropriately massive outer foundation.
The cantilevers support loads by tension of the upper beams and compression of the lower ones. The structure then distributes such tension to the supports at the shore, and the compression is usually carried to the foundations beneath the central towers. Many cantilever bridges used pinned joints and are therefore statically determinate with no beams carrying mixed loads. Cantilever bridges were considered a major engineering breakthrough when first put into practice as they are resistant to damage to the structure from slumping, and can be more easily constructed at difficult crossings by virtue of using little or no falsework.
List by length
World's longest cantilever bridges (by longest span)
- Quebec Bridge (Quebec, Canada) 548.64 m
- Forth Bridge (Firth of Forth, Scotland) 2 x 521 m
- Commodore Barry Bridge (Philadelphia, Pennsylvania, USA) 501 m
- Crescent City Connection (New Orleans, Louisiana, USA) 480 m
- Howrah Bridge (Calcutta, India) 457 m
- Tappan Zee Bridge (New York, USA) 369.4 m
