 TheWells Street Bridge (Chicago), a double-leaf bascule bridge | |
| Ancestor | Drawbridge,Plate girder bridge,cantilever bridge |
|---|---|
| Related | Lift bridge,swing bridge |
| Descendant | None |
| Carries | Pedestrian, bicycle, automobile, truck, light rail, heavy rail |
| Span range | Short |
| Material | Steel |
| Movable | Yes |
| Design effort | Medium |
| Falsework required | Site and prefabrication specific |
Abascule bridge (also referred to as adrawbridge or alifting bridge) is amoveable bridge with a counterweight that continuously balances aspan, or leaf, throughout its upward swing to provide clearance for boat traffic. It may be single- or double-leafed.
The name comes from the French term forbalance scale, which employs the same principle. Bascule bridges are the most common type of movable span because they open quickly and require relatively littleenergy to operate, while providing the possibility for unlimited vertical clearance for marine traffic.
Bascule bridges have been in use since ancient times, but until the adoption ofsteam power in the 1850s, very long, heavy spans could not be moved quickly enough for practical application.
There are three types of bascule bridge[1] and thecounterweights to the span may be located above or below the bridge deck.
Thefixed-trunnion (sometimes a "Chicago" bascule) rotates around a largeaxle that raises the span(s). The Chicago bascule name derives from the location where it is widely used, and is a refinement byJoseph Strauss of the fixed-trunnion.[2] There are 44 movable bridges in Chicago, however 12 are not in operation. TheJackknife Bascule Bridge inFort William, Ontario (nowThunder Bay, Ontario) was the first double-decked bascule bridge in the world, accommodating rail on the bottom and road/foot traffic on top. It was designed byJoseph Strauss for theCanadian Pacific Railway.
Therolling lift trunnion (sometimes a "Scherzer" rolling lift), raises the span by rolling on a track resembling a rocking-chair base. The "Scherzer" rolling lift is a refinement patented in 1893 by American engineerWilliam Donald Scherzer.[3]
The rarerRall type combines rolling lift with longitudinal motion on trunnions when opening.[4] It was patented (1901) by Theodor Rall.[2][4][5] One of the few surviving examples is theBroadway Bridge (1913), in Portland, Oregon.[4][6]
![The counterweight is often hidden below the road surface in the bridge abutment.[7]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aAmaliabrug_(Waddinxveen)_-_opening_2.jpg)
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