There are three types of bascule bridge and the
counterweights to the span may be located above or below the bridge deck. The
fixed-trunnion (sometimes a "Chicago" bascule) rotates around a large
axle that raises the span(s). The Chicago bascule name derives from the location where it is widely used, and is a refinement by
Joseph Strauss of the fixed-trunnion. There are 44 movable bridges in Chicago, however 12 are not in operation. The
Jackknife Bascule Bridge in
Fort William, Ontario (now
Thunder 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 by
Joseph Strauss for the
Canadian Pacific Railway. The '''''' 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 engineer
William Donald Scherzer. The rarer
Rall bascule consists of a trunnion integral to the bascule leaf which moves horizontally away from the channel along a track. A pivotally connected strut links the leaf to a fixed point in the structure, constraining the motion of the leaf. As the trunnion travels along the track, this linkage causes the leaf to rotate about the trunnion, converting horizontal motion into angular motion. It was patented in 1901 by Theodor Rall. One of the few surviving examples is the
Broadway Bridge (1913), in Portland, Oregon, though it is driven through the pivotal link rather than a motor on the trunnion. File:Amaliabrug_(Waddinxveen)_-_opening_2.jpg|The counterweight is often hidden below the road surface in the bridge
abutment. File:Ford Bridge Schematic open-close.gif|Animation of a double-leaf Strauss fixed-trunnion bridge (based on engineering drawings from the
Henry Ford Bridge) File:MovableBridge roll.gif|Animation of a rolling lift bridge (such as the
Pegasus Bridge) File:Bascule bridge.jpg|A rolling-lift bascule bridge in the down position ==See also==