The bascules rotate through an angle of 82°, and their rear ends in the bascule chambers of the piers carry 365 tons of counterweight, the total weight of each being 1070 tons.
13), is a suspension bridge with a secondary bascule bridge in the centre span to permit the passage of ships.
The lattice girders of the side spans were first rolled into place, so as to project some distance beyond the piers, and then the arch ribs were built out, being partly supported by wire-rope cables from (3) Draw or Bascule Bridges.
- The fortress draw-bridge is the original type, in which a single leaf, or bascule, turns round a horizontal hinge at one abutment.
In these bridges each bascule is prolonged backwards beyond the hinge so as to balance at the hinge, the prolongation sinking into the piers when the bridge is opened.
Each bascule consists of two main girders with cross girders and stringers.