Movable Bridges

In cities with little space and without options for high access to transverse traffic, bascule bridges offer a solution for crossing road traffic and waterways. Single leaf bascule bridges or symmetrical bascule bridges with two wings and an aperture angle of up to 85° allow passage for ships without height restrictions. Bascule bridges are particularly suitable for shipping canals close to the coast where large ocean-going ships travel because their large span widths mean that wide shipping canals can be spanned.

To facilitate design of the moving parts, the bridge wings with the decks for road and railway traffic are usually made of steel. Simple and proven electro-mechanical and electro-hydraulic drives are available. Today, the most economic drive option is represented by electro-hydraulic drives with hydraulic pistons, guaranteeing maximum availability with low maintenance outlay. The necessary locking systems for the centre and ends of the bridges are also hydraulically operated. The opening times from 90 to 180 seconds are shorter than the time required to control the road and shipping traffic.

Swing bridges are particularly suitable for bridging inland waterways, where high road or railway bridges are not suitable for financial or building reasons. To bridge larger shipping channels, it can be advantageous to combine swing bridges with fixed bridges. In such cases a higher deck is selected for the entire bridge so that the clearance height is achieved for normal ships and the swing bridge only needs to be operated for larger ships.

In most cases, swing bridges are designed as symmetrical structures with central piers so that two shipping channels with unlimited passage height are available on both sides of the central pier. A special rotating connection with conical rollers was developed by Waagner-Biro to support the high vertical loads. A combination of hydraulic pressure cylinder to absorb the vertical intrinsic weight during rotation and two plain bearing systems for the horizontal forces and stabilisation are used for particularly heavy bridges.

Classic vertical lift bridges have been used so far in restricted city areas for bridging inland waterways. However, the passage height for shipping is restricted. The support structure of the bridge is made of steel to reduce the weight being lifting and to provide an economic solution for the lifting mechanism. The bridge is connected via supporting cables to the counterweights which are normally located in all four corners. The weight of the bridge girders is thereby compensated for to a great extent and the remaining load is raised and lowered with a cable winch.