Bascule bridges are impressive examples of the art of modern engineering. To enable ships to pass, one or two of the bridge's sections are raised and then lowered again. Bascule bridges are often chosen for places like urban areas that don't have enough space in which to build the high approaches required for conventional types of bridge. The emphasis is on causing as little interruption as possible to the flow of traffic both crossing and passing under the bridge. Therefore, the greatest challenge is to have the shortest possible opening and closing times. Waagner-Biro's Bascule bridges require opening times of between 90 and 180 seconds, depending on the requirements of our customers. Bascule bridges must operate with a high degree of reliability.
If a defect prevents a bridge from opening or closing, there are serious consequences on the flow of traffic. This means that the bridge's core element is its drive mechanism. Today, electro hydraulic drive mechanisms with hydraulic cylinders are the most economic type of drive mechanisms. They guarantee maximum effectiveness with the minimum of maintenance.
Swing bridges often move loads of over 1,000 tonnes in just a few minutes, thereby freeing a shipping channel. They are particularly suited as river crossings when high street or rail bridges are considered too expensive or would have too great an impact on the environment. When bridging major shipping channels, it might be advantageous to combine swing bridges and fixed bridges. When this option is chosen, the complete bridge structure has a higher crossing so that the headroom is sufficient for normal shipping and the swing bridge only has to be opened for the largest ships.
Most swing bridges are built as symmetrical structures with a central pillar so that two shipping lanes with unlimited headroom are available, one on either side of the pillar. Like all movable bridge systems, swing bridges must function quickly and efficiently to ensure an uninterrupted flow of traffic.
Vertical Lift Bridges
The traditional vertical-lift bridge has, up to now, been used to bridge rivers in crowded urban environments. They do, however, have a limited headroom for shipping traffic. The bridge's supporting structure is made of steel. This reduces the weight which needs to be raised and makes an operating hoist economically viable. A vertical-lift bridge is supported by cables which are usually connected to counter-weights that are positioned at the bridge's four corners. This compensates the bridge deck's weight and any residual load is raised and lowered using a winch.