Aerial Transfer Bridges
Learn how transporter bridges carry cargo and passengers across water one of the biggest challenges in bridge.
building across busy rivers is allowing boats to navigate them freely. Solutions have been invented in the form of a variety of movable bridges, with sections that retract, lift up or even sink to make room. A rare example is the transporter bridge, or aerial transfer bridge, which uses a movable platform, or gondola, to carry loads from one bank to the other. There are very few examples worldwide – indeed, less than 25 of these bridges have ever been constructed – and only a few remain in use today.
The construction of transporter bridges varies. The Vizcaya Bridge in Spain has two pillars connected by a crossbeam and supported suspension cables, while the Tees Transporter Bridge (pictured) in the UK is acantilevered design with two halves, each supported entirely by two towers at either end. Despite the differences in their overall structure, transporter bridges all work using the same fundamental mechanics. The gondola is suspended below the bridge by a series of steel cables, which attach to an overhead trolley. The trolley sits on a track, which runs the length of the bridge, and a winch system is used to draw the platform and its cargo back and forth across the waterway.
The gondolas have a large carrying capacity and can often transport several hundred people or several vehicles at once. They also provide an advantage over traditional bridges in that they can take passengers directly from ground level. If the riverbanks are very low, a long approach road is required to get vehicles to the correct altitude to cross a normal bridge.
Five bridges that move
Followings are the types of moving bridges. These bridges can move and hence of great utility.
Drawbridges were one of the ﬁrst types of movable bridge. Attached to rope or chain and a counterweight, they are raised and lowered by turning a crank, and function not just as a bridge over a moat or ditch but also as a door.
Folding bridges are made from several segments. As the bridge opens, the segments are pulled into a concertina by counterweights, forming a folded ‘N’ shape and allowing boats to pass underneath.
The arms of a bascule bridge like London’s Tower Bridge swing up, so boats pass through the centre. They work in a similar manner to a seesaw, using a counterweight to move the arms upwards.
A tilt bridge has a curved deck, which rotates around its central axis. When a boat needs to pass, the bridge spins upwards, transforming the walkway into an arch for the vessel to travel beneath.
Instead of rising up, a submersible bridge, like that in the Corinth Canal in Greece, has a section that sinks below the water to allow boats to pass. This means no height restriction is imposed on the river traffic.