Moving

In some locations, especially flat areas around rivers, provision for navigation can mean building a high bridge. You then have to find the right compromise between the length and the steepness of the approaches. These approaches can be expensive.

A possible solution is to build a low bridge, and move some part of it when water craft need to pass. The main methods are lifting the bridge on one or two horizontal axes (bascule bridge), and rotating it about a vertical axis (swing bridge). Against this is the interruption to road traffic when the bridge is moved.

A famous example is the Tower bridge in London, opened in 1894. This very strange construction includes two 100-foot lifting trussed cantilevers between the towers, and an asymmetric suspension bridge at each end. These suspension bridges could almost be described as cable-stiffened, as opposed to the usual deck-stiffened design.

Over the central span, trusses carry the chains that take the tension between the two suspension bridges, so that the towers are not pulled sideways. The footways across the top are no longer in use.

The suspension spans are held up by unusual chains, which cross over, and are linked by diagonal bracing, making them rather truss-like

This bridge in Amsterdam has two lifting leaves, counterbalanced by weights overhead. This is a design that has been used many times in the Netherlands.

A similar bridge, but with only one lifting section, is located in Gloucester, where the Sharpness to Gloucester canal reaches the docks. A massive counterweight sits over the road.

Numerous swing bridges are found along the canal, which traverses the flood-plain of the river Severn. These bridges are turned about a vertical axis by means of a geared windlass. This one, at Fretherne, is fully open, and a boat is passing through. Barriers warn people on the road to stop.

Some other types of bridge use a rolling bearing, instead of rotating on a horizontal axle. This one is Peto’s bridge in Bristol. The arc and track have large teeth that prevent slipping. The two large objects that look a bit like funnels are the counterweights. Perhaps they are intended to look like lilies or ear-trumpets. The movement is controlled by a single hydraulic cylinder and piston.

Still others have a vertically lifted section. Transporter bridges have a high gantry from which a movable platform is suspended.

An earlier method is to sling a rope across the river, and to pull a boat across by hand. An ingenious variation is to provide a rudder, with which the boat can be steered at an angle to the current. Energy from the flow carries the boat across the river: the ferryman doesn’t have to do anything except steer. The boat is linked to the transverse rope by a rope with a pulley at the end, which runs along the transverse rope.

An Unusual Curved Bridge

On the cover of "Ekiben – The art of the Japanese box lunch" (Kamekura, Bosker and Watanabe – Chronicle Books – San Francisco – ISBN 0-87701-490-6) there is a picture of a pontoon bridge. The bridge makes a sweeping curve across a bay or estuary, pushed by the flow of the tide or the river. Had the builders tried to make it straight, the tension would have been too great. The curve is not a catenary because the speed of the water is greater near the middle than it is near the edges, but it is an example of a funicular. The ekiben was sold at Hokuriku Honsen Toyama station.

Why is this mentioned under moving bridges? It is here because the shape will vary with the flow of water, and with the wind. It will also vary slightly with the loads, because the loaded boats will sink a little more, increasing the drag from the water. And of course in tidal water, or on a river with variable depth, a pontoon bridge will move up and down. All these movements are, however, passive, and so this type of bridge is not a moving bridge as normally understood.

Bascule bridges

Tower bridge – extensive notes – photograph

Moving bridges

Seattle photographs

Milwaukee photograph

Florida bridge – data – photograph

Pomeranian bridge – photograph

Explanation – diagrams

Erasmus bridge – extensive notes – photographs

Philadelphia bridge

Various types

Ennerdale bridge

Virginia bridge

Amtsgraben – picture – notes

Wisconsin bridge – photograph

Explananation and photograph

Van Gogh – Bridge at Langois, Arles

Canada – pictures

Lifting Bridges

Huddersfield bridge – photograph

Canaletto – painting

Canary Wharf

Swing Bridges and Rotating Bridges

Newcastle swing bridge – photograph

Calatrava – moving bridge

Baltimore – rotating bridge

Millenium_Eye_bridge – Newcastle -_under_construction

Taranto bridge

Transporter Bridges

Biscay

Marseille – data – photograph – resources

Middlesbrough transporter bridge

Middlesbrough – good photograph

Newport transporter bridge – history – photographs

Links

Newport bridge – notes – photographs

Runcorn-Widnes transporter bridge