Cable stayed bridges

Cable-stayed bridges are a recent adaptation of the suspension bridge principle. The deck structure is supported by tension stays sloping from one or more towers. There may be either a single plane of stays down the centre of the bridge, or two planes; one on each side of the bridge.

The towers act in compression and can have a variety of forms (A-frame, H-frame or columns). The deck girders sustain compression forces as well as bending forces.

Economic spans range from 200m to over 850m, and as such cable-stayed bridges fill the gap between large arches / trusses and small suspension bridges. The very large spans have only recently been feasible due to developments in dynamic analysis, and methods for damping oscillations. On a more modest scale, they are also suitable for footbridges > 40m span, to provide stiffness and support to an otherwise flexible light-weight structure.

In terms of aesthetics, the low profile decks, striking towers and raking cables are effective and dramatic. Such bridges are usually landmark structures like the Erasmus Bridge, Rotterdam, Netherlands, shown right.

The Kap Shui Mun Bridge in Hong Kong, shown right,  forms a key element of the road & rail link to the new airport at Chek Lap Kok. It carries a dual 3-lane expressway on the top deck and a 2-track rail line and emergency access lanes on the lower deck. It has a 430m main span over the Kap Shui Mun channel, and was completed in 1997.

The table below shows details of famous cable-stayed bridges. The largest is currently the Tatara Bridge, Japan, (1998) with a main span 890m. However, the Pont du Normandie is probably more significant as it represented a major leap in the spans of such structures to 856m in 1995.   This was only feasible due to advances in computerised dynamic analysis.