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A Look At The Different Types Of Cable-Stayed Bridges

By Alexander Mason

Republish: EasyPublish™
Published: 06Jan2012
Word count: 444
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Cable-stayed bridges have been in existence since 1840 but it was only from the 1950s that they become a popular form in bridge construction. The first modern-day cable-stayed bridges (Sweden's Strosund and Germany's North Bridge) were designed with steel decks, although this is no longer part of standard practice.

Cable-stayed bridges comprise one or more columns, supported by cables, and are constructed in either a harp design or fan design. In the harp design, the cables are drawn parallel by linking them to various sections on the tower so that the attachment height is similar to the length from the tower to the lower attachment. In a fan design, the cables connect or go over the top of the tower.

Multiple-span cable-stayed bridge

The design challenges involved with cable-stayed bridges which have more than three spans are far greater than those that have two or three spans. In a 2-span or 3-span cable-stayed bridge, the loads are normally fixed near the rear abutments. However, for more spans, the bridge structure is less rigid. This can cause problems in the design of the deck and the towers, however.

Providing support to the strands within the stays, a cradle system underpins the bridge which removes the need for anchors in the pylons, whilst each steel strand is relayed inside the cradle in a one-inch steel tube. In order to make inspection by structural engineers and eventual replacement more accessible, each strand is independently secured.

Side-spar cable-stayed bridge

A side-spar cable-stayed bridge has a central tower which is only supported on one side.

Cantilever-spar cable-stayed bridge

The force distribution of the cantilever-spar cable-stayed bridge does not rely completely on the cantilever action of the spar. The angle of the spar with regards to the bridge and the weight distribution serve to minimise the overturning forces charging the spar's footing.

Extradosed bridge

The extradosed bridge has a more extensive bridge deck which allows the cables to be excluded towards the tower and for the towers to be positioned lower in relation to the span.

In comparison to other bridge types, the cable-stayed bridge is ideal for spans which are longer than those in cantilever bridges, and shorter than those which would warrant a suspension bridge. This is the range in which cantilever spans would progressively become heavier should they be scaled up, whilst the suspension cabling similarly does not become more economical if the span is reduced.

Allcott Associates LLP Residential is an independent practice of Surveyors and Structural Engineers.

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