Clark Bridge in Alton Ill.

A typical cable-stayed bridge is a continuous girder with one or two towers erected above piers in the middle of the span. From these piers, cables are attached diagonally to the girder to provide additional support. Cable-stayed bridges have a low center of gravity which makes them strong against earthquakes, but at the same time makes them vulnerable to uneven sinking of the ground.

Cables are extremely well suited for axial tension, however are weak against compression and bending forces. As a result, long span cable stayed bridges, though strong under normal traffic loads, are vulnerable to the forces of winds. Special measures are taken to assure that the bridge does not vibrate or sway under heavy winds.

Because the only part of the structure that extends above the road is the towers and cables, cable stayed bridges have a simple and elegant look.

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In Depth

Cable-stayed bridges have been around for the last couple of centuries but have become more prevalent in the last 50 years.  Cable-stayed bridges are very price competitive in the 500-2000 ft span lengths range.  They offer greater stiffness, torsional and lateral rigidity over that of suspension bridges.  This helps make cable-stayed bridges stable against the wind and offers aerodynamic effects.

Cable-stayed bridges are different from suspension bridges that the cables are more taut the flexible cables of suspension bridges.  This creates stable points supports in the main span which minimizes deflections.

Cable-stayed bridges offer outstanding architectural appearances due to it's small diameter cables, minimum overhead structure, and wide choice of design methods.  This includes using single or multiple cables, in a fan, harp, bundle or star  design. The pylon design can also vary significantly.   

HISTORY

Cable-stayed bridges have been around since at least 1840 (Hartley System) but it was not until the 1950's did the start becoming prevalent. Even before 1840 their was evidence of primitive bridges had decks stayed from above by ropes or vines. The first cable-stayed bridges of modern time (Strösund Bridge in Sweden and North Bridge in Düsseldorf) were designed with steel decks. This is no longer the standard but is used in cases where weight is a concern. The Strösund Bridge in Sweden was designed by a German, Franz Dischinger, while the North Bridge (or Theodor Heuss) Bridge was designed by another German, Theodor Heuss.  He designed a family of three cable-stayed bridges over the Rhine at Düsseldorf.

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