Suspension bridges come in two different designs: the suspension bridge, recognized by the elongated 'M' shape, and the less-common cable-stayed design, which has more of an 'A' shape. The cable-stayed bridge does not require two towers and four anchorages as does the suspension bridge. Instead, the cables are run from the roadway up to a single tower where they are secured.
Forces on a cable-stayed bridge
A cable-stayed bridge near Savannah, Georgia, USA
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.
Cable-stayed bridges carry the vertical main-span loads by nearly straight diagonal cables in tension. The towers transfer the cable forces to the foundations through vertical compression. The tensile forces in the cables also put the deck into horizontal compression. in bridge: Cable-stayed bridges )
Construction of cable-stayed bridges usually follows the cantilever method. After the tower is built, one cable and a section of the deck are constructed in each direction. Each section of the deck is prestressed before continuing. The process is repeated until the deck sections meet in the middle, where they are connected. The ends are anchored at the abutments.
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