One question that frequently comes up during our community presentations and tours is the difference between cable-stayed and suspension bridges. Since the Bridge Project is the first cable-stayed vehicular bridge in California, people are still becoming acquainted with this new-to-the-area type of design.
The primary difference between the two kinds of bridges is how the weight of the road deck is borne. With suspension bridges like the Golden Gate Bridge, the cables that support the road deck are attached to main cables that drape over the towers and are anchored at both ends of the bridge. These anchorages, which typically are massive concrete structures, bear a great deal of the load of the road deck. The remaining load is borne through downward compression on the towers caused by the weight of the draped main cables.
In cable-stayed bridges, cables directly connect from road deck to the towers, and they become the primary load-bearing structures that transfer the weight to the ground. A few key advantages of cable-stayed design include the following:
• Using balanced-cantilever construction whereby bridge segments are added symmetrically to both sides of the tower to balance the load, the cables act as both temporary (during construction) and permanent supports for the road deck.
• The symmetrical building of the road deck balances the load, eliminating the need for large ground anchorages.
• Cable-stayed bridges are far less costly for road-deck lengths of 500 to 3,000 feet (the Bridge Project has a 2,000-foot main span); and they can be built in far less time.
• They require much less steel cable and use more precast concrete sections, which accelerates construction.
In short, cable-stayed bridges bear the road-deck weight differently, are faster to build and require less construction materials than suspension bridges.