Suspension bridges - Computational Analysis and Design of Bridge Structures - page 369

Suspension bridges
12.1 BaSicS of SuSpenSion BridgeS
A typical three-span suspension bridge, as shown in Figure 12.1, consists
of main cables, two pylons, stiffened girder, and hangers. The weight and
vehicular loads from the deck are transferred to the main cables by ver-
tical hangers or suspenders. Unlike cables in a cable-stayed bridge that
are anchored on the deck on both sides of a pylon at an angle, hangers
of a suspension bridge are perpendicular to the deck and will not create
any horizontal force on the deck. Except in the self-anchored suspension
bridges, the main cables carry and transfer loads to anchorages that are
separated from the bridge. For this respect, cable-stayed bridges are self-
anchored systems, whereas most of the suspension bridges are externally
anchored systems. As horizontal forces in cables are transferred to ground
rather than to the girder, the stiffened girder will not have the P-Delta
effects as in cable-stayed bridges and therefore the spanning capacity is
much increased.
In terms of span layout, as shown in Figures 12.2 and 12.3, variations of
suspension bridges include single-span and multispan suspension bridges.
The stiffened girders can be two hinged or continuous at the locations of
pylons. The two-hinged stiffened girder, which is commonly used, is dis-
continued from the side span to the main span and simply supported by the
pylons. When deck continuity is required, the continuous stiffened girder
can be used (Chen and Duan 1999).
Vertical hangers are commonly used. Diagonal hangers, as shown in
Figure 12.4, are also used to enhance structural damping so as to improve
aerodynamic behaviors.
Most suspension bridges are externally anchored, in which the main
cables are anchored into anchor blocks that are built on ground. This type
of anchorage relies on the gravity of the massive anchor blocks. Where
such massive anchor blocks are not feasible, main cables can be anchored
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