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Structural Elements of Bridges

A bridge is subdivided into the superstructure, substructure and foundation.

Deck: The portion of the bridge that directly carries traffic.

Superstructure: The portion of the bridge that supports the deck and connects one substructure element to another.

Substructure: The portion of the bridge that supports the superstructure and distributes all bridge loads to below-ground bridge footings.

Structural elements of a typical highway bridge

Structural elements of a typical highway bridge

Structural elements are used in bridge designs

Foundation

Foundation is required to support the bridge towers, portal frames or piers. Usual foundation methods such as H-pile, pipe-pile, bore pile or precast concrete pile can be used for such purpose.

Bridge Tower

This is the vertical supporting structure only for cable suspension or cable-stayed bridges. The tower is usually construction in high-strength concrete using in-situ method. Mechanical climb form is most efficient for casting the bridge tower. In some cases, the tower can be constructed in a structural frame type.

Pier

Pier is the vertical supporting structure for the usual spanned bridges. Pier is more suitable for bridge with maximum width of deck up to about 8m (2 traffic lanes). Usually, bridge pier is constructed using in-situ method with large panel formwork.

Portal frame

A portal usually consists on two piers on each side with cross beam in between to support the deck. In this case, the width of deck can be up to 20m (6 traffic lanes). In some situations, the height of a portal frame can be up to 50m from the ground. Climb form can be used in this high headroom cases. The erection of a complicated falsework system to support the portal construction is usually involved.

Bridge deck

The bridge deck is the horizontal part of a bridge that supports pedestrian or traffic activities.

Bridge anchor

Bridge anchor is required only for suspension or cable-stay bridges to resist the pull from the suspension cable or counter-span of the bridge. Bridge anchor can be of gravity type using great mass for the counter-balancing, or using ground anchors for the same purpose.

Suspension cable

Suspension cable is applicable for suspension and cable-stayed bridges for the hanging, support or counter-balancing of the bridge deck.

Different methods to form the deck of bridges

1. Balanced cantilever method

2. Construct in-situ

3. Construct using precast beam

4. Construct using precast girder section and erected by a launching machine (viaduct)

5. Construct using incremental launching method