Precast Concrete Cap Beam

Precast concrete cap beams are the most common prefabricated elements in bridge substructures. These are generally the most difficult elements to construct on site using cast-in-place concrete, where shoring and forming can be extensive. This issue shows the amount of benefit that can come from prefabricating the element off-site and only needing to be concerned with transportation and connection of the element on-site.

Precast Concrete Cap Beam – Diagram

Precast concrete cap beams connect to the tops of the piles/columns of the bridge substructure and support the bridge deck

Precast Concrete Cap Beam

Due to the tolerance of cast-in-place columns and piers, large blockouts in the pier caps have been used successfully. Another type of connection used for this situation is large grouted pockets to develop semi-moment connections. Simple bolted connections can be used as well as a pinned connection.

Due to the time and difficulty involved in the placement of a cast-in-place concrete cap beam, a prefabricated element should be considered; it is easier and faster to transport and connect the element than it is to cast the element on-site.

Photo Credit: Arizona Department of Transportation Research Center

Where is the substructure and/or foundation on a bridge?

Substructure

The substructure consists of the portion of the bridge that supports the entire structure on the given surrounding soil. There are varying designs due to the different soil conditions for each bridge site and the different weights of the structures for each project.

Foundation

The role of the foundation of a bridge structure is to create a smooth transition allowing the internal forces to flow between the bridge and the ground. Foundations are the ‘bridges’ or links between the bridge and the ground.

There are really only two types of bridge foundations – although each has many variations – ‘spread’ foundations and ‘piled’ foundations. Both types must transfer forces into the soil beneath the bridge.

Spread Foundation

Piles Foundation

Photo Credit: Bridges