SUBSTRUCTURE TYPES
The type of foundation generally depends on the soil loading or waterway conditions. Early in the development of a bridge, geotechnical information may not be available and the project foundation engineer may have to rely on existing soils information from a nearby structure to determine the most practical foundation type.
Typical Foundation types are:
Field splices for steel H piles, plate dimensions, and weld symbols. Permissible field splices for pipe piles. Details of the splices, plates, and sizes of welds should be shown on the plans.
The type of bridge bearing selected can have large force impacts on substructure when stiff substructures are used. It is very important to select a bearing/substructure system that is functional and economical. Sometimes the process can become quite iterative.
1. PIERS
Piers can be multiple or single column bents. If the structure is not too wide, A single column bent may be used to reduce the clutter underneath the bridge. Single columns usually rest on a pile cap footing or drilled shaft.
The bents of many structures have multiple round columns with a rectangular pier cap. The columns usually rest on single drilled shafts or a pile cap footing. For very short bents on stream crossings, a line of piling many be extended into the pier cap and encased in concrete to form a curtain wall.
2. ABUTMENTS
There are two basic types of abutments, open end and closed end (or retaining). Each has several subtypes. Open end abutments are located near the top of the approaching roadway embankment. Closed end abutments retain the soil so that an embankment does not exist under the bridge. The type of abutment used is based on economic considerations.
Open end abutments may be backwall, integral and semi-integral, or spill-through type. The backwall type is generally supported on piles or drilled shafts which extend through the embankment. The spill-through abutment is a common type used in New Mexico. The fill extends from the bottom of the cap beam and is allowed to spill through the open spaces between the columns.
Closed end abutments can be mechanically stabilized earth (MSE), double T, or conventionally reinforced retaining walls. The MSE wall is not a true closed type abutment because it is not load bearing and is used with an open type abutment. The recommended minimum offsets required for an MSE abutment. The earthwork requirements for both open and closed type abutments.
Since the abutments and the bridge settle with the MSE wall and the approach embankment, smooth riding bridges can be obtained. This same settlement of the abutments can however be problematic if it is large or if the abutment is part of a continuous multi-span bridge. Use of this type of abutment should therefore be carefully considered and discussed with both the State Bridge Engineer and the Foundation Engineer before design is begun.
The type of foundation generally depends on the soil loading or waterway conditions. Early in the development of a bridge, geotechnical information may not be available and the project foundation engineer may have to rely on existing soils information from a nearby structure to determine the most practical foundation type.
Typical Foundation types are:
- Drilled Shafts (wet or dry conditions)
- Steel H Piling
- Pipe Piling (closed or open end)
- Spread Footing
Field splices for steel H piles, plate dimensions, and weld symbols. Permissible field splices for pipe piles. Details of the splices, plates, and sizes of welds should be shown on the plans.
The type of bridge bearing selected can have large force impacts on substructure when stiff substructures are used. It is very important to select a bearing/substructure system that is functional and economical. Sometimes the process can become quite iterative.
1. PIERS
Piers can be multiple or single column bents. If the structure is not too wide, A single column bent may be used to reduce the clutter underneath the bridge. Single columns usually rest on a pile cap footing or drilled shaft.
The bents of many structures have multiple round columns with a rectangular pier cap. The columns usually rest on single drilled shafts or a pile cap footing. For very short bents on stream crossings, a line of piling many be extended into the pier cap and encased in concrete to form a curtain wall.
2. ABUTMENTS
There are two basic types of abutments, open end and closed end (or retaining). Each has several subtypes. Open end abutments are located near the top of the approaching roadway embankment. Closed end abutments retain the soil so that an embankment does not exist under the bridge. The type of abutment used is based on economic considerations.
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| Types of Abutment |
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