What is Bridge Abutment?
A bridge abutment is a component of bridge that connects the bridge to the approach roadway and provides vertical support to the bridge superstructure at the bridge ends.
One Abutment is erected at each end of a short bridge and is joined to the embankment, which may include a retaining wall.
Longer bridges have extra abutments installed at regular intervals throughout the length or span of the bridge to provide the necessary support. While there will be no retaining wall, these will nevertheless give vertical support.
The type of Abutment chosen is determined by available space, geologic factors of the bridge site, and project budget. Abutments at either end of a bridge generally have the five components described below, but those located along the bridge span will lack both the wing walls and the back wall.
Parts Of Bridge Abutment
1. Bridge Seat
A horizontal shelf that supports the bridge deck and is located close to or on top of an abutment. These would hold the end of a span on the embankment, while those placed along a span will offer support to reduce protracted stress.
2. Wing Walls
Wing walls are only seen in abutments that link to the embankment. They are short retaining walls that provide stability and prevent erosion. Wing walls can be seen on the right side of the photograph but are not represented in the figure.
3. Back Wall
This type of wall is only found in embankment walls. Back walls are built vertically at the ends of the majority of bridges. The expansion joints of the bridge span/deck are supported by the back walls.
4. Abutment Pile
An abutment pile is the strand of the Abutment that connects the Abutment’s ground foundation to the bridge’s seat. The length of the pile is determined by the bridge’s height and the depth of the obstruction (stream, river, and canal).
5. Abutment Footing
The abutment footing is also known as the bridge foundation. The footing is what ties the pile to the ground. The footing is wider and heavier. The function of the footing is to keep the Abutment from sinking into the ground.
Functions Of Abutments
- Load transmission from a superstructure to its foundation components.
- Self-weight, lateral loads (such as earth pressure), and wind loads must be resisted or transmitted.
- To provide support for one edge of an approach slab.
- To maintain the equilibrium of an arch bridge’s vertical and horizontal force factors, Abutment.
Types Of Abutments
1. Gravity Abutments
The function of a gravity abutment is to use its dead weight to resist horizontal earth and water pressure. These abutments have a broad and solid foundation.
As the name implies, the abutment construction is totally seated on the ground, and the Abutment is sustained by the gravitational pull of the earth.
This bridge abutment has wings that are perpendicular to the face and serve as counter-forts. These are abutments that are relatively stable.
2. U-shaped Abutments
This bridge abutment features perpendicular to the face wings that function as counter-forts. These are abutments that are relatively stable.
The wing walls of an abutment form a 90° angle (perpendicular) to the bridge’s seat. A U-shaped abutment is supported by a series of piles spaced at intervals equal to the width of the spans.
These types of abutments are made of reinforced cement concrete. At the bottom, both abutment piles are connected to each other via the foundation. The heaps have a common foot.
3. Spill-through Abutments
These abutments are typically used to hold the bridge at various points throughout its span. The deck is supported by columns or a short wall, as there are no wing walls or back walls to maintain the embankment in place.
Water and highways can pass between the supports. The length of the support structure varies to account for the distance between the level bridge and the varied terrain below.
4. Cantilever Wall Abutment
It serves two purposes: the first is to retain soil behind the bridge’s sides, and the second is to support the bridge superstructure. One of the most popular types of abutment constructions is a retaining wall.
However, A retaining wall is used to hold back an earth embankment or water and to keep an abrupt elevation shift from occurring.
The Abutment performs the following tasks locating loads from the bridge ends to the ground, resisting any loads put directly on it, and providing automobile and pedestrian access to the bridge. In the case of retaining walls, the bearing capacity and sliding resistance of the foundation materials, as well as the overturning stability.
5. Mechanically Stabilized Earth (MSE)
Mechanically Stabilized Earth is abbreviated as MSE. MSE true abutments (no piles) are less expensive than other types of abutments (piles under the bridge seat).
Both are significantly less expensive than conventional concrete abutments and significantly less expensive than concrete abutments on piles.
6. Full Height Abutments
This is a huge height abutment erected at the lower level roadway that is designed to support the entire embankment. Full height abutments are more difficult to construct, although they tend to shorten the end spans.
This Abutment is costly and is typically used in densely populated urban and metropolitan areas where structure depth is crucial.
7. Stub Abutments
They are short abutments that are usually supported by piles and are located at the top of an embankment or on the slope of an embankment. They are little and not noticeable from above ground. Stub abutments refer to a variety of wall abutments.
Stub abutments are designed to be as short as possible and are placed at the top of fill embankments. Stub abutments often only maintain soils that are somewhat thicker than the superstructure.
These are particularly cost-effective, yet, they tend to increase the length of the end spans. Additional wall abutments can be significantly taller and are frequently built to the full height of the crossing.
8. Semi-stub Abutment
Semi-stub abutment is between the full-height and stub-abutment heights. Others, unlike stub abutments, are constructed on or near the top of the embankment, whereas full-height abutments are constructed at the bottom.
These abutments are built between the embankments’ top and bottom. They are known as Semi-Stub abutments because they are larger than stub abutments but shorter than full-height abutments.
9. Counterfort Abutment
A counterfort abutment is very much similar to a counterfort retaining wall. In this type of abutment, a thin wall called counterfort connects the breast wall to the footing. These counterforts are spaced at regular intervals so that the breast wall is designed as a supported slab rather than as a cantilever.