A bridge abutment is a portion that connects the bridge to the approach road, also supports the superstructure of the bridge vertically at the bridge ends, and separates the highway foundation materials from the bridge spans.
In this article you’ll learn:
So, if you’re ready to go with a bridge abutment, this article is for you.
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What is Bridge Abutment?
An abutment is a vital component of a bridge that vertically within the water or obstruct on a broad and sturdy base that supports the bridge and circulate the bridge’s weight.
Abutments on a bridge attach the span to the embankment, they are next to the bridge’s ground and deck that support the load or weight of the bridge deck.
The abutments can endure pressure from soil and water flow because of their weight.
Purpose of Bridge Abutment:
- To provide the necessary support, longer bridges have extra abutments built at regular intervals throughout their length or span.
- The Abutment is influenced by available space, geology considerations at the bridge site, and the project budget.
- When deciding on the category of abutment to use, the cost is usually the most important consideration.
Types of Bridge Concrete Abutments:
1. Gravity Abutment:
Gravity abutment uses its dead weight to counter horizontal earth and water pressure, such abutments have very wide, massive foundations.
The entire structure of the abutments is supported by the earth’s gravitational pull.
2. U-shaped Gravity Abutment:
A bridge abutment with a U-shape has wings that are parallel to the face.
These abutment types have a good deal of stability. The wing walls of an abutment form a 90° angle with the seat of the bridge.
The breadth of the spans is roughly equal to the distance between a group of piles that form a U-shaped abutment.
These kinds of abutments are constructed out of cement-fortified concrete.
The foundation is used to join the two piles of the abutment together at the bottom.
3. Cantilever Wall Abutments:
A cantilever wall abutment has two purposes:
- To hold the earth in place behind the bridge’s sides.
- It supports the superstructure of the bridge.
One of the most typical types of abutment constructions is a retaining wall.
A retaining wall is used to contain a rapid elevation change and to keep back water or an earth embankment.
In addition to providing access for both vehicles and people, it distributes the loads from the bridge ends to the ground, and resists any loads applied directly to it.
Bridge abutment bearing capacity, sliding resistance of foundation materials, and overturning stability must be investigated in the retaining walls.
4. Full Height Abutments:
The lower-level roadway’s great height abutment is constructed with the goal of supporting the entire embankment.
This expensive abutment is frequently used in crowded urban and metropolitan locations where structure depth is significant.
Despite the fact that they tend to shorten the end spans, full-height abutments are more challenging to build.
5. Stub Abutment:
They are small abutments that are often supported by piles that are built at the peak of an embankment’s slope.
From above ground level, they are generally hidden.
Stub abutments are a term used to describe a number of wall abutments constructed and that are positioned at the top of fill embankments.
Normally, stub abutments can only support soils that are slightly denser than the superstructure.
Stub abutments have the potential to be very cost-effective, but they frequently lengthen the end spans.
Additional wall abutments can be considerably taller and frequently built to the crossing’s entire height.
6. Semi-Stub Abutments:
The height of a semi-stub abutment is midway between a full-height abutment and a stub abutment.
In contrast to stub abutments, other abutments are built close to the top of the embankment.
A full-height abutment is also created at the foot of the embankment.
The construction of these abutments takes place between the top and bottom of the embankments.
They are known as semi-stub abutments because they are longer than stub abutments and larger than full-height bridge abutment.
7. Counterfort Abutment:
The counterfort retaining wall also refers to counterfort abutments.
The breast wall is joined to the footing by a thin wall known as the counterfort abutment.
In order to make the breast wall a supported slab rather than a cantilever, these counterforts are built at regular intervals.
8. Spill-Through Abutment:
Spill-through abutments primarily function to lessen the amount of soil pressure on the abutment by generating large voids in the stem.
The majority of the construction is below grade; however, piers and spill-through abutments are equally distributed across them.
9. Mechanically Stabilized Earth System:
Mechanically Stabilized Earth is the abbreviation for this system.
MSE true abutments (no piles) are more economically beneficial than other abutments (piles under the bridge seat).
Both are significantly more cost-effective than concrete abutments on piles and considerably less expensive than customary concrete abutments.
10. Pile Bent Abutment:
The pile bent abutment is a variant of a spill-through abutment that restores the wall-like supports by employing a number of piles, or columns to carry the support beam.
Abutment Parts of a Bridge:
1. Bridge Seat:
A nearby or atop an abutment horizontal shelf that supports the bridge deck.
These would support the end of a bridge on an embankment, while along a span will provide support to lessen prolonged stress.
2. Wing Walls:
The abutments that connect to the embankment can be observed to have wing walls.
They are little retaining walls that support the ground and stop erosion.
3. Back Wall:
The majority of bridges have back walls that are constructed vertically at their ends.
The back walls support the expansion joints of the bridge span or deck.
Only embankment walls contain this kind of wall.
4. Abutment Pile:
The section of an abutment that runs from the ground foundation of the abutment to the seat of the bridge is known as an abutment pile.
The length of the pile is determined by the height of the bridge and the depth of the obstruction (stream, river, and canal).
5. Abutment Footing:
The bridge foundation is another name for abutment footing, they have wider and heavier footing.
The footing’s purpose is to prevent the Abutment from burial itself in the earth.
Design considerations for Bridge Abutments:
- When planning the bridge abutment, the following factors are considered as follows:
- The approach slab (landing) and deck of the bridge are not allowed to settle differently because it provides a trip hazard and detract from the appearance of the road.
- Prevent approach slab (landing) shear failures from improper subsurface support caused by poor soils, fill from the bridge abutment excavation, or other circumstances.
- According to the specifications of a qualified, the length of the approach slab must match the width of the bridge deck and the height of the abutments.
- By inserting the approach slab into an appropriately sized notch in the bridge abutment, the approach slab is combined with the bridge abutment.
- The approach slab’s subsurface components include flowable fill, aggregate, and well-compacted soil.
- To prevent the newly dug area from being used to build the bridge abutment, and increase the subsurface design of the road as needed.
- It is possible to adopt a long-term seamless transition from the approach slab to the bridge deck while avoiding approach slab shear failure.
Different Forms of Support for Bridge Abutment:
Abutment supports are categorized based on their structure and purposes; each category of abutment support is described as follows:
1. Drilled shafts or piles:
To prevent abutment settling, the majority of the abutments are supported by piles.
Bridge approach embankments are prone to a settlement over time so they are frequently made of fill material.
The type of embankment material employed or the foundation material underneath the embankment may be to blame for this settlement.
Bridge Abutment can prevent the embankment from settling with them by pushing piles through the embankment into the earth.
Due to friction created by their contact with the fill, the abutment piles may be able to withstand an embankment.
It is important to assess the increased stress on the friction piles and need for pre-boring.
2. Spread Footings:
When the actual soil can withstand adequate stresses without excessive settling, only cut sections of the spread footings typically use abutments.
The bearing resistance is decided by the geotechnical adviser.
Spread footings can be used successfully on fill material with improved procedures and acceptable control of embankment construction.
Construction must be scheduled to permit the foundation material to solidify before spreading footings.
Spread footings have the benefit of minimizing the various types of settlement between approach fills and abutments.
Advantages of Bridge Abutment:
- This bridge transfer of loads from a superstructure to the elements of its foundation.
- Also, it is necessary to resist or transfer self-weight, lateral pressures (such as ground pressure), and wind loads.
- To support a slab’s approach edge on one side.
- The abutment is used to maintain equilibrium between the vertical and horizontal force components of an arch bridge.
Disadvantages of Bridge Abutment:
- A bridge should be designed specifically to take a long time to complete.
- The sheer number of materials needed to build a bridge abutment will greatly increase its price.
- It can require more maintenance than usual.
- It takes a particular skill set to develop.
Also read: Segmental Bridge | Types of Bridges | Cantilever Bridge
A bridge abutment is a building that connects the bridge’s deck to the ground at each end of a span that helps to support the bridge’s weight both horizontally and vertically.