You must have seen various iconic Bridges along with Bridge Foundations or Bridge Piers. But do you know what is a Bridge Foundation or Bridge Pier?
Please read this blog for details.
What is a Bridge Foundation or Bridge Pier?
Foundation is an integral part of a bridge and placed below the substructure and sits underneath the level of the soil and rests above the hard or solid strata. The foundation carries the load of superstructure, substructure and transfers it to the underlying hard ground.
To know the details of all bridge components, please read this blog for details:
Bridge foundation or Bridge Pier is provided to holds the bridge span and transmit the load to the ground. This simply means that the Bridge Foundation needs to be robust enough to not only holds the vertical load of the substructure but also holds the lateral stress of the bridge span.
As a result, bridge foundation is imperilled of the load from all the directions, also called as multi-axial loads. But still, most of the load it bears comes in the form of vertical load and termed as compression load.
The top-level division of Bridge Foundation mainly depends on allowable bearing compression of the underground strata and the type of superstructure that is considered for the design.
So, the top-level division of the bridge is as below:
- Strip Footings Foundation,
- Pile Foundation
Strip footing Foundation:
As the name suggests, strip footing foundation is a fairly minor strip of concrete sited into a trough (to resist differential settlements) and steel reinforcements are placed as per design and recommendation.
These types of foundations are not recommended for giant and very long span bridge support. These type of foundations are recommended low moderate structure loading and for the soil which has a fairly good bearing capacity.
Pile foundations are deep foundations in long cylinder shape columns and they are made of concrete and steel to support the substructure and superstructure of the bridge deck. The load of the bridge is supported by the surrounding surface of the pile foundation as a frictional force.
Type of Pile Foundation Based on Function and Based on the Method of Construction:
|Based on Function||Based on the Method of Construction|
|Sheet Piles||Timber Piles|
|Load Bearing Piles||Concrete Piles|
|End bearing Piles||Steel Piles|
|Friction Piles||Composite Piles|
|Soil Compactor Piles|
Types of Bridge Columns or Bridge Pier
The selection of type bridge columns mainly dependent on the ground condition, type of bridge deck, sub-soil conditions, and method of construction adopted for bridge superstructure and substructure.
There are two key types of bridge columns commonly recommended:
- Solid Columns
- Open Columns
Solid Columns are hard and impervious assembly and made of construction material like Concrete, Stone Masonry or RCC, etc.
Open Columns are modern design elements and they are compact hallow structures to allow water to pass across it. As a result, these types of columns are considered as much environment friendly (strong against water flow) and robust to sustain the load of superstructure and substructure of the bridge.
There are four key types of columns foundation commonly used for Bridge Foundation Design:
- Single or Dual Cylinder shape Columns
- Trestle Columns
- Single or Multi-Column Bents
- Framed Columns
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Single or Dual Cylinder shape Columns
Single or Dual Cylinder shape columns are proposed in case of Moderate to low height Bridge design options and where the bearing capacity of the underlying soil is also good. These columns are commonly made of Reinforced concrete.
Trestle Columns are made of numerous short bridge deck columns, spaced very closely. These types of columns are not recommended to long-span bridges or viaduct type bridge structures.
Trestle Columns are predominantly made of Timber or Iron and they were very common in the early 20th century.
Single or Multi-Column Bents
Column Bent basically means the beam across the columns that unite the width of the bridge deck and transmits the load to the subsoil. These types of Columns or Bridge Piers are normally recommended larger heights and longer span bridges.
Framed Columns are commonly part of a Rigid-frame bridge and they act as a monolithic unit. There are numerous advantages to the rigid-frame bridge. They are very robust to hold all combination of loads like bending moment, shear forces, axial forces, etc.
Although the assembly or construction of these type of bridge is a complex task due to its gigantic size.
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With Rapid advancement of design and construction technology, the bridge design has made leapfrog movement from traditionally heavy and less environmentally friendly Bridges to modern, sleek, robust and eco-friendly bridges.
Bridge Engineering is passing through an exciting time and it’s highly recommended to our newbie civil engineers to join the industry as a Bridge Engineer.
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