Types of bridge foundation – Suitable foundation for different Strata

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This article covers the different types of bridges and the types of bridge foundation that is used in the design of bridges.

A bridge refers to a structure that provides passage over a physical obstacle such as a valley, road, or a water body. The obstacle may be something that is difficult or impossible to cross, and this necessitates the building of a structure (bridge) to span the obstacle.

Types of bridge foundation

The foundation of a bridge depends on nature and depth. The following types of foundations are constructed.

Spread foundation

Types of bridge foundation

The spread foundation is also called an open foundation and is suitable for bridges of average height built on a firm and dry ground to provide support for the structure. This type of foundation is suitable where there is minimum scouring and the hard ground begins from 1.5-3 m below the level of the watercourse.

Raft foundation

Types of bridge foundation

These types of bridge foundation are used where the allowable bearing capacity of the soil is low and the bed of watercourse contains soft clay and silt. It favors foundations where hard soil is not found within reasonable depth (1.5-2.5m) below the watercourse.

Pile foundation

Types of bridge foundation

Pile foundation is used in conditions where there is very soft soil and hard strata are not available at a reasonable depth. It is also used where scouring of a river as to be done and a large concentrated load is to be taken by the foundation.

Well foundation

Types of bridge foundation

Well foundation of bridge is used when the bed has sandy soil and hard soil is available at 3-4 m below the level of the watercourse. Best suited on soil a condition having soft soils and sandy soils and heavy scouring is expected due to the large velocity of approach of the river.

Caisson foundationTypes of bridge foundation

Caisson foundation is a types of bridge foundation that is used where there is a hard stratum near the river bed and there is excessive water depth that is not economically sound to remove the water to enable sinking wells for well foundation.

We studied different types of bridge foundation. Now let us discuss some types of bridge.

Read in detail here, Different types of bridges – All Types of Bridge used in Civil Engineering

Types of bridges

There are different types of bridges based on the structure (how it distributes the load), the usage of the bridge, and the material used to make it. This enables the bridges to serve various roles in various conditions without failure.

Bridges by structure

The structure of a bridge dictates how the internal forces are distributed. The internal forces that act on a bridge are tension, compression, torsion, bending, and shear forces.

The structure of a bridge will enable it to handle a specific type of force more and this is attributed to the notable structural members of a bride. Based on this criterion, the following bridge types exist;

Arch bridges

The main structural component of this bridge is the arch, usually located below the bridge. These types of bridges can only be fixed.

The arch can be made of masonry stone, concrete, structural steel, cast iron, or even timber. Examples of these bridge types are the Hell Gate bridge in New York, Solkan bridge in Slovenia.

Beam bridges

Beam bridges are the simplest because they use horizontal beams. The beams can either span the area between abutments or transfer the forces to structural piers. Beam bridges mainly experience the transformation of vertical forces to shear at the support structures.

Their simplicity makes them the oldest bridge types by man. They are further divided into girder bridges, simple beam bridges, and plate and box girder bridges. The known example of this bridge type is Lake Pontchartrain Causeway in Lousiana.

Truss bridges

it makes use of a diagonal mesh of posts placed in a triangle shape above the bridge to aid the distribution of forces across the whole bridge structure.

The ability of the individual elements (usually straight beams) to endure dynamic tensional and compressional forces by distributing them across the entire structure makes the bridge to handle much stronger forces in comparison to other bridge types. The truss can either be fixed or movable.

Cantilever bridges

Cantilever bridges resemble the arch bridge in appearance except that they support their load at only one end through diagonal bracing with horizontal beams instead of vertical bracing.

The number of segments in a cantilever bridge is dictated by the size and weight capacity of the bridge. They don’t span long distances. An example of such a bridge is the Quebec Bridge in Canada.

Suspension bridges

Suspension bridges use spreading ropes/ cables connected on vertical suspenders to sustain the traffic and bridge deck weights. This bridge type can suspend decking over very large spans.

The abutments and piers remain fixed with most of the bridge structure being flexible and able to respond to forces of nature such as wind, earthquake, and vibrations from traffic. Some of the known bridges of this type are Brooklyn Bridge in New York and Akashi Kaikyo in Japan.

Fixed bridges

have no movable parts because they are designed to remain where they are until they are cleared unusable due to age or demolishing.

Temporary bridges

Temporary bridges used in instances where there is the repair of a fixed bridge. Are not usually intended to be used for a long duration of time.

Movable bridges

Movable bridges combine aspects of strength, flexibility, and carrying capacity in their designs. They facilitate the safe passage of variations of loads, ranging from passenger to freight.

Types by use

Bridges are so versatile and are used for various purposes. Several bridges are also designed to support multiple usages. The following bridge types exist on the basis of use;

  1. Pedestrian bridges – Pedestrian bridges the oldest bridges were designed to facilitate the movement of passengers over rugged terrain or water bodies. These types allow usage of pedestrians only.
  2. Car traffic – it remains the most common bridge use, able to carry car traffic of various intensities. Modern types employ multiple lanes that allow movement in a single direction.
  3. Train bridges – This bridge specifically carry a single or multiple train lanes. They are the second most common bridge types after the car bridges.
  4. Commercial bridges – It hosts buildings used for commercial purposes such as restaurants and shops. They are common in urban environments due to constant pedestrian traffic.

Types by materials

Bridges need to span a stable decking for transportation of pedestrians, cars, and trains besides carrying the structure weight and those from natural forces. Several materials can be used to achieve this as described below;

  1. Wooden bridges – Wooden bridges are used in small to medium-sized bridges for pedestrians or cars of low weight. They span short distances.
  2. Stone bridges – stone is a natural material that is long-lasting. They are able to build large structures of the bridge that can last for centuries.
  3. Concrete and steel bridges – They are the most common materials used in bridge construction made up of concrete and steel. Concrete and steel are selected according to the daily traffic and strata found at the construction site.

I hope this article on “Types of bridge foundation” remains helpful for you.

Happy Learning – Civil Concept

Contributed by,

Civil Engineer – Frankline Molo

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