There are different types of bridges, each serving a specific purpose and selected in different situations.
The bridge is a man-made rigid structure built over a barrier to provide passage over a barrier, the passage may be for railway, road, canal, pipeline etc.
The design of the bridges will vary depend on the efficiency of the bridge and characteristic of the area where the bridge is to be constructed.
Component parts of various types of bridges:
The bridge structure consists of the following parts as follows:
Superstructures include slabs or girder or truss, etc.
The super-structure carries the load passing over the passage and transmits the forces caused by the sub-structures.
The substructure does not have sufficient bearing strength to carry the superstructure load directly on it.
To assist these loads the bearings are designed, it helps carry the load from the deck and evenly distributes it over the substructure.
Substructures include piers, abutments, wing walls that are provided to transmit a load of superstructure to the earth.
Different types of bridges in construction:
1.Beam bridge or Stringer Bridge:
Beam bridges are simply supported bridges with horizontal beams and vertical piers also known as stringer bridges or girder bridges.
These bridges are usually characterized by two or more spans that are supported by abutment or pier at each end constructed using RCC, wood, steel.
They are simply supported bridges (beams that are supported on piers), where the beams are placed in support, while the length of the beam bridges is less than 80 meters.
In such bridges, the beam must be strong enough to bear the load on it, these loads are subsequently used to support the bridge over the earth.
There is compression in the top edge of the beam as the load is applied to the lower part of the beam, it has been pulled and under tension.
Forces on Beam Bridge:
The forces mostly act on the upper and lower surfaces of a beam bridge, while the force of gravity acts downward on the objects on the bridge and the bridge reactions support the beam turning in the middle.
This squash (compressed) on the upper surface of the beam.
Advantages of Beam Bridge:
- This beam bridge is very easy to construct and erect.
- These beams are good for short spans.
- Wide distances can be seen by resting smilingly on the platform.
Disadvantages of Beam Bridge:
- They are expensive & require RCC for construction.
- They are restricted by boundaries.
An arched bridge is the most popular bridge that is used extensively by the ancient Romans which is usually constructed from stone, concrete, or steel in the shape of an arch.
This bridge is a curve-shaped bridge, where the load on the curve is not applied immediately below, but instead, the load is carried along the curve of the arch to the tip of the support.
It is understandable that no part of the bridge exerts a large amount of pressure, these supports are also called abatements.
The abutments carries the weight of the entire bridge, which is responsible for keeping the arch in precise position.
Force on arch bridge:
The number of curves (arches) in a bridge depends on the stress and load that the bridge must support.
The span length of arch bridges is generally up to 250 meters and the road to the bridge is located on the arch structure.
Advantage of Arch Bridge:
- These bridges are easy to manufacture with locally available materials.
- These types of bridges are very rigid and extremely strong.
- Arc bridges are constructed with various materials such as stone, concrete, steel, etc.
Disadvantages of Arch Bridge:
- It takes a very long time to make assemble.
- It requires a considerable amount of construction materials for its development.
The truss bridge is a framework consisting of struts (inclined members), these bridges are constructed using trusses that consist of several small elements forming a triangular truss.
The span length of the truss bridge is between 50 m-1100 m.
Force on truss bridge:
The single-span bridge is similar to the supported beam because it bends and loads vertically.
Bending causes compression in the top chords (or horizontal members), tension in the bottom chords, and tension or compression in the vertical or oblique members depending on their orientation.
The trusses are very rigid, lightweight that can support heavy loads, while they serve to move the load from one point to a wider area.
The bridge weighs is very little than other bridge.
When the load is applied to the truss bridge, compression happens within the top edge and load is shared between the angled members to support.
Advantages of Truss Bridge:
- These types of bridges are easy to construct.
- The piers or supports are comparatively shorter than the beam bridge.
- They are strong and rigid which makes efficient use of very light material.
Disadvantages of truss bridge:
- It requires highly specialized laborers to design.
- They are more complex than beam bridges for designing.
Suspension bridges are constructed by suspending the deck slabs using suspension cables.
The roadway is hung using a metal cable that connects the two towers which are secured by anchors at each end of the bridge.
In addition to the deck slab, the truss system also features with the truss system just below the deck that helps to stiffen and position the deck to reduce the tendency to block the passage.
When the load is applied to a suspension bridge, compression occurs in the deck slab, then ropes, cables, or chains to transfer compression to the towers.
The towers then dissolve the compression directly into the earth by anchoring, while auxiliary cables that run parallel to the bridge have tension forces attached to the anchor.
Bridge anchorages are large-scale concrete blocks that serve to stretch the tension force onto the ground while bridge anchors are essentially concrete rock or massive concrete blocks in which the bridge is formed.
The tensional force passes into the anchorage and ground, the span length of the suspension bridge is between 150m-2000m.
Forces on Suspension bridges:
The primary forces in a suspension bridge are tension within the cable and compression within the towers.
The deck which is normally a truss or a box girder is connected to suspension cables by vertical suspender cables or rods known as hangers under tension.
Advantages of Suspension Bridge:
- It is robust and lightweight.
- These types of bridges provide long spans which help in crossing the river.
Disadvantages to the suspension bridge:
- They are expensive to manufacture.
- It is prone to drifting and rippling with the wind, so this bridges are not suitable for railways.
Cable stayed bridge is a modern bridge similar to a suspension bridge.
In these bridges, cables are attached directly to the tower instead of suspended cables, the tension on the cables is continuously working that are increased when attached along the road.
These types of bridges have no anchorage to bear compression and a tower to hold compression which has a size is between 500m – 1000m.
Force on cable-stayed bridge:
In force on cable-stayed bridges, cables are radially coupled on the roadway at varying factors and the towers bear compression forces alone.
Advantages of cable-stay Bridge:
- These bridges are more economical as compared to suspension bridges.
- It is good for medium spans and simply made by cantilever out of the tower.
Disadvantages of cable-stayed bridge:
- In these bridges, maintenance and inspection can be more difficult.
- These types of bridges are not suitable for far distances.
The term cantilever means that the beam which has only one support and the other end is kept free in space.
The cantilever bridges are similar to continuous bridges, however, do not assume that one end of the bridge is kept free.
Cantilever bridge are constructed in parts and two free ends are linked with suspended decks in between 150- 500 m size.
Force on cantilever bridge with suspension deck:
This bridge is subjected to compression and tension forces.
In these types of bridges, a suspended deck is supplied to connect the two free ends of the cantilever bridge.
When the load is applied to the cantilever bridge, the top supports are subject to a dimensional force (pulling force), and the decrease supports are subjected to the compression force (pushing force) that makes the bridge balanced.
As long as the force is balanced, the bridge will remain in a steady state.
Advantages of cantilever bridge:
- These bridges are adopted only when assistance cannot be provided to specific positions.
- Supports are required only at one side of the cantilever.
Disadvantages of cantilever bridge:
- Cantilever bridges are prone to high bend stresses during construction.
- If forces are not balanced the bridge may buckle.
Also read: Types of Trusses, Types of Roads & Types of Arches