BRIDGES | CLASSIFICATION

Bridges are superstructures which are built across roads, railways, canal, etc. They provide passage over the obstacles. The construction methods vary according to the purpose, loads to be carried, materials, etc. For more articles CLICK HERE

Designing the bridge is based on the structure, fixed or movable, etc. Many structural forces acting on it such as tension, compression, bending torsion.

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TYPES OF BRIDGES

On the basis of the materials used in the construction process, they are classified into

Timber
Masonry
RCC
Steel

TIMBER BRIDGE

Timber bridges are a commonly used type of bridge that is very easy to construct. These are known as temporary bridges. Timber is an easily available material but it has a short life span. They are again classified into two types namely

Timber Cantilever
Timber Suspension

TIMBER CANTILEVER BRIDGE

This bridge is constructed in layers. They are easy to construct. It is used in places where low traffic is seen.

The timber layers are embedded in layers on the side bank. Then again another layer of timber is laid at a distance of 2 - 3m from the lower layers. This is repeated till it reaches a length of 5 to 7m in the middle.

In between the gaps, road bearers are laid. Stone ballast is used on the surface for smoothening.

TIMBER SUSPENSION BRIDGE

Suspension bridges are used in hilly areas. These are constructed across valley or streams. They consist of cables or ropes which holds the load in them. They are also known as sling bridges. The cables are anchored at the banks.

MASONRY BRIDGE

The masonry bridges consist of the arch. The arch may be of semi-circular, semi-elliptical, parabolic or multi-centred types. They also consist of parts like abutments, Hand rad, Roadway, piers. These are only suitable for a short span.

RCC BRIDGE

This type of bridge uses concrete slabs. They are more rigid, durable. The construction of these types is easy. They have a good life span.

These are further classified into three types.

Slab
Tee beam and slab
Rigid frame

SLAB BRIDGES

Slab bridges are built by placing a slab of uniform thickness in two abutments. These have a short span. These have large loads. But the cost of construction materials is high. It suitable only for a span of about 8m and are more economical.

TEE BEAM AND SLAB BRIDGES

In this type, piers and abutments are used to support rectangular beams. These are suitable for spans up to 20m. The slabs are made monolithically. Usually, they are constructed over the canals over roadways and railway lines.

RIGID FRAME BRIDGES

The main components of rigid frame buildings are abutments, slab, parapet walls, portal frame, roadway, etc. The slab is made of monolithic with abutments. They provide stability against lateral forces such as wind and earthquake.

RCC ARCH BRIDGES

These bridges have a span of up to 200m. RCC arch bridges are more economical. Suspenders are vertical members that are hung vertically. Girders are used to support the structure. They have a good load carrying capacity

STEEL BRIDGE

Steel bridges are constructed in places where high traffic is needed. The load-carrying capacity is high for this type of structure. These are mainly used over railways, highways, oil pipes, etc. Some common type of Steel bridge is

Plate girder
Steel truss
Steel arch

On the basis of the forces acting on the surface, different designs are adopted.

PLATE GIRDER BRIDGES

Plate girder bridge is long-span bridges which are laid over a long distance. They have transverse load distribution. It has a built-up beam to carry the heavy loads. Simply supported spans less than 50m are used. Continuous support of a span of 26m is used. These are mainly used in cities in structures like flyovers.

STEEL TRUSS BRIDGE

These are long spans which have a span of 375m. They use truss for support. These trusses design on the basis of the loads. Some commonly used steel truss used are

Warren truss with vertical, Baltimore truss, Curved chord Pratt truss, Deck Warren truss.

STEEL ARCH BRIDGES

Steel arch Bridges are bow-shaped. The beams are curved and are called arch ribs. The flooring of the bridges rests in ties. The suspenders transmit the load to the arch ribs. Generally, they adopt a span of 250m. They may use fixed or hinged support.

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