Bridges And Their Types | Components | Span Length | Uses | materials

BRIDGES AND THEIR TYPES

 

 

INTRODUCTION OF THE ARTICLE

A bridge is a man-made structure that avoids physical obstructions by blocking an underlying path such as water, valley or road. It is built for the purpose of crossing the barrier. The first man-made bridges may have been made of cut wooden logs or boards and finally stones, using a simple support and cross-section arrangement.

The Romans built arch bridges and waterways. They also used cement, which reduced the variation in strength found in natural stone. The design of the bridges will vary depending on the activities of the bridge, the nature of the terrain on which the bridge is built, the material used to build it, and the funds available to build it.

THE MAJOR PARTS OF BRIDGES

Every bridge can be divided broadly into three parts:

Superstructure / Substructure / Foundation.

 

Superstructure: Superstructure is a part of a structure that supports traffic and includes decks, slabs and beams. All parts of the bridge installed on the substructure can be called as a superstructure.

 

Substructure: That part of the structure, i.e. the piers and abutments, supports the superstructure and transfers the structural loads to the foundations.

 

Foundation: The foundation is the component that transfers load from the substructure to the bearing strata Depending on the geotechnical characteristics of the bearing layers shallow or deep foundations are followed. Usually, piles and well foundations are followed for bridge foundations.

 

Span is the distance between two bridge supports, be they columns, towers or the wall of a valley.

Deck is a bridge platform that carries loads of traffic directly. Transfers deck loads to girders depending on deck material.

Beam/Girder a rigid, usually horizontal, structural component

The beam or girder is a part of the superstructure that bends at span intervals. This is the load-bearing area that supports the deck.

Bearing: It Transfers loads from grinders to pier caps.

Pier: its vertical supporting structure, such as a pillar.

Pier Cap/headstock: Is the element that transfers loads from the superstructure to the piers. Pier cap provides sufficient seating for the Bridge girders.

Cantilever: A projecting structure supported only at one end, like a shelf bracket or a diving board.

Truss: A rigid frame made of short, straight pieces joined together to create continuous triangles or other standard shapes.

Pile cap and Piles: Pile foundation is the most commonly used foundation structure for bridges. The pile is a thin compression member that is driven or formed on the ground to resist loads. This is called a pile cap to ensure that the reinforced concrete mass cast around the head of the group of piles works together and distributes the loads on them.

FACTORS WHICH WILL AFFECT BRIDGE STRUCTURE ARE:

Forces-Loads-Materials-Shapes

Force - Any action to maintain or alter the condition of a structure.

Compression - It is a force that acts to compress or reduce the size.

Tension - A force acting to expand or extend the matter in which it operates.

Load - weight distribution throughout a structure.

Stable - (adj.) Ability to resist collapse and decay; Stability (n.) Is a characteristic of a structure that can withstand a realistic load without collapsing or significantly deforming.

Deform - to change shape.

Bucking is a sudden change (deformation) in the form of a structural component under load, i.e. bending of a column under compression or contraction of a plate under shear.

 

TYPES OF BRIDGES

All bridges are designed to allow loads to cross obstacles. These barriers may be rivers, valleys or lakes. Loads are usually vehicular traffic, pedestrians or animals.

There are four basic types of bridges.  

·       Beam bridges

·       Arch bridges

·       Cantilever bridges

·       Suspension bridges.

Bridges can be twisted or bent under severe weather conditions, which can have catastrophic consequences. To prevent this from happening the bridges must be strong enough to resist this movement and each member of the bridge must be strong enough to withstand the loads placed on it

Bridges can be categorized in several different ways.

Common categories include the type of 3 structural elements used, by what they carry, whether they are fixed or movable, and by the materials used.

Common types include 3 structural elements used,

·       What they carry

·       Whether they are fixed or movable

·       The materials used.

 

TYPE-1: FIXED OR MOVEABLE BRIDGES

Fixed – Most bridges are fixed bridges, which means they have no moving parts and will last until they fail or are demolished. They have been designed where they are considered unusable or demolished.

 

Temporary bridges – Bridges made of basic modular elements on which medium or light machinery can be moved. They are typically used in military engineering or in circumstances where fixed bridges are repaired.

 

Moveable – They have movable platforms and are often powered by electricity.

TYPE- 2 CLASSIFICATION OF BRIDGES BASED ON STRUCTURES:

Bridges can be characterized by how the forces of tension, contraction, bending, torque and shear are distributed through their structure.

 

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BRIDGES BY STRUCTURE  

 

Arch Bridges – An arch bridge is a very popular type of bridge that was widely used by the ancient Romans. The arch bridge is usually made of stone, concrete or steel. The bridge is in the shape of an arch, as the name implies. An arch bridge is a curved bridge where the load of the arch is not applied directly downwards, instead, the loads are carried along the curve to the end of the support. This means that no part of the bridge will take on too much pressure. These supports are also called abutments. The apartments carry the load of the entire bridge and are responsible for keeping the arch in an accurate position.

No. The curves (curves) in a bridge depending on the stress and loads that the bridge must support. The length of curved bridges is usually up to 250 m, and the roadway structure of the bridge.

 

Forces: The compressive forces generated by the loads are shifted downward through the arch and resisted by supports or abutments at its base. Abutment support prevents the arch from spreading under load.

 

The span length of arch bridges is normally up to 250m,

 

Advantages of Arch Bridge:

1. It is easy to build with locally available material.

2. These types of bridges are very hard and very strong.

3. Arch bridges are built of various materials such as stone, concrete and steel.

Disadvantages of Arch bridge:

1. They take a long time to build.

2. It requires a large number of construction materials to build.

3. Limited spans unless multiple arches (or viaducts) are used and uneconomical use of materials

 

Beam bridges are the oldest and simplest bridge design consisting of horizontal beams and vertical piers - e.g. just a simple plank or stone slab. They are suitable only for short spans but can be used for larger crossings by adding additional piers.

 

Forces: As the bridge is loaded, by transport, the beam bends, causing the upper surface to shrink and the lower surface to stretch or tension.

 

Beam bridges have span less than 80m.

 

Advantages: They are easy to build and cheap compared to other bridge types, and therefore more common.

Disadvantages: They have a certain spacing and do not allow large boats or vehicles to go under.

 

Truss Bridge is a triangle assembly. Truss bridges are usually made from a series of straight steel bars.

Rigid arms extend from both sides of two piers. Diagonal steel tubes, protruding from the top and bottom of each pier, hold the arms in place. The arms that go towards the center are only supported on one side, like very strong diving boards. These “diving boards” called cantilever weapons, support a central span.

Truss Bridges are structures made by joining lengths of material together to form an open framework - based primarily on triangles due to their rigidity. They are very strong and can support heavy loads.

Forces: As with Beam Bridge, a loaded truss top is placed in compression and the bottom in tension. These forces are divided among the right-angled members.

 

The span length of truss bridge is in between 50m-110m.

 

Advantages of Truss Bridge:

1. This type of bridge is easily built in the factory and then built on site.

2. Ships or supports are relatively low compared to the Beam Bridge,

3. They are strong and tough and very light in weight with efficient use of materials.

Disadvantages of truss bridges:

1. Highly skilled professionals are needed to design this.

2. In terms of design they are more complex than beam bridges.

 

Cantilever bridges are based on horizontally projected structures in space supported only at one end - like a springboard.

 

Forces: if two cantilevers project out from a central pier the forces are balanced.

 

Cantilever bridge has a span in between 150m-500m.

 

Advantages of Cantilever Bridge:

1. These types of bridges are accepted only when support cannot be provided at certain levels.

2. Support is required only on one side of the cantilever.

 

Disadvantages of Cantilever Bridge:

1. Cantilever bridges undergo major breakthroughs during construction.

2. If the forces are not in balance, the bridge may hook.

 

Tied arch bridges have an arch-shaped superstructure, but differ from conventional arch bridges. Instead of converting the weight and transport loads of the bridge into propulsion forces, the ends of the curves are controlled by the tension in the country under the structure. These are similar to arch bridges, but they transfer the weight and transport load of the bridge to the upper chord which is attached to the lower cords at the foundation of the bridge. They are often called bowstring arches or bowstring bridges.

 

Suspension Bridges Key Elements is A pair of main suspension cables extend over two towers and are attached to an anchor buried deep in the ground at each end. Small vertical suspender cables are connected to the main cables.

Forces: Any load applied to the bridge is converted into a tension in the main cables, which must be firmly anchored to resist.

 

The span length of Suspension bridge is in between

150m-2000m

 

Advantages: Strong and can spread over long distances across rivers.

Disadvantages: The build is expensive and complicated

 

Cable-stayed bridges may look similar to suspension bridges, but in reality they are completely different in principle and in their construction. There are two main classes of cable-stayed bridges: fan type, which are more efficient, and harp or parallel type, which allow more space for adjustments.

 

Forces: As traffic on the road is pushed down, the cables connected to the road shift the loads to the towers, keeping them short. The tension in the cables continues to act as they are stretched as they are connected to the roadway.

 

The span length of Cable-stayed bridge is in between

500m-1000m.

 

Advantages of cable-stayed bridge:

1. It is very economical compared to the suspension bridge.

2. It is good for medium spaces and can be easily created by exiting the tower.

Disadvantages of cable-stayed bridge:

1. Maintenance and inspection can be very difficult.

2. These types of bridges are not suitable for long distances.

 

Roving Bridge/Change line Bridge/Turnover bridge Is a bridge over a canal constructed to allow a horse towing a boat to cross the canal when the towpath changes sides. 

 

Also Read: TOP 10 CIVIL ENGINEERS INTERVIEW QUESTIONS

TYPES OF BRIDGES BY USE

Car Traffic bridge: The most common type of bridge, with two or more lanes designed to carry car and truck traffic of various intensities.

Pedestrian bridge: They are usually made in urban environments or in terrain inaccessible to car traffic (rough hills, forests, etc.).

Double-decked bridge: Built to provide better flow of traffic on water or rough terrain. Most of the off they have high car lanes, sometimes with an area dedicated to railroad tracks.

Train bridges: Bridges made specifically to carry one or multiple lane of train tracks.

Pipelines: Bridges made to carry pipelines across water or inaccessible terrains. Pipelines can carry water, air, gas and communication cables.

Viaducts:  A viaduct is made up of multiple bridges connected into one longer structure. Ancient structures created to carry water from water-rich areas to dry cities.

Commercial bridges: Modern bridges that host commercial buildings such as restaurants and shops.

 

FAQs

 

1.  What are the types of bridges based on materials?

Types of Bridges by materials used:

•       Natural materials

•       Wood

•       Stone

•       Concrete and Steel

•       Advanced materials

 

2.  What are the types of bridges based on structures?

·       Arch Bridges

·       Beam bridges

·       Truss Bridge

·       Cantilever bridges

·       Tied arch bridges

·       Suspension Bridges

·       Cable-stayed bridges

·       Roving Bridge/Change line Bridge/Turnover Bridge  

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