Bridge Engineering introduction

In this article we discuss introduction of bridges.

 After reading this article you will be able to answer 👇

1) what is bridge.

2)why we construct bridge.

3) points that should be kept in mind while selecting site for bridge.

4) components of bridges.

5) requirements of good ideal bridge.

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Introduction 

A bridge is a structure providing passage over an obstacle without clossing the way beneath 

The desired passage may be for a road railway, pedestrians canal or pipeline.

The obstacle to be crossed may be

River, road, railway  or valley

Bridge engineering

Selection of Bridge Site 

A ideal site for a bridge across a river should have following characteristics

1. At bridge to the reach of the stream should be right

 2. The site should be geologically sound 

I.e it should be away from fault zone And should have underyielding non erodible foundation for pier and abudments

3.At site the river flow should be without whirls and current

4.at site the steam should be narrow with well defined and firm bank

5. On the constitution site there should be suitable high banks above (HFL) High flood level on each side of river.

6.The approaches should be economical 

7. They should not be very high or long or liable to flank attack of the floods

 They should be free from obstacle such as hill ,frequent drainage, crossings, built up areas, sacred area as graveyards or troublesome and acquisitions etc.

8.The site should be a reasonable proximity to a direct alignment of the road to be connected

9.There should be no sharp curves in the approaches

10. Absence of costly river training workers where they are unavoidable they should be executed in dry far as possible.

11.Avoidance of excess be underwater construction work

12. If it is unavoidable necessity for the approaches of the bridge to cross the spill zone of a river they should (while processing through the stone toward the river), Face down stream and not up stream .Facing upstream causing heading  up and Causes pocket formation and danger to approaches.

Requirements of an Ideal Bridge

 An ideal bridge must meet the following requirements 

It should be economical.

it should serve the intended functions with safety and convenience.

It should give asthetic and elegant look

Components Parts of a Bridge

The bridge structure can be divided into two parts as follows:

1. Superstructure

2. Substructure 

Superstructure:-

it is that part of the bridge over which the traffic moves safely

It consist of parapet, roadway, girders, arches or trusses over which the road is supported

Substructure:

 The function of substructure is similar to that of foundations, columns and walls etc. Of building Thus the substructure supports the superstructure and distributes the loads to the soil  below through foundation 

The substructure consist of foundation, piles, abutments, wing walls and approaches

Definitions

Valley: A depression in between two banks or sides with water is known as a valley.

Viaduct: A deep valley without perennial water is known as a viaduct.

Span: The centre to centre distance between two piers or supports is known as span.

The clear distance between the two supports is known as clear span.

Abutments: The end supports of the super-structure of a bridge are called abutments.

They may be either arched shaped or flat.

Piers: The intermediate support of the super-structure are called piers. They transfer the load from the super-structure to the sub-soil through the foundation. They are spaced as per design. They obstruct the flow of water on the up stream.

Abutment Piers: In arch bridges, sometimes, some of the intermediate supports or piers are made of a stronger section than others.

They are designed to function as a abutment, except retaining and protecting the earth fill.

Wing Walls: The walls constructed on both sides of the abutments are called wing walls. They support the soil behind them or embankments of approach roads and also protect the embankments etc., from the wave action of the running water.

Approaches: The structures that carry the road or railway track upto the bridge are known as approaches

Generally they are embankments

Foundations:- The structures used for transferring and distributing the dead load of super-structures, piers and abutments etc. along with live loads likely to come on the bridge to so underneath are known as foundations

High Flood Level: The highest water level ever recorded during a flood in a river or stream is known as high flood level.

Free Board: The difference between the high flood level and the level of the crown of the road at its lowest point is called free board.

Low Water Level: The lowest or minimum water level in the stream or river during dry weather is known as low water level.

Scour: The vertical increase in depth of river bed from the point of  river bed atcat the time of construction of bridges 

Afflux: The rise in water level of the river near bridge due to the obstruction created by the construction of piers is called afflux.

Water Way: The area of opening sufficient to pass the maximum food discharge expected in the river without increasing velocity of flow beyond safe limits is called the water way Generally the safe limits of velocity under bridges is taken as 20 m per second

Actually for big bridges the water way is calculated from the formula

A =Q/V

Economic Span: The length of the span for which the cost of construction of the bridge will be least is known as economic span.

Head Room: The distance between the highest point of the vehicle and road using that bridge is called headroom.

 It is a very important factor to be considered in through bridges 

Clearance:-

 The least or minimum distance between the specified positions of a bridge is knowns as clearance 

It may be horizontal as well as vertical 

The vertical clearance is the clear height from the HFL to the lowest point of the bridge structure.