Question

write an detailed essay on the type of concrete used for a bridge that has a bridge deck of 170m

Answer 1

Bridge with a bridge deck of 170m is a large structure.In this type of mega construction structures,prestressed concrete is preffered.In this type of concretes high strength wires called tendons are used.They provide the required initial compression before application of external loads.As a result,Streeses produced during service period can be counteracted in a efficient manner.The load carying capacity of concrete increases,if it is stressed before application of loads.

It is known that concrete is weak in tension and strong in compression.Due to this tensile cracks are often produced in concrete structures.In prestressing process,compressive stress is induced and this stress helps to counter act the tensile stress the concrete will face during it's service conditions.A properly engineered prestressed concrete can span longer distance than a reinforced concrete beam and use less concrete without cracking.Generally prestressed concrete are of two types-Pre tensioned prestressed concrete and post tensioned prestressed concrete.

In pretensioned prestressed concrete,tendons are provided before the concrete is placed.The tendons are placed temporariliy and they are removed after the concrete is placed and hardened.The stress is transferred from external anchorages to the concrete.It is generally done in various pre cast factories and plants.

In post tensioned prestressed concrete,the concrete is first allowed to set but ducts are cut through it to provide the tendons or cables after the concrete is hardened.After the concrete gains the maximum strength,tendons are removed accordingly.It must be done before the application of the extenal loads.

Prestreesed concrete memebers resist the effect of impact,cracks and stresses and thus help in prevention of th development of cracks.It has a long term durability and joints required is less than the ordinary rcc structures.That is why it is very useful in mega structurers likes bridges,dams,tunnels etc.