Pre-Stress Concrete and it's losses

In this article we discuss the Pre-stress Concrete

Like share and follow

Pre-Stress Concrete

Concrete in which stresses are developed before it's use is known as pre stress concrete

In Pre-stress  concrete High grade of steel or high grade of concrete is used

In pre stress concrete High grade of steel is used to reduce shrinkage and creep

Steel used in Pre-stress concrete have ultimate stress 1500 N/mm2

 (Yield stress =0.6x1500=900-1000 N/mm2) steel

Method or system of Pre-stress

In Concrete pre-stress is  developed by following system 

1. Pre-tension Method

2. Post-Tension Method

Pre-Tension Method

In this method tension is developed in steel bar before concreting 

In this method the grade of concrete used should be at least M-40 and Minimum Nominal concrete cover 20 mm( not less than 20mm)

Pre tension method can be achieved by two method

1. Unit Mould Method 

2. Long line Method

In Unit mould method  pre-stress is developed in one member at a time

 

In long line method pre-stress is developed in many members at a time

factory production prefer Long line method to develope pre stress

Post-tension Method: 

It is a method in which first concreting is done then stress is developed in steel reinforcement 

During pre-stressing in post tension method  Min.Grade of concrete used is M-30 

minimum nominal concrete cover 30mm

(Not less than 30 mm)

Post  tension method 

This methods are of following types 

 (I)Fressinet Method

(ii) Megnal Balton Method

(iii) Lee-McCall Method

Losses In Pre-Stress Concrete:

Pre-stress concrete Losses mainly Classified

In two types

• Loss due to elastic shorting of conc. Is developed only in pre tension method
• Loss due to friction is developed only in post tension method
• In Pre tension method total losses is  approx 20% 
•  Post tension method total losses is approx 15%