5. pre stressed & pre-cast members

1. PRESENTATION TOPIC :

6. CONCEPT OF PRE-STRESSING :
1- The concept of pre stressing was invented many years
ago when metal brands were wound around wooden pieces
to form barrels.
2-The metal brands were tighten under tensile stress which
creates compression between the staves allowing them to
resist internal liquid pressure

7. PRINCIPLE OF PRE-STRESSING :
Pre-stressing is a method in which compression force is applied to the
reinforced concrete section.
The effect of pre stressing is to reduce the tensile stress in the section
to the point till the tensile stress is below the cracking stress.Thus the
concrete does not crack.
It is then possible to treat concrete as a elastic material.The concrete
can be visualized to have two compressive force
i . Internal pre-stressing force.
ii . External forces
These two forces must counteract each other.
PRE-STRESSED CONCRETE METHODS
There are two basic methods of applying pre-stress to a concrete
member
Pre-tension concrete – most often used in factory situations
Post-tension concrete (bounded & unbounded) – site use

14. ADVANTAGES & DIS-ADVANTAGES
ADVANTAGES :
Need less materials
Smaller and lighter structure
No cracks
Use the entire section to resist the load
Better corrosion resistance
Good for water tanks and nuclear plant
Very effective for deflection control
Better shear resistance
DISADVANTAGES COMPAREDTO RC:
Need higher quality materials
More complex technically
More expensive
Harder to re-cycle
APPLICATION:
Bridges Slabs in buildings WaterTank concrete Pile thin Shell
Structures Offshore Platform Nuclear Power Plant
Repair and Rehabilitations

16. Precast concrete means a concrete member that is
cast and cured at a location other than its final
designated location.The use of reinforced
concrete is a relatively recent invention, usually
dated to 1848 when jean- Louis Lambot became
the first to use it. Joseph Monier, a French
gardener, patented a design for reinforced
garden tubs in 1868, and later patented
reinforced concrete beams and posts for railway
and road guardrails.

19. PRECAST CONCRETE FRAMING
SYSTEMS