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Pre-stressed concrete is a method of casting concrete with steel bars or cables that are tensed and then released. This forces the concrete to go under compression.
Pre-stressed concrete is used to overcome the tensile weakness concrete has, it is generally used for beams.
Concrete is strong in compression but weak in tension. to overcome this drawback of concrete we provide reinforcement in the concrete where tension is likely to occur. The normal reinforcement holds good when the span of that particular member is small or you can say- mtr. In case of longer span, by providing reinforcement steel strands in tension form keeps that concrete section in compression in which concrete is strong. when this member section after applying load comes under tension, its existing compressive force nullifies its load effect. Hence we use prestressed concrete members generally where spans are longer and loads are heavy.
A common use of pre stressed beams is in long spans that encounter frequent variable loads.
Envision a playing card over a void that is laid level, or flat, and a playing card that has been bent resulting in an arch or curve in the card over a similar void. If you roll a toy car over the flat playing card, the resulting deflection in the card may result in a failure because the ends of the card no longer span the distance of the void. Roll the toy car over a void spanned by the 'pre stressed'(bent into a curve) card and the deflection is absorbed by the tension in the stressed material and the buttress of the connections at each side of the anchoring void.
Pre stressed components are usually cast off site, where a tensioned material, typically braided or wound metal strand, is stressed like pulling a rubber band and concrete/fill is poured into the form assembly and allowed to cure to varying degrees, the stressed strands are released from their anchors, compressing the fill material in compression. This often results in an assembly that is visibly arched. The members are exponentially stronger than a static steel reinforced concrete member of similar construction.
The Concrete in which reinforcing steel bars are stretched and enchored to compress it to increase its resistance to stress.
Generally concrete is weak in tension. to overcome this weakness ,the conrete is stressed with tensile force by stressing tendons by mechanical means in pre-stressed concrete.
Pre-stressed Concrete is an architectural and structural material possessing great strength. The unique characteristics of pre-stressed concrete allow predetermined, engineering stresses to be placed in members to counteract stresses that occur when the unit is subjected to service loads.
Actually, prestressing is quite simple.
High tensile strands are stretched between abutments at each end of long casting beds. Concrete is then poured into the forms encasing the strands, As the concrete sets, it bonds to the tensioned steel.
When the concrete reaches a specific strength, the strands are released from the abutments. This compresses the concrete, arches the member, and creates a built in resistance to service loads.
As it is known the concrete is very weak in tesion but strong in compression .Thats why we put bars in the concrete to resist the tension where it might occurs .But under heavy load and longer span there will be cracks in the concrete so to overcome this Freyssinet got the idea of pre stressing concrete.
Prestressed concrete's principle is applying compression forces to the reinforce concrete thus the concrete will not crack.
This concrete which titend by strand ,for large spans and for fast and more loads
the concrete will get opposite load means prestressed beforeif get hardness ,the strans will be titted to the fully load within 96 hours gradually and the concrete will be ready to recive the actual load at short period ,the actual load will be against the pre stress load .
pre-stress concrete is where the steel is stretched and does not allow the steel to move, thus making the beam or slab stronger and resistant to movement
Concrete is weak in tension and strong in compression, the prestressed concrete idea is to form a structural material that is strong in both compression and tension
