Prestressing & Post Tensioning
As explained by wikipedia, Prestressed Concrete is a method for overcoming concrete’s natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that balances the tensile stress that the concrete compression member would otherwise experience due to a bending load. Traditional reinforced concrete is based on the use of steel reinforcement bars, rebars, inside poured concrete. The technique functions on the principle of using high tensile strength steel alloys producing permanent pre-compression in areas subjected to Tension.
A portion of tensile stress is counteracted thereby reducing the cross-sectional area of the steel reinforcement. Prestressing can be accomplished in two ways –
- Pre Tensioning Concrete
- Post Tensioning Concrete
PRETENSIONING :- Placing of concrete around reinforcing tendons that have been stressed to the desired degree.
POST-TENSIONING :- Reinforcing tendons are stretched by jacks whilst keeping them inserted in voids left pre-hand during curing of concrete. These spaces are then pumped full of grout to bond steel tightly to the concrete.
Here is a presentation on the methods of pre-stressing in concrete and details about post-tensioning and pre-stressing by Rajesh Burde (Source : Slideshare)