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- 1. Topic- Prestressed Concrete Presented by- Sayan Saha. Silliguri Institute of Technology (SIT). Department- Civil Engineering. Year- 4th Sem-7th Roll No- 11901320033. Registration No- 201190101320009 of 2020-21 Subject- Prestressed Concrete. Subject code-CE(PE) 702A(7684)
- 2. Introduction 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. It is often used in commercial and residential construction as a beam and slab.
- 3. Principle of Prestressed The principle behind Prestressed concrete is that compressive stresses induced by high-strength steel tendons in a concrete member before loads are applied will balance the tensile stresses imposed in the member during service. Prestressed concrete is basically concrete in which internal stresses of a suitable magnitude and distribution are introduced so that the stresses resulting from the external loads are counteracted to a desired degree.
- 4. Method Of Prestressing Pre -tensioning- It is a method where Prestressing steels are pre- stressed, prior to concreting, against two rigid abutments. This method is most widely used for mass production of short span structures, where pre-stressing is also a prerequisite, such as Railway Sleepers, Electric Polls, Fencing Polls ,Pre-Tensioned Slabs and I-Section Bridge girders etc. Post-tensioning- Post-tensioning is a method where Prestressing Steels are stressed after concrete attains its preliminary strength. Two extreme ends of the structure are considered as a reaction face, against which force is applied. Ducts are placed inside the formwork along with reinforcement and the concreting is completed. After achieving required concrete strength, stipulated numbers of Prestressing Steel Is then inserted each duct for stressing purpose. After achieving required elongation and stresses they are blocked at two ends with the help of Anchor Plates and grip.
- 5. Advantages of Prestressing Structures Reduction of member thickness.(material saving) Reduction of deflections. Reduction of building height. Reduction of building weight (foundation savings). Because prestressing steel has higher strength then mild steel. PT slabs are built with approximately 60 to 70% less steel (More space for MEP installations.) Reduction of cracking due to permanent pre-compression. Better corrosion resistance. Reduction in construction time .
- 6. Disadvantages of Prestressing Structures The major problem with Prestressed concrete is that it needs specialized construction machineries like jacks anchorage etc. Advanced technical knowledge and strict supervision is very important. For concrete prestressing, high tensile reinforcement bars are needed which costs greater than generally used mild steel reinforcement bars. Highly skilled labor is needed for Prestressed concrete constructions.
- 7. Thank You