Prestressed Concrete is a type of concrete. In which the stress taking capacity of concrete is increased to overcome the weak property of concrete beam. Generally prestressed concrete is used where beam or slab is in long length.
As we know that the concrete undergo compressive stress and reinforcement rebar undergo in tension stress. We use rebar because concrete is weak in tension. Here
tendons, wires, cables or bars are stressed by anchoring at the end by mechanical, hydraulic jack or electrical devices.
Watch the procedure:
As we see here in the above video, for concreting we adjust the shape and size of frame in which we introduce the tendons. After the proper placing of tendons, the tendons are anchored at the end.
Advantages of PRESTRESSED CONCRETE:
Prestressed concrete overcomes the weak property of concrete which can be difficult as in regular RCC Reinforced Cement Concrete.
After prestresssing we are able to reduce the thickness of beams and self weight. Normal concrete have span to depth 28:1 increased to 45:1.
It will not crack easily so no effect of corrosion on steel.
Prestressing is more beneficial in the long span of beam because it reduces the deflection of beams.
Prestressed concrete is used in Civil structure like high rise building slab, beam and foundation, bridges, Dam, industrial pavement, storage tanks and nuclear & blast furnace etc.
This process takes minimum time with better quality and which will lower maintenance.
Disadvantages of PRESTRESSED CONCRETE:
Prestressed concrete require skilled labour and regular inspection at the time of concrete placing.
Tendons stressing require extra mechanical devices.
The material used in prestressing concrete is costly but overall economical.
TYPES of PRESTRESSED CONCRETE:
Prestressing of concrete is classified into different types as per applied load or force used to do prestress. Here above we discuss about hydraulic jack, mechanical pulley type or electrical thermal system.
Pre-tensioning and Post-tensining:
Tensioning is the process of applying tendons in the concrete beam which provides tension strength, if it is placed before concrete pouring is known as pre-tensioning and if it is placed in ducts after concrete is hardened is known as post tensioning.
External or Internal prestressing :
The location of anchoring system we apply whether it is internal or external of structure.
Linear or Circular Prestressing:
Based on the shape and size of structure, most likely it is linear or circular in shape.
Full, limited or partial prestressing:
Based on the amount of tendons used in structure. Prestressing used in full structure or limited structure.
Uniaxial, biaxial or multi-axial prestressing:
The direction of prestressing structure like 1D, 2D, 3D etc. uniaxial is similar to one directional, biaxial means two direction and multi-axial means multiple direction of prestressing concrete.
The reinforcement used in prestressing is tendons, cable, wires, strands and bars.
It is used in civil structure like high rise building, dam, pavement, tanks, silos, bridges and where large span is necessary.
Every Country have their own code for desing of prestressed concrete structre
1. IS 1343 is Code of Practice for Prestressed Concrete used in India Free Download HERE
2. European Standard EN 1992-2:2005 – Eurocode : Design of Concrete Structures,
3. US Standard ACI318: Building Code Requirements for Reinforced Concrete
4. Australian Standard AS 3600-2009: Concrete Structures.
By introducing tendons, the weak property of normal concrete structure is enhanced.
French civil and structural engineer Eugène Freyssinet invented the concept of prestressed concrete.
The normal concrete capacity is increased by introducing tension stress taking cables thats why prestressing is done.
The prestressed force which is gained by tendons which is connected by mean of coupler from one tendons to another.
The anchoring system like jake and machines used to do prestressing of concrete known by prestressing system.