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WELCOME

Project by : Vikram Desai Sanket Badle Pratik Patel Project guided by Prof. A.G Pawade. WELCOME. THEORY & APPLICATIONS OF PRESTRESSED CONCRETE. (Prestressed concrete poles for overhead power traction and telecommunication lines.). What is Prestressed concrete ?.

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WELCOME

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  1. Project by : Vikram Desai Sanket Badle Pratik Patel Project guided by Prof. A.G Pawade WELCOME THEORY & APPLICATIONS OF PRESTRESSED CONCRETE. (Prestressed concrete poles for overhead power traction and telecommunication lines.)

  2. What is Prestressed concrete ? • Consider a row of books, can withstand only compression but not tension. • The tensile strength of concrete is very less and can be neglected. Steel can take both tension as well as compression. • Prestressing means application of tensile force in steel and then transferring that tensile force as compressive force to concrete. • Thus increasing the load carrying capacity of member with same cross-sectional area.

  3. Applications of prestressed concrete. • Structural components like floor slab, columns & beams. • Structural components for bridges. • Watertanks and reservoirs where water tightness is of paramount importance. • Construction components like piles, power transmission poles, wall panels, posts. • Construction of relatively slender structural frames.

  4. Advantages of Prestressed concrete over RCC. • Prestressed concrete needs about 1/3rd quantity of concrete and 1/4th quantity of steel as compared to R.C.C. • In RCC only 30% to 40% concrete actively resists bending, thus material is wasted. • In prestressed members the dead loads can be counterbalanced by eccentric prestressing. • Better resistance to shearing forces. • Use of high grade materials increases the durability & less cracks are developed. • Members like the prestressed poles, sleepers can be pre-cast rather than cast in situ. • Members can be tested before use. • Multiple members can be cast in same time reducing labor and manufacturing cost.

  5. Long line method of Pretensioning • Advantages: • Most economical and efficient method suitable for the required span. • Efficient mass production technique. • Disadvantages: • Need more space for production. • A single error in tensioning may cause failure in all members.

  6. Design of poles

  7. Materials used • Cement • Ordinary Portland cement (53 Grade). • High bond strength • Conformed to IS:12269. • Steel • Prestressing steel wires & untensioned wires conformed to IS: 1785-1966 with ultimate strength of 175 Kg/mm². • High modulus of elasticity. • Small elastic and creep strain. • High resistance in shear & bearing. • Smaller loss of prestress in steel. • Aggregates • Conform to IS:383 – 1970. • Nominal max size should be 12mm. • Water • Free from chlorides, sulphates, other salts, organic matter etc. • Sand : River sand.

  8. Concrete mix design • Grade of concrete : M450 • Free w/c ratio : 0.37 • Max agg. Size : 20mm. • Agg. cement ratio : 4.30 • Type of cement : OPC • Cement content : 432kg/m³ • Actual slump : 45mm • Assumed density : 2500 Kg/m³ • Actual density : 2486 Kg/m³

  9. Use of Admixtures • Accelerators (MC-Schnell OC) • Its an chloride free accelerator. • Accelerates setting time of concrete even at low temperatures. • Enables reduction in water and subsequent increase in strength • Quicker de-moulding of formwork. • Dosage: One litre per Bag of cement. • It needs to be tested before use on site. • Plasticizer(Dr. Fixit Pidicrete CF 111- S) • Reduces water up to 25%. • Improves workability. • Dosage : One litre per bag of cement.

  10. Process of manufacturing

  11. Relationship : Compressive Strength vs Time

  12. Relationship : Compressive Strength vs Time

  13. Steam curing

  14. Bar chart : Conventional curing method

  15. Transverse test for poles

  16. Compression test for concrete.

  17. Steam Curing • Used to gain early strength in concrete. • Steam temperature should kept about 60°C until desired strength of concrete has developed. • Steam curing shall not be applied before 3 hrs after placing of concrete. • Temperature inside the jacket shall be kept constantly at a rate not to exceed 40°F per hour. • Rate of temperature decrease operation should be constant at about 40°F/hr curing jacket. • Members shall be protected until the difference between inside temperature & outside air is not more than 25°F.

  18. Conclusion • Prestressed concrete will be widely used in future for different structural components. • Many projects projected by the world bank in India are usi

  19. Specifications

  20. Sampling and inspection • Compression test is carried out for checking grade of concrete. • Tensile strength is used for finding strength of steel.

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