Gandhi Setu Bridge Patna that is the Longest fully prestressed concrete bridge in India .pptx

It's a presentation about Basic Prestressing and the first Complete prestressed concrete bridge in India that is Gandhi Setu Bridge in Patna. It contains information ABOUT BASIC PRESTRESSING IT'S TYPES AND METHODS. Along with losses in prestress and use of high strength concrete and steel for prestressing.

1. PRESTRESSED CONCRETE & STRUCTURES 1 MCE1S07 SEMINAR 1

2. Content Prestressing Prestressed Concrete Types of Prestressing Methodology Losses in Prestress Advantages and Disadvantages Application of Prestress Case Study 2

3. Prestressing refers to the intentional application of a predetermined force to a system, enabling it to counteract the stresses from subsequent loads during its service life Thus enhancing the structure's strength, stability, and overall performance 3 What is prestressing ?

4. What is Prestressed Concrete ? It’s concrete in which internal stresses of suitable magnitude and distribution are introduced, to counteract the stresses due to external loads to a desired degree This prestress is introduced by tensioning the steel reinforcement 4 Reinforced concrete Prestressed concrete

5. Types of Prestressing : 5 Pre-tensioning Internal Prestressing Post- tensioning External Prestressing Internal prestressing of Box Girder External prestressing of Box Girder

6. On the basis of source of Prestressing : 6 1. Hydraulic Prestressing Hydraulic jack used for prestressing 2. Mechanical Prestressing Devices like gears, pulley, screw jacks, weights used 3. Electrical Prestressing the steel wires are electrically heated and anchored before placing concrete in the moulds 4. Chemical Prestressing expanding cement is used

7. 7 1. Linear Prestressing 2. Circular Prestressing On the basis of axis of prestressing : 1. Uniaxial Prestressing 2. Biaxial Prestressing 3. Multiaxial Prestressing On the basis of extent of prestressing : 1. Full 2. Limited 3. Partial On the basis of direction of prestressing :

8. Methodology : 8 Pre-tensioning Anchoring of tendons against end abutments Placing of jacks Applying tension to tendon Casting of concrete Cutting of tendon Used for small repetitive works e.g. railway sleepers, piles, poles Various methods e.g. Hoyer’s method /Long line Method used

9. Methodology : 9 Post-tensioning Casting of concrete with ducts Placement of tendons, anchorage blocks and jacks Application of tension to tendons Seating of suitable anchors and cutting of tendons Used for very heavy casting e.g. bridge girders Various prestressing systems used e.g. Freyssinet , Gifford Udall, Magnel Blaton etc.

10. 10 Freyssinet System Lee-McCall System Gifford Udall System BBRV System

11. Losses in Prestressing : Immediate/ Short Term Loss Time Dependent/Long Term Loss Elastic Shortening Friction loss Anchorage Slip Loss Creep Loss Shrinkage Loss Relaxation Loss 11 Number of losses in post tensioned member are more than pre tensioned member Total loss of prestress of pre-tensioned member is invariably higher than that of post tensioned member All these losses account for around 15 – 20% of the total prestressing force

12. Why use High Strength Steel and Concrete ? Loss of prestress in Mild steel -120 N/mm 2 Normal loss of prestress in steel -100 to 240 N/mm 2 of initial stress Hence, initial stress =1200 to 2000 N/mm 2 . High strength concrete used as it offers : High resistance to tension, shear and bearing Less liable to shrinkage cracks, small ultimate creep strain, high modulus of elasticity hence less loss of prestress Reduction in the cross sectional dimensions of elements, reducing dead weight 12

13. Advantages of Prestressing: 13 Section remains uncracked under service loads Full section is utilized Reduction of steel corrosion Increase in durability Less deformations and improved serviceability High span-to-depth ratios Use of higher strength concrete and steel results in smaller cross section High strength to weight and strength to cost ratio Rapid construction Better quality control Suitable for repetitive construction

14. Disadvantages of Prestressing: 14 Prestressing needs skilled technology Use of high strength materials is costly Additional cost in auxiliary equipments such as jacks and anchorages etc. Need for quality control and inspection Needs highly skilled workers under skilled supervision

15. Applications of Prestressed Concrete : Hollow core and Ribbed slab Precast prestressed Double T beams 15

16. 16 Flat Slab Floor Box Girder Bridge

17. 17 Railway Sleepers Prestressed Piles Prestressed Concrete Vessels

18. The Mahatma Gandhi Setu Bridge: A Landmark of Engineering Ingenuity Mahatma Gandhi Setu (also known as Ganga Bridge) Longest fully prestressed concrete bridge in India Total length - 5.75 kilometers Span length - 121.65 m Project contract : Gammon India Limited Built period : 1972-1982 Rehabilitation project : 2020-2022 by Afcon Infrastructures 18

19. How prestressing was employed in bridge construction ? Prestressed Concrete System Box Girder Design Continuous cantilever configuration 19

20. Cantilever Method Balanced cantilever method used 20

21. 2. Precasting of Girders Precast concrete elements used Both pre-tensioning and post-tensioning methods employed Tendons placed in a curved or draped profile 21 Precast segment stacking yard

22. 22 Prestress segment casting yard

23. 23

24. Well-Sinking Foundations and Prestressing Integration Supported by well foundations Foundations sunk into the riverbed Prestressing allowed for a lighter superstructure 24 Bridge Pier Head

25. Advantages of Prestressing in Ganga Bridge Longer Spans Durability Load-Bearing Capacity 25

26. Challenges in Prestressing 26 Construction Timeline Transportation of large precast prestressed elements to the construction site Maintenance Issues

27. 27 After renovation Before

28. Conclusion The Mahatma Gandhi Setu stands as a testament to the effective use of prestressing technology in large infrastructure projects. The combination of prestressed concrete box girders , curved tendon profiles , and the balanced cantilever method allowed for the creation of one of the longest and most significant bridges in India. Prestressing played a vital role in its ability to span the Ganges with fewer piers, carry heavy traffic, and resist environmental forces, though its maintenance challenges also highlight the importance of ongoing care for such structures. 28

29. References “Prestressed Concrete” by N. Krishna Raju Principles and practice of Bridge Engineering- Rangwala The Indian Concrete Journal Feb 2005 Ganga Bridge Patna: Case Study in Project Management by Ravi Datta IS 1343 : 2012 Prestressed Concrete – Code of Practice IS 456 : 2000 Plain and Reinforced Concrete – Code of Practice 29