Pre-stressing
- 1. PRE-STRESSING Made by :- 1) Manisha Khandelwal 2) Kashif
- 2. Introduction Definition of pre-stress is to introduce internal stresses into (something, such as a structural beam) to counteract the stresses that will result from applied load (as in incorporating cables under tension in concrete). Prestressed concrete is a form of concrete used in construction which is "pre- stressed" by being placed under compression prior to supporting any loads beyond its own dead weight. This compression is produced by the tensioning of high-strength "tendons" located within or adjacent to the concrete volume, and is done to improve the performance of the concrete in service.
- 3. Types / Classification Prestressing of concrete can be classified in two ways:- Pre-tensioning process
- 6. Post tensioned concrete types Bonded post-tensioning Unbonded post-tensioning Comparison between bonded and unbonded post-tensioning
- 7. Bonded post-tensioning:- Bonded post-tensioning has prestressing tendons permanently bonded to the surrounding concrete by the in site grouting of their encapsulating ducting following tendon tensioning. This grouting is undertaken for three main purposes: to protect the tendons against corrosion; to permanently "lock-in" the tendon pre-tension, thereby removing the long-term reliance upon the end- anchorage systems to improve certain structural behaviors of the final concrete structure Unbonded post-tensioning:- Unbonded post-tensioning differs from bonded post-tensioning by allowing the tendons permanent freedom of longitudinal movement relative to the concrete. Both bonded and unbonded post-tensioning:- Both bonded and unbonded post-tensioning technologies are widely used around the world, and the choice of system to use is often dictated by regional preferences, contractor experience, or the availability of alternative systems. Either one is capable of delivering code-compliant, durable structures meeting the structural strength.
- 8. Availability Prestressed can be available in various materials such as concrete, steel etc. Some notable building structures constructed from prestressed concrete include: Examples :- Gateway Bridge, Sydney Opera House, World Tower Sydney, CN Tower Toronto, Capital Gate Abu Dhabi UAE.
- 9. Characteristics The essence of prestressed concrete is that once the initial compression has been applied, the resulting material has the characteristics of :- high-strength concrete when subject to any subsequent compression forces, ductile high-strength steel when subject to tension forces. Durability Corrosion protection. Improves crack control. Improves fire performances. Beam with different types of structures Beam with reinforced and beam with prestressed concrete
- 10. Uses Building structures Building structures are typically required to satisfy a broad range of structural, aesthetic and economic requirements. Bridges materials that are available for the construction of bridges, concrete remains the most popular structural material, Dams Concrete dams have used prestressing to counter uplift and increase their overall stability. Silos and tanks Circular storage structures such as silos and tanks can use prestressing forces to directly resist the outward pressures generated by stored liquids or bulk-solids. Nuclear and blast-containment structures Prestressed concrete is long-established as a reliable construction material for high-pressure containment structures Hardstands and pavements Heavily loaded concrete ground-slabs and pavements can be sensitive to cracking and subsequent traffic-driven deterioration. As a result, prestressed concrete is regularly used in such structures
- 11. Capital gate, building structure Ringhals nuclear plant, Sweden Incheon bridge, South Korea Roseires dam, Sudan
- 12. prestressing of concrete Advantages Rapid construction Better quality control Reduced maintenance Suitable for repetitive construction Section remains uncracked under service loads Larger spans possible with prestressing Suitable for precast construction Disadvantages Prestressing needs skilled technology. Hence, it is not as common as reinforced concrete The use of high strength materials is costly. There is additional cost in auxiliary equipments. There is need for quality control and inspection.
- 13. Thankyou