Presentation1
- 1. PRESTRESS CONCRETE Submitted to submitted by: Prof A.B.GUPTA BATTI LAL MEENA 2011UCE1094
- 2. What is prestressed concrete ? Definition: “Pre-stressed concrete is a form of reinforced concrete that builds in compressive stresses during construction to oppose those found when in use.” In other words it is a combination of steel and concrete that takes advantages of the strengths of each material.
- 3. Types of Internal Prestressed Concrete Main three types of prestressed concrete:- Pre-Tension Concrete:- : pre-stressing steel is tension stressed earlier to the placement of the concrete and unloaded after concrete has harden Bonded post-tensioned concrete: unstressed pre-stressing steel is placed with in the concrete and then tension stressed after concrete has harden to required strength Un-bonded post-tensioned concrete: differs from bonded post-tensioning by providing the pre-stressing steel permanent freedom of movement relative to the concrete http://en.wikipedia.org/wiki/Prestressed_concrete#Bonded_po st-tensioned_concrete
- 4. Pre-tensioned Concrete:- Pre-tensioned concrete is when the steel reinforcement is stressed prior to concrete being placed around the steel This method produces a good bond between the tendon and concrete which both protects the tendon from corrosion and allows for direct transfer of tension.
- 5. Advantages of Pretension:- Pretension is the easiest controlled of the bonded stresings with the least chance of error in the bonding process. Allow to carry a greater load or soan greater distance then ordinary reinforce concrete . It permits steel to be used at stresses serveral times large then permitted for reinforcing bars
- 6. Post-tensioned Concrete:- Post tensioning is a method of reinforcing concrete or other materials with strength steel stands or bars typically referred to as tendons . Post tensioning application include office and apartment building parking structures slabs –on-ground bridge sports stadiums rocks and soil anchors and water tanks
- 7. Type of post tensioned concrete:- They are classified two types tensioned concrete :– 1 . bonded post tensioned concrete . 2 . Unbonded post tensioned concrete .
- 8. Bonded post tensioned concrete :- Concrete is the descriptive term for a method of applying “ compression” after the pouring concrete process . The concrete is cast around a plastic steel or aluminium curved duct to follow the area where othereise tension would occur in the element
- 9. Un bonded post tensioned concrete :- Un bonded post tensioned concrete differs from bounded post tension by providing each individual cable permanent freedom of movement relative to the concrete . To achieve this individual tension (generally lithium based )and covered by a plastic sheathing formed in an extrusion process .
- 10. Advantages of post-tensioned concrete:- Tendons can be easily “woven” allowing a move efficient design approach Higher ultimate strength due to bond generated between strand and concrete Large reduction in traditional reinforcement requirement as tendons can not distress in accidents
- 11. Post tension cable :-
- 12. APPLICATIONS: Post-tensioning allows longer clear spans, thinner slabs, fewer beams and more slender, dramatic elements. Thinner slabs mean less concrete is required. It means a lower overall building height for the same floor-to-floor height. Post-tensioning can thus allow a significant reduction in building weight versus a conventional concrete building with the same number of floors reducing the foundation load and can be a major advantage in seismic areas. A lower building height can also translate to considerable savings in mechanical systems and façade costs. This innovative form is result of post tensioning.
- 13. Conti… Another advantage of post-tensioning is that beams and slabs can be continuous, i.e. a single beam can run continuously from one end of the building to the other. Reduces occurrence of cracks . Freezing & thawing durability is higher than non prestressed concrete. Bridge decks
- 14. Conti.. Post-tensioning is the system of choice for parking structures ,since it allows a high degree of flexibility in the column layout, span lengths and ramp configurations. In areas where there are expansive clays or soils with low bearing capacity, post-tensioned slabs-on-ground and mat foundations reduce problems with cracking and differential settlement. Post-tensioning allows bridges to be built to very demanding geometry requirements, including complex curves, and significant grade changes. Post-tensioning also allows extremely long span bridges to be constructed without the use of temporary intermediate supports. This minimizes the impact on the environment and avoids disruption to water or road traffic below. In stadiums, post-tensioning allows long clear spans and very creative architecture.
- 15. Conti… Post-tensioning can also be used to produce virtually crack-free concrete for water-tanks. The high tensile strength & precision of placement gives maximum efficiency in size & weight of structural members. Applications of various prestressed techniques enable quick assembly of standard units such as bridge members, building frames, bridge decks providing cost-time savings.
- 16. References: http://en.wikipedia.org/wiki/Prestressed_concrete http://www.aboutcivil.org/concrete-technology www.cement.org/cement-concrete-basics/concrete... How is Unbonded Post Tensioning Made? Jump up^ Detensioning Unbonded Post-Tension Tendons Jump up^ Barrier Cable Jump up^ Cement & Concrete Basics: Prestressed Concrete | Portland Cement Association (PCA) www.grtinc.com/ www.theconcreteinstitute.org.za/wp...
- 17. Thank you