Table of Contents
- 1 What is partial and full prestressing?
- 2 What are the types of prestressing?
- 3 What is the example of linear prestressing?
- 4 What is Pretensioning and post tensioning?
- 5 What is the source of prestressing?
- 6 When to use full or limited Prestressing in concrete?
- 7 Where does the prestressing of a building take place?
What is partial and full prestressing?
Generally, prestressing tendon is used to obtain full prestressed concrete (PC) structures. Partial prestressed concrete (PPC) allows some tension and cracking under full service load while ensuring sufficient ultimate strength. Therefore, it is used to control camber and deflection, increase ductility and save costs.
What is called partial prestressing?
The degree of prestress applied to concrete in which tensile stresses to a limited degree are permitted in concrete under working load.
What are the types of prestressing?
The basic types of prestressing are:
- Precompression with mostly the structure’s own weight.
- Pre-tensioning with high-strength embedded tendons.
- Post-tensioning with high-strength bonded or unbonded tendons.
What is partially prestressed concrete members?
Partial prestressing is basically a prestressed concrete approach in which prestressed reinforcement or prestressed and non prestressed reinforcement is used such that tension and cracking in concrete is allowed under service loads.
What is the example of linear prestressing?
When the prestressed members are straight or flat, in the direction of prestressing, the prestressing is called linear prestressing. For example, prestressing of beams, piles, poles and slabs. The profile of the prestressing tendon may be curved.
What is relaxation of steel?
Relaxation is assumed to mean the loss of stress in steel under nearly constant strain at constant temperature. It is similar to creep of concrete. This loss is generally of the order of 2 to 8% of the initial stress.
What is Pretensioning and post tensioning?
Pretension is the technique in which we are imparting tension in strands before placing the concrete. Post tensioning is done by forming a duct in which strands are pulled (tensioned) after the concrete gains it’s full strength.
What is external prestressing?
External. prestressing is when unbonded tendons are placed, and prestressed, outside the structure anchored at the ends. and sometimes with one or several deviators during the length of the structure. This method is advantageous for. the strengthening of a structural member to obtain improved load carrying capacity.
What is the source of prestressing?
There are four sources of prestressing force: Mechanical, hydraulic, electrical and chemical.
What do you need to know about prestressing?
Prestressing is the introduction of a compressive force to the concrete to counteract the stresses that will result from an applied load. There are two methods of introducing prestressing to a concrete, namely pre tensioning and post tensioning. Pre tensioning happens before the casting of the concrete.
When to use full or limited Prestressing in concrete?
When the level of prestressing is such that no tensile stress is allowed in concrete under service loads, it is called Full Prestressing (Type 1, as per IS:1343 – 1980). When the level of prestressing is such that the tensile stress under service loads is within the cracking stress of concrete, it is called Limited Prestressing (Type 2).
When to use uniaxial or partial prestressing?
When the level of prestressing is such that under tensile stresses due to service loads, the crack width is within the allowable limit, it is called Partial Prestressing (Type 3). When the prestressing tendons are parallel to one axis, it is called Uniaxial Prestressing.
Where does the prestressing of a building take place?
When the prestressing is achieved by elements located outside the concrete, it is called external prestressing. The tendons can lie outside the member (for example in I-girders or walls) or inside the hollow space of a box girder. This technique is adopted in bridges and strengthening of buildings.