What are the losses of pre stressed concrete?
In pretensioned concrete, the four major sources of prestress losses are elastic shortening (ES), creep (CR), shrinkage (SH) and relaxation (RE).
What are the time-dependent losses in prestressed concrete?
Time-dependent deformations in prestressed concrete are attributed to creep and shrinkage of the concrete and relaxation of the steel. Each of these is a function of numerous other effects. Creep and shrinkage are affected by almost every variable mvolved in the fabrication and loading of a member.
What are the limitations of pre stressed concrete structures?
Followings are the disadvantages of prestressed concrete:
- It requires high strength concrete and high tensile strength steel wires.
- The main disadvantage is construction requires additional special equipment like jacks, anchorage, etc.
- It requires highly skilled workers under skilled supervision.
What are the losses in pre-tensioning and post-tensioning?
Pretensioned: All kind of immediate and time-dependent losses may occur. Post-tensioned: All forms of time-dependent losses occur, but the only immediate loss to occur is elastic deformation of concrete that too if tendons are stressed sequentially.
What is pre stressing of concrete?
Prestressing is the process by which a concrete element is compressed, generally by steel wires or strands. Precast elements may be prestressed during the construction process (pre-tensioning) or structures may be stressed once completed (post-tensioning).
What is the reason for using pre stressed concrete?
Prestressing can reduce the volume of concrete required in construction, lowering the use and transportation of materials, as well as boosting durability and service life. Concrete is intrinsically resistant to compressive stresses, but its resistance to tension is much lower.
What causes loss of prestress?
In the case of post-tensioning, the tendons are provided inside the duct of a precast concrete member. So the loss in prestress occurs due to friction between the concrete surface and the tendon in the process of tensioning. The loss of friction is also accompanied by the wobble effect.
How do you compute the loss of stress due to shrinkage of concrete?
e= EcEs/=modular ratio. If the initial stress in steel is known, the percentage loss of stress due to the elastic deformation of concrete can be computed. and the methowd of curing used of high-strength concrete with low water cement ratios result in a reduction in shrinkage and consequent loss of prestress.
Which of these is the time Dependend loss?
The time-dependent losses consist of creep and shrinkage of concrete and relaxation of the prestressing steel. These losses vary throughout the lifetime of a member and increase rapidly at the early age of the concrete, while increase over the remaining life occurs at a decreasing rate.
What are the advantages and limitations of pre stressing?
Advantages of Prestressed Concrete Longer span length increases untroubled floor space and parking facilities. Longer spans results in fewer joints, as a result, less maintenance is needed. Possibility of steel corrosion and subsequent concrete deterioration is declined because concrete is crack-free.
What are the advantages of pre stressed concrete?