Demolition of Pre-stressed Concrete Structures
Pre-stressed concrete is defined as concrete in which there has been introduced internal stresses of such magnitude and distribution that the stresses resulting from given external loadings are counteracted to a desired degree.
Prestressing, Post Tensioning, and Pretensioning
In reinforced concrete members, the pre-stress is commonly introduced by tensioning the steel reinforcement.
This internal stress is induced into the member by either of the following two pre-stressing methods:
- Pre-tensioning: In pre-tensioning, the tendons are first stressed to a given level and then the concrete is cast around them. The tendons may be composed of wires, bars or strands.
- Post-tensioning: In post-tensioning, the concrete member is first cast with one or more post-tensioning ducts or tubes for future insertion of tendons. Once the concrete is sufficiently strong, the tendons are stressed by jacking against the concrete. When the desired prestress level is reached, the tendons are locked under stress by means of end anchorages or clamps. Subsequently, the duct is filled with grout to protect the steel from corrosion and give the added safeguard of bond.
Knowledge Check Choose the best answer for the question.
4-1. In which of the pre-stressing methods are the tendons first stressed to a given level and then the concrete is cast around them?
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