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Ground-supported concrete floor slabs can be designed and constructed with some benefits using post-tensioning systems. There may be additional cost compared with normal reinforcing techniques but the potential technical benefits available may counter that factor. Post-tensioning may not be suitable for floors where changes in service use for example in some factories, would require frequent removal of slab areas to add new plant.
Post-tensioning is usually achieved incorporating steel wire strand tendons, typically placed horizontally at about 1m centres both ways in the slab and supported on chairs at the slab mid-depth. A compressive stress of about 1 N/mm˛ applied in the slab virtually eliminates the risk of concrete cracking from shrinkage restraint effects and keeps any construction joints tightly closed. Movement joints are required around the perimeter of the post-tensioned slab panels.
Both bonded and unbonded post-tensioning systems are available in the UK through member companies of the Post-Tensioning Association.
Acknowledgement: Concrete Society
Other references:Federation International du Beton (FIB), Bulletin 31, Post-tensioning in buildings, February 2005.
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