[PDF] Recommendations For The Design Of Flat Slabs In Post Tension Concrete Using Unbonded And Bonded Tendons eBook

Author : fib Fédération internationale du béton
Publisher : fib Fédération internationale du béton
Page : 132 pages
File Size : 28,4 MB
Release : 2005-01-01
Category : Technology & Engineering
ISBN : 9782883940710

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The development of prestressing technology has constituted one of the more important improvements in the fields of structural engineering and construction. Referring particularly to post-tensioning applications, it is generally recognized how it opens the possibility to improve economy, structural behaviour and aesthetic aspects in concrete solutions. In spite of the simplicity of its basic concepts and well-known advantages, the application extent of post-tensioning solutions cannot be considered harmonized in the different areas and structural applications. In fact, for various reasons, it appears that the potential offered by prestressing is far from being fully exploited, especially in building structures field. In many cases where post-tensioning would provide a visibly superior solution, it happens after all that a more conventional non-prestressed solution is often selected. The main objective of this fib Technical Report is therefore to show the benefits of using post-tensioning for the more common practical applications in concrete buildings. The document is mainly addressed to architects, contractors and owners. It is also drafted with the goal of motivating building designers to use post-tensioning: basic design aspects related to prestressing effects and design criteria are summarized and conceptual design aspects are emphasized. A set of practical examples is presented, showing the adopted solutions and their advantages when meeting the requirements of specific problems. The selected examples were precisely not chosen because they are outstanding structures. As a matter of fact, post-tensioning principles and technology can be used in any structure, independently of its importance, covering a wide range of building structural applications, improving the structure quality and promoting concrete as a structural material. The advantages of using post-tensioning, concerning structural behaviour, economy, detailing and constructive aspects, are illustrated by the presentation of several existing structures, most of them designed by Working Party members. General design calculations are not presented, but design results showing the improvement in structural behaviour are illustrated.

Author : Jasmin Abdelhalim
Publisher :
Page : 0 pages
File Size : 48,96 MB
Release : 2021
Category : Prestressed concrete
ISBN :

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Abstract: Post-tensioning concrete technology increases the resistance of flexural concrete members. This technology allows for the production of slenderer sections, and sequentially less usage of material preserving the sustainability concept in construction engineering. Post-tensioning process can be done using bonded or unbonded steel tendons. The unbonded tendons are thought to have better resistance to corrosion for structures exposed to severe environmental conditions. The unbonded tendon's steel strands are painted with grease and covered with plastic sheathing to prevent the moisture from reaching the steel strands thus they can provide high corrosion resistance. According to the ACI 318-19 and other codes of practice, the stress in the unbonded tendon at the ultimate limit state is limited to less than or equal to the tendon's yield stress. On the other hand, the bonded tendon's stress at this state is determined to be more than or equal to the tendon's yield stress. This limitation for the unbonded tendons restrained the widespread usage of the unbonded system. Through this research, six-simply supported one-way slabs; two with bonded tendons, two with unbonded tendons and two with unbonded tendons and non-prestressing steel reinforcement are tested in flexure to failure. The post-tension slabs are of 4.0-meters in span and the flexural tests are carried in the AUC structural engineering laboratory in a four-point loading scheme. The ultimate stress of the unbonded tendons are measured at the failure stage. The results of both systems are compared against each other and against the provisions of the ACI 318-19. The unbonded post-tension slabs with non-prestressing steel reinforcement showed higher failure loads than the bonded and unbonded slabs without reinforcement. The ACI 318-19 provisions were critically reviewed versus the results of the experimental investigation. The review reveals that the limitation of the unbonded tendon's ultimate stress is not accurate and can be reviewed.