Analysis of elongation variance of tendons using stress-strain graphs
- Authors: Dundu, Morgan , Rupieper, Sebastian
- Date: 2014
- Subjects: South African Design Standards , Tendons (Prestressed concrete) , Bonded tendons , Building materials
- Type: Article
- Identifier: uj:5079 , http://hdl.handle.net/10210/13650
- Description: The South African design standards (SANS 2001-CC1 and COLTO) prescribes an elongation variation limit of ±6% and an average variation limit of ±3%. Most often these limits are exceeded in practice. If the elongation variation of a tendon falls outside the prescribed elongation limits it must be assessed by the engineer. This paper analyses data of bonded tendons from post-tensioned structures. The aim of this study is to explain the elongation variance of tendons in post-tensioned structures using selected stress-strain graphs. These structures include a reservoir (Mthatha 1-10) and a viaduct (Gautrain Jean Avenue P80).
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Factors that influence friction in tendons of unbonded post-tensioning systems
- Authors: Dundu, Morgan , Ward, Michelle
- Date: 2014
- Subjects: Tendons (Prestressed concrete) , Corrosion and anti-corrosives , Steel, Structural - Protection
- Type: Article
- Identifier: uj:5059 , ISSN 9781614994657 , ISSN 9781614994664 , http://hdl.handle.net/10210/13621
- Description: The coefficient of friction in an unbonded post tensioning system is influenced by many factors, and these factors include the thickness of lubricant or grease present in the system, clearance between the strand and the plastic sheath, surface characteristics of the strand and plastic sheath. In order to determine the effect of these factors, a series of friction tests were performed on two different diameters of strand, namely; 12.7 mm and 15.24 mm diameters. Through a regression analysis, it was found that the frictional force decreases with increase in the thickness of the grease and that friction increases with increase in the mass of the strand. The amount of friction was found to be dependent on the surface characteristics of the strand and plastic sheath, clearance between the plastic sheath and the strand and the extrusion process of the plastic sheath.
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Limits of elongation variation of tenadons in post-tensioning
- Authors: Dundu, Morgan , Rupieper, Sebastian
- Date: 2014
- Subjects: Tendons (Prestressed concrete) , Prestressed concrete construction , South African Design Standards
- Type: Article
- Identifier: uj:5069 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13640
- Description: This paper analyses tensioning data obtained from a variety of projects that have been completed in South Africa in recent years in order to determine the causes of variation in elongation and suggest practical elongation limits. Current limits, prescribed by the South African standards (SANS 2001-CC1 and COLTO), of elongation variation limit of ±6% and an average elongation variation limit of ±3% are causing huge problems to the post-tensioning industry. The scatter of tendon elongation results is often greater than the range prescribed by these standards. This usually requires the contractor to re-tension the tendons at huge financial costs. In most cases the results obtained after re-tensioning are the same.
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