Creep of prestressing steels in fire. (November 2016)

• Record Type: Journal Article
• Authors: Gales, John; Robertson, Lucie; Bisby, Luke
• Is Part Of: Fire and materials. Volume 40:Number 7(2016)
• Page Start: 875
• Page End: 895
• Publication Date: 2016-11
• Subjects: high temperature creep -- prestressing steel -- optical strain measurement -- necking -- chemical composition -- metallurgy; Fire-testing -- Periodicals; Fire -- Periodicals; Materials -- Periodicals; 620.11217
• DOI: 10.1002/fam.2345
• Languages: English
• ISSNs: 0308-0501

Abstract

Summary: When prestressing steel (PS) is applied as continuous unbonded tendons within concrete, as in the case of post‐tensioned (PT) construction, localized damage to the tendons may affect the integrity of the entire structure. When fire exposed, unbonded PT concrete structures are prone to tendon rupture because of a complex relaxation and strength reduction relationship influenced by high temperature PS creep. Explicit consideration of creep is necessary for the fire safe design of such buildings. High temperature PS creep has received limited research: few models can be used within the expected service stress range; none reliably model tertiary creep; and no studies are available investigating the influences of metallurgy on high temperature PS creep. A BS 5896 PS creep model is developed and validated. This model is used to provide PS failure insights at high temperatures. This understanding can be used to build validated models of structural fire experiments on PT concrete structural elements and to develop defensible, validated structural models that are essential towards performance based structural fire design of such systems. Finally, the high temperature creep performance of equivalent PS from different mills is compared, demonstrating strong influence of manufacturing and alloying techniques used. Future research is discussed. Copyright © 2015 John Wiley & Sons, Ltd.