Creep of prestressing steels in fire

Abstract

SUMMARYWhen 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.

Postfire mechanical properties of Galfan‐coated steel cables

“…Unrecoverable plastic deformation generated due to the thermal creep during the heating process, which could affect the mechanical properties reduction factors of Galfan-coated steel cables after experiencing elevated temperature. 18,19 In order to considering the influence of the thermo- After that, a constant tensile load increment of 10 MPa/s, as per the GB/T 31314-2014, 20 was applied until failure at ambient Table 2.…”

Development of a rheological model for creep strain evolution in steel and aluminium at high temperature

“…Previously conducted research on the effects of creep at high temperature has mostly focused on conducting experimental creep‐test studies on coupons of various steel and aluminium grades. The influence of creep on flush end‐plate steel connections in fire has recently been studied by El Ghor et al Recent creep‐related research within the past 2 years has been conducted by Gales et al on the BS5896‐compliant steels used in prestressing tendons. Further studies have been conducted by Wei et al on the BS5896‐compliant prestressing steel and by Kodur and Aziz on the American steel grade A572.…”

“…Further studies have been conducted by Wei et al on the BS5896‐compliant prestressing steel and by Kodur and Aziz on the American steel grade A572. This research has relied mostly on stationary creep tests (with the exception of Gales et al in which transient creep tests were conducted). The creep behaviour of British and European steel grades was previously investigated by Kirby and Preston, Rubert and Schaumann (transient tests on grades S235 and S355), Brnić et al, and Torić et al (stationary tests on grade S275).…”

Development of a high temperature material model for grade s275jr steel

“…Gales et al [10] investigated the creep behaviour of the BS 5896-compliant steel used in prestressing tendons for unbonded concrete structures. The testing methodology included both stationary and transient creep tests, in which strain was measured by using the Digital Image Correlation technique.…”

“…The creep behaviour of the American steel grades A572 and A992 was recently investigated by Morovat et al [14] and by Kodur and Aziz [15] with the help of stationary creep tests. Inspection of these recent studies shows that most of them (except study [10] …”