Guidance for Treatment of High-Temperature Creep in Fire Resistance Analysis of Concrete Structures
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Guidance for Treatment of High-Temperature Creep in Fire Resistance Analysis of Concrete Structures V. Kodur*, Department of Civil and Environmental Engineering, Michigan State University, 3546 Engineering Building, East Lansing, MI, USA S. M. Alogla, Department of Civil Engineering, College of Engineering, Qassim University, Buraydah, Qassim 51452, Saudi Arabia S. Venkatachari, Department of Civil and Environmental Engineering, Michigan State University, 3546 Engineering Building, East Lansing, MI, USA Received: 11 July 2020/Accepted: 2 September 2020
Abstract. Concrete structures develop high levels of transient creep strain when exposed to fire, especially when temperatures in a member exceed 500°C. This hightemperature creep strain can dominate the deformation response under severe fire scenarios and needs to be properly accounted for in the fire resistance analysis. Most of the current approaches for fire resistance calculations, including advanced analysis methods, do not consider the transient creep strain to the full extent. This paper presents design recommendations for the treatment of creep in the fire resistance analysis of concrete structures. Three design alternatives are proposed for incorporating creep in fire resistance analysis depending on the conditions encountered during fire exposure. The first solution is ‘creep-not critical’ scenario where the temperature-induced creep strain can be neglected in a structural member subjected to low stress level and experiencing low sectional temperatures. In the second scenario (‘creep-implicit’), where temperature-induced creep strain is moderate, creep can be incorporated implicitly in the analysis. Finally, in situations where creep is significant (as in the case of high stress level and sectional temperatures), it needs to be incorporated explicitly in the fire resistance analysis (‘creep-explicit’ scenario). The practicality of the proposed solution in accounting for creep in the fire resistance analysis of concrete members at different levels is demonstrated using three case studies. Keywords: Transient creep, Explicit creep, Design recommendations, Reinforced concrete, Concrete columns
1. Introduction Reinforced and prestressed concrete members can develop significant levels of transient creep strain in addition to thermal and mechanical strains under exposure to elevated temperatures owing to the microstructural changes that occur in concrete under combined effects of transient heating and loading conditions. This * Correspondence should be addressed to: V. Kodur, E-mail: [email protected]
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Fire Technology 2020 transient creep (or high-temperature creep) strain of concrete can form a substantial portion of the total strain at elevated temperatures thereby responsible for much of the deformations that occur in concrete members in the later stages of fire exposure. Under prolonged exposure to fire, the temperatures within concrete increases beyond 500°C accompanied by increasing stress levels, due to the deterioration of strength and stiffness modulus of concrete
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