Development of a creep-free stress-strain law for fire analysis of steel structures

© 2015 John Wiley & Sons, Ltd.This paper presents a practical procedure for obtaining creep-free stress-strain laws for steel exposed to fire, on the basis of codified stress-strain laws that consider creep implicitly. The applicability of the proposed procedure has been tested on two commonly used stress-strain laws for steel at elevated temperature, the Eurocode 3 law and a Ramberg-Osgood model, both of which have implicit consideration of creep. The simulation of two published steel coupon experiments on steel of grades S275 and S355 shows that both the Eurocode and Ramberg-Osgood stress-strain laws produce inaccurate predictions of creep in fire at elevated temperatures. The proposed procedure was thereby used to extract the implicit creep according to the heating rates of the transient coupon tests and to derive the creep-free stress-strain laws. It has been shown that, by combining the creep-free stress strain law obtained by the proposed methodology with an explicit creep model, a more realistic prediction of steel behaviour in the selected coupon test studies can be achieved.