A unified rheological model for modelling steel behaviour in fire conditions

This paper presents a newly developed rheological model capable of modelling the behaviour of carbon steel at high temperature under stress- and strain-rate controlled tests. By combining two serial Kelvin elements with the appropriate spring-and-damper constitutive behaviour models it is possible to model creep strain development under stationary and transient heating conditions. Furthermore, the model is able to take into account the inherent increase of the yield strength if the strain rate is raised to moderately high levels usually expected in a fire-induced collapse of the structure. Constitutive behaviour models for each of the rheological elements are based on the test data from which the Eurocode 3 stress-strain law originated. The model was verified by using the test results of constant stress- and strain-rate tests from various sources. Overall comparison of results indicates the applicability of the proposed rheological model to structural fire engineering analysis for steel grades S275 and S355.