The finite-element method (FEM) requires accurate constitutive models for predicting the behaviour of steel components, structural members, or systems subjected to fire. As part of the World Trade Centre collapse investigation, the National Institute of Standards and Technology (NIST) developed an elevated temperature stress-strain model for structural steel, based on a combination of critically evaluated literature data and high temperature tensile tests conducted on structural steel recovered from the collapse site. The proposed stress-strain model accounts for temperature-dependence of elastic modulus, yield stress, and post-yield strain hardening as well as the strain-rate sensitivity. This paper presents (i) the strain-rate dependent behaviour of steel at elevated temperature using a prescribed heating rate, which can be used for the finite-element modelling of steel members subjected to increasing temperatures and (ii) detailed finite element models to predict the inelastic buckling behaviour and failure temperature of column specimens tested at Purdue University, USA. In this study, two full-scale ASTM A992 W14x53 column specimens, tested under transient heating conditions, are modelled. Each column specimen (with the length of 3.5 m) was subjected to a constant axial load but different heating (uniform or non-uniform temperatures through the cross-sections). The results of the 3D FEM analyses using the NIST proposed high temperature stress-strain models are thoroughly compared with those using Eurocode-3 and with the Purdue experimental results. The influence of thermal gradients and temperature-dependent strain- rate sensitivity on the inelastic column buckling is also discussed.
8th International Conference on Structures in Fire
June 11-13, 2014