Fire Design of Steel Members
The New Zealand Steel Code consists of few practical design tools other than finding the time and temperature that a simply supported steel member will fail. Many other design methods that consistently give accurate estimations of the behaviour of steel members have been published, and computer programmes developed to assist in the prediction of the temperature rise of steel when subjected to elevated temperatures environments. This report describes the origins of the fire design methods used in the New Zealand Steel Code, NZS 3404:1997. The New Zealand Steel Code is reviewed and the design features are compared with the equivalent method found in the Eurocode, ENV 1993-1-2, which is the most advanced international steel fire code. The methods of evaluating the temperature rise of protected and unprotected steel beams are also investigated. Results from the simple formulas included in the New Zealand Code, and those developed by the European Convention for Constructional Steelwork, ECCS, are compared with results from the time step 'spreadsheet' method and from the finite element computer programme, SAFIR, for the ISO 834 standard fire. The comparisons show that the spreadsheet method gives temperatures very close to the average temperatures calculated by SAFIR for all cross sections and protection layouts. The equations from ECCS and NZS 3404 give good results for unprotected steel, and for protected steel the ECCS equations appear to represent the thermal response of the steel quite accurately while the New Zealand Steel Code has no simple method of estimating the temperatures for protected steel. The methods used for comparing the results with the ISO fire are then repeated with Eurocode Parametric fires, and with results from a real fire test. Suggested improvements are made for the New Zealand Steel Code, to improve the concepts and information available to engineers designing for fire safety.