Reducing design steel temperature by accurate temperature calculation

Ulf Wickström, Alexandra Byström, Joakim Sandström, Milan Veljkovic

Abstract


In this paper an un-insulated I-beam (HE400B) supporting a concrete slab was analyzed.  The steel temperature was calculated with the simplest approach according to EC 3 and compared to temperatures calculated considering the cooling by the concrete.  In addition the so called shadow effect was considered.  The I-beam is then assumed not fully exposed to the incident radiation from the fire as the surfaces between the flanges will be partly shadowed.  Temperatures of the I-beam after a fire exposure of 30 minutes was calculated and discussed.   The calculations were performed with the finite element code Tasef(Sterner et al, 1990).  The mean temperatures of the beam flanges were reduced by more than 200 °C (from 827 °C to 609 °C) when the cooling at the top of the beam and shadow effects were considered.  The structure was supposed to be exposed to the standard time-temperature conditions according to EN1363-1 or ISO 834.

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