Resistance of partially protected steel beams in fire

Abstract Intumescent coating is often used as a fire protection on steel members due to its attractive appearance and ease of use. In the case when the member is fully covered by the coating, the response during the fire can be predicted rather accurately. However, if the member is covered only partially, the member's temperature profile and the structural response during the fire are not trivial to define. Partially covered members appear e.g. in cases in which the member is coated on the building site, but some previously installed adjacent structures disturb the coating process. Such partially covered members have been studied in the literature mainly from the temperature point of view, but in the present paper, also the structural behavior during the fire is considered. The paper presents a general procedure how to define the resistance of a partially protected steel member during the fire. As a result, time-resistance curves are defined for bending, shear and torsion and standard IPE and HEA profiles are used in the example simulations and the results are compared to fully protected and unprotected cases. The finite element method is adopted both for the thermal and structural analyses. The expansion of the intumescent coating is taken into account using the so called effective thermal conductivity, hence the same model can be used for both analyses. The simulated temperature results are validated against experimental and simulation results from previous researches. The results for bending, shear and torsion resistance show, that when compared to the unprotected case, the partial protection increases the resistances and the improvement is at its height during 15-30 minutes from the beginning of the standard fire.