Composite beams with partial fire protection

This paper presents the results of a theoretical investigation into the effectiveness of a novel way to significantly reduce the fire protection cost to a composite beam. In this method, only the steel lower flange and a fraction of the steel web ave protected. The effectiveness of a partially protected composite beam is assessed by comparing its plastic moment capacity with that of a fully protected beam subject to both the standard fire exposure and design fires. The parametric time-temperature curves in Eurocode 1 are used to determine the time-temperature relationships of design fires. A finite element analysis computer program for hear transfer is used to evaluate the temperature field in the composite cross-section. The plastic moment capacity is calculated by dividing the composite cross-section into many small blocks and summing their contributions. Partial protection is suitable for situations where the protection is applied along the steel profile. Results fr om this study indicate that the total fire protection cost may be reduced considerably due to more than 50% reduction in the protected surface area, despite similar material costs. (C) 1998 Building Research Establishment. Published by Elsevier Science Ltd. All rights reserved.