In a wood construction, larger openings on the ground floor are achieved by spanning steel beams. These beams need to be fireproofed for a 2 hour rating while the structure above is 1 hour rated in a peculiar case. We plan to use spray on fireproofing on the steel beams, but the top of the beam may not be sprayed on; as 2" of gap is necessary to maintain for effective fire proofing either spray on or intumescent paint application. As the wood trusses / joists are in direct contact with Steel beam for load transfer to steel beams, do you have a suggestion how this steel beam's 2 hour fire protection can be maintained at the top of the flange?
Good morning NITIN and thank you for reaching out to ASK Hilti with regards to your intumescent needs. You are correct, it is preferred to have a 2" expansion to allow the intumescent to char and protect the structural steel in the event of a fire. With regards to your project, it is not a traditional beam and concrete decking assembly; therefore, the only solution that is viable for your project would be to apply the intumescent on all sides of the beam using a column design (4 sided exposure) which does not account for a concrete heat sink on one side. In this situation, you will apply the intumescent on all sides and then attach your wood structure for support. We have the understanding that the wood will burn off after an hour and then the intumescent will be allowed to char and protect the structure for the 2 hours.
If you have additional questions, please send your questions to our engineering team at Usspeng@hilti.com.