Indicative fire tests to investigate the behaviour of cellular beams protected with intumescent coatings

Applying intumescent coatings, as fire protection, to cellular beams has generally followed a simple design rule based on calculating the Section Factor from which the cellular section was manufactured and then increasing the required thickness by 20%. The validity of the simple design rule has recently been questioned by the Steel Construction Institute who have published new, alternative, design guidance. It was argued that new design guidance was justified since higher than expected web-post temperatures were experienced in recent fire tests on cellular beams. However, these tests were commercially confidential and were not open to scrutiny by the scientific community. This paper presents the results from preliminary indicative fire tests on unprotected and protected cellular and solid beams to investigate the temperatures experienced by the web-post on a cellular beam. It was found that for an unprotected cellular beam there was no increase in web-post temperatures, but for a protected cellular beam the web-post temperatures were higher compared to the web temperatures of an identical solid beam. Observations from the tests, presented in this paper, suggest that the increase in web-post temperatures was due to the intumescent char being 'pulled-back' from the circumference of the hole. The tests also indicated that the difference between web-post temperatures and the bottom flange of the cellular beam is dependent on the type and thickness of intumescent coating used. Further tests are required to investigate the behaviour of intumescent coatings around holes before the proposed new generic design guidance is endorsed.