Behaviour of cellular beams protected with intumescent coatings

A new engineering practice in modern buildings is to use beams with web openings to allow the passage of services within the depth of the beam instead of underneath the beam. This helps to reduce the floor height of the building and optimises the available space. The openings are cut in the web of a beam or a beam profile cut and re-welded to form the so called cellular beam. Usually the bending resistance is increased, in comparison to the original solid section, but the failure mode occurs generally at lower critical temperatures. The failure mode in fire is related to the distance between holes, web post slenderness in addition to the web and flange section factor. The loss of the beam strength with temperature promotes an early web post failure that occurs before the section reaches the critical temperature, reason why an increase in the fire protection may be required for these beams to achieve the same fire resistance time as the equivalent solid beams. Recent research on beams with closely spaced web openings has shown that the web posts between adjacent openings become significantly hotter than the bottom flange of the section, and that web post buckling can often be the failure mode for a member in the fire condition. The present study aims at investigating the behaviour of cellular beams under fire conditions when considering unprotected and intumescent protected cellular steel beams. Experimental tests are conducted in both cases with and without protection where temperature profiles are produced and analysed. The behaviour of the intumescent fire protection with different properties and thicknesses is studied and compared using fire resistance tests. Simplified method of analysis and finite element models are used to study and compare results from tests.