Experimental Study on Fire Behavior of Steel–Concrete Composite Cellular Beams with Large Opening Ratio

The aim of this study is to examine the behavior of protected and unprotected steel–concrete composite I-beams with large cell diameters (D₀/H = 0.7) and closely spaced cell configurations under the ISO 834 fire curve. Previous studies on experimental full-scale fire performances of cellular beams have been somewhat limited under vertical service loads and different insulation properties. To address this limitation, a total of four composite beams, two unprotected (one beam with a solid web, and one cellular beam) and two protected cellular beams (60 min fire resistance with implementation of water and solvent-based intumescent coatings) were tested. As outputs of the tests, the failure modes observed, such as web buckling, the Vierendeel effect, the slab behavior, including the mechanism of concrete cracking, the overall displacement behavior (i.e., deflected shapes) up to collapse at very large deflections, and temperature changes in the steel elements are discussed. It was concluded that the quality of the intumescent coating applied is crucial in achieving the desired fire resistance. Experiments showed that unprotected trapezoid deck voids did not have a decisive influence on the behavior of the beams for up to 60 min of fire testing. At high temperatures, similar crack patterns occurred in the composite slabs of the protected and unprotected steel–concrete composite cellular beams. In the protected beams, the behavior of reactive coatings was significant and resulted in a non-uniform temperature distribution in these beams’ web and flanges.