Experimental and Analytical Investigations on Thermal Performance of Slim Floor Beams with Web Openings in Fire

Steel beams with web openings are widely used in constructions to reduce the weight of steelwork, especially in structures comprising of traditional composite beams with down-stand steel sections. In recent times, the use of steel sections with web openings has become common as slim floor beams since they offer a reduction in weight of the steelwork, accommodate services within the floor depth and provide the plug composite action. Though these web openings offer several benefits in slim floor beams, however, they induce the material discontinuity in the web affecting their shear capacity and thermal behaviour. During the pouring of concrete, the steel in the web openings is replaced by the concrete with a low thermal conductivity. This research presents findings from experimental and analytical investigations conducted to study the thermal behaviour of slim floor beams with web openings in fire. For this purpose, an experimental investigation was conducted to study the thermal response of slim floor beams in fire. Data obtained from the fire test shows that the presence of web openings has a significant influence on temperature development across the steel section as well as along the span of these beams. The temperatures on the web below the openings are higher in comparison to those on the adjacent web-posts. It is also observed that temperatures on the web above the openings are significantly lesser than those on the adjacent web-posts. Parametric studies conducted using the finite element modelling show that smaller opening spacings and larger opening sizes have a severe influence on the thermal behaviour of these beams in fire. The findings of this research will help in selecting appropriate opening sizes and spacings in slim floor beams to avoid any severe temperature distributions in fire and to ensure their suitable utility.