Nonlinear analysis of composite castellated beams with profiled steel sheeting exposed to different fire conditions

Abstract

This paper discusses the nonlinear analysis and design of unprotected composite castellated and noncastellated steel beams with profiled steel sheeting at elevated temperatures. The nonlinear material properties of steel, concrete, profiled steel sheeting, longitudinal and lateral reinforcement bars as well as shear connection behaviour at ambient and elevated temperatures were considered in the finite element models. The thermal properties at the steel section/profiled steel sheeting and profiled steel sheeting/concrete element interfaces were considered in the thermal heat transfer analysis that allowed the temperatures to be accurately predicted in the composite slab during fire exposure. It has been shown that the finite element models can efficiently predict the thermal and thermal–structural behaviour of the composite beams at elevated temperatures during the heating and cooling phases of fire. Furthermore, the variables that influence the fire resistance and behaviour of the composite beams comprising different load ratios during fire, different fire curves, presence of web openings and different steel grades were investigated in parametric studies. It is shown that the fire resistances of the unprotected simply supported composite castellated and noncastellated steel beams could be below 30min when heated using the standard fire curve. It is also shown that the strength of steel beam has a considerable effect on the behaviour and failure modes of the composite beams, which could change the failure mode of the composite beams in fire. The fire resistances of the castellated and noncastellated composite beams obtained from the finite element analyses were compared with the design values obtained from the Eurocode 4 for composite beams at elevated temperatures. It is shown that the EC4 is conservative for most of the unprotected composite castellated and noncastellated steel beams, except for some composite beams heated using the standard fire curve under load ratios of 0.4 and 0.5.