Sequentially coupled thermal-stress analysis of a new steel-concrete composite slab under fire (original) (raw)
The paper describes the numerical simulations required to estimate the performance of a composite slab using a re-entrant profiled steel sheet, prior to conducting a loaded fire test to verify the performance predicted by the simulations and obtain a fire rating according to accepted international standards. The purpose of the simulations was to optimize the design of the composite slab, by eliminating unnecessary reinforcement bars. Heat transfer analysis involving convection, conduction and boundary radiation was undertaken on a detailed solid modelled slab as part of a new steel-concrete slab product development. The simulation accounted for the thermal contact resistance at the cold-formed steel-concrete interface. The novelties of the model to incorporate the temperature dependent formulation of the interface thermal conductance provided a realistic prediction of the cross-sectional temperature field, which matched the fire test measurements. The slab top surface temperatures were assessed according to EN 1363-1:2012 to enable comparisons to be made with the insulation performance criteria. Following the uncoupled heat transfer analysis, the temperatures calculated through the thickness were used as an input into a sequentially coupled thermal-stress analysis of an equivalent shell modelled slab. This was necessary due to the excessive computing time required for the detailed solid modelled concrete slab that was used for the heat transfer analysis. Nevertheless, the calibrated shell that represented the composite slab model accounted for the dissimilar temperature-time (T-t) curves through the slab depth, since the bottom surface, close to the fire source, heats up at a much higher rate than the top surface. From the explicit-quasi static simulation, the load bearing capacity was calculated, which is expressed by the limiting largest deflection and deflection rate for flexural loaded structural members as given in EN 1363-1:2012. From these analyses, it was found that the overall fire resistance was limited by the load bearing capacity criteria. The predicted insulation and load bearing capacity compared very favourably with the fire test measurements, which are also presented in this paper, and provides confidence in the methodology used in this study.
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