Finite element analysis criteria for composite steel decking concrete slabs subjected to fire

Abstract

In composite steel decking concrete slabs, fire design has to be made according to EN 1994-1-2. However, its procedures are questionable by many references. This is due to the divergence between full-scale experimental research methodologies and numerical studies with different analysis criteria, producing different conclusions. This research sought to numerically study the fire performance of composite steel decking concrete slabs according to two criteria (C): C1, assuming the same temperature field in the cross section, corresponding to a pre-defined ISO 834 fire rating of 30, 45, 60, 90, 120, 150 and 180 min, and an applied load increasing over time; and C2, assuming the increasing temperature field (slab is heated following ISO 834 fire curve) and a constant load over time applied to the slab. C1 allows to define the ultimate load for each pre-defined time of ISO 834 fire curve, while C2 the thermo-physical-mechanical effects. For the parametric calibration of the numerical models, 12 full-scale slabs were tested. 6 slabs under four-point bending test for mechanical parameter definition. Other 6 slabs for fire testing according to ISO 834 fire curve, for thermal and thermomechanical parameter definition. It was clearly noticed that current requirements of the standard are based on criterion C1, as it presented results that are close to the simple flexural theory. However, C1 does not allow defining increase in stresses produced by heating, which is noted only in C2. In C2 it was possible to identify the concrete cracks and detachment of the decking. In some cases, the concrete stresses produced in C2 were opposite to those shown in C1. It is understood that C2 shows more realistic results, but generates greater complexity and processing time for defining the ultimate load for each ISO 834 fire curve time.