Behaviour of composite steel–concrete cellular beams in fire

The main results from an experimental and numerical investigation on cellular beams at elevated temperatures are presented. Full-scale fire tests on four specimens are presented and used to analyse the behaviour of composite steel and concrete cellular beams with evenly spaced circular and/or elongated web holes. The four beams were made of European hot-rolled sections. They were applied a two-point mechanical load. The beams were not fire protected and they were tested with an ISO fire or a bilinear thermal curve representing the behaviour of a protected beam. The results were then used to calibrate a non-linear 3D finite element model. The behaviour of the tested beams was simulated using two FEM codes (Cast3M and ANSYS). The first code was used for the thermal analysis and the second for the thermo-mechanical analysis. A comparison between the experimental and numerical results highlights the good accuracy of the model. The validated model was used in a parametric study varying geometry (span, steel cross-section depth, diameter and pitch of the openings, concrete or composite slab), mechanical properties and loading conditions (line load only or combined to point-load). The results were then compared to those from an analytical design method to check its validity. The results show that the analytical design method is conservative, with little discrepancy when compared to the numerical model.