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In this paper, a numerical model is developed to predict the behaviour of castellated beams with hexagonal. The numerical model takes into account both material and geometric non-linearity. To initiate buckling, an initial small out-of-plane geometric imperfection, obtained from an eigenvalues buckling analysis, was imposed to the model. Calibration with experimental data obtained from previous work shows that the model is able to predict, with relatively good accuracy, the ultimate load. A parametric study is then followed to determine the effect of web thickness, yielding stress and opening height on the ultimate load of the beams. Based on the parametric studies results, the accuracy of the cross-section classification for castellated beams proposed in the Annex N of Eurocode 3 is assessed.

The main results from a numerical investigation on a composite floor made of cellular beams at elevated temperatures are presented. From a full-scale natural fire test, a 3D finite element model has been developed under ANSYS code to simulate the thermo-mechanical behaviour of a composite floor with cellular beams. The calibration of this numerical model is based on the measured material properties and temperatures. A good correlation between the test and the numerical simulation is observed, in terms of temperatures, deformed shape and deflections. The finite element model is then used in a parametric study varying bay size, mechanical load and fire resistance rate. The results from this parametric study are compared to those from an analytical method, highlighting the conservativeness of the latter.

Two different configurations of steel-to-timber connections are tested in bending in normal conditions and under ISO-fire exposure. To observe the influence of clearances in the connection area on the fire resistance of the connections, two specimens were previously tested under cyclic loadings. These tests consist in the application of loading-unloading cycles by controlled displacements. The experimental results of connections tested in cold and under ISO-fire conditions are analyzed and commented. These results are then used to validate a finite element model. This model allows to simulate numerically the evolution of the temperatures inside the connections as well as their mechanical and thermo-mechanical behaviours. The thermal modelling is validated on the basis of the temperature-time evolutions measured during fire tests. The nonlinear modelling of the mechanical behaviour of timber is done using the Hill yield criterion in combination with the Tsaï-Wu failure criterion. The thermo-mechanical modelling allows obtaining fire resistances of the tested connections in good agreement with the experimental ones.