Résumé:
Composite structures are composed of two or more different materials called composite elements.
These elements have many benefits due to their combined properties that allow them to behave as a
single unit to perform better in overall this work is about the Composite slabs, which are horizontal
elements used for many types of buildings. They are made by casting concrete above a profiled steel
sheet. The main objective of this research is to study the influence of lightweight concrete on the
thermal-mechanical behaviour of composite slabs by developing a 3D finite element model the study
is divided into three major parts. Starting with a literature review of experimental and numerical
works on the thermal-mechanical behaviour of Composite slabs passing to a thermal analysis using
ANSYS; this study shows that the moisture content of lightweight concrete significantly impacts fire
resistance time. When the moisture content exceeds 3%, the Eurocode method predicts a lower fire
resistance time compared to the simulation method. The prediction models indicate that to achieve
the same fire resistance time, a normal-weight concrete section must be 7% thicker than a lightweight
concrete section. Finally, a thermal-mechanical analysis was conducted using a hybrid method based
on the thermal results of the finite elements study and the analytical equations mentioned in the
Eurocodes. The results of this study show that concretes with higher mechanical performances result
in a significant residual moment after heating, while the stability is still monitored. The development
of the deflection is more important in LWC than in NWC and the positions of the rebars have a
significant impact on the thermal and mechanical results of the composite slab.
