Failure of lightly reinforced concrete members under fire. II: Parametric studies and design considerations

This paper deals with the behavior of lightly reinforced concrete members under fire conditions, focusing on the failure state associated with rupture of the reinforcement. The work transpires from the need to examine the underlying mechanisms related to the failure of composite floor slabs, which become effectively lightly reinforced in a fire situation due to the early loss of the steel deck. The analytical model proposed in the companion paper is utilized to perform a parametric investigation into the salient factors influencing the failure of lightly reinforced restrained members. A detailed account of the analytical results is given, and the relative importance of the main material and geometric parameters is illustrated. It is shown that in addition to temperature effects, the bond characteristics, member length, and the steel material response have a direct and significant influence on failure. The implications on structural fire resistance are highlighted, and simplified expressions for failure prediction, which capture the effect of key parameters, are proposed. This work provides a necessary step toward a fundamental methodology which may be employed for developing quantified failure criteria, with a view to the provision of more rational performance based approaches for structural fire design.