Reliability-based structural response of single-bay steel frames in case of fire and in post-fire conditions

Abstract

The actual codes on design procedures to assess the structural reliability in case of fire allows for a whole scope of methodologies to be used. At one end of the spectrum, the codes allow to simply combine design rules with member analysis using tabulated data or simplified calculation models. On the other extreme end of the spectrum, complex performance-based design approaches are proposed, the results of which are unique and highly dependent on the system’s boundary conditions. Between those two extreme options, there are several other methodologies including the possibility to use probabilistic approaches. In this paper, reliability assessment of structures is based on the force-based method including temperature effects as well. This method is developed for single-bay portal frame and is based on the combined failure probability of five critical sections. All data needed to generate a probability density functions of the thermal actions on the structure is collected and described. Heat transfer equations of unprotected steel are used to calculate the profile temperature and reduction of mechanical characteristics during and after the fire. Coupling of the probabilistic-based thermal actions to the force-based method enables to create numerous simulations (Monte Carlo technique), and thus enable the system during and after a fire. This analysis is done for different load levels (self-weight), portal frame geometries and for several fire scenarios. Last, the post-fire behaviour of structural carbon steel single-bay portal frames is carefully investigated.