Multi-Hazard Analysis of Steel Buildings Subjected to Earthquake and Fire

Fire produces unique effects on steel structures which can compromise the residual capacity and therefore the structural response if they impact jointly with other natural hazards, such as earthquakes. This work presents a procedure that allows for the extension of the analysis method introduced in the 1990s by Fajfar and Gaspersic and outlined in EC8 (referred to as the N2 method) for the case of Multi-Hazard (MH) analysis, specifically for hazard-chain scenarios involving earthquake and fire. The goal is to assess the structural performance at the end of the sequence of considered events. By appropriately modeling the structure considering elasto-plastic behaviour, it becomes possible to observe the structural response as the plasticization of structural elements progresses: in this context, accounting for material and geometric nonlinearities has proven essential, since the material and structure's behaviour under fire are governed by complex phenomena, due to the significant deformations and distortions involved. The hazard-chain scenario here discussed is characterised by the consecutiveness of main earthquake event and fire; the proposed procedure is then applied to a 2D steel structure. Results highlight that neglecting possible hazard interactions could lead to an erroneous evaluation of the residual structural capacity.