1 INTRODUCTION This paper builds on assumptions and findings from a second paper presented at the same conference (Gkoumas, in press), and is part of a broader re- search focusing on structural analyses carried out on long tunnels subjected to fire action. The structural analyses performed are based on prescriptions of In- ternational Codes and Standards. Eurocode 3 (Commission of the European Com- munities, 1993) classifies the fire action as an acci- dental action, intended as the one occurring after an accident. In the above sense, the design of a struc- ture subject to fire must highlight the capacity of the structural system to achieve the objective of safety for assigned performance levels. Thus, the designer is called to make a responsible choice of the perfor- mance to assign. This liberty of allows finding the most effective solution, one that avoids useless op- erations, something that is reminiscent of a prescrip- tive approach. It is important though to highlight that the per- formance based approach is not easy and immediate as is the case of a prescriptive approach. In fact, the latter involves the understanding of the safety levels and the accomplishment of a precise prescription and in this sense, seems straightforward to apply. On the contrary, the performance-based approach re- quires specific knowledge from the designer. More- over, another important difference between these two kinds of approaches is that the prescriptive one divides the situations in “checked” or “not checked”, while the performance one allows graduating the consequences on the structure and to the persons, in function of accepted risk levels. 2 STRUCTURAL ANALYSIS OF A TUNNEL LINING UNDER FIRE In this paragraph, the structural behavior of a tempo- rary steel lining for a tunnel construction is investi- gated. Objective of the analysis is, in a first place, to highlight some of the peculiar effects arising from the fire loading, and to some extent, provide a start- ing point for the characterization of the collapse re- sistance of the construction. The performed analyses (implemented in a commercial FEM code) account for the material and geometry nonlinearities, thus being able to accurately describe the actual behavior of the structure. In order to assess the safety of the structure under fire, the performance level that does not contemplate collapse for all the duration of fire has to be guaran- teed. Consequently, in order to evaluate the fire re- sistance, a check is performed by modeling the fire action using the nominal standard curve (ISO834) provided in the Eurocode 3. The methods for fire resistance checking imple- mented in this research are those detailed in Interna- tional Codes and Standards, which require checking in the time, temperature and resistance domain. A final observation is that the evaluation of the structural collapse is tricky and depends from many Fire safety assessment of long tunnels F. Gentili & C. Crosti University of Rome La Sapienza, Rome, Italy K. Gkoumas Consulting Civil Engineer, Athens, Greece ABSTRACT: The problem of structural fire safety in the recent years has gained a predominant position with- in the engineering design, with the affirmation of Performance Based structural Codes and Standards, replac- ing more and more the traditional Prescriptive Based ones. This is because nowadays, structures always big- ger and more complex are designed and build, with the use of particularly fire sensitive materials. In modeling such complex structures, there are important aspects that need to be taken into account, especially when setting the boundary conditions of the structural problem as defined by the design environment. This is the case of long tunnels, which present exceptional characteristics and performance requirements. The aim is to evaluate by means of nonlinear non-stationary analyses what happens to the structural elements and to the construction as a whole, when the fire is not restrained.