Structural assement and design of concrete structures under fire conditions

Abstract: Behaviour under fire circumstances is becoming more and more crucial for designing a concrete structureand authorities require more often a fire-resistance time. In fact, engineers need a powerful, user-friendly,accurate and non time-consuming method that can be used to design reinforced concrete structures. Inthis study, the author has developed a method to design any fire-exposed reinforced concrete crosssections under flexure that takes into account second order effect. The first part focuses on the thermal analysis of the reinforced concrete cross section. Fourier'sequation is solved using finite differences method and the development tool of Excel: Virtual BasicAdvanced macro. Thus, it could easily be used on every personal computer (reasonably powerful) andneeds no extra investment. The accuracy of this thermal analysis is checked by comparison with resultsfrom commercial softwares (FAGUS edited by Cubus and SAFIR developed by the university of Liege). The second part deals with the mechanical analysis. Indeed, the concrete compressive strengthtogether with the yield strength of the steel reinforcement bars will decrease when the temperature willraise inside the concrete cross section. This loss of characteristic will be regarded as a loss of area andnew dimensions are set up. Finally a classic analysis (as it can be done at ambient temperature) isperformed. The mechanical analysis which takes into account second order effect is based on the Eulerbuckling load. The last chapter presents a comparison study between this new method and the two commercialsoftwares FAGUS and SAFIR, both of them are using finite element method. Several cross sections havebeen modelled, T-shaped ones with various dimensions and rectangular ones with various dimensionsand various steel areas. The two aspects (mechanical and thermal) have been studied and the resultsshowed good correspondance.