The master’s thesis presents advanced fire analysis of the construction in a case of a fire outbreak in a steel extension that was later built next to the existing production hall made of reinforced concrete. Load bearing structure of the extension is directly anchored into the construction of the existing part of the hall. The extension represents a separate fire sector. Due to the expansion of steel in case of high temperatures during a fire, a significant increase of forces on a contact of both parts of the building can occur. In the thesis, we assume that these forces can have a significant impact on the stability of the existing part of the hall made of reinforced concrete, although it is situated on the cool side of the fire. Engineers often forget about this in every day engineering practice. As these forces cannot be defined by simplified calculation procedures available in Eurocode, we verify the chosen structure by an advanced fire analysis. A steel part of the construction that is directly exposed to the fire is dealt with using a geometrical and material non-linear finite element analysis using solid finite elements. Such analyses are often numerically demanding, thus at the same time the thesis deals with the possible simplifications of a model. Conclusions reveal that there is really a distinct increase of forces on the contact of a new and old part of the building during a fire. Therefore the axial-bending load can be significantly increased also in otherwise cold part of the construction made of the reinforced concrete, namely to the level that is comparable with the one corresponding to persistent and seismic design state. Furthermore, conclusions reveal that in addition to the very precise construction model, a much simplified version of the model would be possible which would be on the safe side. Unfortunately, this would mean as much as 30 % higher bending loads of the existing part of the building made of a reinforced concrete, which could lead to less favourably solutions in terms of costs.