The paper presents a study of fire behaviour of butt-welded connections taken into account the post fire conditions and the possibility of welding strengthening of fire exposed structures. The need of in service life of a steel structure after being exposed to fire raises the problem of strengthening or replacement of some structural elements. The degradation of steel properties with increasing temperature is considered according to Eurocode 3: Part 1-2 provisions. Following the experimental part, the behavior of the welded connections after fire exposure was compared with the original behaviour at the ambient temperature. The results and conclusions can be used for damage assessment and strengthening technique of post fire steel structure.