Identification methods for the on-finding of the material behaviour over the time and consequently for the on-finding of the uncertainties connected to strengthening measures are introduced. The strengthening measures are suitable to equip themselves with permanent strain gauges. The results of the strain gauges serve for identification methods. Dealing with these methods it must be considered that the results of the strain gauges are also influenced by application methods and the formation of the interface between the concrete structure and the strengthening element. The influence of these aspects on the assessment of the safety index will be discussed.