One of the most important stages of creation of the diagnostic system «Signal – damage – remaining strength» is a multilevel strength analysis. This idea was considered earlier. Present work is dedicated to the ways of its realization and gives some results of it. A surface of contact of stringer and skin is considered as an object of the first level research. The essence of this research for concrete joint is to determine the shear forces, which occur because of an internal surplus pressure on a fuselage. With the help of parametrical modeling several models of a joint with the different relations between its independent variable parameters were created. The problem was solved by a finite element method. Graphical dependencies of distribution of shear forces along a surface of contact of stringer and skin, and also ones of the maximal values of shear forces on the independent variable parameters of a model when their different combinations were obtained as result. Using of such results allow predicting a probable place of the crack occurrence. Next step may be calculation of stress intensity factor as a main characteristic of crack resistance of the airframes. It can be done by the treatment and generalization of already existing data in order to obtain functional dependencies of stress intensity factor on characteristic parameters of a local zone of concentration. There are some results obtained also in this level.