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The article presents the results of the natural frequencies of vibrations of the span structure during the express-diagnostics, to excite the process of vibrations of the structure the pulse impact of the concentrated load of small mass is applied in the middle of the span structure (the method of small pulse impacts – “human jump”). The analysis of the obtained data, allowed to establish the parameters of free vibrations of unloaded span structures, the predominant frequencies on the graph of spectral density of dispersion are identical, regardless of the number of jumps, that is, the frequency of impact, if the time between jumps corresponds to the complete damping of vibrations. Of practical interest in the assessment of the technical condition is a quantitative assessment of the change in the natural frequency of vibration of girder metal and reinforced concrete spans depending on the presence of defects accumulated during the operation of the bridge. The obtained characteristics can serve as initial data, increasing the accuracy of calculations for calculations of artificial structures for seismic resistance, as well as in dynamic stability calculations for prospective loads and in the development of a model of the structure, the formation of algorithms of tasks to identify defects.