Identification of damage to a steel I-beam based on changes in frequency and curvature of the mode shape in a steel-concrete composite beam

This paper presents changes in modal parameters, i.e. natural frequencies and the curvature of the mode shape, as a result of damage in the steel I-beam of a composite member. A steel-concrete composite beam was analyzed, for which numerical simulations (rigid finite element model) and experimental tests were carried out. The damage analyzed was intended to simulate actual propagation of cracking in the steel I-beam. Two levels of damage occurring at two different locations in the beam were studied. The value of frequency changes of experimental and numerical evaluations have shown high consistency (margin of a few percent). Natural frequencies turned out to be sensitive to the introduced damage – their values decreased as the degree of damage in the beam increased. The Curvature Damage Factor was used to analyze the curvature of the mode of vibration. The results obtained in the numerical evaluations were satisfactory. In relation to experimental tests, lower effectiveness was achieved, which was most likely caused by a different density of the measurement grid compared to numerical analyses.