PSI - Issue 64

Paul Winkler et al. / Procedia Structural Integrity 64 (2024) 1264–1270 Winkler et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2a: MAC-matrix

Fig. 2b: Change in eigenfrequency

the next load step. Also the degree of reduction of the eigenfrequencies varies over the modes. As examples, the mode shapes no. 2 and no. 11 are considered here. Eigenmode No. 2 describes a torsion of the slab around the vertical axis, while eigenmode No. 11 is a bending mode with two vibration bellows. Figures 2a and 2b show these two mode shapes, the decisive cracks that have formed as a result of the load are shown in red. These horizontal cracks have a smaller influence on the torsional stiffness, which is decisive for mode shape no. 2, while the bending stiffness particularly in the areas with high modal curvatures is significantly more influenced by horizontal cracking. Accordingly, the degree of change in modal parameters alone cannot be used to infer the presence of damage. The type of damage and the localisation of crack zones can also be determined by comparing the natural vibrations affected to a greater or lesser extent by a change in the modal parameters. Another modal parameter for damage identification is the damping of the eigenfrequencies, which was determined for every mode. As the damage to the structure increases, the eigenfrequencies of an eigenmode decrease, but the corresponding damping of that frequency increases. This behaviour is well known and could be observed here too. Although the reliability of the results is not yet good enough to be used as a damage indicator, work is in progress.

Fig. 3a: Modeshape 2 - torsion

Fig. 3b: Modeshape 11 - bending