Damage Identification in Elastic Suspended Cables through Frequency Measurement

Structural cables in cable-stayed systems are subject to potential damage, mainly due to fatigue phenomena and galvanic corrosion. The paper analyzes how the dynamical behavior of cables is affected by diffuse damage, and investigates whether the damage can be identified through information selected from the dynamical response. A continuous monodimensional model of a damaged cable is used for this purpose. Damage is described as a reduction of the cable cross section, and defined in terms of its intensity, extent and position. The major effects of these different damage parameters on the cable static response and spectral properties are evidenced and discussed to verify the observability of the damage. The frequencies of the dominant transversal motion of the cable are chosen as damage indicators, since they are sufficiently sensitive to the damage intensity and extent, while the damage position requires additional information. The damage identification problem is formulated by defining an objective error function between the measured and the model frequencies, to be minimized in the space of the damage parameters. Pseudo-experimental data are initially used to test the effectiveness and resolution of the procedure. The results confirm the uniqueness of the problem solution and its correctness. The robustness of the solution is discussed while considering the presence of random errors of increasing amplitude. The procedure is also positively verified with experimental measures from a prototype model of an artificially damaged spiral strand.