Vibration Based Damage Identification in Thin-Walled Beams with diffused cracking

PATRICIA N. DOMÍNGUEZ; VÍCTOR H. CORTÍNEZ

Río de Janeiro

Congreso; XXXVI Ibero-Latin American Congress on Computational Methods in Engineering; 2015

Brazilian Association of Computational Methods in Engineering (ABMEC) y Pontifical Catholic University of Rio de Janeiro

The presence of damage represents a crucial topic regarding safety of engineering structures. Considering that early crack detection may prevent the possibility of catastrophic failures, the development of structural health monitoring techniques has acquired a remarkable importance. In the last years, vibration-based techniques for damage identification have emerged as an attractive alternative to local inspection. They are based on the fact that damage induces a change in structural stiffness distribution, thus modifying the dynamic response. Accordingly, by measuring vibration of the damaged structure under known loadings, it is possible to estimate the location and magnitude of the cracks with the help of mathematical models as interpretive tools. These techniques were extensively studied in relation with slender structures. For these ones, a beam model captures the most significant features of the structural dynamics. Most studies have focused on Bernoulli-Euler and/or Timoshenko solid section beams. Thin-walled beams have not been addressed in depth, perhaps due to their more complex dynamics. Many of these studies were directed to the identification of concentrated damage, such as fatigue cracks in metallic structures. However, there exist situations where the damage has the form of diffuse cracking. That is the case of reinforced concrete beams. Some studies were directed to the identification of continuously cracked beams with solid cross-sections, but according to the authors´ knowledge, no study has dealt with this type of damage in thin-walled beams. This work deals with the identification of diffused damage in thin-walled beams. The study is based on a structural model for the dynamics of thin-walled beams, developed by the authors, modified by the presence of diffuse damage. The identification problem consists in obtaining the damage parameters that minimize an objective function given by the quadratic relative difference between theoretical displacement values and experimental ones (and or natural frequency values). The optimization problem is solved by means of the element finite method to evaluate the objective function and the "simulated annealing" technique to direct the search of the optimal parameters (location and magnitude) of the cracks. The methodology is shown to be efficient for identifying diffuse damage even in the case of existing measurement errors.