Modal analysis based structural damage localisation under varying operating conditions: Fid-Bau Portal

Modal analysis based structural damage localisation under varying operating conditions

Parloo, Eli / Vanlanduit, Steve / Verboven, Peter / Guillaume, Patrick

During the last decades there has been an increasing interest in modal analysis based structural health monitoring techniques for mechanical and civil structures. These methods differ from classic damage identification techniques (e.g. X-rays, liquid penetrant technique) by the fact that the global structure can be monitored from a (single) localized measurement. The latter aspect avoids the use of time-consuming local inspections that are usually necessary for the more classic techniques. On the other hand, modal-based techniques are generally highly sensitive to disturbances caused by changes in boundary conditions. A variation in the operating condition of a structure under test can have a very bad influence on the reliability of modal based structural health monitoring results. For instance, if no extra effort is made to compensate the natural frequencies for the effect of variations in the environmental temperature, the resulting changes in modal parameters will be erroneously interpreted as evidence of structural defects. In this paper, a simple computation scheme is used for compensating the natural frequencies for overall uniform changes in condition. Examples of such changes are given by a uniform temperature variation, a uniform mass or stiffness variation (as would result from the application of a uniform coating on a mechanical structure). The technique was designed for natural frequency data and assumes that the correction can be accomplished by removing the common relative shift in the observed natural frequency. Unlike other methods, the compensated results are used for localising as well as detecting structural damage.