Diagnosis of Damage in a Steel Tank Model by Shaking Table Harmonic Tests

Abstract

Diagnosis of damage in civil engineering structures has recently become an important issue in the safety assessment procedure. Among a number of different approaches, a method of measuring the changes in natural frequencies is one of the most effective indicators of global damage. It has been successfully applied to relatively small structures, however, the tests on large structures are very difficult and the practical application of the method still requires further investigations. The aim of the present paper is to show the results of the shaking table experimental study concerning the diagnosis of damage in a model of cylindrical steel tank with self-supported roof which is filled with liquid. During the tests, the base of the structure was excited under the harmonic loading with variable frequency. The tests were repeated for different stages of damage, which was introduced in the model by easing the bolts of structural supports as well as by cutting the welds between the shell and roof as well as between roof elements. The results of the study show a characteristic decrease in the natural frequencies for the case of structural supports with reduced stiffness (global type of damage). On the other hand, cutting the welds (local type of damage) has lead to the considerable increase in the power spectral density values for higher vibration modes.