Diagnosis of Damage in a Steel Tank with Self-Supported Roof through Numerical Analysis

Abstract

The safety of civil engineering structures is one of the most important issues of building industry. That is why the assessment of the damage-involved structural response has recently become of major concern to engineers. Among a number of different approaches to diagnosis of damage, the method of measuring the changes in natural frequencies is considered to be one of the most effective indicators of global damage. From the practical point of view, the method has been successfully applied to relatively small structures, while in-situ tests on large structures, such as bridges, tanks or dams, are very difficult. The aim of the present paper is to show the results of the numerical analysis concerning the diagnosis of damage in a cylindrical steel tank with self-supported roof which is filled with liquid. The tests have been conducted for various stages of damage, introduced in the numerical model by reducing the stiffness of tank-soil system as well as by cutting the connection between the shell and roof of the tank as well as between roof elements. The results of the numerical analysis have shown the characteristic decrease in the natural frequencies for the case of tank-soil system with reduced stiffness, which is the global type of damage. On the other hand, cutting the welds, which can be considered as the local type of damage, has not lead to the differences in the natural frequency values, although differences in local deformations of shell in the vicinity of cuts have been observed in vibration modes.