Prediction of buckling capacity of liquid-filled steel conical tanks considering field-measured imperfections

Abstract

Geometric imperfections caused by fabrication and welding reduce the buckling capacity of steel conical tanks. Few studies have considered field-measured geometric imperfections in such type of shell structures. This study carries out elastoplastic finite element analyses (FEA) to evaluate the buckling capacity of a full-scale stiffened conical steel water tank by considering its imperfections extracted from high-resolution laser scan data. Both global and local imperfections are obtained by comparing the laser scan data with the nominal tank geometry. The global imperfection involves deviation of the actual central axis of the tank from its nominal axis and ovalization of the tank circumference, whereas the local imperfection involves local fluctuations of the tank geometry around the circumference at a given elevation. The FEA is conducted using the commercial package ANSYS where both geometric and material nonlinearities are considered in the analysis. A four-node shell element with a six degrees of freedom per node is utilized in the model. The analysis results shed light on the shapes and magnitudes of global and local imperfections in an existing stiffened steel conical tank and their impact on the buckling capacity of the tank. Furthermore, the adequacy of imperfection tolerances recommended in widely used design standards for steel tanks are examined and compared with those extracted from the field measurements. The analysis results suggest that the local imperfections can be more critical than the combination of global and local imperfections in terms of the buckling capacity of the conical steel tank.