BUCKLING RESPONSE OF CORRODING GROUND BASED STEEL STORAGE TANKS UNDER SEISMIC LOADING

Steel liquid storage tanks are highly susceptible to corrosion from within. Shell corrosion significantly alters the seismic response of ground-based cylindrical steel storage tanks. Investigations on the effects of imperfections in thin cylindrical shells show that large local buckling can occur at the locations of the corrosion-induced imperfections. In this paper, a numerical study is conducted to investigate the effects of internal shell corrosion on the dynamic buckling of three cone roof ground-based, steel cylindrical tanks with height to diameter ratios (H/D) of 0.40, 0.63 and 0.95, subjected to horizontal seismic base excitations. Internal corrosion is considered as a time dependent uniform thinning of the wall at the upper and the lower parts of the tank. Detailed numerical models of the tank-liquid systems at different stages of corrosion degradation are subjected to two representing accelerograms and for each model the critical peak ground acceleration (PGA) for dynamic buckling of the shell and its associated mode of failure are evaluated. It is found that in all three tanks, the critical PGA is markedly reduced with thinning of the shell, irrespective of the type of ground input. The buckling mode of failure of the tanks also changed from an elastic diamondshaped failure at the top of the shell to an elasto-plastic elephant foot type failure near the base, after 10 years for the shorter tanks (H/D = 0.4 and 0.63) and after 15 years for the tallest tank.