On the seismic behaviour and design of liquid storage tanks

Abstract

The paper examines some special issues on the structural behaviour of upright-cylindrical liquid storage tanks, which are widely used in industrial facilities and for water storage. Two main design standards are considered: EN 1998-4, a relatively new standard, and Appendix E of API 650, which has been through substantial amendments and revisions in its new version (11th edition, 2007). There are significant differences between the two specifications, which are due to the fact that there exist several controversial issues on this subject, open to further research. These issues are (a) the number of modes necessary to estimate ac-curately the convective seismic force due to the hydrodynamic behaviour of the liquid con-tainment; (b) the appropriate combination of the impulsive and the convective component of seismic force; (c) the uplifting behaviour of unanchored tanks, with emphasis on the base plate behaviour and the increase of meridional compression; (d) the choice of an appropriate reduction (behaviour) factor for calculating both the impulsive and the convective force; (e) the calculation of hydrodynamic hoop stresses due to liquid hydrodynamic motion; (f) the de-sign of tanks against buckling at the top due to liquid sloshing; (g) the importance of nonlin-ear wave sloshing effects. The present paper is aimed at addressing the above issues based mainly on numerical simulations. To simulate the tank shell and its structural behaviour, general-purpose finite element software ABAQUS is employed, whereas to examine hydrodynamic effects, an in-house numerical technique is developed. Existing data from previous investigations are also considered. The results are aimed at better understanding of liquid storage tank seismic be-haviour, bridging the gap between the two major design standards (EN 1998-4 and API 650-Appendix E), towards safer seismic design of industrial facilities.