A STUDY ON ELASTIC-PLASTIC BUCKLING OF CYLINDRICAL STORAGE TANKS UNDER SEISMIC LOADING

Liquid storage tanks, either made of steel or concrete, are used widely in various industries,such as petroleum and water supply systems. Thus, their damage is one of the major concerns. A well-known serious failure mode, which usually occurs during earthquake, is a bulge near the base of the tank called elephants foot buckling so called due to its deformed shape recent studies have showed that storage tanks designed with API (American Petroleum Institute) code, one of the most prevalent references for engineers, have suffered of different earthquake loadings. API code considers elastic buckling stresses based on classic relations, while elephants foot buckling is an elastic -plastic phenomenon. Current study includes a nonlinear seismic analysis of 13 cylindrical steel storage tanks using ANSYS12 package. Different diameter to height ratios have been considered and compared to results of API design code. Analyses are conducted on models with a liquid level of 85% of cylinder height, representing the full performance level. As a result, buckling stresses of seismic analysis and API allowable stresses are presented to show that in general, a design on the basis of API criteria cannot prevent the tank wall from buckling.

Keywords:

Storage Tank , Seismic Loading , Nonlinear Analysis , Elastic-Plastic Buckling