Analysis and Stability of Floating Roofs

An oil storage tank floating roof, of the type considered, consists essentially of a circular membrane stiffened around its edge by a compartmented buoyant ring or pontoon. A method is presented for the static stress analysis of this type of roof. Solution of the membrane large deflections equations is accomplished numerically by assuming a range of starting values for the boundary parameters. The unique values which correspond to equilibrium and compatibility at the pontoon/membrane interface are established by cross-plotting those parameters that are common to both at their connection point. Elastic buckling stresses are derived for the pontoon on the basis of small displacements, and the complete analysis procedure is illustrated by application to a particular roof design. The effects of nonsymmetrical normal loading are examined and related to the probability of various types of collapse. In this context, it is demonstrated that partial loss of pontoon buoyancy is likely to seriously reduce a floating roof operating safety factor.