The client requested a Finite Element Analysis (FEA) of a flat bottom FRP tank at the bottom knuckle.
Subpart 3B of ASME RTP-1 (Design by Stress Analysis) lists various methods for designing parts of FRP tanks, one of which is FEA. It was requested by the client that the stresses in the tank near the anchor lug be determined using FEA.
The flat bottom, shell wall, anchor lug and attachment layups were modeled and analyzed using the finite element method. All parts were connected with either glued or contact connections as appropriate. The tank had twelve anchors lugs spaced at 30 degrees. Thus, a 30 degree tank with symmetry boundary conditions was modeled. The loads applied to the tank were uplift from internal pressure and tension and shear from wind and seismic forces. The maximum stress was determined to be in the shell wall above the attachment layup. The stress was less than the allowable stress of the FRP material.