• Steel and Composite Structures
• /
• v.10 no.4
• /
• pp.361-371
• /
• 2010

Enhancement in the seismic buckling capacity of steel tanks caused by the addition of fiber reinforced polymers (FRP) retrofit layers attached to the outer walls of the steel tank is investigated. Three-dimensional non-linear finite element modeling is utilized to perform such analysis considering non linear material properties and non-linear large deformation large strain analysis. FRP composites which possess high stiffness and high failure strength are used to reduce the steel hoop stress and consequently improve the tank capacity. A number of tanks with varying dimensions and shell thicknesses are examined using FRP composites added in symmetric layers attached to the outer surface of the steel shell. The FRP shows its effectiveness in carrying part of the hoop stresses along with the steel before steel yielding. Following steel yielding, the FRP restrains the outward bulging of the tank and continues to resist higher hoop stresses. The percentage improvement in the ultimate base moment capacity of the tank due to the addition of more FRP layers is shown to be as high as 60% for some tanks. The percentage of increase in the tank moment capacity is shown to be dependent on the ratio of the shell thickness to the tank radius (t/R). Finally a new methodology has been explained to calculate the location of Elephant foot buckling and consequently the best location of FRP application.

• Structural Engineering and Mechanics
• /
• v.81 no.6
• /
• pp.781-790
• /
• 2022

The present paper describes a general procedure of the structural safety assessment for the independent type C tank of LNG bunkering ship. This strength assessment procedure consists of two main scheme, global Finite Element Analysis (FEA) model primarily for hull structure assessment and detailed LNG Tank structures FEA model including the cylindrical tank itself and saddle-support structures. Two kinds of mechanism are used, fixed and slides constraints in fore and rear of the saddle-support structures that result in a variation of the reaction forces. Finite Element (FE) analyses have been performed and verified by the strength acceptance criteria to evaluate the safety adequacy of yielding and buckling of the hull and supporting structures. The detail of FE model for an LNG type C tank and its saddle supports was made, which includes the structural members such as cylindrical tank shell, ring stiffeners, swash bulkhead, and saddle supports. Subsequently, the FE buckling analysis of the Type C tank has been performed under external pressure following International Gas Containment (IGC) code requirements. Meanwhile, the assessment is also performed for yielding and buckling strength evaluation of the cylindrical LNG tank according to the PD 5500 unfired fusion welded pressure vessels code. Finally, a complete procedure for assessing the structural strength of 500 CBM LNG cargo tank, saddle support and hull structures have been provided.