The elastic stability of rings/long FRP tubes under external fluid pressure is very well studied. The formula for critical hydrostatic buckling pressure of thin cylindrical shells has been derived in closed form. These composite shells have attracted a lot of attention to use in deep water offshore drilling due to the weight advantage. A new design is proposed here using an FRP tube lined with a steel pipe. The metal shell also acts as a permanent mandrel for the filament winding process of the outer laminated composite shell. A generalized closed form analytical formula for the buckling of thin FRP-Steel multi-angle laminated long cylinders is developed. Standard energy based formulation is used to express the kinematics and equilibrium equations of the shells. Effective moduli are obtained to introduce the constitutive equations of thin shells. These equations are directly integrated to produce effective axial, coupling and flexural rigidities. Comparisons are made with some existing results.
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