Stability of Stiffened Cylinders

Design of efficient cylindrical shells for carrying moderate compressive loads leads to the requirement that they be stiffened. The buckling behavior of such stiffened cylinders differs considerably from that of thin monocoque cylinders in several noteworthy respects: 1) Stiffened cylinders are often effectively 'thick,' and exhibit large buckle wavelengths. Their strength is consequently influenced little by imperfections and can be predicted accurately by linear buckling analysis. Refined and sophisticated linear analysis thus becomes a powerful design tool. 2) One-sidedness of stringers and rings produces strong interaction between 'membrane' and bending forces. Calculations and tests have revealed instances where change of reinforcement from one surface to the other changes buckling strength by a ratio of two or more. 3) Because of the larger, well defined wave form, the strength of stiffened cylinders always depends on the constraint (or lack of it) from adjoining cylinders and domes (or test fixtures), and the resistance to bending moment may appreciably exceed the resistance to uniform load. This paper describes several methods, having varying complexity and versatility, for treating buckling of stiffened cylinders. The determination of the required ring stiffness for preventing general instability is identified as being central to optimum design; commonly used methods of determination are shown to be unreliable. Theoretical and experimental results are compared, and future development is outlined.