Buckling behaviour of FRP strengthened cylindrical metallic shells with cut-outs

•Effect of cut-out size on buckling capacity of the shell is a function of its imperfection magnitude.•Long rectangular cut-out along longitudinal direction exhibits higher buckling load Pu for perfect and imperfect shells than other orientations.•Loss of flexural stiffness at cut-out cross-section leads to early buckling of imperfect shells with large circumferential opening.•FRP strengthening is effective in resisting pre-buckle deformations i.e. lip opening as well as alleviating stress concentration effects, leading to increase in Pu especially for large longitudinal cutouts.•Elliptical cut-outs exhibit higher Pu than rectangular cut-outs with different corner radii for imperfect bare shells.•Photo-frame stiffening around cut-out with large overlap width and thin stiffener is beneficial for perfect shells and thick stiffener is beneficial for imperfect shells.•Stiffener around cut-out is relatively more effective than FRP strengthening to compensate the loss of flexural resistance at cut-out cross-section. This paper presents a detailed buckling study on FRP strengthening of metallic cylindrical shells with different geometric imperfections and centrally located unstiffened and stiffened cut-outs. Initially, bare and FRP strengthened aluminium cylindrical shells have been manufactured. Geometric imperfections have been measured and implemented in the numerical model. Interfacial bond quality has been assessed by two different non-destructive techniques. The buckling response of bare and FRP strengthened shells have been numerically simulated and validated with respective experiments. Subsequently, the difference in buckling response between FRP strengthened and bare aluminium shells with variations in cut-out’s size, orientation, shape, and corner radius has been analysed for unstiffened cut-outs. The effect of increase in stiffener’s thickness and overlap width for photo-frame type stiffening of rectangular cut-outs with and without closure has been investigated. The study has revealed interesting observations. (1) Effect of cut-out size on buckling capacity of the shell is a function of its imperfection magnitude. For shells with large initial imperfections, introducing a cut-out as well as with increase in its size, relatively smaller drop in buckling capacity is found; while shells with small initial imperfections resulted in a steep and large drop in buckling load even with a small cut-out size. (2) FRP strengthening is more effective for shells w