A unified analytical approach is applied to investigate the vibrational behavior of grid-stiffened cylindrical shells with different boundary conditions. A smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of shell in order to obtain the equivalent stiffness parameters of the whole panel. Theoretical formulation is established based on Sanders’ thin shell theory. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stoke's transformation. A 3D finite element model is also built using ABAQUS software which takes into consideration the exact geometric configuration of the stiffeners and the shell. The achievements from the two types of analyses are compared with each other and good agreement has been obtained. The Influences of variations in shell geometrical parameters, boundary condition, and changes in the cross stiffeners angle on the natural frequencies are studied. The results obtained are novel and can be used as a benchmark for further studies. The simplicity and the capability of the present method are also discussed. 1. Introduction Investigating the vibrational behavior of cylindrical shells (e.g., frequencies, mode shapes, and modal forces) is of high importance in structural dynamics. Cylindrical shells due to their high strength as well as light weight have gained many applications in the aviation and aerospace industries (e.g., launch vehicles, reentry vehicles, aircraft fuselages, spacecrafts, etc.) in particular. Great number of researches have been emerged rapidly in the past decades concerning with the vibrational analysis of composite cylindrical shells. An excellent review of researches in this area was collected by Leissa [1]. There are also some good reviews on vibration of composite shells using experimental [2, 3] and analytical methods [4–9] and numerical techniques [10–14]. Recently, Hemmatnezhad et al. [15] investigated the vibrational behavior of composite cylindrical shells using a unified analytical approach and based on different shell theories. Grid-stiffened cylinders are cylinders reinforced with different types of stiffening structures either on the inner, outer, or both sides of the shell. These stiffeners significantly increase the load resistance of a cylinder without much increase in weight. The selection of stiffener configuration depends on several factors such as the loading condition, cost, and other factors. The promising future of stiffened cylinders, with reinforcing grids or ribs, has led
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