In this paper, the vibration characteristics of GFRP-stiffened pipes, in intact and cracked conditions are investigated. The results have different applications, which the most important ones are optimized designs of such pipes and diagnosis of the damage in them. Therefore, by Love theory, governing equations of motion for the GFRP-stiffened pipes were obtained. Having obtained characteristic equation, the natural frequencies of the problem were calculated for intact case. Then by modeling a sample of these pipes in the ANSYS software and using Modal analysis, natural frequencies and related mode shapes due to finite element method were calculated in cracked and intact conditions. Then by using the experimental modal analysis method, the natural frequencies of a sample, which was built similar to these pipes, were obtained in cracked and intact conditions. The results of the analytical method, finite element method, and the experimental modal analysis were compared and it was shown that the results have a good compatibility. The same process was performed on carbon fiber composites.
