The present trend in shell construction is to make them as thin as possible which makes it desirable to know more about buckling strength. At present very little is known about the stability of cylindrical shell roofs. It is the aim of this paper to propose a non-destructwe testing method to predict the buckling load of thin cylindrical shell roof models made of plexiglas. The mathematical similarity between simple problems in frcc vibration and elastic instability is well known. In a beam-column, the effect of axial compressive force P is to decrease the natural frequency of transverse vibration. In addition, the variation of the square of the frequency with P is linear and finally the frequency falls to zero when P approaches P or which is the buckling load of the beam-column. The question naturally arises about the genItality of the variation and whether such a behaviour can be expected in structures other than simply supported beams. Physical intuition would lead one to’ beIieve that if axial compression does decrease the natural frequency, frequency of any structure would fall to zero when buckling is reached (5).