The free vibration of stiffened composite plate subjected to inplane force is investigated using the finite element method. The effects of transeverse shear deformation and rotatory inertia on the vibration characteristics are considered. First, membrane stresses occurring in the stiffened plate due to inplane force is analyzed using the virtual work principle. Next in the vibration analysis the presence of the membrane stresses is accounted for by including the potential energy of these stresses acting on the non-linear parts of the corresponding Green's strain components. It is shown that the increase of compression result in the decrease of the frequency. Present results are compared with the previous numerical results and are found to be very accurate. In the case of the composite rectangular plate, the effects of the fiber orientation on the vibration characteristics are investigated. Also, the effect of various moment of inertia of stiffener on natural frequency is discussed.
