Hadi Ebrahimi-khah - Lecturer, Member of Iran Construction Engineering Organization (IRCEO), Tehran, Iran,
Mobina Mohammadkhani - M.Sc. Student, Department of Civil Engineering, Science and Research Branch, Islamic Azad University,Tehran, Iran,
Romina Mohammadkhani - M.Sc. Student, Department of Civil Engineering, Central Tehran Branch, Islamic Azad University, Tehran,Iran,
Behrouz Babaloo - Lecturer, Member of Iran Construction Engineering Organization (IRCEO), Tehran, Iran,

In this article, we investigate and apply the Homotopy Perturbation Method as one of theapproximate analytical techniques to solve the equation of free vibration of a ۲-D structural frameconnected to the nonlinear springs. The comparison of the results which are obtained by the homotopyperturbation method with the numerical method and the Hamiltonian approach reveal that this methodis efficient, convenient, and convergent for small values of time and vibration amplitude and can beextended to the other nonlinear dynamical systems and can therefore be found widely applicable inengineering and other sciences

Free Vibration, ۲-D Structural Frame; Nonlinear Spring, Approximate Analytical Method,Homotopy Perturbation Method