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Structural Engineering and Mechanics
  Volume 55, Number 3, August10 2015, pages 655-674

new analytical approach for determination of flexural, axial and torsional natural frequencies of beams
Mehrdad Mohammadnejad

    In this paper, a new and simplified method is presented in which the natural frequencies of the uniform and non-uniform beams are calculated through simple mathematical relationships. The various vibration problems such as: Rayleigh beam under variable axial force, axial vibration of a bar with and without end discrete spring, torsional vibration of a bar with an attached mass moment of inertia, flexural vibration of the beam with laterally distributed elastic springs and also flexural vibration of the beam with effects of viscose damping are investigated. The governing differential equations are first obtained and then; according to a harmonic vibration, are converted into single variable equations in terms of location. Through repetitive integrations, the governing equations are converted into weak form integral equations. The mode shape functions of the vibration are approximated using a power series. Substitution of the power series into the integral equations results in a system of linear algebraic equations. The natural frequencies are determined by calculation of a non-trivial solution for system of equations. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained with those obtained from other published references and results of available finite element software.
Key Words
    natural frequency; Rayleigh beam; axial vibration; torsional vibration; flexural vibration; weak form integral equation
Mehrdad Mohammadnejad: Department of Civil Engineering, Faculty of Engineering, Birjand University of Technology, Birjand, Iran

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