Frequencies of Gantries Free Oscillation at Internal Ball-Joints

Abstract

This paper deals with the determination of free oscillation frequencies of internal ball-joints systems having a broken configuration and supporting the action of several construction masses. At first, a gantry with an internal ball-joint was examined by the force method, and the results were compared to those obtained by stiffness matrix method proposed in this article. This method has therefore been extended to the analysis of fairly complex gantries. It has been found that for rigid structures, frequencies of the free oscillations increase and the natural period of vibration decreases. On the other hand, for the more flexible structures: the rigidity decreases, which decreases the frequencies of the free oscillations and thus increases the natural period of vibration of the structures. Also these frequencies of free oscillations depend neither on the time, nor the amplitude of the oscillations, nor the phase angle but rather on the stiffness and the mass of the structures. Application of method purposed in this article for determination of the frequencies of free oscillations of systems is very advantageous because of the reliability of the results obtained, its ease of execution and above all the time saved during the study phase.