The study of the dynamics of metal gantry crane structures when lifting the cargo

The metal structures of gantry cranes undergo vertical and horizontal vibrations when lifting the cargo. In this case, to calculate stresses in the crane rods, the relevant dynamic loads should be taken into account. The vertical dynamic loads in gantry cranes are computed by the techniques developed for bridge cranes. However, the horizontal dynamic loads are scarcely studied and the formulas for determining them are not substantiated. The dynamic model proposed in this study indicates how the dynamic loads and corresponding stresses change if the cargo is located at the end of the console or in the middle of the span. The equations of motion of the reduced masses are used to derive relationships between the displacements and dynamic loads and to determine the time variation of the maximum stresses in the elements of the structure under maximum loads. The results of the simulation of the gantry crane with a rigid and a flexible supports are presented. It is shown that the cargo oscillates after takeoff, with the fundamental frequency being close to the partial frequency of the bridge in the horizontal direction. The effect of the rigid support compliance on the fundamental and partial frequencies of the bridge is investigated numerically. The dynamic coefficients calculated in terms of the displacements and stresses are compared. The approach suggested in this paper for evaluating dynamic stresses caused by lifting the cargos makes it possible to improve the accuracy of calculations of metal gantry cranes structures.

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