ABSTRACT
We present a study of the effects of geometric nonlinearities on vibrations of rotating machines support structures. Dynamic characteristics of structures depend on their stiffness and mass. The initial stiffness of a structure, computed in its unloaded state, is affected by the applied forces, the so-called geometric stiffness. Compressive forces reduce the stiffness and the frequencies and may lead to buckling, for zero frequencies. Traction loads tends to increase stiffness and frequencies, as in tensostructures. In bases of machines excited by the supported equipment, vibrations may affect the structures but, in general, may generate damage to the suspended equipment and the quality of the production. Although machine support structures are, as a rule, very bulky, little affected by geometric stiffness considerations, the tendency of modern structural engineering is towards slender members, due to efficient materials and powerful analysis tools. Here we study these effects via theoretical, numerical and experimental methods. Laboratory essays and Finite Element larger models are developed. A first model is a metal beam under pretension supporting a rotational machine. We suppose the original design provided for natural frequencies away from the excitation frequency. Nevertheless, the presence of large axial compressive force will reduce the beam stiffness and natural frequencies leading to unexpected potentially dangerous resonance states.
