Nonlinear Effect on Instability of Steel Columns under Dynamic Axial Loads

The usual methods of investigating dynamic instability concentrate on elastic instabilities. These standard methods are limited because the strength of the structural component is independent of how much spread there is in the unloading and reloading of the yielding parts in the cross section and along the length of the component. Therefore, such methods are of limited practical use in assessing the performance of actual structures. This paper examines inelastic dynamic instabilities of steel columns alternately subjected to a steady axial force and an alternating dynamic axial force. The variable factors considered include the support condition and the frequency of the periodic axial force. During dynamic loading the amplitude behavior of the inelastic nonlinear column at the instability condition was found to be different from that of the elastic linear column at the resonance condition. It was also found that the presence of the material nonlinearity makes the instability regions different from those given by the solution of Mathieuʹs equation for linear, elastic columns.