DYNAMIC INSTABILITY ANALYSES OF AXIALLY IMPACTED COLUMNS.

This problem is analyzed by solving the dynamic Bernoulli-Euler equation with an axial inertia effect within the framework of finite difference approach. The influence of strain-rate effects on the dynamic response is first examined by using an elastic-viscoplastic theory, and then the critical values of an initial velocity and a mass of striking body for losing stability are evaluated within the context of the numerical results from different initial and boundary conditions. It is found that strain-rate effects are important in the range of post-dynamic instability, and that the mode of the lateral displacement after an impact depends on the initial velocity of the striking body and also on the relationship between the natural period of the first-order lateral mode and that of the first-order axial mode.