On Computational Dynamic Buckling Criteria for Shells under Transient Loads

摘要

This paper reports on the dynamic buckling of thin-walled steel storage tanks under a horizontal excitation at the base. The structure is modeled using finite elements and a geometrical and material nonlinear analysis to compute the transient response in the time domain [1]. The liquid stored in the tank is modeled taking into account the impulsive action. The excitation is introduced in terms of inertial forces with a time variation equal to the acceleration induced by the earthquake. The load factor is the horizontal peak ground acceleration of an earthquake.The dynamic buckling criteria initially employed is due to Budiansky and Roth [2], according to which dynamic buckling occurs whenever a small increase in the load parameter leads to a large increase in the transient displacements. The paper shows that dynamic buckling problems may occur in two ways: when there is a sudden change in the displacements and the deflected shape of the shell during the oscillation (i.e. the deflected mode) changes due to dynamic buckling, then a "bifurcation behavior" may be said to occur [3]. The original mode of small vibration changes to a different mode under large amplitude vibrations. But there is a second way, in which the transient displacements increase progressively and there is no change in the mode of vibration. However, there is a significant change in the slope of the curve of load parameter versus first maximum amplitude of oscillation. This indicates a change in the stiffness at some load level, but with the same mode of vibration. Such process may be called "limit point behavior" in the sense that instability preserves the shape of deflections.