Ductile design of steel pipes for missile impact

Efficient and economical design of a steel duct or pipe for missile impact loads need to exploit all its capacity to absorb the impact energy by deforming plastically to the fullest extent allowable. In the case of an impact, energy can be dissipated locally in the vicinity of impact through flexure of pipe wall, globally through pipe bending and rotation at flexural plastic hinges. These considerations are complicated by the system geometric and material nonlinearities. In this paper, a multi-degree nonlinear structural dynamic model is presented and applied to coupled local and global ductility of a steel pipe subjected to impact loads. Optimization of the pipe design can then be achieved by progressively adjust response ductility between local and global energy dissipation mechanisms. The approach presented could be utilized to evaluate steel pipe/duct system against not only missile impact loadings, but other type of transient loads as well. The proposed method is implemented to a practical example after its validation by using the finite element analysis.