A simplified model for estimating axial impact forces resulting from debris with non-uniform nonstructural mass

The impact forces resulting from the debris strikes during tsunami and flood events can lead to extreme damage to the structures located in inundation zones. It is important to estimate reliably such impact demands in order to design structures safely. This study is aimed to develop a simplified one-dimensional model to predict the impact force and duration for axial impact of the debris with non-uniformly distributed nonstructural mass. The focus herein is on in-air impact. An experimental study is carried out on a 6.1-m rectangular steel tube with different configurations of rigidly attached nonstructural mass under elastic response. A nonlinear dynamic finite element model of a steel tube with nonstructural mass is also developed and validated by comparing with the experimental data. Parametric studies are carried out to investigate the effect of nonlinearity on impact demands. The results reveal that the peak impact force is sensitive to the location of the nonstructural mass. It is also observed that the peak impact force is not affected by the magnitude of nonstructural mass during inelastic response. The experimental and simulation results are also used to assess the applicability of the simplified design-oriented one-dimensional model. It is found that the debris impact demands are well represented by the proposed one-dimensional model.