Estimation of demands resulting from inelastic axial impact of steel debris

Impact of debris generated during extreme events such as floods, tsunamis, and hurricane storm surge and waves can cause severe structural damage. It is necessary to be able to estimate debris impact forces properly in order to design the structures to resist typical water-borne debris. The objective of this study is to characterize the impact demands generated during inelastic response of the debris and to develop a simple model that can estimate impact force and duration accurately. In previous work, a series of debris axial impact experiments were conducted at full scale under increasing impact velocities of up to 3.8 m/s. In this paper, the results are used to validate nonlinear dynamic finite element models of simplified and complex debris-types and are used to examine response under impact velocities up to 15 m/s. A simplified one-dimensional (1D) model is developed, illustrated, and validated using a simple debris-type consisting of a steel tube under axial impact. The model is also extended to estimate impact demands for complex debris-types such as shipping containers. This model is examined using numerical models and validated with data from full-scale impact experiments of a container. The numerical and simplified models provide accurate estimation of the axial impact demands generated under inelastic response of the debris. Results indicate that as the debris response changes from elastic to inelastic the duration of the impact event increases and the peak impact force generated reaches a limit. The maximum impact force is found to be equal to the strength of the axial members under impact. The results also show that impact forces estimated by current design guidelines are not accurate and can lead to over or under prediction of the design force levels.