Multiple Debris Impact Loads in Extreme Hydrodynamic Conditions

Abstract

Video footage from the 2004 Indian Ocean and 2011 Tohoku tsunamis showed large quantities of debris entrained within the inundating flows. Such extreme debris conditions can lead to a high probability for multiple impacts on structures particularly in built-in coastal communities. In the current North American design guidelines and standards, common methods of addressing debris impact loads have focused on a single debris impacting a structure. Hence, the study presented herein examines the mechanisms and consequences of multiple debris impacting a structure simultaneously. The experiments consisted of examining several impact conditions for free-floating debris in a dam-break wave, similar to a broken tsunami wave advancing inland, and classifying each impact based on the debris configuration as well as the number of debris impacting the structure. The debris were modeled as scaled-down (1:40 scale) shipping containers. The number of debris and hydrodynamic forcing conditions were varied to investigate a wide range of impact conditions. The results of this study showed that an increase in the number of impacting debris resulted in an increase in the measured impact load. To aid in the consideration of multiple debris impact in future design standards, a methodology that would complement the framework of the single-degree-of-freedom impact model is proposed.