Experimental investigation of floating debris impact loading on structures during extreme waves like tsunami

Debris generated during extreme events like the tsunami can impose substantial impact loading on structures closer in the coastal zone. Majority of design codes do not quantify the impact forces close to reality owing to uncertainties in defining the wave characteristics and a lack of knowledge in understanding the underlying physical processes. The present study focuses on the measurement of forces which a coastal structure would encounter due to the impact of debris in motion during such an extreme event. The study herein focuses the motion of the debris due to undular bores. 1:20 scaled model of structure and the debris were used. Experiments were conducted in a wave flume 72.5 m long and 2 m wide. A beach slope of 1:30 is laid to replicate the coastal zone. By varying the wave heights and time periods, different types of waves such as elongated single pulse waves, symmetrical N waves and unsymmetrical N waves were generated replicating the characteristics of a tsunami as close as possible. The impact tests were conducted using box shaped smart devices as debris of weight 4.62 kg, 5.82 kg and 7.02 kg. The debris is attached with an accelerometer for measuring the impact acceleration. In order to have a better understanding of the behavior of debris during the impact, a camera at a speed of 120 fps is operated. The force acting on the structure is measured with a load cell. The forces due to the velocity of the debris and the mass is compared with the force measured using load cell. The details of the testing facility, model parameters, test set-up, test procedure, analysis of results and discussion are presented in the paper.