Debris impact forces on flexible structures in extreme hydrodynamic conditions

Abstract Field surveys of recent major flood events have emphasized the need for an in-depth examination of debris loading. Debris loading occurs when solid objects entrained within the flow interact with a structure in its movement path, exerting loads through direct impacts or damming. Until now, the focus of research into debris impacts has concentrated on single debris impacting a rigid structure. This study extends to examining the influence of debris impacting a flexible structure. A two degree-of-freedom (2DOF) system was used to model the debris–structure interaction. The model is compared with two experimental data sets using a rigid body and the effective stiffness model. The proposed 2DOF model was shown to be more accurate in estimating the impact force than those to which it was compared to. However, due to difficulties in estimating the stiffness and inertia of the structure and the debris, the proposed model under predicted the maximum measured impact loads. The effective stiffness model was shown to represent the maximum measured impact loads, and should therefore be implemented in the design process when considering debris impacts on flexible structures.