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This study presents experimental findings on debris damming loads on columns of an elevated coastal structure under tsunami-like wave conditions. A total of 183 cases (140 with and 43 without debris) were tested at a 1:20 scale to understand the impact of various factors on debris-driven damming loads, including wave characteristics, structure configurations, and debris shapes. The debris impact and damming processes were observed and quantified from optical measurements, and corresponding loads were measured on the entire structure using a force balance plate and on an individual column in the front row using a multi-axial load cell. The experimental results indicated the horizontal debris damming load on the entire column structure increased by up to 3.2 times compared to conditions without debris, while the load on the individual column increased by up to 11.0 times. The total damming loads for the whole structure increased, but the load for the individual column decreased at a reduced opening ratio. The smaller debris sizes relative to column spacing showed significantly lower chances of debris damming across different column configurations. Overall, the load on the whole structure showed stronger correlations between debris damming loads and hydro-kinematic variables such as flow depth, velocity, momentum flux, and Froude number compared to the loads on the individual column. Among these variables, momentum flux emerged as the most consistently influential across all categories. • 1:20 scale experiment was performed to study tsunami-driven debris loads on structures. • Debris damming loads at an individual column and whole specimen were compared. • The impact of opening of columns and size of debris are evaluated. • Likelihood of damming and its correlation to flow conditions are investigated. [ABSTRACT FROM AUTHOR]

Debris loading during extreme flooding events has been documented by many post-tsunami field surveys of disaster-stricken communities and, as such, it is now considered and accounted for as a critical design consideration in the design of resilient infrastructure. Debris damming is one of the debris loads of concern, occurring when solid objects entrained within the inundating flow accumulate at the face of a structure or structural element. The presence of the debris dam results in increased drag loads on the structure and can have other associated effects, such as flow runup and flow accelerations, that can influence design conditions. The focus of debris damming studies has been within river engineering: therefore, previous studies have been performed in steady-state conditions. The study presented here is the first to examine debris damming in transient, supercritical flow conditions. The study uses a modified dam-break wave as the hydrodynamic forcing condition and the debris are scaled down debris types common in coastal areas (shipping containers, hydro poles, and boards). The analysis includes a qualitative examination of the difference in the debris damming mechanisms as a result of distinct flow conditions associated with a dam-break wave interacting with a surface-piercing obstacle. Additionally, the study determined the influence of the debris dam resulted in a maximum loading condition that occurred earlier and was of greater magnitude than the clear water case. [ABSTRACT FROM AUTHOR]