Common misconceptions in determining wind/water damage causation

Recent severe tropical storms such as Hurricanes Katrina ∥2005∥ and Ike ∥2008∥ have resulted in questions of whether wind or water ∥storm surge∥ is responsible for severely damaging or destroying structures along the coast. Because of a separation of insurance for wind and storm-surge ∥flood∥ damages in the U.S., the determination of whether hurricane damages are the result of wind or of storm surge becomes a crucial issue in the settlement of insurance claims. Disagreements as to the cause of such damages have led to an unprecedented series of legal challenges between homeowners and insurers. Engineering and meteorological reports directed at the performance of residential buildings have been prepared in support of both sides of this issue. Many such reports employ failure theories that are implausible and that can be potentially misleading. The failure theories in question appear to stem primarily from a misunderstanding of wind and storm-surge loading of structures, from a misunderstanding of the behavior of structures under extreme loads, from selective or incomplete use of physical principles, from the use of incorrect or non-standardized wind and surge data, and/or from incomplete analysis of clues provided by the damaged structure and surroundings. Physical principles that are mistakenly or inaccurately applied include fluid-structure interaction, buoyancy, and transport of structures and debris. Among the data improperly employed in recent analyses are unverified and non-standardized wind speeds and data from preliminary ∥non-calibrated∥ numerical models. Improper application of the EF-Scale relating tornado damage to wind speed ranges to hurricane damage also has been frequently observed. The supposition that tornado damage is responsible for the "selective" destruction of structures has also been mistakenly used in place of considering variations in structural resistance. Our experience has prompted the following recounting of physical principles, anecdotes, observations, and recommendations. This paper examines common misconceptions and provides guidance for application of the appropriate physical principles.