Effects of initial conditions on the flight of windborne plate debris

Using the ‘failure’ model approach, the effects of initial conditions on the flight of roof tiles and asphalt shingles in extreme winds were investigated. In total 26 different configurations were examined by varying the wind angle, element location on the roof, and surroundings. While the initial failure in these experiments depends on the global pressure induced by the wind acting on the building, the effects on the subsequent flight are based on local wind speeds above the roof and the aerodynamics of the debris element. This leads to debris flight behaviour which differs significantly from that observed in uniform flow. For example, elements failing in the highest wind speeds did not always travel the farthest due to the details of the flow field above the roof and in the wake. In particular, failures within large separation bubbles did not always lead to flight since the flow above the roof surface is moving upstream and slowly. It was observed that the in-flight shingle velocities span a range of 40–120% of the estimated roof height gust speed at failure and tile velocities span a range of 30–60%.