The bounce and roll of masonry debris

When a detonation occurs inside a building masonry debris is projected into the air. This flying debris can cause damage to buildings and injure or potentially kill people in the vicinity. In order to be able to model the explosion and what happens to the debris, it is essential to have a complete understanding of the debris’ impacts with the ground. This paper details the development of an experimental and modelling programme that was set up to study what happens at the first impact of the debris with the ground. Concrete spheres and cubes were fired at speeds of 50–150 m s−1 and at impact angles of 5–25° onto surfaces of concrete, sand, water and different clays. The results showed that the post impact velocity was predictable using simple empirical formulae. The analysis also shows that cubes can be treated as spheres and that the impacted materials can be divided into two types, those that deform under impact and those that do not. A study of the post impact rotation showed that it could only be predicted under certain instances, but that the rotation rate is high enough for the lift it generates due to the Magnus force to significantly affect the debris’ flight.