Experimental studies on fragments of reinforced concrete slabs under close-in explosions

Most of the injuries resulting from an explosion are not caused by the shock waves, but rather by the high-speed flying sharp fragments due to concrete spalling and crushing. The commonly used reinforced concrete (RC) components in building and infrastructure construction suffer this typical damage when subjected to close-in blast loads. The numerous ejecting concrete fragments generated from the crushing and spalling damage would threaten the occupants and equipment inside the building structures. Therefore, it is of great significance to study the local damage and fragments of RC members under close-in explosions. In this paper, five RC slabs in size of 1 x 2 x 0.12 m were tested under blast loads generated by 2kg, 4kg and 6kg TNT charges detonated with 0.4 m standoff distance. Significant local damage such as spalling and crushing of the RC slabs were observed, and a lot of ejecting fragments with different sizes and splattering distances were collected. The fragment mass, fragment size and splash distributions were analyzed in detail with respect to the mass of the TNT charge. It is found that higher charge weight will lead to more fragments and also propel them to a farther distance. The proportion of small fragments increases as the charge weight increases. High-speed camera was used to monitor the projection of fragments and found that the maximum ejecting velocity of fragments from RC slab under close-in blast loads is up to 100 m/s when the mass of TNT charge is 6kg. The concrete fragment with such high ejecting velocity could be very dangerous to the occupants and equipment.