Impact resistance of common building materials to tornado missiles

Abstract

Objects and debris picked up and transported by tornado winds range in size from roof gravel to railroad cars. The objectives of this project were to identify the most probable missiles transported by tornadoes, to estimate the speeds achieved by these missiles, and to determine the speeds required to perforate walls used in ordinary construction. The two most relevant missiles were identified as a 2 × 4 in. timber plank weighing 15 lbs and a 3 in. diameter steel pipe weighing 75 lbs. The two missiles are typical of a wide variety of objects and debris found in tornado paths passing through residential neighborhoods. The plank and pipe can be accelerated to speeds up to 170 mph and 90 mph, respectively in a tornado rated F5 on the Fujita Scale. Impact tests using an air-actuated missile cannon revealed that residential stud walls consisting of exterior materials other than masonry could not stop the plank at speeds above 50 mph. Most wall configurations defined in Architectural Graphic Standards were tested. Both 8-in. and 12-in. reinforced concrete masonry walls were able to stop the 2 × 4 in. plank, if the cells in the block were reinforced and grouted. At speeds above 100 mph, the planks disintegrated, but the walls remained intact. The 2 × 4 in. plank perforates the face shell of unreinforced concrete masonry at about 65 mph. There-in. diameter pipe impacts have not been tested to date.