Experimental Investigation of Ultra-High-Performance Concrete Panels Under Tornado Impact Loads
Tornado events pose a threat to millions of people living in the tornadic-prone areas of the United States. Although many tornado shelters and safe rooms are commercially available that satisfy the extreme loading conditions required by the International Code Council and National Storm Shelter Association, there is a need for a simple yet safe design which can be easily assembled and used for multiple purposes. New engineering materials, such as ultra-highperformance concrete (UHPC), have the potential to improve tornado shelter options and save lives. This study experimentally investigates the performance of thin UHPC panels subjected to impact of standard wood 2x4 projectiles, following the requirements of ICC/NSSA 500, the leading standard on storm shelter design. 1.25-inch-thick and 1.625-inch-thick UHPC panels were cast and impacted with 15-lb wood projectiles at speeds ranging from 50 mph to 100 mph to maintain a similar impact-energy-to-panel-mass ratio. The failure response of each panel was characterized by excessive flexural deflection or punching shear. In the case of excessive deflection, a single-degree-of-freedom dynamic displacement model describes the motion of the panel during impact and the profile of the maximum deflection. In the case of punching shear, a modified equation from ACI 318 predicts the capacity of the panel. The results of the impact testing show UHPC is a promising material for future tornado shelters: UHPC panels with half the thickness of a traditional concrete shelter can be built for a similar or lower price, creatively integrated into homes, and increase accessibility of the tornado shelter for residents.