Engineering services for the ECO-SPAN® Arch System are based in Southwest Ohio. Like much of the Midwest, the lower Ohio River valley is part of an area known as Tornado Alley. From Texas to Pennsylvania and Minnesota to Alabama, this time of year can be dangerous. I was recently reminded of this fact as I watched the news, ready to head to the basement for shelter during a tornado warning.
Fortunately we have a basement. Many homes, schools, churches, offices and warehouses do not. Even new homes designed and built according to building codes in many tornado-prone areas are only designed to withstand 90-MPH winds. Actual wind speeds in recent events have more than doubled that. The March, 2012 tornado in Henryville, Indiana produced 175 MPH winds and the El Reno, Oklahoma tornado on May 31, 2013 saw winds of 296 MPH. These storms both left wide paths of destruction with nothing standing.
The Federal Emergency Management Agency (FEMA) has developed criteria for safe rooms which provide “near-absolute protection” in the event of extreme winds. These rooms are designed above and beyond standard building codes to preserve life in the event of a tornado or hurricane. Two FEMA documents provide guidance for engineers, architects and users regarding safe rooms: FEMA 320 and FEMA 361. FEMA and the National Storm Shelter Association (NSSA) have also worked with the International Code Council (ICC) to develop the Standard for the Design and Construction of Storm Shelters (ICC-500).
Debris impact testing was recently conducted at Texas Tech University to determine the wind resistance of various building materials. The standard criteria according to ICC-500 is that a safe room must stop a 2×4 traveling at 140 mph. Reinforced concrete was able to comply at only 4″ thickness.
In areas where a high-wind event is a possibility, a concrete structure such as the ECO-SPAN® storm shelter can be a life-saver. These structures may be installed above or below grade and on the interior or exterior of a building.
This post is based in part on a recent article in the National Precast Concrete Association’s (NPCA) Precast Solutions Magazine, Fall, 2013 edition titled “Precast Concrete’s Resistance to High-Velocity Projectiles” by Evan Gurley.