April 20, 2017

Best Practices in Tornado Resistant Construction - Utilize ICB in a Continuous Load Path

Tornado-resistant construction is essential in the United States where an average of 1253 tornadoes occur annually and can produce wind speeds of more than 200 mph. Because tornadoes are unpredictable and violent, their destruction is often widespread. According to the National Oceanic and Atmospheric Administration (NOAA) tornadoes cause an average of 60-65 fatalities and 1,500 injuries each year. Tornado Alley is hit particularly hard by the occurrence of tornadoes. Tornado Alley is unofficially a region from central Texas, northward to northern Iowa, and from central Kansas and Nebraska east to western Ohio. It is a region where cold, dry air from the northwest, warm dry air from the southwest, and warm, wet air from the southeast clash. The collision of these three weather systems frequently results in intense thunderstorms and violent tornadoes. In Texas alone, between the years of 1991 and 2010, there was an annual average of 155 tornadoes, more than any other State. In addition, Texas averages annually 2.8, EF-31 to EF-5 tornadoes. Tornado resistant construction is essential for the protection of a building and its occupants from disastrous outcomes during a tornado emergency.

A Continuous Load Path Protects a Building's Integrity When Under Attack from a Tornado

FEMA highly recommends a safe room for maximum safety to a building's occupants during a tornado emergency. However, a tornado-resilient design of the entire building is ultimately the best protection of lives and the structure. A continuous load path is the best defense towards holding a building together when the high winds of a tornado try to pull it apart. The continuous load path ensures that when a load, including lateral (horizontal) and uplift loads, attacks a building, the load will move from the roof, wall and other components toward the foundation and into the ground. A strong continuous load path is essential to holding the roof, walls, floors and foundation together during a tornado or other extreme wind event.

Insulated Concrete Blocks Build Tornado Resistant Buildings

Buildings constructed with insulated concrete blocks (ICB) maintain their integrity during the intense winds of a tornado. Insulating concrete blocks can withstand winds of over 200 mph. Buildings constructed of concrete blocks are much stronger than wood and steel-framed buildings under severe wind events. In fact, a study published by the Portland Cement Association (PCA), compared the structural load resistance of insulating concrete form (ICF) walls to conventionally framed walls. The study concluded that concrete walls have a much higher structural capacity and stiffness to resist the in-plane shear forces of high wind than wood or steel framed walls. The strength of concrete walls results in less lateral twists and damage to non-structural elements of a building such as the plumbing and electrical. Utilizing insulated concrete blocks for tornado-resistant construction can maintain a building's integrity during a strong tornado event.  

Insulated concrete blocks (ICB) can also resist damage from flying debris traveling over 100 mph.  A study by Texas Tech University compared the impact resistance of wind driven debris between ICF walls and conventionally framed walls. The study found that ICF walls resist the impact of wind driven debris. Conventional framed walls, however, failed to stop the penetration of airborne hazards. Insulated concrete walls are the best protection from windblown debris to a building and its occupants.

The Bautex Wall System Stands up to a Tornado’s Strength

The Bautex Wall System has the strength to resist the heavy winds and flying debris of the strongest tornado. The Blocks meet the Federal Emergency Management Agency FEMA 320 and FEMA 361 guidelines in storm zones with wind speeds up to 250 miles per hour. The Bautex Block also has the strength and mass to resist the impact to wind driven debris at speeds greater than 100 mph. In addition to severe weather resistance, Bautex Blocks have the thermal performance required by the IRC and IBC and are fire-rated, noise-reducing, and easy to install. Bautex Walls are a good choice when designing for tornado-resistant construction.

The National Weather Service Ratings of Tornadoes - EF-Scale

In 2007, the National Weather Service implemented the “Enhanced Fujita Scale (EF-Scale). The scale determines a tornado's strength based on the destruction it caused. The scale ranges from one to five, with five being the most intense. The EF-Scale considers 28 damage indicators such as building type, structures, and trees. Each damage indicator has eight degrees of damage ranging from the beginning of visible damage to complete destruction of the damage indicator.

A safe room is a space within or nearby a building, that provides near perfect protection during tornadoes and hurricanes, according to FEMA guidelines. A FEMA safe room is designed and constructed as specified in FEMA P-361, and FEMA P-320.