The Simple Structural Solution for Surviving Tornadoes

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Wednesday, May 21st, 2014
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Saving more structures and lives when tornados strike could be as simple as addressing the weak link of lightweight garage doors, according to a study led by researchers from the University of Alabama.

The new report presents findings from the performance of critical facility buildings and residences following the May 20, 2013 tornado that struck Moore, Oklahoma.

The Enhanced Fujita (EF) 5 tornado created a 17-mile long swath of destruction which levelled over 12,000 buildings and killed 24 people. The total economic loss from this single event was estimated at $3 billion.

The mortality rates from tornado events have not decreased in years, while building damage and overall economic losses continue to grow, said the report. New methods are needed to improve engineering design and construction practices in tornado-prone areas. In addition, revision of structural retrofit practices need to be considered for mitigating future losses from tornadoes.

Surviving a tornado in a wood-frame residential home is enhanced by an intact roof and standing walls, but lightweight garage doors can allow high winds and pressure changes into a home that can lead to the removal of the roof and collapsed walls.

“Once the roof over the garage is blown off, there usually is a significant hole into the main portion of the house,” said Dr. Andrew J. Graettinger, associate professor of civil, construction and environmental engineering and lead author of the report.

“We need to consider the building components that are the starting points for damage that lead to loss of life, injuries and economic loss during a tornado. If we engineer for these weak areas, we can start keeping these buildings together during all but the strongest winds a tornado can produce.”

The research builds on initial investigations launched in 2011 to study damage left in the wake of massive tornadoes in Tuscaloosa and Joplin. The goal is to better understand the forces generated by large tornadoes and the distribution of wind force across a tornado’s path, as well as to make recommendations for design code improvements and general safety guidelines.

From the data collected in 2011, the researchers concluded that light-frame wood structures are unable to withstand a direct hit from the forces of powerful EF4 or EF5 tornadoes which produce winds stronger than 166 miles per hour.

However areas on the edges of those systems could see dramatic improvements in safety and overall structure through better engineering design and construction practices. The 2011 tornado study concluded that applying techniques to build homes against hurricanes is probably the easiest, low-cost solution to strengthening homes against lower-wind speed tornadoes, and safe rooms and shelters are needed to save lives for those in the centre of a tornado.

The study of the tornado in Moore reinforced that conclusion and vindicates recent research methods of tornadoes in laboratories and numerical analysis. It also led to further investigation of garage doors, especially on garages that extend from the house. According to the Moore damage assessments, in areas with lower wind speeds, the root of failure for residential structures was often the garage.

Below Ground Shelter

Below ground shelter

In addition to the findings on garage doors, the team found more use of residential shelters in Moore than in similar studies in Tuscaloosa and Joplin, Missouri. This is likely because the tornado in Moore a year ago was the third major tornado to strike the city since 1999. The conclusion of the study is simple: below-ground storm shelters and above-ground safe rooms protect against the worst storms and save lives.

During the research in Moore, social media was used to identify locations to survey damage. It was a novel approach that helped locate the best places to study structural damage, said Dr. Laura Myers, senior research social scientist at The Center for Advanced Public Safety at UA.

“Not only does this assist with the research process, but it also helps establish a community network for storm damage recovery,” Myers said. “Once recovery begins, this community network becomes integral in documenting what the infrastructure strengths were, such as storm shelters, and what needs to change, such as better building codes, to help the rebuilding process.”

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