Engineering study shows wind speeds below 135 mph caused majority of damage in Joplin

Engineers said many of the homes destroyed were built 30 or more years ago.

SPRINGFIELD, Mo. -- An investigative team of engineers affiliated with the American Society of Civil Engineers found EF-2 winds, not EF-4 or EF-5, caused more than 80 percent of the damage in the Joplin tornado in May 2011.

The twister had a 22-mile-long path, and it took out 7,000 structures.  However, the new study shows only 4 percent of the damage in Joplin could be linked to a EF-4.  None of the damage could be linked to an EF-5, even though the twister reached EF-5 wind speeds at some points.

"It was surprising, just from the scope the extent of the damage," said Ben Jennings of J & M Engineering in Springfield.

Jennings is one of the engineers who surveyed neighborhood after neighborhood in Joplin.  He said many of the houses he saw were built in the 1980s or before.  Some of them were simply resting on blocks or slabs similar to mobile homes.

"The only thing you've got connecting your house to your slab is a little bitty nail," Jennings said.

New homes are typically built to withstand 90 mile per hour winds, but that is not what engineers found in Joplin.

"A lot of the structures that were destroyed, we would never be able, from an engineering standpoint, to even show that they worked for 90 mph winds," Jennings said.

Engineers said some of the biggest lessons learned from Joplin should apply directly to new home construction. They would like to see metal fasteners applied to roofs and better anchoring for foundations.

"The hurricane ties (metal fasteners) are a couple of bucks a piece," Jennings said.

A recent study conducted by the American Plywood Association for the State of Georgia showed the cost of making those changes, to keep a roof better attached to the house and the house better attached to its foundation, would be less than $600 for a 2,100 square foot ranch-style home.  Jennings said those changes would potentially be life-saving.

"You wouldn't have a window left anywhere, and you'd likely still have holes in roof, but your odds of not having the thing fall down on you would be greatly improved," Jennings said.

Engineers say the study shows the importance of having access to a basement or storm shelter for emergency situations.  Jennings said the best storm shelters are tested to withstand wind as well as the impact of flying debris.