Anatomy of a Tornado: How Garage Doors Fared in the November Twisters
© 2002 Door & Access Systems
Publish Date: Winter 2002
Author: Tom Wadsworth
Anatomy of a Tornado:
How Garage Doors Fared in the November Twisters
On Nov. 10 and 11, 2002, swarms of tornadoes ripped through several Midwestern and southern U.S. states, killing at least 36 people and injuring 200. The storms set a record for tornado fatalities occurring in the month of November.
One of these tornadoes left a path of destruction through northern Summit County, Ohio. Joe Hetzel, DASMA technical director, inspected three different areas on Nov. 13 to analyze how garage doors performed in the storms. One of the areas is represented in the accompanying photograph that appeared in the Cleveland Plain Dealer on Nov. 12.
Here are Hetzel's observations about what happened to each house and garage door in the photograph:
Unique Tornado Winds
Hetzel says tornadoes produce conditions and winds that are unique. Two such conditions were evident in the photograph.
The first was the horizontal rotating winds in the tornado itself. The highest winds in this tornado were reported in the range of an F2 (113-157 MPH sustained wind).
"The tornado's rotation-type winds are clearly evident in the damage," says Hetzel. The photograph, he says, reveals that the wind was "pushing" on garage doors located on the right (2, 3, and 8) and "pulling" on garage doors located on the left (1 and 7.)
The second aspect was the tornado's "updraft" or suction-type effect, which can cause a structure to explode or collapse, says Hetzel. He notes that houses 1, 5, and 8 appeared to suffer powerful updrafts.
Structures 2, 3, 4, 6, 7, and 9 sustained damage from high winds. But since less damage was evident, these buildings appear to have been outside or on the outer fringe of the tornado.
Hetzel says the probability of any structure being struck by a tornado is relatively low. He also says that powerful tornado updrafts and wind speeds in an F2 tornado are beyond the scope of any building code.
Good Advice for Dealers
However, Hetzel recommends that dealers should:
1. Know the local code wind requirements. DASMA Wind Load Guides, found at www.dasma.com and on Technical Data Sheet 155, can be useful tools.
2. Select the appropriate garage door product. Products enrolled in the DASMA garage door label program (begun on Jan. 1, 2003) will help to identify a garage door's wind load capabilities.
3. Install the product to the manufacturer's instructions. To protect the door's intended structural strength, dealers must properly install the required fasteners, horizontal struts, and other hardware.