AMS Journals Online - Tornado Damage Survey at Moore, Oklahoma

American Meteorology Society Journals Online - Tornado Damage Survey at Moore, Oklahoma

After the May 3, 1999, Moore / Midwest City tornado, the Wind Science and Engineering Research Center at Texas Tech University conducted a damage survey to determine the causes of structural failure. The team found that methods of construction -- joining roof to walls to slab -- permitted by code were inadequate to handle structural loads caused when the wind lifts up the roof. When a home is destroyed by a tornado, it becomes a collection of projectiles that the tornado can use to destroy the next house. Even if you build a sturdier house, it can be destroyed by the whirling remains of the shoddy home next door. The team was disappointed to learn that new houses being built after the tornado failed to incorporate improvements that would make the structures more resilient to high winds.

"Although it is true there are no provisions in building codes to construct houses to resist tornadoes, building codes are still important in mitigating tornado damage. A better-built house would yield less debris in a tornado, and occupants would have a better chance of surviving in such a house. In addition, structural improvements could reduce the level of damage to a house that experiences weaker tornadoes or straight-line thunderstorm winds that are just above code-required design levels and hence could mitigate economic loss and improve safety."

"As noted from our damage survey, numerous housing failures initiated with destruction of attached garages. In a typical case, garage doors blew in, allowing internal pressures to act in combination with external aerodynamic uplift pressures to remove the garage roof structure. Uplift on the roof structure caused toenailed connections in the wooden top plates to pull apart. Destruction of the attached garage frequently led to damage or the removal of the remaining roof structure on the residence."

"When the author visited the post-tornado reconstruction area, 6 of the 40 new houses contained tornado shelters or safe rooms; however, these homes generally were not built any better than prior to the tornado. Thus, homeowners appeared to be making the decision to provide for personal safety (i.e., building a safe room) instead of to increase housing strength (to provide property protection and increased safety). This decision may, in part, be based on the assumption that it is unreasonable or uneconomical to try to construct houses for the high wind speeds described on the F scale."