The mile-wide EF5 tornado that struck Moore, Oklahoma was partof a succession of 22 tornadoes that spun across six states on Monday. This camejust one day after a northeast-moving storm from Texas to Minnesota produced about300 appearances of hail and high winds.

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Though it's too early to draw accurate or justifiablecomparisons, current scenes from Moore look eerily familiar to the devastation foundin Joplin almost two years ago, when an EF5 tornado ripped throughthe Missouri town. Far less deadly than the Joplin twister—whichclaimed 161 lives while injuring hundreds more—Monday's tornado inMoore, Okla. similarly carved a path through a heavily populatedswath of the city.

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Related Slideshow: All About Tornadoes

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So what kind of structural damage can insurers expect? Moreover,could they be similar in magnitude to the Joplin disaster, whichgenerated $2.8 billion in claims? We consulted two engineers at EFIGlobal, Inc. to find out—Shawn Johnson, PE, a seniorcivil/structural engineer, and David P. Amori, PE, RRC, a senior structural and geotechnicalengineer and senior district manager. Here's what they had to sayin the immediate aftermath of the tragic events this week.

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Explain the general types of damage we can expect to seefrom the tornado that collided with Moore, Oklahoma on Monday,especially given its width and force.

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Johnson: Home or property owners often thinktheir house or building may have been hit by a tornado. Inreality, there is typically no doubt when your house or building ishit by a tornado because of the devastating damage. Sometimes,a tornado behaves in a near-sentient way, taking out a long row ofbuildings and/or homes, lifting off the ground for a moment,effectively skipping over one or more structures, then touchingback down to continue its destruction. In the process, thehome that was “skipped” suffered minor damage to its roof, whileits neighbors' roofs were completely blown away.

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Some reports indicate the Moore twister was 1.3 mileswide at its peak and an EF4 or EF5. What are some typicaldamages—in terms of scale and area affected—insurers could see fromsuch a powerful storm?

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Johnson: The general types of damage resultingfrom a powerful tornado can range from denuded trees and minordisplacement of shingles to total destruction of every building inthe vicinity. Based on initial reports of the Moore, Okla.tornado being an EF4 or higher, homes and buildings at or near thepath of the tornado's eye will likely have suffered totalloss. Properties farther out from the eye will naturally havesuffered gradually diminishing damage with the distance away fromthe eye.

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Specifically, in or near the path of the eye of an EF4 tornado,one would expect to see devastating damage, includingwell-constructed houses destroyed, some structures lifted fromfoundations and blown away, as well as cars and other large debrisblown away. Just to the right or left (relative to itsdirection of movement) of the path of the eye and its eye wall,damages would likely be more similar to an extreme wind event,including but not limited to shingle damage, breaches in thebuilding envelope, impact damage from flying debris, electrical andmechanical failures, and above-ground plumbing failures.

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Have building codes evolved since an EF5 tornado struckthe same area in 1999? What building codes are in place tomitigate loss from tornadoes?

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Amori: There have been significant changes tothe Building Code Requirements that are adopted by most U.S.municipalities with respect to how wind forces are calculated andapplied to the design of new buildings. This affects newconstruction but seldom (depending on the local municipality) isthe change retroactive; so it does not affect existingbuildings.

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There is more bad news: Even though in general the building coderequirements have been ramped up in recent years, the codes arebased on statistical probabilities of peak wind gusts, not actualtornados. For example, the latest codeprovisions (ASCE 7-10) would require designing for 120mile-per-hour (mph) wind for structures in central Oklahoma wheremore than 300 people congregate. Tornados can produce winds as fastas 200 mph (EF4), or even higher. Because forces acting on astructure are exponentially related to the wind velocity, this80-mph difference would require almost three times more lateralload resistance.

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The simple fact is that almost all buildings are not designed towithstand tornados. Tornado resistant construction would be anowner driven requirement and typically not that of a municipalityor national building code. From a life-safety standpointcommunities in tornado prone areas often have selected buildingsdesigned to withstand tornado related forces that serve ascommunity tornado shelters. This allows for an economicallyfeasible solution for this type of construction.

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