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Poor construction likely a factor in extent of late-December tornado damage in Dallas area, expert says

An expert found that poor construction may be a factor for the extent of damage during late December tornadoes that ravaged the Dallas area.

Haag Engineering Co. Structural Engineer and Meteorologist Tim Marshall, who has conducted hundreds of damage surveys after severe weather events across the United States, examined the damage after the Dallas area tornadoes.

In determining whether the damage is from poor construction or the tornado itself, Marshall looks at three factors: anchors, braces and connections.

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"There are three critical areas for connections: wall to foundation, wall to wall and roof to wall," Marshall said. Using anchor bolts, straps and solid wall sheathing can help improve construction and make structures more durable during extreme weather events like tornadoes.

"The [Dallas area] tornado exploited poor connections by tearing away roofs and toppling walls," Marshall said.

"We found 'cut nails' used around the perimeter of the house to secure the wall bottom plate to the foundation. Still, more homes were attached by shot pins. Some homes [were] anchored with bolts [that] did not have nuts or washers to secure the wall," Marshall said.

Other faulty constructions included an elementary school in Glenn Heights where walls were not attached properly, Marshall told the Dallas Morning News.

The strong tornadoes that tore through the Dallas area in late December were both deadly and destructive.

Garland, Texas, a town located just northeast of Dallas, was hit by the strongest tornado of the outbreak on Saturday, Dec. 26. The National Weather Service (NWS) rated the tornado as an EF4, the second strongest classification of tornadoes with winds up to 200 mph.

Several homes were completely destroyed by the tornado, leaving some people trapped and injured in their homes until fire and rescue crews were able to arrive at the scene.

Another strong tornado, rated an EF3 with winds up to 165 mph by the NWS, damaged at least 600 homes and injured at least 23 people in Rowlette, Texas.

The tornadoes that touched down around the Dallas area led to at least 11 deaths and dozens of injuries, according to the Associated Press.

Building codes in the United States are not geared for extreme weather events such as tornadoes because of the rarity in which they occur, according to Marshall. Buildings, outside of hurricane-prone areas, are typically designed for winds of 90 mph lasting for three seconds at 10 meters above the ground.