Scouring concrete in a tornado

[Danny Neal]

What are the processes involved in the scouring of concrete from a tornado? I was thinking about it after I watched the famous video from the TX nader. I was just wondering how it happens? Is it simply a vortex lifting the pavement like debris? Or is it more complex where as air pockets are exposed and causes one section to lift and its like a chain reaction as the storm moves over. Its 3 AM, I am just brain storming. For all you construction engineers out there, this ones for you.

 

[Jerry Prsha]

What are the processes involved in the scouring of concrete from a tornado? I was thinking about it after I watched the famous video from the TX nader. I was just wondering how it happens? Is it simply a vortex lifting the pavement like debris? Or is it more complex where as air pockets are exposed and causes one section to lift and its like a chain reaction as the storm moves over. Its 3 AM, I am just brain storming. For all you construction engineers out there, this ones for you.

I think about things like this when I hear about the "TIV." ...Storms tipping over train engines and such...

 

[Paul Austin]

I think often pavement scouring is the result of debris within the tornado being raked over the pavement's surface, like a massive powerful sand-blaster. I don't know if this is always the case, but I believe it accounts for scouring much of the time.

 

[Danny Neal]

I think often pavement scouring is the result of debris within the tornado being raked over the pavement's surface, like a massive powerful sand-blaster. I don't know if this is always the case, but I believe it accounts for scouring much of the time.

That makes sense and I could see that being legitimate. I can't remember if the new scale mentioned anything about concrete being scoured or not.

 

[Bobby Prentice]

What are the processes involved in the scouring of concrete from a tornado? I was thinking about it after I watched the famous video from the TX nader. I was just wondering how it happens? Is it simply a vortex lifting the pavement like debris? Or is it more complex where as air pockets are exposed and causes one section to lift and its like a chain reaction as the storm moves over.

To my knowledge and experience, tornadoes don't scour (lift/remove) the concrete from a roadway or home foundation. Concrete is too dense and too cohesive to become airborne and its base is often embedded under the ground where the wind can't impart lifting forces on it. Smaller chunks of concrete? Perhaps. Large sections of roadbeds and home foundations? No.

However, it only takes a strong (F2/3) tornado to scour asphalt from a roadway. I've observed tornadoes scour asphalt from roadways numerous times. The Dimmitt, Texas tornado (June 4, 1995) and Kellerville, Texas (June 8, 1995) were both good examples of this. After all, when used for a road surface, asphalt is just gravel held together by sticky oil. The key is that the winds are able to get under the asphalt which allows lift to trigger a chain-reaction that leads to catastrophic failure within a section of the road bed. The effect is sort of like placing a butter knife (the "wind") horizontally under a bed of Rice Crispy treats ("asphalt") sitting on a flat baking pan ("road bed"), pushing the butter knife and lifting up ("scouring") a section of the treats.

Asphalt

Here is an example of a tornado scouring an asphalt road bed in Webster County, Georgia on March 1, 2007:

Zoomed image:[FONT=arial,helvetica,sans-serif]Webster County, Georgia Tornado Road Damage [/FONT](NWS)

Notice that the "strongest tornado every recorded" (Bridge Creek/Moore, OK F5) did not scour (lift/remove) the concrete road when it crossed I-44 near Newcastle, Oklahoma on May 3, 1999.

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[Greg Stumpf]

Notice that the "strongest tornado every recorded" ((Bridge Creek/Moore, OK F5) did not scour (lift/remove) the concrete road when it crossed I-44 near Newcastle, Oklahoma on May 3, 1999.

However, the 5/3/99 tornado scoured asphalt from a county road 1-2 miles SW of Bridge Creek. I have a sample of that pavement peel in my office at the NWC (along with a sample of the Dimmitt 6/2/95 peel).

 

[Danny Neal]

I am sorry I should have clarified....asphalt instead of actual concrete. That's what I meant to say. The fundamentals that Bobby mention about section by section air pockets I meant to say for asphalt being removed.

 

[Jason Foster]

Good point, some further.

Bobby's point and analogy was right on. And to further the concrete point:

Unlike asphalt, concrete has a WWM (Welded Wire Mesh) usually of 4" square mesh that is withing the concrete bed when it is poured. Many of the new techniques for building concrete highways has significantly improved of the past few years. They build them more quickly, with great strength, and continuous reinforcement.

The other thing to consider, is that with the extreme winds and debris, there is a chance that the impact of some items against any road might break up the surface to allow for the wind to then lift up on the surface. There could also be a vacuum affect, as with an airplane wing, that anytime there is more airflow overtop a surface vs. below the surface it will produce lift. I'm sure someone with a better physics background can elaborate further, but that's the basic point.