Tornadoes and Concrete

[Simon Timm]

In the fujita and advanced fujita scale, (E) F5's are defined as severely damaging reinforced concrete. I personally have never observed this occurring(though I live in Wisconsin and I have only observed weak tornadoes), I have only seen pictures and read a few reports of reinforced concrete being severely damaged.

Here is one case in Wichita Falls tornado, where steel Reinforced McNeil high school was destroyed

http://www.srh.noaa.gov/oun/wxevents/19790410/burgess.php

In what tornado cases have you observed the destruction of a steel-reinforced building?

[Jason Foster]

"McNiel Junior High, a new concrete/steel-reinforced building was not built well enough to provide safe shelter from the tornado. The Southwest National Bank Building was totally destroyed except for its concrete vault, a proxy for an above-ground shelter." -- Quote taken from link.

I think the idea here was that the structure of that particular building was not enough. In general, concrete reinforced with typical rebar in a wall of about 8" thick or more, and having a surface area that is not expansive enough will withstand high winds included and F4 or F5. It is true, as the report indicated that not all wall, even concrete reinforced one, will withstand 200+ mph winds. It is important that any structure that is designed to survive such conditions have the least about of surface area perpendicular to the strongest winds. smaller structures or thicker walls may be required.

I'll look into deeper, maybe add more later. Perhaps you can pose this question to Tim Marshall, a structural engineer, and known tornado damage analyst, who can comment further. I'm an architect and have limited detailed knowledge on the subject.

[shane turner]

I believe the high school in Greensburg was made out of three layer concrete load bearing walls and mortar and about two-thirds of that building was completely destroyed. I also believe the Parkersburg tornado completely destroyed a steel-reinforced structure.

[Greg Higgins]

Back on 10 Apr 1979, I was a brand new EMT (hired as we watched the tornado come through town) and one of the "high" moments of the evening is when we got to the Southwest Bank and discovered survivors where we were sure we would find victims. I know there are pictures that exist of the vault and as I recall, there was a hadite block wall around 2 sides of the vault, which itself was steel.

Greg Higgins

[Dennis Sherrod]

I am not sure if this may be helpful to look into or not. March 1, 2007, a low end EF-4 struck Enterprise, AL. partially destroying a concrete / brick high school killing 9 students. I have not looked into the exact construction, but do know that some of the high school was destroyed. There may be some useful info from that.

[scott r currens]

I've never heard of steel-reinforced concrete losing its structural integrity as a result of a tornado. I'd bet that any steel-reinforced concrete buildings that were destroyed in a tornado were not destroyed as a result of the steel-reinforced concrete losing integrity. I seems more likely that windows, roof's, and non-reinforced walls are what failed with in those structures. If I am wrong I would love to see images of that damage.

[Simon Timm]

I did find this image of what looks like a warehouse in Memphis Tennessee that was destroyed by the tornado this year

http://www.flickr.com/photos/mckeephotographer/2705536226/sizes/l/

[shane turner]

I believe Simon that the Oakfield, Wisconsin F5 tornado on July 18, 1996did some very intense damage although it was pretty narrow. I think it cleaned four homes that were very well-built off their foundations and in addition I believe it bent or snapped rebar from the base of one of the homes foundation.

[Dann Cianca]

It would be interesting to see if similar buildings would fare the same in different debris situations, i.e. just vegetation or a lot full of cars. There's an obvious assumption ...

[mike scantlin]

I believe Simon that the Oakfield, Wisconsin F5 tornado on July 18, 1996did some very intense damage although it was pretty narrow. I think it cleaned four homes that were very well-built off their foundations and in addition I believe it bent or snapped rebar from the base of one of the homes foundation.

I couldn't imagine rebar being snapped by winds alone.

I'm sure any damage done to steel re-enforced structures would be done by large debris, not the winds.

Kind of off-topic, but how does this play into the Ratings?

* Let's say there's a Large tornado out in a field. In this field, there is a car and a steel re-enforced wall. If the tornado, not capable of destroying the wall alone, throws the car into the wall knocking it to the ground, how is this rated?

I know that it's still the tornado causing the damage, I'm just wondering what thought processes go into rating damage like this.

[Jeff Duda]

I couldn't imagine rebar being snapped by winds alone.

I'm sure any damage done to steel re-enforced structures would be done by large debris, not the winds.

Kind of off-topic, but how does this play into the Ratings?

* Let's say there's a Large tornado out in a field. In this field, there is a car and a steel re-enforced wall. If the tornado, not capable of destroying the wall alone, throws the car into the wall knocking it to the ground, how is this rated?

I know that it's still the tornado causing the damage, I'm just wondering what thought processes go into rating damage like this.

Sounds like the beginning of a philosophy discussion titled, "If a tornado breaks a tree in the woods and no one is around, did it make a sound?" :)

[S. McMullen]

I remember one of the first chase videos I got was "Chasers of Tornado Alley". In the video, Greg Stumpf comes across a concrete road that had been peeled back by a tornado. I don't recall if it was steel reinforced like a highway or an interstate though, maybe if Greg were reading this he might be able to explain.

[Greg Stumpf]

I remember one of the first chase videos I got was "Chasers of Tornado Alley". In the video, Greg Stumpf comes across a concrete road that had been peeled back by a tornado. I don't recall if it was steel reinforced like a highway or an interstate though, maybe if Greg were reading this he might be able to explain.
IIRC, not having watched the program in many years, I was referring the asphalt peel on Hwy 86 just east of Dimmitt, TX on 2 June 1995. I have a portion of the peeled asphalt in my office, and it was about 3" thick. The specimen is next to another asphalt peel I collected from 3 May 1999 SW of Bridge Creek, OK. The Bridge Creek asphalt was about 1.5" thick.

Neither were steel reinforced concrete roads. I have never witnessed a concrete road "peel", and I would suspect it would be extraordinary given the theoretical upper limit for tornado wind speeds.

Other asphalt peels I have witnessed were in Jarrell, TX (5/27/97), Kellerville, TX (6/8/95). Both were about 1.5" thick as well. I did not collect specimens of those two events.

[Stephen Levine]

Monolithic Domes are rated for F-5 tornado damage and are proven to be safe tornado and hurricane proof homes.
For more information, go to their web site www.monolithic.com.

I once saw a picture on their site of a dome home that took a direct hit by a tornado. A telephone pole was laying against the roof. There was zero damage to the structure.

Someday I would like to build one.

[shane turner]

Yeah I am no expert but would think it would take more than windspeed alone to snap rebar. I think it would have to be blasted with debris and winds to do that type of damage. I still think that even that still would take a violent tornado to do that type of damage to rebar on the foundation of a well-built home.

[Greg Higgins]

Let me preface this by saying that I have not witnessed this, but one thing that comes to mind is that rebar is "tied" together with wire. IF, and I say IF, the concrete wall, be it solid concrete or a block wall, was either poorly constructed (i.e., the concrete mix was inadequate, not cured properly, etc) or damaged by flying debris, then I think it would be possible for the rebar to appear that it had snapped when in reality, the wire tie simply did not maintain its integrity and "released" the 2 pieces of rebar, thus appearing that the rebar had failed.

As for steel buildings, I have seen these fail due to not enough connections (nuts and bolts) holding the pieces together. This is a builder failure and not a construction failure. In other words, if the assembly had been constructed properly, it would not have failed.

Greg Higgins

[Jason Foster]

I did find this image of what looks like a warehouse in Memphis Tennessee that was destroyed by the tornado this year

http://www.flickr.com/photos/mckeephotographer/2705536226/sizes/l/

This photo illustrates some interesting things. While it obviously demonstrates that a simple concrete wall does not make for a safe structure. In evaluating the photo, it looks to be a warehouse type building that had truck docks. The building was like an exposed steel structure, with concrete walls. This was NOT a concrete reinforced building. The concrete wall seem very thin in comparison to it's height...perhaps 6", yet 25' tall or more. I suspect the rebar shown was only to maintain the structure of the wall itself and was not weight bearing. I suspect there was internal steel wide flange columns that acted as the building skeleton structure. That failed as shown in the photo with the amount of debris located within the building. I also suspect that there were some rather large spans to the roof and could not withstand the wind load during the tornadic event.

Overall, more study as to building structures and severe weather events is warranted. As an architect, I'm paying more and more attention to this every chase.

[Rob Herman]

Let me preface this by saying that I have not witnessed this, but one thing that comes to mind is that rebar is "tied" together with wire. IF, and I say IF, the concrete wall, be it solid concrete or a block wall, was either poorly constructed (i.e., the concrete mix was inadequate, not cured properly, etc) or damaged by flying debris, then I think it would be possible for the rebar to appear that it had snapped when in reality, the wire tie simply did not maintain its integrity and "released" the 2 pieces of rebar, thus appearing that the rebar had failed.


I believe the wire ties are simply there to hold the reinforcing steel in position until the concrete is placed, not for structural integrity.

[Greg Higgins]

Rob you are exactly right. I was not referring to the wire ties providing structural integrity, but rather holding the rebar in place. Once the concrete has cured, the wire ties serves no purpose. However, if the concrete wall was compromised by flying debris (check out the Texas Tech Wind Damage Assessment tests) then the concrete could break away exposing the rebar (I've seen this numerous times during demolition and at high explosives testing). If this occurred near where 2 pieces had been held together with the wire ties, some folks may think that the storm damage "snapped" the rebar.

Jason, what you are referring to is "tilt wall construction", a pain in the back side of the fire service as this type of building tends to fail very quickly in a fire situation. My comments regarding "lack of" or "poor" connection points are readily seen in these buildings. You can research damage due to high winds and find many examples of this type of construction falling / failing under moderate wind conditions. You might also check out "Building Construction for the Fire Service" by Frank Brannigan; an excellent resource of how buildings are constructed and fail.

[Simon Timm]

Can regular poured concrete (excluding concrete block and base foundations) be severely damaged in strong tornadoes?

[craig buchanan]

Can regular poured concrete (excluding concrete block and base foundations) be severely damaged in strong tornadoes?

The answer to this really depends on your question. The simple answer is YES. The more complex answer comes down to what a tornado actually is in the real world. The rapidly moving wind even at the top end probably would not tend to harm concrete. Tornado's are very seldom just wind. They are more closely related to a blender with stuff thrown in. The wind is OK. All the little bits is what can "erode" the concrete or puncture it with something.

[Heidi Farrar]

For what it's worth, here (http://mesonet.agron.iastate.edu/cases/080525/dmx_parkersburg_damage/IMG_2011.JPG) is a photo of damage at Parkersburg that shows snapped rebar. I had originally posted this in the 5/25/08 DISC (http://www.stormtrack.org/forum/showthread.php?t=16587&page=5) thread. This of course still doesn't answer any questions regarding whether this was really caused by just wind or by a wind-debris combination... but it's obviously something that caught the survey photographer's eye. (Larger storm damage catalog found here (http://mesonet.agron.iastate.edu/cases/080525/dmx_parkersburg_damage/).) Also, if I am not mistaken, this (http://mesonet.agron.iastate.edu/cases/080525/dmx_parkersburg_damage/IMG_2077.JPG) appears to be asphalt plastered to a power pole (again, for what it's worth).

[david diehl]

Heidi,
from what I can see of that Re-bar is that it was snapped off before the tornado damaged the building, it appears to me that there is rust on the segment that should be shiny due to the snap-off.

[Rob Herman]

Also, if I am not mistaken, this (http://mesonet.agron.iastate.edu/cases/080525/dmx_parkersburg_damage/IMG_2077.JPG) appears to be asphalt plastered to a power pole (again, for what it's worth).

Does look like asphalt, but I think its just mud.

[Greg Higgins]

The pictures of the hadite block wall shows that the wall was not constructed to any type of specification. A kink in the EF scale ratings is that the construction was built to code.

[Heidi Farrar]

Heidi,
from what I can see of that Re-bar is that it was snapped off before the tornado damaged the building, it appears to me that there is rust on the segment that should be shiny due to the snap-off.

Yeah, I noticed both the rust and how that smaller piece is just laying there beside the part that's still in the block. The presence of that photo in the larger catalog does seem to imply that the survey team placed some level of significance on that example, but now I wonder "of what significance" did they intend it to mean? Did they want to show that there was a structural defect? or did they just see snapped rebar and become captivated by it? We'll probably never know, but it is pretty intriguing.

On closer inspection, that does look like mud, now that you mention it, Rob. I must have still had Greg's asphalt-peeling story in my mind when I saw that photo a while ago; I had noticed it back when the photos were released and it never occurred to me that it was asphalt then. I guess it just goes to show how things can seem when your mind is in a certain place (which may also explain what happened with the survey team and the rebar...)