Tilt-Up Failure During Tornado

[JedClampett]

I was looking at something else and ran into this. Maybe it's been mentioned in this Forum already. It's a pretty well thought out article, but I guess I disagree with the whole premise. I doubt tilt-up is more likely to fail than other building systems, but when it does, it's pretty deadly.

 

[MikeHalloran]

Did you find a followup about what Home Depot actually built to replace the failed structure?

I'm thinking that the apparent success of interior structures in saving lives in nearby large span buildings probably had more to do with their interior location, away from falling tilt-up panels, than with being made of concrete block, or any other material.

I should note that wind-related changes to the building code in South Florida have not noticeably affected the rate of new construction, and a lot of new construction is tilt-ups.

As for wind-resistant construction, I wonder how big an increment in construction cost would accrue if the code required the walls to stand in the absence of a roof?

Or if the code just required resistance to say 150 mph winds, or 200 mph winds, or X00 mph winds, how many fewer people would die in tornadoes, and how much would building costs increase? That seems like a logical problem to pose to an engineering/ actuarial/ econometric team, say at a university, instead of just declaring that tornado resistant buildings are too expensive or technically impossible to achieve. There must be enough historical data available to construct at least a crude parametric model.





Mike Halloran
Pembroke Pines, FL, USA

 

[hokie66]

Structures like big box stores can't be expected to withstand the worst of tornadoes. That said, I don't like bearing wall tiltup structures. There are too many conflicting requirements of the connections. Connections of the roof structure to the panels, and also panels to panels, need to be robust in order to resist applied forces. But if too robust, deflection of the steel and shrinkage of the concrete can and often does cause distress in the concrete in the vicinity of connections. My preference is for a steel portal frame in one direction, with the tilt panels used as cladding and shear walls only. With that type system, there are still issues with connection detailing, but not of the same magnitude in terms of collapse. Load bearing tilt up is cheap, therefore its popularity.

 

[Triangled]

Can't remember reading such a thoroughly detailed article, thank you.
I didn't notice the age of the structure, but certainly here on the west coast, the design and detailing of the roof to wall connection and the uplift requirement for the roof joists has evolved substantially, particularly since Northridge 1994 and several inland empire wind events. Those two items caused some grumblings in the community but I don't think they added significantly to the completed costs of the structure although I am sure they added significantly to the quality of the structure. Definitely not F5 proof though.

 

[IRstuff]

http://www.kansascity.com/2012/01/11/3365873/home-depot-in-joplin-reopens-amid.html

basically the same approach, except, as noted in the first article, the walls are pre-fabbed, off-site. However, the new building does have a reinforced room, inside, with a 150-person capacity, according to this article.

TTFN
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[JAE]

I went to a short seminar meeting a while ago and one of the Missouri structural engineers who was involved in the Joplin, MO, tornado damage assessment indicated that one thing that might come out in future recommendations was to include in the design a redundant diaphragm system....i.e. if portions of the roof deck are lost there is still a secondary diaphragm element left - like older buildings used to use horizontal trusses around the perimeter of the building.

 

[hokie66]

"like older buildings used to use horizontal trusses around the perimeter of the building"...which is done in most buildings in Australia. The roofing is not considered as a diaphragm here.

 

[darthsoilsguy2]

As a welding inspector, i use to hate tilt-up walls. The joist bearing points make sense to pin the walls that run perpendicular to joists. but parallel with joists all that is there is the bridging termination and deck welds. I don't like so much riding on the long-term quality of decking welds. Luckily, i haven't had to deal with one since 2005.

 

[JedClampett]

Does anyone else think that open web joists are being overused? They're a component that's designed to meet the design loads and not one ounce more. And anything out of plane or in an unexpected direction and they're toast. In fires, tornados or other disasters, they're often the weak link of the structure. Add to that they're dangerous to construct. I see them as one of the major villains in this failure.
Whenever I get to choose, I go with plain old wide flange shapes. I justify this, when asked, that the building will be easier to remodel in the future. But I guess most owners figure that they'll sell the building before that ever is a consideration.

 

[ztengguy]

how did the other 154 people die, perhaps we should focus on those structures. Unfair to tilt-up in my mind.

 

[JAE]

Here is an aerial view of the collapse of the Home Depot (tilt panel walls clearly visible).

There apparently were 7 deaths there. I think tilt up is a good concept - just need to have a redundant system of stability beyond light gage metal decking.

 

[hokie66]

A lot to be learned from that aerial view, I'm sure. The panels at the bottom and on the right rear fell out, and those at the left and rear in. Looks like the panels snapped off at the floor line. Those on the bottom right remained standing.

Agree with JAE, a more reliable method of transferring the horizontal loads in the roof plane would help in maintaining structural stability. One way of improving life safety in these buildings would be to make the weak link uplift of the roof sheeting, so venting can occur and protect the structure. But then you would have people injured by flying roof sheets....

 

[msquared48]

Also interesting to note that those panels that did not fail were at internal and external corners, or very close to them.

Mike McCann
MMC Engineering

 

[darthsoilsguy2]

Looks like the safest place is to push the products to the side and jump into the stacks.

 

[MikeHalloran]

Also interesting to note that those panels that did not fail were at internal and external corners, or very close to them.

I think that lesson has been applied here in SoFla. Many of the newer tiltups are rather ornate, with panels shaped sort of like sheet piles, on a much larger scale, so the resulting walls are grossly corrugated, rather than completely planar. I have not studied the details, so I don't know if the panels themselves have any great depth, or e.g. if they use lap joints instead of butt joints or some other thing entirely, but the resulting buildings are distinctive.



Mike Halloran
Pembroke Pines, FL, USA

 

[Triangled]

Hokie66
""like older buildings used to use horizontal trusses around the perimeter of the building"...which is done in most buildings in Australia. The roofing is not considered as a diaphragm here."

Am I understanding you correctly that the metal deck would not be utilized as a diaphragm in AU? Are horizontal trusses, as mentioned, the norm for big box buildings?

 

[hokie66]

Yes, we don't tend to use roof deck or built up roofing. The most common roofing materials here are steel roofing profiles, intended to shed water but not to act as bracing.

 

[Duwe6]

"Looks like the safest place is to push the products to the side and jump into the stacks."

Yup. Having been raised in Kansas, I've given tornado safety a LOT of thought over the years. In a big building, the shelving is a good option assuming the stuff surrounding that spot is not going to beat you up [stay away from the gardening tools] or smash you [pallets of sand/cement above your refuge]. Interior 'buildings' are the best - the breakroom and/or bathrooms are usually made of concrete blocks; building-inside-a-building. Another overlooked 'building' are the big walk-in* coolers and freezers. Other than the safety-glass
doors, they are doublewalled steel, and typically of steel internal construction. Come a tornado, I'll be heading for the back of a freezer. Barring that, the bottom shelf in the clothing department, well away from exterior walls.

* some 'walk-ins' are big enough to drive a forklift inside and allow it to turn sideways. BIG steel building-in-a-building.

 

[Compositepro]

I guess pallet racks are usually better protection than nothing, but....

http://www.youtube.com/watch?v=R4pN50yYI5k