Once Again, Texas

[charliealphabravo]

They certainly have all the ingredients for an epic legal battle.

The reported design overstress/overload of 10 or 20 percent is not be enough to cause that kind of cracking under self weight I think. Something else is seriously wrong with the materials or the construction. I take the "isolated" 70% overstress with a grain of salt at this point since the cracking is so widespread. FEA analysis can give wildly unrealistic "isolated" min/max results if that is what they are using.

I wonder how they made that crack map. Maybe a total station and an EI or two?

 

[JStephen]

"The firm identified areas in the stadium where the load demand on the structure exceeded accepted building standards by 10 to 20 percent. In isolated locations, that number was greater than 70 percent, according to the firm’s analysis."

You may be seeing something different than that quote, but that is a very vague quote that could be interpreted a number of ways.

 

[JedClampett]

In the newspaper, they said the stirrups exceeded the maximum spacing by one inch. I know in a court of law, this sounds bad, but one inch? Admittedly, I'm sure the newpaper article was not written from a technical view, but I'm hoping that nothing in the code has that fine of tolerance on it.
I've mistakenly used the beam depth divided by 2 for maximum stirrup spacing, when it's supposed to be "d" divided by 2. I hope nothing will fall down because of it!

 

[dcarr82775]

1" is pretty nitpicky. I am sure the owner paid a geotechnical firm to due important special inspection on the structure which means the rebar probably isn't even close to the drawings anyway.

 

[SteelPE]

The crack pattern is interesting, either they were not allowed into office/closed areas, or those areas are not part of the suspended slab. Also interesting to see two areas that you would expect the same framing (because they are mirror images of each other) have completely different amounts of cracking. I would think this is were QC comes into play onsite?

 

[SteelPE]

Can anyone with more concrete experience figure out what structural system was used based upon the cracking pattern?

 

[JedClampett]

If you look at the little embedded video in the news article, there's about a 5 second shot at the 43 second marker of the bottom of the slabs. They look like traditional beam and slab construction. The slabs look very thin from the way the cracks transmitted through to the bottom. The beams are also thin, four to six inches wide, kind of a joist member. The beams look OK (no cracking), at least in the small sample I could see.

 

[abusementpark]

I don't guess any of the reports have been made public?

 

[charliealphabravo]

I am curious as to how live loads are applied to a structure as large as this. Perhaps there is some engineering judgement in applying live load reductions or live load patterns that might be interpreted differently by a third party peer review.

 

[JAE]

Here's the underside photo that JedClampett was referring to.
Looks like a typical cast-in-place concrete skip-pan joist system. The multitude of cracks on the bottom of the slab don't imply a structural issue - this looks like shrinkage cracks or some kind of material failure.

 

[msquared48]

I think the stadium was overloaded by Saturday Night Lights.

The game of horseshoes is big in TX, so you'd think they wouldknow how to design and build a horseshoe shaped stadium! How hard is that?

Mike McCann
MMC Engineering

 

[NITTANYRAY]

Were the skip joists used under the concourse or is this a picture of the underside of the roof?
Skip joists are generally used for roofs not floors, especially floors that would require a 100 psf live load.

 

[jvvse]

Are those actual crack widths or is someone using the wrong units? 3/4" width, 2" width...those aren't cracks they are gaping holes. With those you could fit rebar inside of the crack and not touch the concrete.

I agree that such widespread cracks don't look as much structural as they do a general material failure. If the slabs were under-reinforced, they are still one-way slabs and the cracks would show that. They are all criss-crossing, so maybe shrinkage or just poor curing? It gets hot in Texas, maybe they didn't keep it wet/cool enough?

Definitely keep us posted on any findings that come in!

 

[JStephen]

Here's an article that shows that same crack plan, only on the the image here, it's cracks 0.02" and wider and cracks 0.02" and smaller. That makes a lot more sense. I would think if there were a bunch of 2" cracks, that's what you'd be seeing photos of.

http://www.businessinsider.com/high-school-football-stadium-closed-2014-5

 

[XR250]

Surprised it is only going to cost 1 mil. to fix.

 

[JAE]

Skip joists are used all the time on floors. I've done many SF using that system...even at 100 psf assembly LL.

 

[JStephen]

If you click on the Dallas News article Jed Clampett references above, it now has a Crack Plan showing 0.02" rather than 2" crack width.

 

[JAE]

You're right - they changed it from the one I posted above.

But some of those cracks looked much larger than 0.02". Some appeared to be close to 3/8".

 

[JStephen]

Well, they categorize it as "larger than 0.02" and "smaller than 0.02", maybe from checking with a feeler gauge.

 

[TXStructural]

Wide module pan joists are the most common construction method in Dallas for floors at all loads. The arguments I have seen on this are entirely about getting someone to pay, not the relative merits of the problems. Obviously something went wrong, and the map cracking visible on the slab looks a lot like construction defect. There may be blame enough to go around, but I have not seen any real information to support design defect yet.