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ATLANTA partial parking deck collapse

ATLANTA partial parking deck collapse

ATLANTA partial parking deck collapse

(OP)
i haven't seen this posted yet. rather unfortunate for the contractor (same one as botanical garden walkway collapse)...they're actually "better" than most contractors i run across.

http://www.wsbtv.com/news/19892813/detail.html

RE: ATLANTA partial parking deck collapse

Yeah, Hardin's a pretty good contractor...certainly above average.  Noticed that a precast soffit beam popped out.  Could be connection deterioration, design, construction...who knows at this point.

RE: ATLANTA partial parking deck collapse

I know it's a speculative generalisation, but I have never felt comfortable in these precast parking structures.  There is not enough robustness in the connections or redundancy in the system for my liking.  Give me a steel framed or cast in place structure anytime.

RE: ATLANTA partial parking deck collapse

hokie66...I agree.  I've wondered if the traffic vibration would push a beam off its corbel/haunch.  Not much holding these things together.

RE: ATLANTA partial parking deck collapse

I've done many Precast, Steel and Reinforced Concrete parkades and nary a problem, yet! The first one I did using 12" Hollowcore about 30 years back just had an couple of floors added.

Dik

RE: ATLANTA partial parking deck collapse

I'm working on one right now.....

I'll be tossing and turning tonight.

Clansman

If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.

RE: ATLANTA partial parking deck collapse

I'm not saying they can't be built so they behave satisfactorily, and I am confident that you fellows will do your best, tossing and turning included, to make sure they are competent structures.  But the first thing I think of when I hear of a parking structure collapse is "not another precast house of cards".

RE: ATLANTA partial parking deck collapse

I am even less confident than hokie66 in this kind of structure. Here it has been used not only in parking but multilevel supermarkets of the "we are the cheapest" type full of people and, locally, racks to the ceiling. Yet till now, and even in spite of too small seats by any *** subjective*** standards, I am not aware of any notorious failure.

The same can't be said of bridges with standard to small seats, some have collapsed upon rotation of the foundation and column, or upon impact of a truck.

RE: ATLANTA partial parking deck collapse

The lack of redundancy in a precast parking structure won't come in to play until a major seismic event or explosion.

The seating of the haunches are more than adequate for normal loading and the welded connections with the chord/diaphragm steel will hold the pieces together under loading.

When I think of a precast double-tee I would consider it better than an open web steel joist floor system which are used all the time for supermarkets.

Problems with precasst DT systems - Welded steel connections need to be maintained.  Flange reinforcing is WWR which may degrade without any visual sign.  Diaphragms may span great distances without lateral support (250 ft between shearwalls).

RE: ATLANTA partial parking deck collapse

(OP)
here's my suggestion to help everyone sleep a little better at night..."completely/strictly" follow the special inspections program (with a good/qualified testing firm on board essentially full time if possible) to help document the construction and so that you/designer are able to say it was built like it was designed. i have not seen the same urgency to follow SI on precast as for steel (which is still lacking by the way). from my independent third party eyes, some of the precast field work is "scary" to say the least(basically iron worker mentality except with precast--you know what i mean if you've been around construction long enough)...all i'm going to say at this point.

been to that parking deck before...nothing out of the ordinary that i noticed (but wasn't looking for anything). and apparently pretty vacant of people at the time of collapse so maybe not traffic vibration. the parking deck only few years old.

and i really do hate to see the hardin folks wrapped up in this one...but it should be an eye opener to everyone as to what the rest of the construction really looks like.....(don't fool yourself--again from these independent eyes)

RE: ATLANTA partial parking deck collapse

Just an anecdote,

once I was asked to start design for some maintenance buildings holding some trucks and in whatever the way, I came with some solution that had precast L and inverted T beams; I did preliminary checks and determined the sections had to be truly massive and of 60 MPa characteristic strength or near 9 ksi. I scrapped the idea.

10 years passed and my job then (last year's) went through a design of akin loads and structural system, then I found there was at town a glistening (wholly new facilities) firm making those gross beams at such 60 MPa strength and seemed to have enough success to stay working.

Simply, that one doesn't want to do something is not warranty of that this won't be done by another. Nor a warrant of that one is right on using it or the contrary.

RE: ATLANTA partial parking deck collapse

Did it seem odd to anyone else where that beam landed on the grass?  It looked like it was yanked straight out. It didn't look like it just fell after the floor gave way.  

RE: ATLANTA partial parking deck collapse

Mike,
Not knowing anything about the structure inside the spandrel beam, I would speculate that the spandrel "ejection" was initiated by either a failure of the spandrel to column connection in torsion, or by a bearing/shear failure of beams bearing on the spandrel, which would have resulted in a big lateral force as the beams fell.

RE: ATLANTA partial parking deck collapse

Spandrel beam takes a lot of torsion if it has a ledge as opposed to being pocketed. As someone mentioned, the spandrel to column connection can take significant tension and can overturn if that connection fails.

Clansman

If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.

RE: ATLANTA partial parking deck collapse

But the beam appears to have overturned in a direction opposite of the torsion. Even then, it looks like the beam moved 30' to 40' laterally. How? It's not a small piece of concrete.
 

RE: ATLANTA partial parking deck collapse

jorton,
Why do you say that?  It ended up on the outside face, but could have come to rest either way.

Looks like from the attached video that there wasn't much tying the floors to the spandrel, and the connection at the spandrel to column connection wasn't enough to prevent the beam from twisting out.  As the floor slipped past the spandrel, boom, the spandrel was ejected.

http://www.wsbtv.com/video/19919886/index.html  

RE: ATLANTA partial parking deck collapse

hokie66,
You're right. It could have come to rest either way. I just have trouble envisioning the beam traveling with enough backspin to land as it did. Perhaps it only made a 1/2 turn in the air and then rolled the other 1/2. OR, maybe it took a bounce off the building. I understand that there is some surveillance video from within the deck. Hopefully it will be released soon.

RE: ATLANTA partial parking deck collapse

There are two things I'd be looking for -
1.  Any rusting at the double-tee to L-beam connections.  If the welded connection (pretopped) or coil rod connection (field topped) between the elements failed, then the torsion of the ledge connection would be transferred to the column coil bolts and consequent failure.
2.  Failure of the coil bolt connections at the columns.  If the column pockets for the coil bolts do not allow sufficient lateral deflections of the coil bolts then every time the spandrel is loaded a shearing action will act on the coil bolts due to beam end rotation.

  

RE: ATLANTA partial parking deck collapse

CIP makes me sleep easier too over Precast. But, well said by MSUCOG about sleeping better: special inspections.

RE: ATLANTA partial parking deck collapse

I'm curious why OSHA would be involved.

RE: ATLANTA partial parking deck collapse

(OP)
all parties involved are reputable in my opinion. i suspect the project was SI (based on the site location) but even that is no guarantee...sometimes "things" happen that cause us to step back and rethink our approaches. at least SI's provide a more detailed documenation process that may help figure out what went wrong. but sometimes one weak link is missed/not evident that could domino in to something bigger. thank goodness there was no loss of life and perhaps this can be a learning experience for us all.

we will never completely remove risk...only limit it.

RE: ATLANTA partial parking deck collapse

Hopefully, this will change the approach to how these things are tied together.  The details which Teguci provided above are basically in accordance with my understanding as to how they are built.  Not good enough to my liking.  No amount of inspection, special or otherwise, will provide robustness and redundancy in the system.

RE: ATLANTA partial parking deck collapse

I'm trying to figure out what would cause the spandrel to pop out so far. I suspect that the spandrel was flexed horizontally and loaded like a spring. If you lightly hold a business card between your thumb and ringfinger and bend it in then release it, you can make it fly a good ways. A spandrel would be a rather stiff spring.

It's interesting that it can be bent either in or out and can be made to fly outward. If you bend it in (toward the deck)then release it from midspan, it will fly out. If you bend it outward then release it from the ends, it will also fly outward.

It was hot, so maybe the tees had expanded and were putting outward pressure on the spandrel. Then the end connections gave out and the spandrel flew away.

Or, shrinkage had caused it to pull the spandrel to flex inward until the deck to spandrel connection gave out and the spandrel flew away. I think this is less likely becuase it was hot and shrinkage takes place in the cold.

The photos show some tabs with bolt holes projecting from the columns that were probably meant to bolt the spandrel to the column. The tabs project straight out. It seems to me that if there were bolts in them the tabs would have bent as the spandrel flew away, but the tabs look pristine like there never was a bolt in them.

I can't get the basic physics to work out. I don't do these types of calculations very often (like once every 20 years), so I could be making some errors.

Assuming the panel width is 38" deep, 16" wide at the haunch and 8" thick it has an I of 5346 in.^4 about the vertical (weak) axis; and if the span is 30 ft., and the concrete is uncracked, I get a spring constant of about 22 kips/inch for a load applied at midspan. If it was bowed in 1", it would have a potential energy of .5Fx or 11 inch-kips, or 0.92 ft.kips.

How much energy would it take to horizontally project an 11.5 kip object 30 ft. while it dropped about 30 ft? It would take 1.86 sec to fall 30 ft., thus it would require a horizontal velocity of 16.1 ft/s to travel 30 ft. horizontally in that time. If I set the potential energy of the flexed spandrel 0.92 = 1/2 mv^2, the velocity of the panel would be 0.17 ft/s. I'm off by a factor of 100.
 

RE: ATLANTA partial parking deck collapse

My brother works for the Atlanta Fire department and was there after the structure had collapsed. Evidently once the engineers arrived and started the initial evaluation of the structure, they took a look at some of the welded connections and saw very poor welds.  They had welders come in and re-weld a majority of the connections in the area near the collapse before they allowed crews back in.

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