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anchor bolts/ deck collapse

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Emery:

ACI 318-02 fully covers bolt groups as well as individual bolts, via the use
of An and Ano. I would review the appendix again.

"I have recently tried the ACI 318-02 appendix D values to design
connections to concrete using "Nelson Studs".  I have the PCA Notes
tables, but these seem to be for single connectors only.  Are there
other useful design aids for groups of studs/anchors?"

Emery Ojala, PE, SE


Chicago Deck Collapse:

I agree with Roger Turk all the way. Why would they be in such a hurry to
clean up the debris, when this is the main and only (besides photos) of
really telling what happened there. If there was a plane crash involving 2
people who died, the FFA would be on the scene and they would spend months
rebuilding the Cessna in a hanger until they had their answer. Why not treat
it like Roger said as a possible crime scene? I have read in some countries
they will hold the contractor and architect/engineer until an investigation
has been complete whenever there is a collapse.

That was just stupid to have one engineer come out, and I hope he was
misquoted, " A structural engineer conducted a preliminary examination and
determined that the porch was sound before the collapse". Correct me if I am
wrong, but how do you determine if a structure was "sound" after a collapse?
The wood could have been cracking for months. Noone said anything about
whether someone as-built this thing to determine exactly how it was built so
someone could do an analysis to see if this thing was built to code in the
first place, with or without a proper structural design.

Is this just another example of blindly allowing prescriptive code use? Is
it non-permitted poor construction? Permitted poor construction with poor
inspection? I would seriously doubt even a half-way competent structural
engineer would screw up a deck design. We have done quite a few wood decks
and bridges, and they are all straightforward and overdesigned. The code
loads are usually so conservative you end up getting really conservative
results and designing the deck for serviceability rather then strength. The
key , like in most things, is in the connections.

EX:
Even using a paltry 40psf for a deck LL (code min, depending on building), a
20'x 25' deck (it looked at least that big from photos) would give you a
total load of 20000lbs. They estimated about 50 (?) people were on the deck,
plus some kegs of beer (which weigh less then 100lbs full, so I am told
:) ). Even if they are big people like me, 200lbs x 50= 10000 lbs. And I
wish I weighed only 200lbs.....

So like I said, you really have to be asleep to screw this up as an
ENGINEER. Which leads me to think it is a prescriptive built type
structure...

Bottom line, who wants to bet it was a connection failure? I guess that is
obvious for many reasons, including deck beam redundancy, progressive
failure, and wood's ability to deflect greatly before yielding/failing.

As soon as I saw that on the news I shook my head and thought, "What a
tragedy. No engineer. Maybe a permit. TOTALLY AVOIDABLE."

What are the more experienced listees thoughts??

Andrew Kester, EI
Longwood, FL
















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