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deck collapse

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I am sorry, but I cannot accept that this was just some horrible accident.
Especially since it is a live load failure, not a 8.1 on the Richter scale
EQ or a Hurricane Andrew. We all know that these types of disasters can be
prevented or mitigated through proper engineering and construction. It is
not like they say in the media, "the unstoppable force of nature" or
something like that. It is an event we know will happen sooner or later, and
we as human beings can accept that fate or look to engineers and builders to
provide safer structures (and government officials to set and enforce
standards). With that said, a live load disaster, in my opinion, is
unacceptable.

As an engineer, we learned about live loads on the first day of our first
structural class. There is not a whole lot to it. The codes can very
conservative in this regard for the very reason of preventing a collapse.
Decks, if designed to the very minimum for this type of structure would be
the same LL as the structure, or not less then 60psf for this type of
building (40psf for a 1 + 2 family) dwelling. I guess you could interpret
this deck and stairwell as a corridor, and design it for 80psf.

I know I already did this calculation on the list yesterday, but I have done
this in my own deck designs to see how realistic the code is. For normal
service it is not very realistic, but it is that high to prevent this type
of disaster. That deck looked to be at least 30x15= 450sf, and even at 60psf
that would give you a total of 27,000lbs. That is 135 people at 200lbs each,
one person per 3.33sf each square foot (a 1.8ft x 1.8ft sq would be shoulder
to shoulder). No stacks of beer kegs, or kids jumping around, or whatever,
can cause this to be overloaded, IMHO. This is just some common sense.

 I went to the nationally recognized party school of the year FSU (who knows
who comes up with these rankings-playboy?) and every apt had a balcony or
deck, including my house. My deck was so overbuilt it was silly, ledgers at
like 16" o.c. and stuff. You could not even sense a slight deflection when
my fat butt bounced up and down on one single deck piece. We had lots of
parties out there, and I have been to more then my fair share, and I do not
see more then 50 people crammed on that little deck. People generally need a
couple square feet to themselves.  I pay little attention to eyewitnesses
estimates (we have all seen those studies where eyewitnesses in an
experiment will give 10 different versions of the same story), they are
probably pissed they are being kept up late..

I am not sure why this tragedy really bothers me. Maybe because I could see
myself totally in these kids shoes. They are about my age, at a party like I
would be at, on a deck like I have been on a thousand times. Now I am a
structural engineer and I have designed wood decks and bridges closely to
code and checked every detail and it would kill me if something like this
happened to a structure I designed. I have even designed and built my own
deck at my house, albeit 2 ft off the ground, and I went way overboard just
to get the serviceability that I wanted, which is no where near any
allowable stress. Also I am very surprised that even with prescriptive
building this would happen, besides at a connection. When I designed and
built my deck for my house, I got a pamphlet at home depot for ideas and
construction tips, and I ran my own calcs, and I was way less conservative
then their plans. Even Simpson connections are usually way over what you
need, it was for my case, and they are so easy to install. All of this
limited knowledge leads me to believe this was completely preventable.

I still think they could have waited a bit to clean up the mess. People are
inconvenienced, yes, but so are the 12 people that are dead. I gotta think
the one thing an engineer or framer could really screw up, that would cause
a sudden failure, would be a wood to wood connection. If they were bolting
to hollow CMU, that could be it too. Maybe it is like someone said and it
was a failed connection to a post, that is something I could see a framer or
even an engineer screw up. Especially if it is a main girder bolted to
posts, with beams spanning in between the girder and the building. They may
have used nails or lag screws when bolts were necessary. That is the one
tricky thing I have seen in wood deck design, bolt or screw connections in
shear can limit your span and loading before anything else...

Sorry for the rant. This thing has me heated.

Andrew Kester, EI
Longwood, FL





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