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Re: deck collapse

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Andrew,

I have heard on at least one news report the same thing that Chris
said...they were unsure if a permit had been issued for the deck.
According to the report that I saw, the building had been renovated in the
recent past to convert it from 6 appartments to 3 (as Chris mentioned).
There apparently was a permit for that work, but no one knew for sure
whether or not that permit also covered the deck or if there was a
seperate permit issued.

As to the issue of clearing away the rubble from the site...have you
considered that make they were able to determine the cause of the collapse
in that amount of time?  After all, you have made the determination that
it cannot possibly be due to accidental circumstances (at least in your
mind) but rather due to negligence by someone (the engineer, contractor,
owner, etc) and you have been on the site for exactly ZERO seconds looking
at the rubble.  My point (without the sarcasim now) is that it is entirely
possible that they may have already gotten all the information that they
needed to determine the cause of the collapse, thus it was perfectly OK to
remove the debris so that people would not be inconvienved in getting in
and out of their homes.  In otherwords, it is entirely possible that they
had gotten all the information that they needed (i.e. photographs, etc)
for their investigation.  After all, this was a rather small wood deck
with no things like exterior cladding.  Think of it in proportional
sense...it took less that a year to clear away the debris from the WTC
collapse and it was TWO 100+ story buildings (with floor plans of
several hundred feet by several hundred feet) with added debris from
furnature, interior partitions, and exterior walls compared to the time
for clearing away the debris for this collapse that was only a 20
something by 20 something foot deck (at least from what others have said).
Thus, if you look at it from a proportional sense, then someone could make
the arguement that if you consider the amount of time clearing away the
debris at this incident then the time for the WTC was totally
insufficient, yet I doubt that there is too many people that feel the
debris at the WTC was cleared away too quickly.

This leads me to my suggestion...maybe we should try avoiding to
conclusions without all the information in hand, eh?  After all, while I
do believe that the lack of WMDs discovered in Iraq TO DATE raise some
questions about the primary rationale that was advertised for the need for
war, I also believe that anyone who wants to claim that Bush lied or
twisted information is just an idiot who is jumping to conclusions.  The
point is that we don't have enough information to make a make a conclusion
on either the Iraq issue nor the cause of the collapse.  So, I would
suggest a little patience before you get too hot under the collar about
anything and get all the INFORMATION.

As to the structural issues at hand...you have focused on pure gravity
live load issues.  Have you considered that the collapse may have occurred
due to insufficient lateral resistance?  And I am not necessarily tallking
about something sufficient enough to reist a significant earthquake.  At
least one person on the list has mentioned eyewitness reports that stated
that the deck was "swaying".  Thus, it is possible that the deck just
swayed too much creating a significant P-delta "extra" load that then
caused the live load to be "exceeded" even though there may not have been
enough people present to exceed 60 psf.  Admittedly, such a possibility
would still lead to a claim that the engineer (if there was one) should
have accounted for this.  My point is that you seem to be "target locked"
on how you believe that the engineer may have goofed which means that you
could be potentially be doing the same thing that you seem to be accusing
the person who designed the deck of doing...not looking at all the
possibilities (although I could be wrong...you could have thought of such
things yourself already).  Thus, again, maybe we should wait a little be
longer before we jump to conclusions.

HTH,

Scott
Ypsilanti, MI




On Wed, 2 Jul 2003, Andrew Kester wrote:

> 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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