Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: steel formdeck as shearwall?

[Subject Prev][Subject Next][Thread Prev][Thread Next]
John,

I think that you may have forgotten another 0 in your first statement.  To
my knowledge, the codes based upon the "older" NEHRP provisions (i.e. BOCA
and SBC) where based upon 10 percent probability of exceedance in 50 years
which results in about a 500 year return period (about 475 to be more
precise, although probability stuff still makes my head spin and
hurt...can't you see the smoke?).  You are correct that the "newer"
(1997 and on) NEHRP based codes (i.e. IBC and NFPA and ASCE 7) are based
upon 2 percent probability of exceedance in 50 years which results in
about a 2500 year return period.

The NEHRP commentary does comment that it is prudent to consider something
like a 50 percent probability of exceedance in 50 years (return period of
about 50 or so years) in areas of high seismicity such as California (i.e.
places that get frequent moderate to major seismic events).  And I believe
that this "thought" is put some into practice in that the seismic values
for California and other West coast areas are determined slightly
different that the rest of the nation.

You are correct that times have are changing...but that have been for
awhile.  I have watched the seismic provisions become MUCH more of an
issue just during my career life time (started around 1993...so I am a
"young pup" so to speak...all though I am already losing my memory and
hair) in my area.  When I started, the 1990 and 1987 BOCA where still in
use in my neck of the woods.  The seismic in them was a few pages at most
and generally did not "control".  Along came the 1993 BOCA that was based
upon the 1991 NEHRP provisions, and suddenly seismic could control in some
cases.  Still not too many engineers in my neck of the woods really felt
or understood the "impact" of those changes.  Now with the IBC (and the
NFPA), seismic can really be "felt", especially since the soil type
effects the SDC.  There can now realistically be important structures in
my area that can reach a SDC of D, which as Harold pointed out results in
some STIFF seismic requirements that we would have used to thought were
only for places like California.

So, we should all be a little more prepared to design for a little more
shake, rattle and rollin'.

Regards,

Scott
Ypsilanti, MI (where seismic events are when I turn up my stereo with the
subwoofer at max level...scares the crap out of my dog but is fun for
watching movies)


On Fri, 31 Oct 2003, John C. Jones wrote:

> The current recurrence interval is about 50.  IBC it goes to 2500 years.
>
> Very rough calcs (as in 10 minutes worth)
>
> IBC2000 V=550k   I used soil "D"
> SBC99  V = 220k  I used soil factor of 1.2
>
> The last one of these I did was 4 stories instead of 6.  Seismic DOES control for the 6 story version regardless of code or direction.  For SBC it barely controls in one direction and controls by a good amount in the short direction.
>
> The times they are a changin'!
>
> John C. Jones, PE
> Barnett Associates
> Pell City, AL
> 205-884-5334
> 205-884-0099 (fax)
>
>
> -----Original Message-----
> From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
> Sent: Friday, October 31, 2003 8:41 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: steel formdeck as shearwall?
>
>
> John Jones wrote:
>
> . > The recurrence interval is now about 2500 years under IBC.
>
> What interval does next year bring?
>
> . > I'm not using that unless dictated by law.
>
> Yes, and there was a fire recently in Chicago in which fire sprinklers were
> not installed because they were not *required* by the building code.
> However, fire sprinklers were not prohibited by law either.  Talk to the
> families of the victims and see what they think about things not being
> installed because they were not "dictated by law."  See what it will cost
> Cook County for compensation to the victims' families and compare that to
> what the cost of installing fire sprinklers would have been if they had been
> originally installed.
>
> Compare the cost of prudent life safety considerations to the amount of time
> and money expended on aesthetic considerations, such as paint color, ceiling
> texture, light fixtures, floor covering, etc.
>
> A. Roger Turk, P.E.(Structural)
> Tucson, Arizona
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********
>
>


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********