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

Re: Seismic Joint Size

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I had a building in LA with an 8" seismic separation to the adjacent
building.   This was a one story building with about 20 ft to the roof.
So, 13" for a 3 story building doesn't sound out of line.   I used the
97UBC requirements which takes the elastic deflection times 0.7R.  The two
building design drifts are then combined by SRSS.

We only had to provide a weather cover over this joint, not a fire
protected corridor, so it wasn't a big problem.  I do know of a hospital
complex in the LA area which needed to provide a fire protected joint
between 2 base isolated buildings.   The design team decided it was cheaper
to tie the two buildings together  structurally, at the first level slab,
than to pay for a fire protected joint.  This is the Saint John's Health
Center and is described in the 2001 SEAOC proceedings.

Ed Haninger
Fluor Daniel
Aliso Viejo, CA





                    Peter Griem
                    <griem@slamcoll      To:     "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
                    .com>
                    03/28/02 09:44       cc:
                    AM
                    Please respond       Subject:     Seismic Joint Size.
                    to seaint
                                                                                                                 .





I interpret the building codes to read that the seismic joint between two
buildings must be sized by:
1. taking the elastic deflection calculated for each building (say by RAM,
STAAD, etc.)
2. multiplying that value for each building by the appropriate Cd factor of
the lateral system (to account for additional plastic deflection)
3. adding those amplified deflection values for each building together (so
that if the buildings move toward each other in an earthquake they don't
crash into each other)

First question - do you agree that that is the way the code READS?  Second
question - do you agree that is the INTENT of the code?  Third question -
Do
you size seismic joints this way?

Here's the problem - take a building categorized in a lower Seismic Hazard
Exposure Group, e.g. SHEG I in the BOCA or IBC.  The allowable story drift
(inc. Cd) = .020hsx.  For a four story building at 12' per story, the
allowable deflection at the 3rd floor would be (3)x12'x12"/'x.020=8.6in.
Say the design shows that two adjacent MF bldg are limited to 75% of that
value - you need a seismic joint between them of .75x8.6x2= 13 in.  A 13"
jt
at the third story of a building.  Try to explain to the architect -
especially in a low/moderate seismic zone.

How do you or others you know treat this issue.  I would especially like to
know how this is treated on the west coast.  What is the largest
manufactured seismic joint that can be found to bridge a corridor?

******* ****** ******* ******** ******* ******* ******* ***
*   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
******* ****** ****** ****** ******* ****** ****** ********





-----------------------------------------------------------------------------------------------------
The information transmitted is intended only for the person
or entity to which it is addressed and may contain confidential
and/or privileged material. If you are not the intended recipient
of this message you are hereby notified that any use, review,
retransmission, dissemination, distribution, reproduction or any
action taken in reliance upon this message is prohibited. If you
received this in error, please contact the sender and delete the
material from any computer.  Any views expressed in this message
are those of the individual sender and may not necessarily reflect
the views of the company.
-------------------------------------------------------------------------------------------------------


******* ****** ******* ******** ******* ******* ******* ***
*   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
******* ****** ****** ****** ******* ****** ****** ********