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RE: Seismic Joint Size

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I have yet to see 26" taken out of a standard 25' wide lot in San Francisco
for a 3-4 story building. Not saying it's right or wrong, but I have yet to
see that in practice. Just today I noticed at Mission at Second Street there
is a new 40 foot or so atrium lobby in front on the high rise portion of the
building (designed by SOM.) They have an accordian type vertical joint with
an adjacent older building that looks like about 7-8".
Jeff

> -----Original Message-----
> From: Ed.Haninger(--nospam--at)Fluor.com [mailto:Ed.Haninger(--nospam--at)Fluor.com]
> Sent: Thursday, March 28, 2002 10:46 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Seismic Joint Size
>
>
>
> 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?
>
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