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Re: Seismic Joint Size

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Both the 8" and 13" sound out of line to me.  I can't imagine drifts from
each building amounting to that much. I usually get 1-2" for a one story
building

Stan Scholl, P.E.
Laguna Beach, CA

On Thu, 28 Mar 2002 10:46:13 -0800 Ed.Haninger(--nospam--at)Fluor.com writes:
>
> 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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