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Re: Seismic design for existing buildings with new additions

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Frank,

IF you are putting an addition on an existing building, then you will
likely HAVE to use the governing local code.  Obviously, the addition
itself will need to be done by the governing local code (UBC?), but only
elements within the existing building that are directly affected by the
new addition would have to be upgraded by following the governing code.
For example, if the addition will be structurally tied to the existing
building (i.e. no expansion joint etc), then the existing building would
have to be "checked" under the local governing code.  There should be a
provision with the UBC (there is on with in the BOCA code, which I am more
familiar with) that outlines WHEN existing members with new seismic
loading imposed upon them need to be reinforced.

IF the new addition is completely structurally independant from the
existing building, then it is likely a matter of what the owner wishes to
do, unless the local (or state or federal) government has mandated a
retrofit requirement.  If that is the case, then the FEMA documents may be
applicable.  If so then, here goes:

FEMA 302 (and 303, the commentary) are the recommended code provisions.
These are the actual NEHRP documents.  They are basically used by the
three (and now "one") model codes.  BOCA & SBC are basically created from
the 1991 NEHRP and UBC 1997 is basically the 1994 NEHRP.  The IBC is
basically the 1997 NEHRP (which IS FEMA 302).  Therefore, any of the NEHRP
documents will not get you TOO much different than the UBC.

FEMA 310 is the pre-standard for evaluation of existing buildings.  It is
not meant to be a "code" (ie something that is adopted by local government
for force specific requirements on buildings).  It is meant to be a
standard that everyone can use to evaluate existing buildings so that
owners can determine the potential seismic deficiencies of their
buildings.  Then they can, on a purley volunteer basis, decided what if
anything to upgrade.  The federal goverment is in the process of
evaluating all their buildings using this pre-standard and then beginning
a "mitigation" program.  I understand this program is a direct result of
the recent seismic events (Northridge, Kobe, Loma Prieta, etc).

FEMA 273 (and 274, the commentary) is the document for the next step...the
voluntary "mitigation" of seismic events.  Again, it is not meant to be a
code document, but a tool that is standardized that everyone can use to do
voluntary upgrades.

Hope that helps some.

Scott


On Fri, 29 Sep 2000, Fariborz Tehrani wrote:

> Dear Colleagues,
> I'm looking for FEMA/NEHRP codes and regulations that
> we can use -besides UBC- to redesign and/or upgrade
> existing buildings with new additions. I appreciate if
> somebody direct me to the most updated references.
> Thanks in advance,
> Frank
> 
> =====
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