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RE: Seismic Retrofit Questions

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Joseph,

It is hard to make an old building conform with new code detailing
requirements.  I've had the exact same questions that you have now, and
I'm anxious to see how the list responds on the wall detailing question.
I agree, that you must attach the diaphragm to the shear wall in the
newer section.  I think I've used Hilti's to the masonry and welding
from below to connect the steel deck to the angle (assuming the deck
gage is adequate).  If that can't be done, have the roofing membrane
pulled up and do it from above (the hard way).

Just for interest, you might try looking at NEHRP Guidelines for the
Seismic Rehabilitation of Buildings, along with the commentary for that
document.  They are FEMA-273 and FEMA-274, and can be ordered for free
at (800) 480-2520.  FEMA also has a few other documents you might want,
including:  FEMA-149, Seismic Considerations of Elementary and Secondary
Schools; FEMA-178, NEHRP Handbook for the Seismic Evaluation of Existing
Buildings; and FEMA-310, Handbook for the Seismic Evaluation of
Buildings - A Prestandard.  The 310 document will eventually replace
178.  These are all free documents.  I think what you'll find with
FEMA-273 and 274 is that they might be more appropriate for
rehabilitation than the UBC.  The 178 and 310 documents will be very
conservative, and if you use their checklists for evaluation, some items
may show as deficient.  However, the reason I put those in, is because
of the Non-Structural checklists.  I think we often get tasked with
looking at the "structural" items in a building, and one of the major
problems during an earthquake is non-structural stuff falling on people,
blocking egress, etc.  Suspended ceilings, bad connections for utilities
(especially gas lines), book cases and shelves that could topple and
block egress.  These things could be especially important to look at for
a school.  If your client hasn't thought about the non-structural
issues, you might bring it up.  

Hope some of that helped,  

Mike Ritter

ps, Often when tasked with seismic studies or upgrades, I will recommend
to the client to have us look at wind also.  A lot of older buildings
simply used, say 20 psf on everything with no consideration for uplift
or other issues that are addressed in the newer codes (ie, ASCE 7).
Have you considered wind effects on the school building?  It probably
would be pretty easy to run a quick number just for comparison.


> -----Original Message-----
> From:	Joseph R. Grill, PE [SMTP:jbotch(--nospam--at)micron.net]
> Sent:	Tuesday, September 19, 2000 8:18 PM
> To:	SEAINT
> Subject:	Seismic Retrofit Questions
> 
> I am in the middle of an investigation of an old school in my area.
> The
> main concerns are with seismic safety, although in the process I've
> found
> other problems.  I'm not in the process of doing calculations for an
> actual
> retrofit, but my findings will be used by the school officials to help
> decide the future of the school.  At the moment I have two questions
> to pose
> to the list.
> 
> In the oldest portion of the school (5 additions since the early 60's)
> there
> are some load bearing masonry walls.  Checking the walls for load
> combinations in UBC (sorry guys using WS design) I have found that the
> reinforcing provided in the walls is adequate strength wise although
> severely lacking in minimum reinforcing requirements for a zone 3
> structure
> if it were being designed today.  I am at a loss as to how to approach
> this
> in the report.  Do these walls need an upgrade in capacity in some
> way, or
> not.  I'm sure I will be pressed on this matter.
> 
> Another question was posted in a similar situation last June, although
> I
> think I remember the metal decking wasn't required as a diaphragm.  In
> this
> school (a newer addition) steel joists were used to support metal
> decking.
> There is no direct connection from the diaphragm to supporting CMU
> walls
> below.  I will be looking for supplying shear transfer from the deck
> to the
> walls, hopefully without disturbing the roofing membrane which is
> fairly
> new.  Back in June Stan Caldwell listed some molly bolts with a
> supplier in
> Denver, although the bolts had no ICBO certification.  Does anyone
> have any
> ideas for an attachment of this sort.  Angles installed below and
> attached
> to the deck from below?  The school district is low on cash, Just
> built a
> new high school, so cost is an issue.  Also, the community has become
> very
> aware of the issues, and it would be nice to have the ICBO thing or
> something substantial to be able to back up the method used.
> 
> Thanks, Joseph Grill, PE
> 
> 
> 
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