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RE: Mass realty check...

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First, you need to get a copy of FEMA-273/274, "NEHRP Guidelines for the
Seismic Rehabilitation of Buildings" and "NEHRP Commentary..." (1997).  This
is free from FEMA and very useful.  You also need the 2003 ICC
"International Existing Building Code" if it's enforced in your area.

Also available:
SEI/ASCE 31-03
"Seismic Evaluation of Existing Buildings"
SEI/ASCE 30-00
"Guideline for Condition Assessment of the Building Envelope"
SEI/ASCE 11-99
"Guideline for Structural Condition Assessment of Existing Buildings"

Back to your questions, actually, there *is* an existing vertical lateral
system - it's an un-reinforced masonry shear wall.  This system *does* have
lateral strength; unfortunately it has little to no ductility and absorbs
energy by disintegrating.

You're right, however, in that that system is not allowed in new buildings,
and also right that major renovations trigger the requirement for a seismic
analysis and possible retrofit.  If the seismic level in your area is
moderate to high (C or above) then you probably have to upgrade with a
modern system.
If most of the following conditions are met, however, you might be able to
avoid this expense:
 - low seismic loads (A or B);
 - the existing structure is in good condition;
 - the local government gives allowances for existing/historic structures;
 - you are LOWERING the seismic risk by going from industrial/commercial to
residential (this does not apply if this is considered a mid- or high-rise);
 - you are lowering the live loads, therefore arguably increasing the extra
capacity available for seismic resistance;
 - if your analysis (the FEMA books give detailed examples and formulas)
proves that the existing URM system has enough capacity; 
 - you are NOT adding new load (penthouses, balconies, or mezzanines); and
 - you feel personally comfortable putting your stamp and signature on this.

Finally, you need to make sure you check everything.  You might determine
that the massive masonry shear walls and wood plank deck have plenty of
capacity, but what about the connection from the deck to the wall?  The
floor-wall connection in a lot of these old buildings consists of as little
as a steel strap buried in the brick every 8' or so and nailed to the floor
deck or beams.  Also, even more dangerous, there are often no mechanical
connections between beams and girders and girders and columns - just gravity
and friction.  

Good luck with this project, and don't be afraid to tell the owner what he
needs to hear (not just what he wants to hear).


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