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RE: Adding a mezzanine to a Masonry Building in Seismic Zone 4

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Dennis

Here is how I would tackle this:

*	Design the mezzanine structural system completely separate from the
existing building. 
*	Leave sufficient seismic gap between the mezzanine edges and the
existing walls to allow for deformation without pounding on each other. 
*	The only portion of mezzanine you may want to tie into the existing
building is the top of second floor walls to the roof framing. Then the only
added mass to the existing building would be the tributary weight from the
top half of these walls. And unless you have a lot of walls on the second
floor the added mass would be negligible.
*	For the new mezzanine structure design all elements per current
code.

Ben Yousefi, SE
San Jose, CA

	-----Original Message-----
	From:	Structuralist [SMTP:dennis.wish(--nospam--at)gte.net]
	Sent:	Wednesday, May 16, 2001 10:38 AM
	To:	aec-residential(--nospam--at)polhemus.cc; SEAINT Listservice
	Subject:	Adding a mezzanine to a Masonry Building in Seismic
Zone 4

	I need to put together a proposal to add a wood frame mezzanine to
an
	existing masonry building in Palm Springs. The building is more than
	40-years old. The building is roughly a 3:1 aspect ratio (about
100-ft x
	35-ft) and the mezzanine (wood frame) will take up only about 1/3 of
the
	floor space (33' of the 100-ft width).
	The mezzanine will provide rooms which will be used for off space on
the
	first and light storage on the second floor. The mezzanine will
attach at
	the second floor diaphragm to the existing masonry building on three
sides.
	The masonry walls are 100% solid where the mezzanine occurs. One
side of the
	mezzanine is open at the second floor (it overlooks the first floor)
and the
	first floor walls will provide shear (lateral) resistance at the
open side.
	However, the second floor open side has no shear connection to the
roof.

	I would normally have added the mezzanine dead load into the
existing roof
	dead load (adding about 5-psf over the entire roof), and
re-calculate the
	lateral analysis to the masonry walls to verify that they have the
capacity
	to resist the additional shear. At the open side of the mezzanine, I
would
	have calculated only the second floor diaphragm shear transfer into
the
	first story walls to resist drift. Considering that there the two
structures
	are tied together, does this seem like a reasonable plan? The
lateral load
	from the roof is distributed to the four masonry walls and would
include the
	weight of the mezzanine - but the open front of the mezzanine is the
only
	side unaccounted for that I would use the first floor shearwalls.

	So here are a couple of questions for Zone 4 areas;

	1. Is it appropriate for me to simplify the design by using the
guestimated
	base shear (conservatively) at 0.186Wd to calculate the lateral load
caused
	by the mezzanine and verify all existing masonry walls to laterally
support
	the addition?

	2. Would I be expected to bring the structure into compliance with
the
	current code (near source values, full-compliance by flexible and
rigid
	design)?

	3. Would I be expected to use flexible design for the unsupported
side of
	the mezzanine based on the Simplified Static Design
[0.3ICa/(1.4R)]*Wd ?


	Regards,
	Dennis S. Wish, PE

	 

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