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RE: Two conditions in residential construction

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I wanted to read a few responses before I sent mine. I agree with the
majority, but want to make a few points very clear. Let me start with
the Let-in strapping first and work backwards.

You did not indicate what seismic zone (or wind zone) you are in. Let-in
bracing is still allowed in all but seismic zone 4 as a braced wall
panel material. However, you designed this project and it was not
permitted as a prescriptive design in compliance with the 2000 IRC or
the 97 UBC Section 2320. The builder has no right to change the details
you designed for lateral bracing and you have the right to stop the job
and make him replace the work he did.

In Seismic zone 4 (or D per the 2000 IRC) let-in braces are used as you
indicated - to keep the walls plumb until sheathing is nailed in place.
The builder may also choose to sheath the wall flat and without diagonal
bracing and tilt the wall up in place. In this manner, the shearwall
sheathing is used to assure that the wall is plumb (although I don't
recall seeing a framer actually do this inasmuch as most low cost labor
is paid by the total length of studs laid up each day).

With regard to issue one - rock foundation; this is not a typical case
in most regions and as others noted, you have no idea who much of the
outcropping exists to secure the foundation to. I am concerned that you
are using an unreinforced foundation as this will not help to resist
uplift on panels in high risk areas - but again, you have not indicated
where this is being constructed.

In my opinion, a home is only as good as the foundation it is
constructed on. If the site condition does not comply with the worst
case code condition and is considered anything better (including the
assumption that you are building on bedrock) then it is best to leave
the liability for the foundation to a geotechnical firm who should be
advising you as what is appropriate. 

Don't be afraid to be conservative - your client will most likely bitch
and moan as the builder accuses you of over-designing. This is normal
since the owner and the builder do not understand the principles of
mechanics and the requirements of the code. I can guarantee you this, if
you give in, the client will seek you out with a vengeance at the first
crack that appears and will probably hire another professional to
evaluate your work so as to find flaws in what you have done. The first
big flaw will be that you did not stop the job and demand the contractor
to do it your way.

Regards
Dennis

Dennis S. Wish, PE
California Professional Engineer
Administrator - The Structuralist.Net
Website: 
http://www.structuralist.net
 
Professional Forum: 
http://www.structuralist.net/cgi-local/yabb/YaBB.cgi
 
Public Forum on Housing: 
http://www.structuralist.net/cgi-local/yabb2/YaBB.cgi

-----Original Message-----
From: Albert Meyer [mailto:Ameyer(--nospam--at)martinaia.com] 
Sent: Thursday, December 06, 2001 10:34 AM
To: seaint(--nospam--at)seaint.org
Subject: Two conditions in residential construction

I have a few questions regarding some conditions that occasionally come
up
in residential construction that we deal with, and I thought I'd solicit
some opinions on two of them that have come up recently.

1) A contactor building a single family home encountered "rock" when
excavating for a basement foundation, and where we had specified an
unreinforced 36"x36"x14" concrete footing, a footing with a 10" depth
was
placed.  The wants to know if this is OK.  There is no soils report, as
is
typical for this type of job, and neither he or I know what type of rock
is
on site.  Many take the attitude that "Oh it's only a single family
home,
it's fine", but what would you do?
	
	Would you say: Hire a geotech to ascertain the allowable soil
value,
use this value to determine what minimum footing size is required and
check
to see 	that the footing works for both bending and punching shear?

	Or: Remove the existing footing and excavate to the required
depth
and replace the footing?

2) A contractor has elected to not provide the required shear wall
sheathing
on some interior unit separation walls of a multi-family dwelling, and
has
instead installed diagonal straps on the walls.  No special nailing or
attachment at the ends of the straps has been done nor was specified by
the
"other" engineer they hired to provide them with an alternate detail.
It is
my feeling that diagonal straps on wood frame shear walls are not a
practical solution since even though you can specify a strap that works
for
the tension load you generally can not provide the attachment required
at
the end of the strap unless you provide a large solid sawn post (not
typically available in this area) or a Parallam post and or solid
blocking
appropriately fastened into the corners of the shear panel.

Am I being too conservative the issues here?
Does any one else do diagonal strapping on wood shear walls and if so,
how?
Any and all opinions are gratefully appreciated!

Albert J. Meyer, Jr., P.E.
Martin-Espenlaub Engineering
(215) 665-8570 Tel
(215) 561-5064 Fax
ameyer(--nospam--at)martinaia.com


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