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Re: Two conditions in residential construction (ACI 'plain concrete')

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Mark,
Does ACI offer any design guidelines for plain concrete, residential spread
footings?
Where in 318 would I find this?

Steven A.
Los Angeles



Mark Nowmos wrote:

> Judging from your area-code, if the project is in the same state as your
> office, you are probably dealing with neither the 2000 IRC or 97 UBC.  Most
> likely 96 or 99 BOCA.  With regards to the footing, it sounds like a spread
> footing for a pipe column.  If a 10" footing works for unreinforced
> concrete, and the bearing pressures seem reasonable to you, then no, you
> could let that one slide.  I usually throw some rebar in any footing I
> design, but if you are using ACI's guidelines for unreinforced concrete, it
> probably won't be a major issue.  If not, have the contractor put in what
> you specified.  Your second question:  I assume you mean diagonal
> gage-metal strapping?  Maybe not, but, I agree with Dennis, if it's not
> what you specified, make the contractor prove to you that it satisfies your
> requirements at his expense.  What about holdowns?  If he's skimping on one
> thing, he's probably trying to skimp on another.  While probably using the
> mantra, "We've been building this way for ...(insert zeros here) years with
> no problem."  You're right about the attachment of the straps.  Unless they
> use bolts, you usually can't develop the load without a big post or a some
> kind of gusset plate.  Has the local building inspector paid a visit and
> raised any issues?  As an aside, the only time I specify diagonal
> gage-metal strapping is when the framework is metal studs.  And they are
> either welded or have gusset plates to transfer the load.  But, it's easier
> just to specify a sheathing and a nailing pattern, rather than introduce a
> lot of, as a colleague of mine says, "gingerbread".
>
> Mark Nowmos
>
> Dennis Wish wrote:
>
> >
> > 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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