Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Two conditions in residential construction

[Subject Prev][Subject Next][Thread Prev][Thread Next]
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
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********