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Re: Two conditions in residential construction

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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
> 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
> 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?

First off, I never use unreinforced foundations of any kind, but I'll give
you my opinion.  If a 14" footing was required for plain concrete shear
based on the bearing area required (3 ft. sq.), then a 14" footing is
required whether the footing bears on rock or whatever.  If the footing
fails in shear, how is the fact that the footing sits on rock going to make
a difference unless you can assume a higher bearing value over less
effective area and somehow justify that the required bearing outside of the
"no-shear cone" is within the footings capacity.  Without a soils report you
are limited in the bearing value you may assume, who is to say the rock is
not sitting on pure garbage.

I would let the contractor know that he has the option of obtaining a soils
report to justify his field decision, which might result in the footing
being replaced anyway, or simply replacing the footing as specified.

> 2) A contractor has elected to not provide the required shear wall
> 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
> "other" engineer they hired to provide them with an alternate detail.  It
> 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
> 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.

They are doing what!!!!.  The "other engineer" is not responsible for the
job, you are.  I would not accept straps instead of a wood shear wall,
period.  If the "other engineer" wants to be responsible for the job, have
them all sign a letter for submittal to the building department that
relieves you of ANY responsibility on the project and designates the "other
engineer" as the engineer of record for the entire project.  The contractor
does not have the option to bring in other engineers to relax the
requirements of your design.  This is bordering unethical in my opinion.  It
is one thing for another engineer to help value engineer something and
assist with means and methods, then have the options with calcs and
justifications submitted to the EOR for approval, but it is quite another
for an engineer to relax the requirements without your consent.

Paul Feather

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