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Re: URM Building per UCBC

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Larry, see comments below.

Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
----- Original Message ----- 
From: <lrhauer(--nospam--at)earthlink.net>
To: "SEAOC" <seaint(--nospam--at)seaint.org>
Sent: Tuesday, November 25, 2003 3:16 PM
Subject: URM Building per UCBC


> I am engineering a seismic retrofit to a one story URM building in seismic
zone 4, using the special procedure of the current UCBC, Appendix Chapter 1
and I am stumped on a couple of things someone out there might be able to
help me with.
>
> First, the 2 exterior 13" thick URM walls have an adhered veneer of about
a 1" thick portland cement backing applied to the face of the 13" URM, and
then about a 3/4" veneer applied with a mortar bed, in other words, no
veneer ties. since it is an adhered veneer without ties, it would seem to me
Section A113.t of the UCBC does not apply. Am I correct??

Correct.  The provisions you refer to are for existing full brick veneer.
Does not do any good to strengthen the wall if an existing veneer crumbles
off and kills the passing pedestrians.  One question is what is being done
to help the wall support the additional seismic mass out of plane?



> Second, I have one interior 13" URM property line wall which had very low
mortar tests with an average Vto of about 15 psi. I can drop these from my
other tests since they are the lowest 20%, but I am concerned over Section
A106.3.3.4, item #2 requiring "Individual unreinf. masonry walls with Vto
consistently less than 30 psi shall be entirely pointed or removed".
Repointing doesn't seem to make sense since it will only effect the outer
3/4" of masonry and I think the mortar strength is low throughout the
thickness of the wall since it is an interior wall. Removing the wall is
uneconomical. If I meet the h/t requirements of 16, provide wall anchors at
the top to the roof, and introduce a lateral resistive element such as a
plywood shear wall directly in front of and parallel with the wall, can I do
away with the pointing/removal requirement, or is the logic such that the
wall is a hazard in its present condition?


I do not see how an interior wall can be a property line wall.  Part of this
is engineering judgement.  The basic premise is that with Vto as low as you
indicate the wall is a hazard, period.  Your values are so low repointing
probably won't be sufficient, and you are correct that it doesn't make sense
in your case.  The wall should be removed or have its structural function
replaced.  If you provide an alternate wall in front of the wall as you
indicate that provides shear and bearing you are meeting the intent.  My
only comments would be the h/t of 16 is dependent on meeting the cross wall
criteria, also I would not be comfortable using a plywood shearwall parallel
to the wall in question.  The plywood cross walls are permissible under the
UCBC, but acting in the same plane I would think the masonry wall will be
stiffer, even with the lousy mortar strengths, and that the masonry wall
will fail and crumble prior to the new plywood shear wall being truly
effective.  If the wall crumbles, will it take out the plywood wall
effectively leaving no wall?  I would lean towards a shotcrete solution.  My
two cents worth.



> Any enlightenment would be appreciated.
>
> Larry Hauer S.E.
>
>
>
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