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RE: Retrofit Masonry walls

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Joe,

Your further information definitely makes me want to ask a question that
your original post was almost causing me to ask...why the need to
reinforce the existing masonry walls?  In otherwords, is there a
structural need to reinforce the walls or is just cause the owner wants to
(talk about a first) and it will give you a "warm fuzzy" feeling?  Have
you run some numbers and determine that the walls should be reinforced due
to the loads on them?

In particular, I look at the basement walls.  According to this most
recent post, they will really no longer be basement walls (i.e. according
to this recent post there will be retaining walls that will relieve the
soil pressure on the basement walls).  If so, the unless you are getting
serious wind or seismic on the walls, they should only be carrying gravity
(axial) load, in which case ungrouted, unreinforced should likely work
well (unless you have REALLY high axial loads in the wall).  Out-of-plane
wind should be minimal, as the basement walls may be sheilded by the
retaining walls (depending on how close they two walls are).  Out-of-plane
seismic could be an issue, as could in-plane wind and/or seismic.  It was
possible that the unreinforced wall could calc out even with the soil
pressure on it, although I admit that I am _NOT_ a fan of unreinforced
basement walls (either in masonry or concrete) and the ungrouted fact
would have still been a problem (in my opinion).

My point is that you have "eliminated" the most significant load that
would likely lead to a calculation that would indicate the need for
reinforcement.  As result, I really wonder if there is a structural need
to reinforce the masonry.

Now assuming that there is a structural need or the owner just plain wants
to do it, then I many of the ideas previously suggested would make sense.
Building a new wall of shotcrete on the inside (or outside since the soil
has been removed according to your post) with existing masonry as a
form/surface to apply to makes sense.  You might also be able to use
standard cast-in-place concrete with the existing masonry as a form if you
are not comfortable with shotcrete.

Using steel (or reinforced concrete
or new reinforced masonry) vertical columns at some uniform distance with
the existing unreinforced masonry spanning horizontally between the
columns could work.  You just pick the spacing based upon how far the wall
can span horizonatally.  Must determine if the foundation can accominidate
the new columns and care should be taken to insure no gravity load in the
columns (unless you can fully transmit that gravity load in the soil in an
appropriate manner as well make all the connections/load path work).  You
will still have to figure a way to tied the new columns to the existing
wall in case wind suction is an issue for the walls.

You can, of course, cut face shells and put in new rebar.  Personally, if
you do that, then I would follow requirements of the current masonry code
for determining things like spacing, size, etc.  After all, if there is a
need for the reinforcing, then that reinforcing should still be designed
to be effective.  And the one provision that would effect the spacing of
the bars is the "effective compression width of bars".  This leads to the
requirements that reinforced be limited to the lesser of bar-to-bar
center-to-center spacing required by analysis, 6 times the thickness of
the wall, or 72 in (assuming that you have running bond).  This basically
leads to 48 in max spacing if your wall is 8" CMU, unless analysis leads
to a need for closer spacing.  The 48" is the maximum compression width
that you can attribute to a bar by code.

HTH,

Scott
Adrian, MI


On Wed, 23 Mar 2005, Joe Grill wrote:

> Bob,
>
> To answer a couple of you questions, which may help others help me.
>
>
>
> Existing footing reinforcing hasn't been determined, although probably
> minimal as the foundation actually rests on a very good rock strata.
> Basement slabs are in great condition.
>
>
>
> Also, the exterior soil has been excavated away from the basement walls.
> Landscaping retaining walls are going to be constructed so the basement will
> no longer retain any soil, and solid grouting should not be required.
> During the "gutting" process past water infiltration was noted, but should
> no longer be a problem.  There may be some joint reinforcing present, but
> probably not in any quantity, if any.  At this point I wouldn't be "skeered"
> of saw cutting some face shells at 4' or maybe 6' spacing, as the walls are
> pretty lightly loaded now, and much, much more lightly loaded laterally than
> they were a couple of weeks ago.
>
>
>
> Joseph R. Grill, P.E. (Structural)
>
> Shephard - Wesnitzer, Inc.
>
> Civil Engineering and Surveying
>
> 1146 W. Hwy 89A Suite B
>
> Sedona, AZ  86340
>
> PHONE (928) 282-1061
>
> FAX (928) 282-2058
>
> jgrill(--nospam--at)swiaz.com
>
>
>
>  <http://inet/index.htm>
>
> -----Original Message-----
> From: Robert Freeman [mailto:robert.freeman(--nospam--at)idsse.com]
> Sent: Wednesday, March 23, 2005 12:28 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Retrofit Masonry walls
>
>
>
> Joe:
>
>
>
> This is a tough one.
>
>
>
> You may want to consider reinforced shotcrete on the interior of the
> basement and other bearing/shear walls.  This approach may be cheaper.  It
> would be dowelled and grouted into the existing hollow masonry and footings.
> Construction shoring may not be required.  The existing un-reinforced and
> un-grouted masonry would be formwork.
>
>
>
> What existing footing/reinforcement do you have?
>
>
>
> What is water infiltration like in the basement?
>
>
>
> I would be concerned about trying to sawcut, dowel and grout the existing
> masonry at the basement since all cells are required to be grouted.  The
> wall appears to need horiz. and vert. rebar.  Shoring of the floor above may
> be needed during construction.
>
>
>
> With the gravity load weakness (and no grouting) of the basement and shear
> walls, this project does not appear to be a candidate for fiber wrap.
>
>
>
> with Joy and Hope,
>
> Bob Freeman, Architect
>
> Structural Designer
>
> Integrated Design Services, Inc.
>
> (949) 387-8500
>
>

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