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RE: Cracks in Masonry

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David,

>From the sounds of your description, I don't see a reason why mortaring
the crack would not be acceptable.  I will offer that standard disclaimer
with that thought...there could be things that are not apparent in your
description that could change the situation.  ;-)

Regards,

Scott
Adrian, MI


On Sat, 13 Jan 2007, M. David Finley, P.E., P.A. wrote:

> The cracking is occuring only at the mortar joints.
>
> There is some movement out of plane, but where that occurs the displacement
> is for the majority of the wall height, so there is still bearing on both
> sides of the cracks - it is not like just a couple of courses are displaced.
> And the displacement is not large - perhaps a quarter of an inch.  This
> occurs on the rear wall on one abutment.
>
> The larger cracks are in plane and are located on the side walls.  This
> makes sense - as the thermal effects occur, the side walls (parallel to the
> tee-beam) are being stressed.  Once the bridge expansion has been addressed
> by proper joints, then the sidewalls should no longer experience that
> loading.
>
> David Finley
> M. David Finley, P.E., P.A.
> 2086 SW Main Boulevard - Suite 111
> Lake City, FL  32025
> 386-752-6400
>
>
>
> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> Sent: Saturday, January 13, 2007 6:05 AM
> To: Seaint(--nospam--at)Seaint.Org
> Subject: Re: Cracks in Masonry
>
>
> David,
>
> I assume based upon your description that the cracks basically occur at
> the masonry mortar joints primarily (i.e. based upon your conclusion of
> thermal effects...presumably thermal effects of the precast t-beam).  Is
> that the case or do you have significant cracking of the CMU units
> themselves?  Is the cracking/movement causing CMU blocks to basically move
> out-of-plane (i.e. pull out from the wall)?  If the later is true, then I
> could see some concerns of continuous bearing of the units at the bed
> joints at the faces of the units (might be only down to bearing at the
> webs if two successive courses don't line up).
>
> I would say that if the "bearing" of the face bed joints is still
> basically good and it is just a matter of some mortart joints opening up,
> then using mortar might be OK.  But, I can't get a good feel for how bad
> things may or may not be from your description.  I would say that the
> biggest issue may not be the repair of the cracks, but rather has the
> masonry lost enough structural integrity (i.e. out of plum or blocks no
> longer sitting directly on top of each other or "buckling" of the the CMU)
> to have general structural problems.  If the wall is stabile and doesn't
> have any serious overall structural deficiencies, then mortaring the
> cracks might be Ok.
>
> Regards,
>
> Scott
> Adrian, MI
>
> On Fri, 12 Jan 2007, M. David Finley, P.E., P.A. wrote:
>
> > Old pedestrian bridge consisting of single web precast t-beam.  60'-0"
> span.
> > Abutments are rectangular (8'-0" wide to match the t-beam and 6'-0" long).
> > The front (bridge side) wall bears on a concrete gravity wall.  The side
> > walls bear partly on the gravity wall and partly on a continuous strip
> > footing.  The rear wall is on a strip footing.  All of the masonry is
> > 8"x8"x16 CMU with no vertical or horizontal reinforcing and no grouted
> > cells.
> >
> > The masonry in the abutments has cracks, including some with in/out of
> plane
> > displacement.  The cracks appear to be caused by the fact that the
> original
> > construction apparently ignored thermal effects and "locked" both ends of
> > the single web t-beam into the front masonry wall.
> >
> > I am correcting the expansion issue by providing expansion joints at each
> > end of the bridge.  No problem there.  And the new expansion joints will
> > significantly reduce the forces being transferred into the masonry.
> >
> > The Owner (small town, so limited funds) wants to repair the masonry by
> > patching the cracks with mortar.  Some of the cracks are 3/4" wide.  Can
> > cracks that wide be adequately repaired with mortar?  Or should some type
> of
> > pressure epoxy grouting be used?
> >
> > Of course this bridge has historical significance, so the "tear down and
> > replace" option is not available.
> > David Finley
> > M. David Finley, P.E., P.A.
> > 2086 SW Main Boulevard - Suite 111
> > Lake City, FL  32025
> > 386-752-6400
> >
> >
>
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