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I read the following text.
 
Gary, you have excelled in drawing pictures with words.
 
I still get drowned.
 
Perhaps I do not have as much imagination.
 
Can you send some pictures?
 
Sincerely,
Gregory from Oz
 
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Subject: Structural Failure
From: "Gary Loomis" <gloomis(--nospam--at)MasterEngineersinc.com>
To: <seaint(--nospam--at)seaint.org>

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We are investigating a failure in a building and designing modifications =
to
repair the structure.  We do not understand the cause of the failure and
would appreciate any thoughts.  We have several theories but have not =
come to
a conclusion.
=20
The building is a two story structure approximately 40' wide and 200' in
length.  It is approximately 30 years old. There are no drawings =
available
and there are a total of 4 buildings built at the same time and in a =
similar
manner.  The exterior walls from grade to the second floor are 8" cmu =
and 4"
brick which supports the second floor.  The structure above the second =
floor
is a pre-engineered building - steel framed structure with metal siding.
There are concrete pilasters in the exterior wall that support the =
columns
(spaced at 25' oc) of the pre-engineered building.  The second floor is =
a
concrete and metal form deck supported by steel bar joists spaced
approximately 2' oc.  There is a bond beam with (2) #3 bars at the top =
of the
cmu with a 1/4" x 3" steel plate for the joists to bear on.  We do not =
know
if the joists are welded to the plate or if there are anchors on the =
plate.
It appears the steel bar joists provide a tie at the top of the wall to
resist the horizontal forces from the pre-engineered building frame.
=20
The first floor is a slab-on-grade cast monolithically with the grade =
beam
and footings at the pilaster.  We have done some selective demolition to
expose the grade beam and footings.  The grade beam is 24" deep and the =
width
at the bottom of the grade beam varies from 6" to 12".  There is a brick
ledge approximately 12" below the top of grade beam (finished floor).  =
We
have not confirmed rebar yet.  There are footings at the pilaster.   The
footing thickness based on core borings is 8" (top of footing is the =
same as
finished floor).  No rebar was found.  There is welded wire fabric in =
the
floor slab - at the bottom of the concrete.  The size of the footing is =
5' x
4'.  However, the outside face of the pilaster is 5" from the outside =
face of
footing/grade beam to allow the brick to pass by (causing an eccentric =
load
on the footing).
=20
The floor slab has settled 2" along the edge near the masonry =
wall/pilaster.
There is a crack in the floor slab approximately 5' from the wall.  The =
width
of the crack is 3/8" minimum.  This occurs along approximately 1/2 the =
length
of the building on one side.  The remaining length shows some settlement =
but
no cracks.  The other side full length is some settlement, but no =
cracks.
There are step cracks in the brick between the pilasters.  Finally, at =
one
end of the building, the steel bar joist has cracked (failed) the top of =
the
pilaster.  The width of the crack is 3".  The rebar in the bond beam has
failed in tension at the pilaster. =20
=20
We have performed soil borings along the outside and on the inside where =
the
crack in the floor was the worst.  At the end of the building where the
pilaster failed, the depth of fill was approximately 18'.  At the other =
end
of the building there was 23' of fill.  However, the fill was well =
compacted
and the geotechnical engineer recommended an allowable soil bearing =
capacity
of 2,500 to 3,000 psf.  The blow counts on the inside were 15 to 18.
=20
The load on the soil is 5 ksf (dead and live) and 3.2 ksf (dead).  If we
assume the grade beam transfers the load to the footings.
=20
We have found no water sources.
=20
There has been cracks in the masonry walls for sometime.  Cracks have =
been
caulked.  Last December a crack in the wall was visually inspected and =
the
width of crack was 1".  We measured it last week and it was 2-1/2".  =
There
were cracks in the concrete floor slab for sometime.  Nobody can define =
when
the cracks first occurred.
=20
One theory is that this a long term settlement problem.  As the =
structure
(floor slab) settled, loads were redistributed and the floor slab =
started
carrying more and more load.  This caused more settlement and the walls =
moved
out causing an increase in axial forces on the joists.
=20
We are thinking of modeling the floor slab, grade beam, and footings
supported by springs to represent the soil to determine how much load =
the
floor slab would support.
=20
Your thoughts would be appreciated.  Why nothing for 30 years?