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RE: Structural Failure

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Jordon, 

Our geotechnical engineer is performing tests but we do not have the results
yet.  But you would think in 30 years there has been droughts worst than this
year.  A few years ago the lakes were much lower than this year in western
VA.  

Appreciate your thoughts.

gary

 

Gary -

Here's a stab in the dark - Is there any chance that the end of the
building which has dropped has an excessive amount of expansive clay
when compared to the rest of the fill?  We've seen a lot of long term
settlement issues get out of hand this summer in the western end of VA
due to the drought.

Jordan



Gary Loomis wrote:
> 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.
> 
> 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.
> 
> 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).
> 
> 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. 
> 
> 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.
> 
> 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.
> 
> We have found no water sources.
> 
> 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.
> 
> 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.
> 
> 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.
> 
> Your thoughts would be appreciated.  Why nothing for 30 years?
> 
> Gary Loomis, PE
> Master Engineers and Designers, Inc.
> 
> 
> 
>
> ________________________________
>
>  

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