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RE: Slab Stripped before time ...

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Thor --

We recently had some very good success with having a large concrete
column scanned using ground-penetrating radar (GPR).  The project was in
Oklahoma and the test was done by a local testing lab there that
provides the service.  It's likely there would be a company with this
capability in your area.  They scanned all sides of the column,
interpreted the results, marked the locations of the ties and main
reinforcement on the column with masking tape so anchors could be
drilled and epoxied into the column, and provided a report detailing
their findings.  I was pretty impressed with the work.  It cost $1300.

-- Joel Adair
    SHW Group
    Plano, TX

-----Original Message-----
From: Thor Tandy [mailto:vicpeng(--nospam--at)telus.net] 
Sent: Sunday, May 08, 2011 5:30 PM
To: SEAInt
Subject: RE: Slab Stripped before time ...

Corrected typos

 

Interesting question .

 

I have been asked to do a structural review of an existing residence
that
has a significant area of the footprint a suspended slab on circular
columns.

 

I understand that the slab formwork was stripped before the slab had
completely cured . yes there is a noticeable trough in the main part of
the
slab.

 

It is a 6"+/- slab and the two-way span is approximately 15ft and the
main
deformation is probably about 2".  Built in 1990 the original owner, who
is
now selling, accepted the flaw.  There has been no
perceived/recorded/admitted problem since.

 

In general the construction looks good and, except for some spalling of
columns due to bits of tie-wire at the surfaces, appears sound.  The
formwork was sonatube and although I have to get the original
construction
dwgs but I assume the reinforcing was tied steel cages.

 

My questions:  

 

1)      Does anyone know of literature on, or record of, impact on the
strength and/or serviceability of slabs that have deformed during the
curing/strength-gain period?

2)      Although the spalling appears localized to the tie-wire
locations,
there is number of them.  Could this also be a sign of deeper issues?
I.e.
would the tie-wire spalling open up access to the stirrups etc in the
column?

3)      Has anyone scanned columns for internal content checks?

 

Thanks

 

Thor A. Tandy P.Eng, C.Eng, Struct.Eng, MIStructE
Victoria, BC
Canada 

 

 




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