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Re: Cambered Slabs

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Gail,
 
It might depend on the type of construction and the type of shoring, but it shouldn't be extra work for the contractor.  It is just a matter of setting the screw jacks higher at mid-span.  All formwork should come with adjustments for fine tuning the deck elevation.
 
With today's technology, survey and/or carpenter crews can use laser levels, pull strings, or shoot elevations the old fashioned way.  In any case, the work needs to be done.  There is just a little bit of extra attention that needs to be paid, and I don't think it should really affect the cost.
 
The contractor will probably screed the slab off of the forms, which would be constant height.  The top of slab elevation should therefore come automatically.
 
You can force the issue in the field by requiring spot deck elevations to be recorded and submitted before placing concrete.  If something goes bad, you have documentation to back it up.
 
James Wilson, P.E.
wilsonengineers(--nospam--at)yahoo.com
Stroudsburg, PA


GSKWY(--nospam--at)aol.com wrote:
How do you figure out how much cambering will increase the cost of the slab.  Do you ask the contractor to bid it both ways, or do you not want to know.

Seems like there would be some cost for the formwork, and also a cost for the finishing.  And particularly, an increased cost for checking the elevations during finishing.  

Gail Kelley



In a message dated 4/27/2004 10:47:32 AM Eastern Daylight Time, dfisher(--nospam--at)fpse.com writes:


Gail:

In Chicago, we simply indicate the value (usually in the neighborhood of 3/4â??-1â??)
in the center of the bay on the framing plan.

He (concrete guy) slopes the formwork up to the center of the bay in each directionâ?¦

Iâ??ve also seen slabs â??double formedâ?? i.e., flat primary forms with an additional plywood overlay
To achieve the camberâ?¦

The decks are typically surveyed within 6 hours of placement then immediately after strippingâ?¦



Regards,


David L. Fisher SE PE
Fisher + partners
372 West Ontario
Chicago 60610

312.573.1701
312.573.1726 fax

312.622.0409 mobile


From: GSKWY(--nospam--at)aol.com [mailto:GSKWY(--nospam--at)aol.com]
Sent: Tuesday, April 27, 2004 7:35 AM
To: seaint(--nospam--at)seaint.org
Subject: Cambered Slabs



I think a little while back there were some comments about cambering reinforced concrete slabs.

I have never actually seen this done.  How is this called out on the drawings?  What is in the specfications?

Also,  how does the contractor actually do this and how is it measured?

Gail Kelley





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