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RE: Concrete slab retrofit (fwd)

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In a similar fashion, I once designed a steel frame above an existing
precast concrete roof to distribute the added loads as follows: Two steel
beams spanned parallel to the precast panels, such that the added loads were
delivered at about the 1/4-points of the span, as four point loads. This
significantly reduced the flexural loads on the existing precast. The steel
beams were set above the top of roofing so that there was no direct load
sharing with the concrete over the middle half of the span. But this does
require that the existing concrete have some excess capacity, just not as
much extra flexural capacity. 

William C. Sherman, PE
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)

> -----Original Message-----
> From: Eric Green [mailto:EGreen(--nospam--at)]
> Sent: Friday, December 20, 2002 11:41 AM
> To: seaint(--nospam--at)
> Subject: RE: Concrete slab retrofit (fwd)
> Do what I have done in the exact same situation (the details are so
> close it is almost scary). Assuming you have head room, construct a
> frame on top of the slab that distributes the weight to three of the
> joist. I used SS tubular steel members to construct a "mat foundation"
> that went under the MRI and spanned 3 joists. The stiffness was chosen
> to ensure that the load was actually spread out to all three members,
> although the center joist did end up with a bit more than the outside
> joists. Much, much cheaper in our case than working underneath b/c the
> space below was a clean room.
> Eric Green

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