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Re: Beam vs "Slab band"

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Slab bands are common in P/T design.  The basis for slab band design was
established by Bijan Aalami and the Post-Tensioning Institute in 1989. (I do
not have the specific paper titles handy)

Slab bands are only applicable in two way  P/T design.  The limitation on
total depth less than twice the slab thickness (including slab thickness)
and total width less than three times the depth (including slab thickness)
is required to avoid altering the two way behavior of the floor system.
Dimensions greater than this will increase the relative stiffness of the
slab band and alter the behavior of the slab system.

Stirrups are not typically required in slab bands since the concentration of
shear forces is offset by the upward component of the P/T tendons.  The
required cover would be the same as for the slab, just like in drop panel
systems.

In my opinion, a non-prestressed application or prestressed application with
dimensions outside of the stated limits for stiffness considerations would
be a beam and not a slab band, regardless of what you call it, and the
resulting modification to the slab behavior would need to be accounted for
and detailed accordingly.

Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
----- Original Message -----
From: "John Diebold" <Jdiebold(--nospam--at)SanDiego.gov>
To: <seaint(--nospam--at)seaint.org>
Sent: Monday, October 21, 2002 10:45 AM
Subject: Beam vs "Slab band"


> I've seen several projects where what appears to be a "beam" element is
> being called a "slab band" by the designers.
>
> Has anyone else seen these?
> Are there any clear definitions of what is a "beam" vs a "slab"?
>
> This so called "slab-band" is being treated by the design engineers as a
> slab, from the point of view of fire protection/cover requirements, and
shear reinforcement,
> although some nominal amount of stirrups are provided at certain "critical
zones".
>
> What I am seeing deviates from the "slab band" concept known in
post-tensioning design,
> in that many of the "slab bands" are deeper than twice the slab thickness,
and their purpose
> has nothing to do with post-tensioning - as they show up on reinforced
concrete slabs.
>
> ACI and UBC appear to not have a clear "beam" definition, hence there is
some difficulty
> in applying the deformation compatibility requirements of 1921.7.
Furthermore, design methodology
> is utilizing SAFE or Adapt Floor or Bommer Coleman's PT program which uses
a finite element mesh
> for design.
>
>
>
>
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