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Re: 33-ft simple span slab

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David,

For a span of 38', 15 1/2" thick slab (12" hollow core plank with 3 1/2"
topping) appears very generous. I just happened to look at an existing
parking structure (built in 1972) a few weeks ago. It has a 48' span (with
continuity at one end) floor slab made of 10" LTW hollow core plank with 2"
topping. In fact I walked many times on the floor with moving cars, I never
had any perceptions of  vibrations.

Personally I don't like to use hollow core planks, especially for buildings
in areas of high seismicity. The cores prevent me from developing sound
details (between planks and between planks and supporting elements) required
for positive diaphragm actions.

As for coring thru the planks required for elec conduits or plumbing,
normally I would add one more strand to each piece of plank (say 8' wide)
than required to compensate the loss just in case. These penetrations are
usually small in diameters and can be easily located between the strands
with metal detectors.

Ben

----- Original Message ----- 
From: "David Topete" <davetopete(--nospam--at)yahoo.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, May 13, 2005 8:03 AM
Subject: Re: 33-ft simple span slab


> I've been following this thread, and i'd like to offer
> my thoughts, if I may...
>
> I just worked on a project where we ended up using
> hollow core precast planks (12" ltwt, I believe...)
> with a 3-1/2" n.w. fill.  That spanned about 38' clr.,
> and was designed for office/clerical spaces, so 50psf
> + 20psf partition + add'l 10psf for misc. DL.  (The
> corridor loading was at one end of the plank, so shear
> was okay.)  That was pushed to the limit for
> deflection, even with the planks cast with up-camber.
> The n.w. topping slab was needed to have adequate
> cover and strength for shear transfer.
>
> I think another thing to consider with the 3" plank is
> when you have the HVAC/mech'l contractor come in to
> attach the duct work...  All of those PAF may or may
> not hit a prestressing strand, but it likely
> accelerate the cracking in the planks.  Well, logic
> tends to lean that way...
>
> David Topete, SE
> SF, CA
>
> --- Rhkratzse(--nospam--at)aol.com wrote:
> > Conventional rebar.   I don't know if it was
> > cambered.
> > Ralph
> >
> > In a message dated 5/13/05 1:41:41 AM,
> > zhoub002(--nospam--at)hawaii.rr.com writes:
> > > Ralph,
> > >  Was the slab post-tensioned or conventionally
> > reinforced?
> > >  Ben
> > >
> > >
> >
> >
> >
> >
> >
> > Ralph
> > Ralph Hueston Kratz
> >
> > Rhkratzse(--nospam--at)aol.com
> >
> > 510-236-6668
> > Fax 510-215-2430
> >
> > 724 McLaughlin Street
> > Richmond CA 94805-1402 USA
> >
>
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