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Re: SAP2k: Modeling concrete floors with monolithic conc. beams

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I agree you should save weight in such a structure. Why don't you go for a steel
structure, with steel plating for deck, and a concrete screed on top? You will
get the benefits of a concrete decking, without losing advantages of steel
construction, which integrates well with your substructure. Joint design between
steel substructure and concrete beams could also be a major problem? I am also
not sure if you can save weight by a finite element analysis of a concrete
beam-slab system.


Khosrownia, Ghassem SPK wrote:

> I agree with your suggestions. The reason I am looking for a more precise
> method is that the concrete structure is sitting 130 feet on top of a
> slender steel control tower in seismic zone 3. I am trying to save weight
> everywhere that I possibly can. Also the concrete structure is modeled along
> with the steel tower itself.
> Ghassem
> -----Original Message-----
> From: Lutz, James [mailto:JLUTZ(--nospam--at)]
> Sent: Tuesday, November 21, 2000 8:57 AM
> To: seaint(--nospam--at)
> Subject: RE: SAP2k: Modeling concrete floors with monolithic conc. beams
> I don't think I would add beams between plate nodes, because the neutral
> axes don't line up. It might be preferable to model the stems below the
> floor slab as a series of vertical plates so the overall model behaves more
> accurately. The problem is that the output is not in a very convenient form.
> In order to design the beam steel, you have to interpret the tensile
> stresses in the stem of the beam plate element (based on an elastic
> analysis)and figure out what that means in terms of steel requirements. It's
> a little messy.
> If your floor consists of closely spaced beams, you can create T-shaped beam
> elements and just lock the end nodes together to simulate the diaphragm
> action.
> Even if the beams aren't closely spaced, you can still analyze the system as
> a frame to get the beam moments, and separately design the floor slab. The
> building code only allows you to count a certain amount of slab width as
> effective flange anyway.
> Unless this is an academic exercise, why get too carried away with an
> over-precise elastic model when you are dealing with elements whose actual
> cracked section properties are distributed in a very unpredictable way?
> -----Original Message-----
> From: Khosrownia, Ghassem SPK [mailto:GKhosrownia(--nospam--at)]
> Sent: Monday, November 20, 2000 10:40 AM
> To: 'seaint(--nospam--at)'
> Subject: SAP2k: Modeling concrete floors with monolithic conc. beams
> How would you define finite elements for a concrete floor structure when
> concrete beams are involved?
> Thanks.
> Ghassem