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

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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.


-----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

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?