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

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Having recently tried to model a monlithic concrete deck and beams in
Risa3d,
I can tell you that you're in for a big headache.  It is very teadious to
obtain
the results needed for design.  I hand checked many of the moments and
shears,
and if they didn't agree with what I thought should be there, I upped the
reinforcing
anyway.  I suspect that I didn't have a fine enough mesh, which would make
the job
even more tedious.

Also, if you are planning to do a dynamic analysis for seismic forces, the
relatively
flexible concrete deck may give you problems.  It may be difficult to get
the 90%
mass participation needed by code.  However, where your structure is so
tall, this
may not be an issue.  I tried it on a two story building, and quickly gave
up.

Dan Goodrich, P.E.


----- Original Message -----
From: "M Hariharan/engg" <hariharan.m(--nospam--at)eil.co.in>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, November 21, 2000 8:07 PM
Subject: Re: SAP2k: Modeling concrete floors with monolithic conc. beams


> 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.
>
> Hariharan
>
> 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)earthtech.com]
> > Sent: Tuesday, November 21, 2000 8:57 AM
> > To: seaint(--nospam--at)seaint.org
> > 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)spk.usace.army.mil]
> > Sent: Monday, November 20, 2000 10:40 AM
> > To: 'seaint(--nospam--at)seaint.org'
> > 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
> >
> >
> >
>
>
>
>
>