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Re: Differential temperature effect

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Bulent,
I completely agree with James Lutz.
The Timoshenko formula provides the moment at the clamped edges of of a
plate that zerors the curvature at this area. In a cylindrical silo wall
every meridian section (parallel to the cylinder axis) lies on a symmetry
plane and therefore it does not rotate, so it can be considered ''clamped''.
The same holds true for infinite plates with no free edges (imagie pavement
plates of very large dimensions).
For that reason the moments along the periphery of the cylinder are
uniformly distributed and at every point satisfy the Timoshenko asumptions,
so they follow his formula. For plates of different shape
 and finite dimensions the results depend on the boundar;y conditions.
Therefore one should not expect to get the Timoshenko momments uniformly
distributed over the plate area.
Although I am not a SAP user I do not think that there is any problem with
the program. Temperature gradient is a rather trivial loading case to be
overlooked by an experienced programer.

Stathis Papageorgiou
Athens, Greece

----- Original Message -----
From: "Lutz, James" <James.Lutz(--nospam--at)earthtech.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, February 27, 2003 8:45 PM
Subject: RE: Differential temperature effect


> Could you describe what you are designing a bit? Sounds like a silo if you
> are using ACI 313. The ACI 313 (Timoshenko) formula only computes flexural
> stresses in simple plates. It would seem to me that boundary conditions
> might effect your results in a more sophisticated model. Also, temperature
> changes induce membrane forces in plates which would also have an impact
on
> the total force experienced in individual elements. What is the relative
> difference in results from your two methods? Which one is giving you
bigger
> numbers?
>
> -----Original Message-----
> From: Bulent Deveci [mailto:bulentdeveci(--nospam--at)superonline.com]
> Sent: Thursday, February 27, 2003 9:52 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Differential temperature effect
>
>
> Lutz,
> In ACI 313 clause 4.4.9 states that :
> The thermal effects of hot stored materails shall be considered for
circular
> walls or wall areas with total restraint to warping (as at corners of
> rectangular silos), the thermal bending moment per unit of wall height or
> width shall be computed by
> Mt = Ec*h2*alfa*DeltaT / 12(1-poission)
> This is the same formula given by Timoshenko.
>
> But as for Sap2000, there are two options. One "temperature t" which is
> constant through the thickness and produces mambrane strains
> The second, "temperature gradient t3" which is lineer in the thickness
> direction and produces bending strains.
> It is obvious that I have to use the second option. But unfortunately, my
> results are very far from those I've obtained from the above given
formula.
>
>
>
>
>
> ----- Original Message -----
> From: "Lutz, James" <James.Lutz(--nospam--at)earthtech.com>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Thursday, February 27, 2003 7:17 PM
> Subject: RE: Differential temperature effect
>
>
> > I haven't done it, but it looks like it is possible. It wasn't clear if
> you
> > are just modeling a frame or if there are plate elements involved, but I
> > think it will handle it either way. It's a pretty powerful program (once
> you
> > figure it out.)
> >
> > I think you may have to create a batch input file since the graphical
> users
> > interface is limited to more routine kinds of problems as far as data
> entry
> > goes. If you have already created a basic model using the GUI, you can
> dump
> > it into a text file and edit it to get the stuff you need in there.
CSI's
> > manuals aren't the greatest for figuring this stuff out. Good luck.
> >
> > -----Original Message-----
> > From: Bulent Deveci [mailto:bulentdeveci(--nospam--at)superonline.com]
> > Sent: Thursday, February 27, 2003 8:26 AM
> > To: seaint(--nospam--at)seaint.org
> > Subject: Differential temperature effect
> >
> >
> > List,
> > Does anyone of you have any experience in designing a reinforced
concrete
> > structure
> > having differential thermal conditions with SAP2000 software? I'm just
> > trying to design a complicated RC structure with nearly 300 C
differential
> > temperature and I don't have the chance of insulating it due to the
> process
> > of the structure.
> > I have tried to obtain the bending moments by means of SAP2000 software
> but
> > I'm not able to satisfy the results given in some text books such as
> "theory
> > of elasticity" by Timoshenko.
> >
> > Any comment would be appreciated.
> >
> > Bulent Deveci
> >
> >
> >
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