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# RE: Plate w/ Large deflections - Need diaphragm stress at edge

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Plate w/ Large deflections - Need diaphragm stress at edge
• Date: Wed, 28 Nov 2001 09:44:55 -0700

to evaluate the membrane component in thin plates you might follow this
algorithm (one-way slabs/beams):

1-input a sag (trial)
2-calculate a new length: you might assume straight segments or a parabolic
curve. the eq. for a par. curve is: Lnew=L(1+2.66667*(s/L)^2); where s is
3-calculate the axial force P, based on the length change.
4-get the vertical reaction V=wL/2
5-calc. the Horizontal Component: R=sqrt(V^2+P^2)
4-calculate Mm=R*s (membrane moment)
5-calculate Mb (as a beam) from the deflection eq. (5/384wL^4/EI)
6-Mtotal=Mb+Mm
7-If (Mtotal <> M=wl^2/8) goes to 1 and change your sag
8-end

I don't have a formal reference. This is based on a spreadsheet that
somebody borrow me,

-----Original Message-----
From: Keith Fix [mailto:kefix(--nospam--at)yahoo.com]
Sent: November 28, 2001 6:37 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Plate w/ Large deflections - Need diaphragm stress at edge

I was under the impression that errors had been discovered in the PCA
tables,
or that there were specific conditions required for them to be valid.

In any case, what I need would be applicable only for thin plates where
diaphragm stress (tensile stresses) form in the plate due to large
deflections.

-Keith Fix, PE
-Little Rock

> Keith,
>
> The book "Rectangular Concrete Tanks"  by Javeed A. Munshi published by
> Portland Cement Association has flat plates with different edge support
> conditions and aspect ratios.  It only considers uniform loads and uniform
>
> The results are moments, shears and deflections along all edges.
>
> You can order the book from:
>
> PCA, 5420 Old Orchard Rd. Skokie IL  60077-1083
> (847) 966-6200  fax (847) 966-9781
>
> If you just have one or two plates that you are interested in you can fax
me
> the plate size, edge support conditions and loading-I'll send you the
> appropriate table and diagram so that you can figure it out yourself.
This
> will take me at least one day to respond to since I will be out of the
> office tomorrow.
>
> CA S2780
>
> (916) 505-0519 fax (916) 482-1173
>
>  -----Original Message-----
> From: 	Keith Fix [mailto:kefix(--nospam--at)yahoo.com]
> Sent:	Tuesday, November 27, 2001 4:04 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Plate w/ Large deflections - Need diaphragm stress at edge
>
> me.
> All I have to get is the stress at the center of the long edge of a
> rectangular
> plate, _simply_ supported, not fixed.
>
>
> -Keith Fix, PE
> -Little Rock, Arkansas
>
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