Need a book? Engineering books recommendations...

# Re: reinforced concrete design question

• To: seaint(--nospam--at)seaint.org
• Subject: Re: reinforced concrete design question
• From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
• Date: Fri, 20 Aug 2004 11:37:06 -0400 (EDT)

```Cliff:

As I understand it, there is really is not a linear relationship even at
low stress-strain levels.  The "rising portion" of the stress-strain curve
is still non-linear, but can be VERY close to linear for a portion.  A
qoute from MacGregor's textbook ("Reinforced Concrete: Mechanics and
Design"):

"For computational purposes the rising portion of hte curve is frequently
approximated by a parabola (ref 3-22)."

(FYI: ref 3-22 is Paul H. Kaar, Norman W. Hanson, and H.T. Capell,
"Stress-Strain Characteristics of High-Strength Concrete," Dougles McHenry
International Symposium on Concrete and Concrete Structures, ACI
Publication SP-55, American Concrete Institute, Detroit, 1978, pp.
161-186)

MacGregor's book does talk about modulus elasticity and where the ACI 318
equation comes from (i.e. Esubc=33*(w^1.5)*sqrt(f'c)).  Apparently, the
ACI 318 modulus of elasticity "...corresponds to the secant modulus of
elasticity at approximately 0.50F'c (ref 3-23)".  It is commented that
the initial tangent modulus is about 10% greater, which shows that even
for the range of 0 to 0.50f'c there is a slight curve.  But, this probably
is what let to the "valid for stress levels below 0.5 x f'c" statement
that you referred to.

Why are you asking?  If you are looking for a more "accurate" method of
determining compressive force in the concrete at various stress-strain
level (i.e. for moment-curvature relationships in beams or column
axial-bending curves), then there are models that you can use that will
more "closely" approximate the concrete stress-strain curve.  I can even
fax some of the information from a class I took back in school (PhD level
concrete course).

Regards,

Scott

On Fri, 20 Aug 2004, Cliff wrote:

> There’s a linear relationship between stress and
> strain in the compression zone of concrete beams when
> stresses are small. When stresses get bigger the
> linear relationship goes away and you use the “Whitney
> Stress Block” to approximate the compression zone in
> concrete beams.
>
> Does anyone know when the linear relationship between
> concrete stress and strain starts to disappear? Can
>
> I found one book that says the linear relationship is
> valid for stress levels below 0.5 x f’c.
>
> TIA,
>
> Cliff Schwinger
>
>
>
>
> _______________________________
> Do you Yahoo!?
> Win 1 of 4,000 free domain names from Yahoo! Enter now.
> http://promotions.yahoo.com/goldrush
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********
>

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted