If you have determined Ru using the bending moment, you have two options to
i) use first principle equation to find out the required "p" from the given
Ru & the material properties of concrete and steel., or
ii) use any design handbook to find out the value of required "p" from the
given Ru & the material properties. In the design handbook, the values of
"p" is provided against the given value of Ru. For example you have the
for: Ru of 10 Kg/cm2, p= 0.3%
for: Ru of 12 kg/cm2, p= 0.45%
and you need to know ( interpolate ) "p" for a Ru of 11kg/cm2.
You know, for a difference value of Ru of 2kg/cm2 (12-10=2kg/cm2), there is
a differernce value for "p" of +0.15% (0.45-0.30=0.15%).And, From a simple
linear interpolation we have as follows:
2kg/cm2 of Ru=0.15% of "p"
1kg/cm2 of Ru=o.15%/2
=0.075% of "p"
Now, for 10kg/cm2 of Ru= 0.3% of "p"
So, for 11kg/cm2 of Ru= 0.3% + 0.075% of "p"
=0.375% of "p"
Therefore, "p" would be=0.00375 for Ru value of 11kg/cm2
Now, Area of steel is :
Therefore, for a Ru value for 11kg/cm2, As = 0.00375*b*d.
Hope this explains your problem as requested.
SYED FAIZ AHMAD
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RIYADH, SAUDI ARABIA
From: ken kirkland <kenmail234(--nospam--at)yahoo.com>
Date: Thu, 7 Jun 2001 16:16:19 -0700 (PDT)
I forgot how to do the interpolate to determine "p" and required
reinforcement in concrete. Can some one please show me.
Thanks in advance.
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