What is the nutral axis location of a singal reinforced concrete section? I have
ID: 1710814 • Letter: W
Question
What is the nutral axis location of a singal reinforced concrete section? I have been trying to calculate this and have found two different methods, the force way and the quadratic way. We have a slab that is b=36" wide h=33" tall with 5 #8 bars located 3" above the bottom equally spaced. The concrete has fc'=3000 psi, fy=60,000psi, M of Elastisity of concrete at 57,000(root(fc'))= 3122018.578 psi, M of elastitiy of steel = 29,000,000 psi. with d=33-3=30"
The two methids are as follows:
(1) T=C
Fy*As=.85*fc'*x*b
and the other
(2) b(x)*(x/2) - (n(As))(d-x) =0
solving for x should give the distance from the top of the section to the nurtal axis.
Should they both result in the same x, I am finding that one is almost doubble the other and need to know which method is the correct way. Thank you
Explanation / Answer
you said that you are found that one is almost doubble the other and need to know which method is the coorrect.
the first method is correct.
(1) T=C
Fy*As=.85*fc'*x*b
because given section is a singly reinforced section.
in that singly reinforced structure we are assuming that section is balanced section i.e(T=C).
that is the reason why we are getting exact neutla axis position in the structure compared to the second method.
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