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 From Equation (37);
0.85K1 f'dc
87,000
Pb =
fdy
87,000 + fdy
0.05 (f'dc - 4,000)
where
K1 = 0.85 -
1,000
= 0.80
0.85 x 0.8 x 5,000
87,000
Pb = ()
66,000
87,000 + 66,000
= 0.0293
Pmax = 0.75 x 0.0293
= 0.0220 > PN = 0.0045 and pp = 0.0044
O.K.
Check for minimum reinforcing ratio using Equation (42).
200
Pmin =
fy
200
=
60,000
= 0.0033
< pN = 0.0045 and pp = 0.0044
O.K.
(4) Moment capacity of the beam using Equations (34) and (35):
Mu = As fdy (d - a/2)
where
As fdy
a=
0.85b f'dc
2.20 x 66,000
=
0.85 x 18 x 5,000
=
1.898 in
at support,
MN = 2.20 x 66,000 x (27.125-1.898/2)
= 3,800,755 in-lb
at mid-span
Mp = 2.20 x 66,000 x (27.625 - 1.898/2)
= 3,873,355 in-lb
2.08-109
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