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<CO> From Table 5, ultimate resistance of a uniformly loaded
beam with fixed ends is:
8 (MN + MP)
ru =
L2
= 8 (3,800,755 + 3,873,355)
2402
= 1,065.85 lb/in
(6) From Chapter 5, Section II of NAVFAC P397, calculate
average moment of inertia of the beam section.
Concrete modulus of elasticity;
Ec = w1.5 x 33 x (f'c)1/2
= 1501.5 x 33 x (4,000)1/2
= 3.8 x 106 psi
Steel modulus of elasticity;
ES = 29 x 106 psi
Modular Ratio;
Es
n
=
Ec
29 x 106
=
3.8 x 106
= 7.6
From Figure 55 of NAVFAC P397 and having n, pN, and
pp, the coefficients for moment of inertia of cracked
sections are:
FN = 0.0235 at support
Fp = 0.0230 at midspan
Cracked moment of inertia from Equation 522 of NAVFAC
P397 is:
Ic = Fbd2
IcN = 0.0235 x 18 x 27.1253
= 8,442 in4
IcP = 0.0230 x 18 x 27.6253
= 8,728 in4
2.08110


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