Calculate stiffness of section

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Hence, the neutral axis is within the flange and the
section can be analyzed as a rectangular section.  If the
neutral axis had extended into the web, a strain
compatibility analysis would be required.
Mu = Apsfps(d - a/2)
= 0.612 x 268.167(22-O.32/2)
= 3584 k-in
(9)
Determine ultimate resistance of section, considering
beam simply-supported.
ru = 8Mu/L2
= 8(3584)/(40 x 12)2
= 0.124k/in
Resistance of section available to resist blast load is
ravail =
ru - DL - LL
=
124 - [497 x 150/123] - (15 x 8/12)
=
124 - 43.1 - 10
=
70.9 lb/in
(10) Calculate stiffness of section.
Elastic range stiffness
KE = 384EcIa/5L4
Modulus of elasticity of concrete
Ec = 33 W1.5(f'c)1/2
= 33(150)1.5(5000)1/2
= 4,286,826 psi
Average moment of inertia
Ia = (Ig + Ic)/2
Ic = nApsd2p(1-(pp)1/2)
n
= Es/Ec
= 29,000,000
4,286,826
= 6.77
Ic = (6.77)(0.612)(22.0)2[1-(.000290)1/2]
= 1970 in4
Ia = (25180 + 1970)/2
= 13575 in4
KE = 384(4286,826)13575/[5 x (40 x 12)4]
= 84.19 lb/in2
2.08-261