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 (4)
Design of flange section.
Critical section of flange is the cantilever portion
L
= 24 - 5.75/2
= 21.125 in
d
= 1.0 in (welded wire fabric is located in the
middle of the flange) per one foot section
a
= (Asfdy)/(.85f'dcb)
= .05(71500)/(.85 x 6250 x 12)
= 0.056 in
Mu = Asfdy (d-a/2)/b
= 0.05 x 71500(1-0.056/2)/12
= 290 in-lb/in
Elastic resistance, ru, is:
ru = 2Mu/L2
= 2 x 290/(21.125)2
= 1.30 psi
Resistance available to resist blast load, r, is:
ravail =
ru
- DL -LL
=
1.30
- (2 x 150/123) - 15/122
=
1.30
- .17 - .10
=
1.03
psi
The elastic range stiffness of section, KE
KE = 8EcIa/L4
where,
Ec = 33(150)1.5(5,000)1/2
= 4,286,825.8 psi
Ia = 0.6Ig
= 0.6(2)3/12
= 0.4 in4/in
KE = 8(4,286,825.8)(0.4)/(21.125)4
= 68.88 psi/in
The mass, m, of element,
m = (150/123 x 2)/(32.2 x 12 x 10 -6)
= 449.30 lb-ms2/in2
Load mass factor (from Table 6-1, NAVFAC P-397) in the
elastic range, KLM = 0.65
2.08-257
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