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 (11) Calculate effective mass of section.
Mass of element
m = [(497 x 150/123)/(32.2 x 12)]
= 0.1116 lb-sec2/in2
Load-mass factor for the elastic range
KLM = 0.79
Effective mass of element
me = mKLM
= 0.1116 x 0.79
= 0.0882 lb-sec2/in2
(12) Calculate natural period of vibration
TN =
2[pi](me/KE)1/2
=
2[pi](0.0882/84.19)1/2
=
0.2034 sec
=
203.4 ms
(13) Determine section response from figure 6-7 of NAVFAC
P- 397
B/ru = (1.1 x 96)/70.9
= 1.49
T/TN = 43.9/203.4
= 0.216
Xm/XE = 1.0
O.K.
Check rotation of beam
X = XE + XDL + XLL
ravail
5(DL + LL)L4
= +
KE
384EIa
70.9
+ 5(43.1 + 10)(40 x 12)4
=
84.19
384(4,286,826)13575
= 0.84 + 0.63
= 1.47 in
[theta] = tan -1(2X/L)
= tan -1[2 x 1.47/(40 x 12)]
= 0.35[deg] < 2[deg]
O.K.
2.08-262
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