Quantcast Example Problems -Cont. - dm2_080191

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Select W12 x 26.
S = 33.4 in3
I = 204 in4
Z = 37.2 in3
S + Z = 70.6 in3
bf/2tf = 8.5 < /= 8.5
O.K.
Mp = (70.6 x 39.6)/(2 x 12) = 116.5 k-ft
Check local buckling criteria.
d/tw = 53.1 < 412/(Fy)1/2 = 68.7
O.K.
(4) Calculate mass, m.
m = w/g
= [(4.5 x 48) + 26](106)/(32.2 x 103)
= 1478.3 (k-ms2)/ft2
(5) Calculate the equivalent mass, me, for a response in the
elasto-plastic range.
KLM = (0.79 + 0.66)/2 = 0.725
me = 0.725 x 1478.3
= 1071.8 (k-ms2)/ft2.
(6) Determine KE (Table 7).
KE = 384EI/5L4
= (384 x 30 x 103 x 204)/(5 x 174 x 144)
= 39.1 k/ft2.
(7) Calculate TN.
TN = 2[pi] (me/KE)1/2
= 2[pi] (1071.8/39.1)1/2
= 33 ms
(8) Establish the ductility ratio and compare with the criteria.
T/TN = 40/33 = 1.21
B=pxb
= (4.3 x 4.5 x 144)/1,000
= 2.79 k/ft.
2.08-174





 


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