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 (3) The required plastic moment capacities for the frame
members are determined from Table 19, based upon rational
assumptions for the moment capacity ratios C1 and C. In
general, the recommended starting values are C1 equal
to 2 and C greater than 2.
From Table 22, for n = 4, [alpha] = 2.32.
H = 15.167 ft, L = 16.5 ft
and pinned bases, values of C1 and C were substituted.
After a few trials, the following solution is obtained:
Mp = 104 k-ft, C = 3.5 and C1 = 2.0.
The various collapse mechanisms and the associated values
of Mp are listed below:
Collapse
w
Mp
Mechanism
(k/ft)
(k-ft)
1
6.12
104
2
6.12
102
3a, 3b
3.06
102
4
3.06
103
5a, 5b
3.06
88
6
3.06
93
The plastic design moments for the frame members are
established as follows:
Girder, Mp = 104 k-ft
Interior column, C1Mp = 208 k-ft
Exterior column, CMp = 364 k-ft
(4) (a) Axial loads ad shears due to horizontal blast
pressure:
w = 3.06 k/ft
From Figure 45, Ru = [alpha]wH
= 2.32 x 3.06 x 15.167
= 108 kips
2.06-188
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