Handbook of Civil Engineering Calculations

Original frame = nonsway frame + sway frame

for Mn, fa M"

FIGURE 43. Frame models for Mnt and M 7 ,.

where K= 1.0, / is the moment of inertia (in^4 ) (cm^4 ) and / is the unbraced length (in) (cm)
(Both 7 and / are taken in the plane of bending only.)
The coefficient Cm is determined as follows.

(1) For restrained beam-columns not subjected to transverse loads between their sup-

ports in the plane of bending

M 1

C 111 = 0.6-0.4-j- (Hl-4)

M 2

where M 1 IM 2 is the ratio of the smaller to larger moment at the ends of the portion

of the member unbraced in the plane of bending under consideration. If the rota-

FIGURE 44. Illustrations of secondary effects, (a) Column in braced frame; (b) Column in
unbraced frame.