Building Design and Construction Handbook - Merritt - Ventech!

7.82 SECTION SEVEN
where M nt � required flexural strength, kip-in, with no relative displacement of the
member ends; for example, for a column that is part of a rigid frame,
drift is assumed prevented
M lt � required flexural strength, kip-in, for the effects only of drift as determined
from a first-order analysis
B1 � magnification factor for Mnt to account for the P-� effects
Cm �
1 � P u/Pe Cm � reduction factor defined for Eq. (7.57)
B2 � magnification factor for Mlt to account for the P-� effects
B 2 may be calculated from either Eq. (7.61) or (7.62), the former usually being the
simpler to evaluate.
1
B2 � (7.61)
1 � (�P /�HL)�
u oh
1
B2 � (7.62)
1 � �P /�P
u e
where �Pu � sum of the axial-load strengths, kips, of all the columns in a story
Pe � AgFy/ 2 �c Ag � gross area of member, in2 Fy � specified yield stress, ksi
� c �
� �
Kl Fy Kl Fy
�
r� E r 286,220
K � effective column length factor in the plane of bending, to be determined
by structural analysis, but not to exceed unity in calculation
of B 1 and not to be less than unity in calculation of B 2
r � governing radius of gyration, in, about the plane of buckling
� oh � drift, in, of the story in which the column is located
L � story height, in
�H � sum of all the horizontal forces on the story that cause � oh
7.25 COMBINED AXIAL TENSION AND
BENDING
For ASD, members subject to both axial tension and bending stresses should be
proportioned to satisfy Eq. (7.55), with ƒ b and F b, respectively, as the computed
and allowable bending tensile stress. But the compressive bending stresses must not
exceed the values given in Art. 7.20.1.
LRFD for Tension and Bending. Symmetric members subject to both axial tension
and bending stresses should be proportioned to satisfy either Eq. (7.58) or Eq.
(7.59), whichever is applicable.