Building Design and Construction Handbook - Merritt - Ventech!

FIGURE 7.26 Configurations of members of
a rigid frame caused by sidesway.
STRUCTURAL STEEL CONSTRUCTION 7.51
For a pin-ended column with translation
of the ends prevented, K � 1. But
in general, K may be greater or less than
unity. For example, consider the columns
in the frame in Fig. 7.26. They are
dependent entirely on their own stiffness
for stability against sidesway. If enough
axial load is applied to them, their effective
length will exceed their actual
length. But if the frame were braced to
prevent sidesway, the effective length
would be less than the actual length because
of the resistance to end rotation
provided by the girder.
Theoretical values of K for six idealized
conditions in which joint rotation
and translation are either fully realized
or nonexistent are given in Fig. 7.27.
Also noted are values recommended by the Column Research Council for use in
design when these conditions are approximated. Since joint fixity is seldom fully
achieved, slightly higher design values than theoretical are given for fixed-end columns.
Specifications do not provide criteria for sidesway resistance under vertical loading,
because it is impossible to evaluate accurately the contribution to stiffness of
the various components of a building. Instead, specifications cite the general conditions
that have proven to be adequate.
FIGURE 7.27 Values of effective column length K for idealized conditions.