column plastic moment strength, reduced by the
These requirements do not apply in any of the
axial stress Puc/Ag, from the top and bottom of
following cases, provided that the columns
the
beam
moment
connection
(including
conform to the above minimum width-thickness
haunches where used). It shall be permitted to
ratios.
take G M*pc as G Zc (Fyc - Puc/Ag).
(a) Column with Puc < 0.3FycAg for all
ΣM ∗b
=
the
moment
at
the
p
load combinations:
intersection of the beam and column center-line
determined by projecting the beam maximum
1. Which are used in the top story of a
developed moments from the column face
multistory structure with a period greater than
thereto. Maximum developed moments shall be
0.7 seconds, or
determined from test results as required by
Paragraph 7-5b(2)(a) or by rational analysis
2. Where the sum of their resistance
based on the tests. Alternately, the maximum
is less than 20 percent of the shear in a story and
developed moment may be taken as 1.1 Ry Mp +
is less than 33 percent of the shear on each of the
Mv where Mv is the additional moment due to the
column lines within that story. A column line is
shear amplification from the location of the
defined for the purpose of this exception as a
plastic hinge to the column centerline. When
single line of columns or parallel lines of
connections with reduced beam sections are
columns located within 10 percent of the plan
used, Mpb may be taken as 1.1 Ry Fy z + Mv,
dimension perpendicular to the line of columns.
where z is the minimum plastic section modulus
(b) Columns in any story that have a
at the reduced section.
ratio of design shear strength to design force 50
2
2
Ag = gross area of column, in (mm ).
percent greater than the story above.
(c)
Any column not included in the
Fyc = specified minimum yield strength
design to resist the required seismic shears, but
of column ksi (Mpa).
included in the design to resist axial overturning
forces.
Puc = required axial strength in column,
kips (kN).
(8)
Lateral support at beams.
Both
flanges of beams shall be laterally supported
Zc =
plastic section modulus of a
directly or indirectly.
The unbraced length
column, in3 (mm3).
between
lateral
support
shall
not
exceed
3,600ry/Fy (689.5 ry/Fy for Fy in MPa).
In
Ry =
ratio of the expected yield
addition, lateral supports shall be placed at
strength, Fye, to the minimum specified yield
concentrated loads where an analysis indicates a
strength, Fy.
7-100
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