(c) Columns may be considered braced in the weak direction if

the distance between any adjacent braced points is not greater than *lcr

defined as:

EQUATIONS:

*lcr/ry = 1,375/Fdy,

-1.0 < /= M/Mp < /= -0.5

(110a)

*lcr/ry = 1,375/Fdy + 25,

-0.5 < M/Mp < /= 1.0

(110b)

Beam columns should also satisfy the requirements of paragraph 3.a.(7) of

this section.

b. Effective Length Ratios for Beam Columns. The basis for determining

the effective lengths of beam columns for use in the calculation of Pu,

Pex, Pey, Mmx, and Mmy in plastic design is outlined below.

(1) For plastically designed braced and unbraced planar frames which

are supported against displacement normal to their planes, the effective

length ratios in Tables 19 and 20 shall apply.

(a) Table 19 corresponds to bending about the strong axis of a

member, while Table 20 corresponds to bending about the weak axis. In each

case, *l, is the distance between points of lateral support corresponding to

rx or ry, as applicable. The effective length factor, K, in the plane

of bending shall be governed by the provisions of paragraph 5.c. of this

section.

(b) For columns subjected to biaxial bending,

the effective

lengths given in Tables 19 and 20 apply for bending about

the respective

axes, except that Pu for unbraced frames shall be based

on the larger of

the ratios K*l/rx or K*l/ry. In addition, the larger

of the slenderness

ratios, *l/rx or *l/ry, shall not exceed Cc.

TABLE 19

Effective Length Ratios for Beam Columns

(Webs of members in the plane of the frame;

i.e., bending about the strong axis)

One- and Two-Story

Braced Planar Frames[*]

Unbraced Planar Frames[*]

Pu Use larger of *l/ry or l/rx Use larger of *l/ry or K*l/rx

Pex Use *l/rx

Use K*l/rx

Mmx Use *l/ry

Use *l/ry

[*]*l/rxshall not exceed Cc.

2.08-153