Page 311 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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DESIGN OF BUILDING MEMBERS

DESIGN OF BUILDING MEMBERS 6.33

The deflection at the left concentrated load P is 0.296 in, and at the second load it is 0.288 in.
From Table 6.5, the live loads with a 40% reduction for size of area supported are P L = 9.0 kips,
w LL = 0.30 kips/ft, and w RL = 0.12 kips/ft. The maximum deflection due to these loads and with an
4
effective moment of inertia of 1888 in is 0.319 in. The deflection at the left load is 0.282 in and at
the second load is 0.275 in.
Total deflections due to superimposed dead loads and live loads are
Maximum deflection = 0.336 + 0.319 = 0.655 in
Deflection at left load P = 0.295 + 0.282 = 0.577 in
Deflection at right load P = 0.288 + 0.275 = 0.563 in

6.15 EXAMPLE—LRFD FOR WIDE-FLANGE COLUMN
IN A MULTISTORY RIGID FRAME

Columns at the ninth level of a multistory building are to be part of a rigid frame that resists wind
loads. Typical floor-to-floor height is 13 ft.
In the ninth story, a wide-flange column of A992 steel is to carry loads from a transfer girder,
which supports an offset column carrying the upper levels. Therefore, the lower column discontin-
ues at the ninth level. The loads on that column are as follows: dead load, 750 kips; superimposed
dead load, 325 kips; and live load, 250 kips. The moments due to gravity loads at the beam–column
connection are
Dead-load major-axis moment = 180 kip⋅ft
Live-load major-axis moment = 75 kip⋅ft
Dead-load major-axis moment = 75 kip⋅ft
Live-load major-axis moment = 40 kip⋅ft
The column axial loads and moments due to service lateral loads with P–∆ effect included are

Axial load = 600 kips
Major-axis moment = 1050 kip⋅ft
Minor-axis moment = 0.0

The beams attached to the flanges of the column with rigid welded connections are part of the rigid
frame and have spans of 30 ft. The following beam sizes and corresponding stiffnesses at the top and
bottom ends of the column apply.
The beams at both sides of the column at the floor above and the floor below are W36 × 300. The
sum of the stiffnesses I b /L b of the beam is
∑ (/IL = 20 ,300 × 2 = 112 .8 in 3
)
b
b
30 ×12
4
where I b is the beam moment of inertia (in ).
The effective length factor K x corresponding to the case of frame with sidesway permitted is used
in determining the axial-load capacity and the moment magnifier B 1 . The moment magnifier B 2 is
considered unity inasmuch as the P–∆ effect is included in the analysis.
Axial-Load Capacity. Since the column is part of a wind-framing system, the K values should
be computed based on column and beam stiffnesses. To determine the major-axis K x , assume that a

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