Page 172 - Handbook of Civil Engineering Calculations, Second Edition

STRUCTURAL STEEL DESIGN 1.155

3. Determine the design flexural strength
To determine b M nx (the design flexural strength), refer to the Load Factor Design Selec-
tion Table for Beams in the AISC LRFD Manual. Since the W14 159 is not tabulated
therein, the basic equations are used instead.

M 1 M 1 2
C b 1.75 + 1.05 + 0.3 2.3
M 2 M 2
Again, M 1 /M 2 –1.0.
2
C b 1.75 + 1.05(–1.0) + 0.3(–1.0) 1.0
If C b 1.0, M n M p Z x F y for bending about the x axis if L b L p ; L p (300r y /F y ) for W
shapes bent about the x axis [Eq. (F1-4)]. For a W14 159, r y 4.0 in. (10.2 cm) and
(300 × 4.0 in.)/(12 in./ft)
L p 16.7 ft (5.1 m)

36
Because (L b 15.0 ft) < (L p 16.7 ft),
3
287 in. × 36 kips/sq.in.
M nx Z x F y 861 kip-ft (1167 kNm)
12 in./ft
and b M nx 0.90 861 kip-ft 775 kip-ft (1050 kNm).
Substituting the interaction formula, we obtain
8 210 kip-ft
0.65 +
9 775 kip-ft
0.63 + 0.24 0.87 < 1.0 o.k.

By a similar solution of interaction formula (H1-1a), it can be shown that a W14 145 is
also adequate.

Related Calculations. This procedure is the work of Abraham J. Rokach, MSCE, As-
sociate Director of Education, American Institute of Steel Construction. SI values were
prepared by the handbook editor.

SELECTION OF CONCRETE-FILLED
STEEL COLUMN

Select a 6-in. (15.2-cm) concrete-filled steel-pipe column for a required axial compressive
strength of 200 kips (889.6 kN), where KL 10.0 ft (3.05 m), F y 36 ksi (248 MPa),
f c
3.5 ksi (24.1 MPa), using normal-weight concrete 145 lb/cu ft (2320 kg/cu m).

Calculation Procedure:

1. Try a standard-weight concrete-filled pipe
2. Analyze the selected column