The unbraced length of Round HSS20 x12 in A500 Grade B Fy 4

The unbraced length of Round HSS20 x1/2 in A500 Grade B (Fy = 42 ksi) column is 36 ft. Determine the design compressive strength of the column using the equations in Chapter E in Part 16 of the AISC Manual. Confirm your answer using the AISCM Table 4-5 (pages 4-68). The column is pin-pin supported columns. Use the LRFD Method.

Solution

Effective length of column=36 ft=432 in

Radius of gyration of section=6.9 in

Slenderness ratio=432/6.9=62.6

4.71*sqrt(E/fy)=4.71*sqrt(29000/42)=123.76

62.6123.76

Fcr=0.658^(fy/fe) * fy

Fe=pi²*29000/62.6²=73 ksi

Fcr=0.658^(42/73) *42=33 ksi

Area of cross section=30.6 in²

Design strength=0.9*30.6*33=909.1 kips