A W12x79 of A573 Grade 60 (Fy = 415 MPa) steel is used as a compression member. It is 6.8 m long, fixed at the top and

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A W12x79 of A573 Grade 60 (Fy = 415 MPa) steel is used as a
compression member. It is 6.8 m long, fixed at the top and
bottom, and has additional support in the weak direction at
mid-height. Properties of the section are as follows:
A = 14,500 mm^2
Ix =
258.6 x 10^6 mm^4
Iy = 84.375 x 10^6 mm^4
Calculate the critical slenderness ratio with respect
to weak axis buckling using theoretical value of k.