Question

Determine the allowable axial compressive load for a 25-foot long A992 W8X40 structural steel column using the AISC procedure as indicated in your textbook. The bottom of the column is fixed, an the top is pinned. Use the material properties and dimensions as indicated in the appendices of your textbook.

		250.3k
		131.4k
		215.8k
		283.4k

Answer 1

Ans) Following rea the specifications of A992 W8 x 40 section :

Ag = 11.7   

Fy = 50 ksi

rx = 3.53 in and ry = 2.04 in

Calculate slenderness ratio ()

In x direction, x = K L / rx  

For column with one end fixed and other , effective length factor, K = 0.80

=> x = 0.80 x 25 ft x 12in/ft / 3.53 in

=> x = 67.98

In y direction, y = K L / ry

=> y = 0.80 x 25 ft x 12in/ft / 2.04 in

=> y = 117.64 (Governing)

Now,calculate ratio 4.71 = 4.71 = 113.43 < 117.64 , so we have to use AISC equation equation E3-3 to calculate Fcr,

Fcr = 0.877 Fe

where, Fcr = critical compressive stress

Fe = critical elastic buckling stress

Also, Fe = E /

=> Fe = x 29000/

=> Fe = 20.66 ksi 21 ksi

=> Fcr = 0.877 x 21 = 18.42 ksi

Allowable axial compressive load (P) = Ag Fcr = 11.7 x 18.42 = 215.5 kips

Hence, option C is correct