(Solved): A pin-jointed steel truss (E = 200GP a) is constructed of rectangular steel tubes of 40mm 20mm an ...

A pin-jointed steel truss (E = 200GP a) is constructed of rectangular steel tubes of 40mm × 20mm and thickness 3mm. Using a safety factor Sf = 2 determine the maximum load Pallow that can be applied without buckling of any bar. Answer: 6.67 kN. Please ensure the solution matches this answer, I've been getting 12kN which is incorrect.

Thank you