A space truss is restrained at joints O, A, B, and C, as shown in the figure. Load P is applied at joint A and load 2P acts downward at joint C. Each member is a slender, circular pipe (E = 73 GPa)...

A space truss is restrained at joints O, A, B, and C, as shown in the figure. Load P is applied at joint A and load 2P acts downward at joint C. Each member is a slender, circular pipe (E = 73 GPa) with an outside diameter of 90 mm and wall thickness of 6.5 mm. Length variable L = 3.5 m. Determine the critical value of load variable P (kN) at which member OB fails by Euler buckling.