The truss ABC shown in the figure supports a vertical load W at joint B. Each member is a slender circular steel pipe (E = 200 GPa) with outside diameter d = 75 mm and wall thickness t = 5.0 mm. The distance between supports is 7.0 m. Joint B is restrained against displacement perpendicular to the plane of the truss. Determine the maximal load of W that the system can handle before buckling.

B W 75 mm 40 A 550 dc 7.0 m