For the bridge truss shown, determine a recommended single size square box section for all members that most closely satisfy the stress requirements stated below. Assume the material is ASTM A500 Cold Formed with Grade B. So the yield strength is 46 ksi and tensile strength is 58 ksi. Assume a factor of safety of 3 based on both yielding in tension and buckling in compression. Use a computer program to aid you in solving this problem. Base your final recommendation on the most critical compression member unless allowable tensile stress based on yielding of the material occurs.
Figure 3-73 Bridge truss

10 kN 5 kN 5 kN (3) (5) 10 2 m (1) (6) 3 m (4)