Dave needed more storage for his school books and clothes, but he did not want to use any floor space. He thought that a hanging shelf would solve the problem to store 6 book boxes and 6 clothes boxes, weighing 45 lb and 20 lb per box, respectively. To save money, he decided to use wood for both the shelf and the hanging rods.

What is known:

• Each box is 1-foot square on its base.
• The shelf board weigts 35 lbs.
• The rod material is Douglas Fir.
• Rods are assumed to be circular.
• To be safe, a factor of safety of 4 is applied.
• Wood rods are available in increments of 1/16".
• There are a total of 4 rods.

What diameter size rod is needed for the hanging shelf?

• Using static equilibrium equations, find load in each rod.
• Apply factor of safety.
• Calculate the needed cross-sectional area, A based on the the allowable stress of Douglas Fir (see appendix for allowable stress).