Suspended shelf

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).
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