You have a cantilever beam, to minimize deflection, you add a support elbow. Would you add this to the top or bottom? Why?


Similar to this image, the interviewer implied the materials for both elbow and beam would be the same.

This topic follows the same thinking as : On which side of a wall-mounted cantilever beam induced with a point load will it fail?

@cocopops To answer your question:

In the case of a wall-mounted cantilever beam, with it being supported at the fixed end of the beam, the placement of the support elbow depends on the material properties of the beam.

For the cantilever beam, the top and bottom sides are subjected to two difference forces: compressive and tensile forces respectively.

  1. Top Side: Tension (-> away from wall)
  2. Bottom Side: Compression (<- toward wall)

If the cantilever beam material has a lower compressive yield strength than tensile yield strength, the beam will fail at the bottom. Alternatively, if the tensile yield strength is lower, the beam will fail at the bottom.

A great example of this would be concrete! Concrete is known for having great compressive strength, but weak in tension. As such, you’d reinforce the top side of the beam.

Wall-Supported Cantilever Beam, Tension & Compression Illustration

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