# Need help with a civil engineering concept

• The-UnKnown82
In summary, the conversation discusses the calculation of the maximum and minimum masses that an oak rod can support and the maximum mass that can be dropped without causing permanent deformation. The relevant numbers to consider are the stiffness, yield tensile strength, and ultimate tensile strength. However, the specific formula to use depends on various factors such as the orientation and fixing of the rod, and the placement of the mass.

#### The-UnKnown82

I can not find a formula to calculate the following question, any help would be appreciated, ty AlephZero for helping me clarify my question.

An example in my problem set (homework help)

An oak rod is hung from a rigid support. The rod has a diameter = 13 mm, length = 7 m, and a catch plate at its base.

a) The maximum mass of a weight that each rod can support.
b) The minimum mass of a weight that will break the rod when dropped from the top of the rod.
c) The maximum mass of weight that when dropped from the top of the rod will not result in permanent deformation of the rod.

Numbers I think can be used:
E (stiffness) = 14000 MPa
Yield Tensile strength = 75 MPa
Ultimate tensile strength = 90 MPa

Last edited:
"weight" is the force that gravity produces when it acts on "mass". A mass of 1 kg has a weight of about 9.8 N, near to the Earth's surface.

The answer to your question depends on several things you didn't tell us, like whether the rod is horizontal or vertical, how the rod is fixed, and where the mass is placed on the rod. Nobody can guess "which formula to use" without all the relevant facts.