Statics: Tension or Compression?

[Elfrid Payton]

When examining a member, how do I tell whether it is undergoing tension or compression?

It's more of a general question, but since a visual might help with the explanation, this could be useful:

 

[mfb]

When examining a member, how do I tell whether it is undergoing tension or compression?

You can calculate it.
Sometimes intuition and some rough analysis are sufficient, sometimes they are not.

 

[Elfrid Payton]

You can calculate it.
Sometimes intuition and some rough analysis are sufficient, sometimes they are not.

The calculations are not the problem. Figuring out whether the members are undergoing tension or compression for the FBDs is what I'm having trouble with.

 

[mfb]

The calculations will give you negative or positive values. There is no need to know that in advance.