Stress and Strain (Finding the thickness of truss members)

[D0m]

Hi guys i have a exam coming up soon and stress is starting to kick in. I am good with stress and strain, but I am just confused on this question and don't understand what i need to be doing. I've tried every formula and i just can't seem to get question 5 out. The answears for this question is underneath the question.

Please have a look at it and tell me what you think, it will also be much appriciated if can write down a solution for them. The question is in the attachment.

Thanks, Dom

 

[PhanthomJay]

What is the formula for determining axial stress in a member?

 

[D0m]

stress= P/A

 

[PhanthomJay]

axial [/color]stress= P/A

Yes.
The controlling case for stress and axial load is the compression case, since the load is the greatest and the allowable stress is the smallest. So you know P and and you know the allowable stress. Solve for the required cross sectional area of the hollow tube, A, and from that you can determine the required wall thickness from the given data of the tube's diameter.

 

[D0m]

I understand what you mean but i just don't know how to get started

 

[PhanthomJay]

A = P/s. Solve for A. Watch units. What do you get for the area ? Show your work.