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Obtaining compressive and tensile stresses in beams

  • Thread starter hashman
  • Start date
  • #1
4
0

Homework Statement



In calculating stresses, how do we determine when we have a negative in front of the question and when we do not have it. I am really confused, meaning I have not understood the concept, but the examples I am looking at some have got σ= My/I whilst others have σ= -My/I.

Homework Equations



σ= My/I

σ= -My/I

Hopefully they get uploaded properly. The first two use the first equation, whilst the the other two use the second equation

Untitled.png


Untitled1.png


Untitled2.png


Untitled3.png



Thanks for the help.
 

Answers and Replies

  • #2
36
0
Just understand that:
  • Compression is always Negative
  • Tension is always Positive

I always just keep my numbers positive in calculation until the end and if I am solving for a compressive stress I add the negative.

Hope this helps!
 
  • #3
4
0
Just understand that:
  • Compression is always Negative
  • Tension is always Positive

I always just keep my numbers positive in calculation until the end and if I am solving for a compressive stress I add the negative.

Hope this helps!
Ah right okay. So basically if they ask for max or anything always use σ=My/I , and then if it is compression, add the negative sign to the final answer. Cheers mate
 
  • #4
36
0
Yup you got it!
 

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