Bending Moment in two directions

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Discussion Overview

The discussion revolves around calculating the total bending moment at the midpoint of a beam subjected to forces acting in two directions. Participants explore the appropriate method for combining moments, considering both vector properties and assumptions related to the beam's support conditions.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions whether the total moment can be found by simply adding the moments from each direction or if a different method, such as using the Pythagorean theorem, is appropriate.
  • Another participant clarifies that moments are vectors with both magnitude and direction, suggesting that it may be better to express the moment in component form rather than combining them directly.
  • A later reply notes the assumptions made in the moment diagrams regarding the support conditions of the beam, indicating that these assumptions may not significantly affect the calculation of the moment at the midpoint.

Areas of Agreement / Disagreement

Participants express differing views on the method for combining moments, with no consensus reached on the best approach. The discussion remains unresolved regarding the appropriate technique for calculating the total moment.

Contextual Notes

Participants highlight the importance of considering the vector nature of moments and the implications of support conditions on the calculations, but specific assumptions and their impacts are not fully explored.

shauntur
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Not Really a homework question but it will help with how i go about the homework.

So i have a beam coming out of the wall and it has force acting on it like this:
Woops, that 20 on the side view should be a 10 :P
Untitled-1-4.png

What i want to find is the total moment at the mid point. I know how to find the moment in each direction but I am not sure if I am aloud to add them together or use pythag??
heres my solution for each direction:
Untitled-2-1.png

Can i just go sqrt(10^2+10^2) to give me 10?
Thanks
Shaun
 
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shauntur said:
Can i just go sqrt(10^2+10^2) to give me 10?
Thanks
Shaun
Hi Shaun, welcome to PF!
Moments are vectors and as such, have both magnitude and direction. So aside from the fact that sqrt(10^2+10^2) = 10(sq root 2) :wink:, its magnitude, there is a direction associated with the moment also (what is it?). Sometimes it is best to leave the moment in its component form...M = Mx + My.
 
thanks heaps mate, probably shouldn't be doing engineering if i can't use pythag properly :-p
really appreciate ur help
 
In your M diagrams, the horizontal one shows an assumed hinge at the wall, whereas the vertical one assumes moment-fixity. This may not affect your answer to the moment at midpoint of the beam.
 

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