Bending Moment in two directions

AI Thread Summary
To find the total moment at the midpoint of a beam with forces acting in two directions, it's important to recognize that moments are vector quantities with both magnitude and direction. While the individual moments can be calculated, they should not simply be added using the Pythagorean theorem, as this does not account for their directional components. Instead, it's advisable to express the moments in their component form, M = Mx + My, to accurately represent their effects. The discussion also highlights the distinction between hinge and moment-fixity assumptions in moment diagrams, which may influence the calculations. Understanding these principles is crucial for correctly analyzing the beam's behavior under applied forces.
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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