Questions and discussion for this lecture live here. Fire away by hitting Reply below 
Question about moment.
Is it the same thing:
a) force applied at a distance from O
b) moment applied in one point O
c) two equivalent opposite horizontal forces with little lever arms d1, d2 at point O
Numerically you treat in your worked examples the same, but is it true when you speak about applying force on a beam versus inner stresses on a beam section?
The three cases you have presented all have the same influence on the overall static equilibrium of the structure AND they will induce the same state of internal bending (normal) stress at O.
Seán
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Thank you.
Interesting that they look completely different but effect is the same.
So in the end it is all tension and compression.
Why on the right side pf the beam you did not take the moment 8kn/m into cosideration?
Is it because it cancels out at that point?
Hey @petrasvestartas - can you give me the time in the video that your question refers to?
Thanks,
S
Minute 11:00. I guess it ia not considered because moment is on that point. But is it true?
When we make a cut in the structure to reveal the internal bending moment, we draw that internal bending moment acting on both faces that have been revealed by the cut - so what you’re actually looking at is two different representations of the same bending moment (note that they both have the same sign according to the deformation sign convention. Also note that when can check moment equilibrium of either sub-structure revealed by the cut and is will be in equilibrium under the action of the loads applied to that substructure and the internal moment on that side of the cut.
I’ve just updated and refreshed my tutorial article on this very topic - you may also find that helpful.
S
Sorry that my question was not clear.
Why 8 kn/m was not considered in equation?
P.S. I like the article a lot, I wish there would be more Python examples with explanations. These calculus equations of diagrams can be automated and very useful.
Ah…I see. Although I say we’re taking the sum of the moments about the right tip, we’re actually taking the sum of the moments and infinitesimal distance to the left of the right tip, this sub-structure to the left of the cut (which is almost the entire structure), technically, does not have the 8kNm (note the units BTW) applied to it - thus we get a resultant internal moment of 8kNm.
If we did in fact evaluate the sum of the moments at the right tip (and not an infinitesimal distance to the left of it - i.e. no cut made), we would include the externally applied 8kNm moment and the total moment would evaluate to zero since the structure must be in a state of static equilibrium.
I hope that helps to clear things up.
Seán