Fixed end beams-Direction of moment

  • Thread starter Thread starter socrates_1
  • Start date Start date
  • Tags Tags
    Moment
AI Thread Summary
The discussion focuses on determining the direction of moments for fixed end beams, emphasizing that moments are directed towards the compressed side of the beam. Confusion arises from unclear diagrams and the lack of a consistent sign convention in the referenced material. Participants note that the author may be using a mathematician's convention, where anticlockwise moments are positive, contrasting with the engineering convention that defines positive and negative moments based on the effects they generate. The importance of understanding one's own interpretation rather than solely relying on the author's intent is highlighted. Clear sign conventions are deemed essential for accurate analysis of beam moments.
socrates_1
Messages
26
Reaction score
0
Hi,I am trying to find out how to decide the direction of moment (clockwise or anticlockwise) for a fixed end beam (for example).
As far as I know the direction is towards the side of the beam which is compressed.

The link below shows some examples with directions of moments.
Can someone explain to me why the directions are like this?

http://www.colincaprani.com/files/notes/SAIV/SAIV - Exam Handout.pdf
 
Last edited:
Engineering news on Phys.org
socrates_1 said:
The link below shows some examples with directions of moments.
Can someone explain to me why the directions are like this?

http://www.colincaprani.com/files/notes/SAIV/SAIV - Exam Handout.pdf

:eek::eek::eek: What a horribly confusing set of diagrams! :eek::eek::eek:

He doesn't say whether the M's are meant to be the reactions, or the moments on the end of the beam in a free body diagram.

And the arrows seems to be showing the direction of the actual (positive) moments, not a consistent sign convention.

There seem to be too many "unknowns" to "explain" exactly what the author meant, but those statements should point you in the direction of figuring out something that YOU understand (which is more important in than trying to second guess the author, IMO)
 
Any such table should be accompanied by a clear set of sign conventions.

Presumabably Dr Caprani is using the same ones taught on your course?

It rather looks as though Dr C is using the mathematicians and programmers reverse convention of anticlockwise moments positive and clockwise moments negative at any point.

This is different from the usual engineering convention that would refer to a short length of beam with two moments (one at each end) with the convention that if the pair generates hogging or sagging moments in the section they are positive or negative (or the other way round).

This alternative convention leads to MA and MB having the same sign in the first three entries in your table, unlike the mathematicians convention.

Note, however, you reported difficulty with some entries but did not say which ones?
 
Last edited:
He shouldn't have put a negative sign on those moments on the right-hand-side. The moments shown on the diagrams are the reactions, and are positive as drawn.
 
Thread 'Turbocharging carbureted petrol 2 stroke engines'
Hi everyone, online I ve seen some images about 2 stroke carbureted turbo (motorcycle derivation engine). Now.. In the past in this forum some members spoke about turbocharging 2 stroke but not in sufficient detail. The intake and the exhaust are open at the same time and there are no valves like a 4 stroke. But if you search online you can find carbureted 2stroke turbo sled or the Am6 turbo. The question is: Is really possible turbocharge a 2 stroke carburated(NOT EFI)petrol engine and...
I need some assistance with calculating hp requirements for moving a load. - The 4000lb load is resting on ball bearing rails so friction is effectively zero and will be covered by my added power contingencies. Load: 4000lbs Distance to travel: 10 meters. Time to Travel: 7.5 seconds Need to accelerate the load from a stop to a nominal speed then decelerate coming to a stop. My power delivery method will be a gearmotor driving a gear rack. - I suspect the pinion gear to be about 3-4in in...
Back
Top