Engineering Moments, not from point load.

[psyclones]

Hi all,

This is most likely a silly question. 

Can a moment anywhere along a beam be equivalently modelled as to two small blocks welded @ 90deg to original beam and have coupling loads applied? (See hand sketch attached)

Can this type of moment be constant or uniform along the beam because point loads are parallel?

I've attached a Text book example showing the Moment being constant along Section B-C of beam due to load being parallel to that section. While Section A-B the moment varies as a function of distance.

I'm just trying to get a better understanding of the difference btw moments along a beam, and a moment created due to a perpendicular point load.

Or are moments just moments, which are caused by any sort of bending?

It's not a simple example - it's using Complementary Strain Energy (theorem) to calculate displacement - if anyone's curious.  But I'm only interested in how the text has derived the moment equations for the two contrasting sections.

NOTE: Distance "x" should be "x/2" (hand sketch)

Edited December 21, 2020 by psyclones
added "see attachment"

[studiot]

A quick answer because I haven't had time to look carefully at your textbook (which one is it ?) and I see you are listed as still online.

 

Remember that a true couple or moment is the same about any point in its plane.
So it does not matter where you apply it.

The moment of a single force is different about almost every point in its plane so varies along a beam.
 

BTW you should not write Mo = Fx   it could be confusing as to what you mean.

[psyclones]

Ok. so yes, moment varies along beam for applied point load & couple is uniform along beam. 

text: Mechanics of Engineering Materials (Benham. Crawford & Armstrong), 2nd Ed.

 

Attached is actual problem, I'm trying to model. 

A Caster wheel causing a moment in a plywood box-cart base. 

I'm wanting to determine the stress at bottom edge of board where it meets the pivot axle.  But to do that I need to determine where the N/A is. Of maybe I'm going about his the wrong way. 

Edited December 21, 2020 by psyclones
edit sketch