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Moment Diagram Sign Convention Poll 2
- Thread starter 271828
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Bottom. I had a boss that said that drawings have not up and down, all is a matter of looking at it properly; so one may imagine a positive axis going downwards; and I would say this is the general convention I have seen in over 90% of the spanish, french and english literature that I may have examined over 3 decades of practice. I only started to see the contrary in the representation output of some analysis programs, and some times just as a device dependent on the choice of local axes.
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- #4
Splitrings
Structural
I believe typical beam convention is positive moment is shown on the compression side. Frame convention is different. I believe positive moments are counterclockwise on both the left and right side for frame convention.
paddingtongreen
Structural
Tension side. Main reason is that that was the general convention where I learned and where I worked. Almost as strong a reason, it seems intuitive to me because it tends to match the shape of the deflected member.
Obviously, I then draw the simple BM on the bottom. The old convention of the top being positive goes out of the window when you have to deal with frames, it gets in the way.
Michael.
Timing has a lot to do with the outcome of a rain dance.
Obviously, I then draw the simple BM on the bottom. The old convention of the top being positive goes out of the window when you have to deal with frames, it gets in the way.
Michael.
Timing has a lot to do with the outcome of a rain dance.
I draw moment diagrams on the tension side for many of the reasons listed above. This is particulary useful in frame analysis.
Textbooks go either way - frame analysis texts seem to always favor moment diagrams on the tension side, whereas basic statics and strenght of materials always focus on drawing the positive moment on the top of the beam.
Textbooks go either way - frame analysis texts seem to always favor moment diagrams on the tension side, whereas basic statics and strenght of materials always focus on drawing the positive moment on the top of the beam.
slickdeals
Structural
Positive moment on tension side. Bottom.
I was taught in school (in the US) to draw positive moments on top of the beam. We were told that the rest of the world did it the other way, with the most obvious benefit of the moment diagram reflecting the deflected shape. Risa draws positive moments on the bottom. When I'm doing them by hand, I still put positive moments on top.
msquared48
Structural
Same as AISC, AITC, DWS, WWUB, etc., etc., etc.
TOP!
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
TOP!
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
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- #12
i guess it only matters 1) if the boss tells you to do it one way or the other, and 2) if you're used to looking at it one way and come across an example plotted the other way.
you should clarify your plot by also plotting the +ve axis (typically deflections +ve down, moments +ve up)
you should clarify your plot by also plotting the +ve axis (typically deflections +ve down, moments +ve up)
DaveAtkins
Structural
Top.
But I have adjusted to RISA-3D, which shows moment on the tension side.
DaveAtkins
But I have adjusted to RISA-3D, which shows moment on the tension side.
DaveAtkins
A positive moment is drawn upwards and negative downwards (opposite from where reinforcing is required in a concrete beam). I've often seen the convention where the positive and negative moments are drawn 'upside down' to reflect reinforcing placement. This latter convention is not standard.
By international convention, using a RH coordinate system, a positive moment is a positive moment vector direction on a positive face (a face where the line normal to it faces in the direction of a positive axis) and also a negative moment vector direction on a negative face. A negative moment is a negative vector on a positive face and a positive vector on a negative face.
Dik
By international convention, using a RH coordinate system, a positive moment is a positive moment vector direction on a positive face (a face where the line normal to it faces in the direction of a positive axis) and also a negative moment vector direction on a negative face. A negative moment is a negative vector on a positive face and a positive vector on a negative face.
Dik
- Thread starter
- #19
Dik, int'l convention or not, a lot of people go the tension side route and they have decent reasons.
The bottom line is that it is a good idea to indicate the sign if the situation isn't completely obvious. With the convention noted, it really doesn't matter.
The bottom line is that it is a good idea to indicate the sign if the situation isn't completely obvious. With the convention noted, it really doesn't matter.
271828,
When I analyze a beam, I draw all my forces and moments in the positive direction, which is up, to my right, and counter-clockwise. I enter downward and leftward force and clockwise moments as negative values when I do calculations. Unless I forget, I show a sign convention on the drawing.
This makes entering data into spreadsheets and analysis programs, easier.
Nobody told me to do this. I just got in the habit.
JHG
When I analyze a beam, I draw all my forces and moments in the positive direction, which is up, to my right, and counter-clockwise. I enter downward and leftward force and clockwise moments as negative values when I do calculations. Unless I forget, I show a sign convention on the drawing.
This makes entering data into spreadsheets and analysis programs, easier.
Nobody told me to do this. I just got in the habit.
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