Moment Calculation from Given Stress on Plate Element
Moment Calculation from Given Stress on Plate Element
(OP)
Hallo everyone,
I have run Beam as 2D plate on SAP2000, and have got the output as attached file. which gives me stress but i need to calculate the amount of moment at peak points so how can i calculate Moment from this stress at the point?
Regards,
Amaid
I have run Beam as 2D plate on SAP2000, and have got the output as attached file. which gives me stress but i need to calculate the amount of moment at peak points so how can i calculate Moment from this stress at the point?
Regards,
Amaid






RE: Moment Calculation from Given Stress on Plate Element
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment Calculation from Given Stress on Plate Element
i hope i clear the my question :)
so now cominng back to the answer, so could u elaborate what is means (Integrate stress x lever arm, over the x-section?
thanks
RE: Moment Calculation from Given Stress on Plate Element
1) Strip out any stresses due to axial loads.
2) Divide section up into a bunch of little areas.
3) Find the stress on each little area.
4) Find the distance from the centroid of each little to the reference axis.
5) Calculate the moment of each little area bout the reference axis as [area x stress x distance]
6) Add up all of the moment contributions from #4.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment Calculation from Given Stress on Plate Element
2) division of section means meshing? that i have already done as am doing FEM
3) finding stress on each little area means, meshing again? okay i have stress in every square,
4) Reference axis?, considering that this plate model is for beam therefore by reference axis do u mean beam top at support in case of region for -ve moment??
5) got this point
6) moment contributed from point 5 not 4 if am wrong please correct, but have mention 4 instead of 5
THanks
RE: Moment Calculation from Given Stress on Plate Element
1) You don't need axial loads to get axial stress. Think membrane action etc. There's a simple way to find out though. Just add up all of your cross section axial stresses and see if they sum to zero. If they don't, you've got some axial only stresses in there.
2) Division means looking at all of your stresses over whatever areas are convenient for you for calculation purposes. If that's just your FEM grid, then so be it.
3) Same as #2.
4) You need to figure out your moments about some reference axis in space. As long as you've stripped out any axial load only effects, you should get the same moment regardless of the reference point/axis that you select.
6) Agreed.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment Calculation from Given Stress on Plate Element
RE: Moment Calculation from Given Stress on Plate Element
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment Calculation from Given Stress on Plate Element
i mean refernce point means from center or top or bottom but when u say reference axis i am kinna confuse because which axis i need to take i already know but for that lever arm for example if ai am checking moment at the bottom of beam then does it means my lever arm is from the center of the area i am checking moment at till the bottom most?
thanks
RE: Moment Calculation from Given Stress on Plate Element
In any case, if the stress has linear distribution from top to bottom, the moment can be calculated from the difference between stress at top and stress at bottom.
Ordinarily, f = My/I where f is the stress, M is the applied moment, y is the distance from the centroid to the point in question and I is the moment of inertia of the plate. Given the stress at any point top and bottom, M = (ft-fb)I/2y. If y is taken as t/2 this reduces to (ft-fb)/I where ft and fb represent stress at top and bottom of plate respectively.
Of course, if the plate has been stressed beyond the elastic limit, the above method will not work.
BA
RE: Moment Calculation from Given Stress on Plate Element
another day in paradise, or is paradise one day closer ?
RE: Moment Calculation from Given Stress on Plate Element
If your axial only stresses are stripped out, or not present to begin with, the reference point/axis will be arbitrary. You'll get the same value for the moment on the cross section regardless of where you take your reference point/axis. The process that I'me envisioning here is as follows:
1) FEM produces cross section stresses.
2) You or the software integrate the stresses into a cross section moment as we've been discussing.
3) You use the cross section moments to design and detail flexural reinforcing.
Per the process described above, this wouldn't make any sense. There's no "moment at the bottom" or "moment at the top". There's just the singular moment on the overall cross section. With that in hand, you'd switch to conventional reinforced concrete design assuming cracked concrete and a plastified section at ultimate capacity.
Agreed. Frankly, I'd be shocked if there isn't some way for SAP to report the aggregated cross sectional actions. Certainly, CSI SAFE can do that.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment Calculation from Given Stress on Plate Element
The output file indicates that stress is positive (tension) in all locations which suggests to me that the output file is wrong.
BA
RE: Moment Calculation from Given Stress on Plate Element
@BAretrued; so in case of nonlinearity what will be the method for calculating moment from stess??
thanks
RE: Moment Calculation from Given Stress on Plate Element
BA
RE: Moment Calculation from Given Stress on Plate Element
Is this FEA non-linear ? or linear ?? if linear, then the high stresses are exaggerated 'cause the FEA doesn't appreciate yielding. but you could still use the stress profile to calculate a moment on the section (plot the stress across the thickness). If the stresses are real, then the FEA is saying you're in the process of developing a plastic hinge.
another day in paradise, or is paradise one day closer ?
RE: Moment Calculation from Given Stress on Plate Element