static safety coefficient according to von mises

[teseo.guerra]

Hello everyone, I have recently enrolled so I take the opportunity provided by the following post as well as to ask for help also for a short and general greeting to the whole community.
as from title I find myself stuck on the static safety coefficient according to von mises (I have to calculate it after a fem analysis with straus7 and the structure in question is a monodimensional structure of the classic ones that are studied in mechanics of the solids composed of beams ipe 180, of course I am also given the sigma of yield)
after various analysis on the internet and on the university books of the previous courses I realized that to have this sympathetic coefficient I have to calculate the ideal sigma with a formula that is function of sigma1, sigma2,sigma3 that if not mistaken are the main tensions true?
My doubt is the following if I work in monodimensional I only have a sigma or all three? and what shall I take?
in fact after having solved the structure rhinestone in the stress results section gives me the following viewing opportunities results:
1)axial stress;
2)bending stress plane 1;
3)bending stress plane 2;
4)total fiber stress;
5)max shearing stress plane 1;
6)max sheraing stress plane 2;
7)Having shearing stress plane 1;
8)Having shearing stress plane 2;
9)maximum torsional stress;
10)minimum principal stress;
11)maximum principal stress;
12)pipe hoope stress;
all elements are single-dimensional beam elements.
I hope I have not wrong section, and possibly someone can give me theoretical delucidations even if you do not know the program but has some fem method infarination is obviously welcome.
a heartfelt thanks to anyone who will respond and/or read

 

[AMinati]

most indicated was the finite element analysis forum! Although the study is two-dimensional, tensions are always three-dimensional (mostly an equal to zero). as a rule all finite element programs also provide the desired output, i.e. equivalent voltage (according to von mises or maximum tangential voltage or other). if the program does not provide it you must calculate it starting from the main tensions or from those according to three directions any (plus the relative cuts in the corresponding plans).

to the eye from the message I seem to understand that however the program uses fem shell models for which the values are those of membrane

aminati

 

[Fulvio Romano]

the finite element programmes generally give the sigma of von mises. strange not to be listed.. .
In general, however, the sigma of von mises is a combination of the main sigma or sigma and tau in any configuration (useless to say that the numeral at the end must be the same).

the safety coefficient will be sigmalimit/sigmamamaximum where sigmalimit is that of yielding or breaking, depending on whether the verification you are doing to yield or break.

 

[teseo.guerra]

Then, first of all, thanks to both for the prompt response, and then perhaps the problem had to be included in the finite elements section but since I also asked for theoretical delucidations I thought that the general section was the most indicated one; however, if by chance the administrators think it appropriate to move the following discussion they do it as well and if they can explain to me how eventually they do so next time not weigh on anyone.
made these due clarifications I tend to emphasize that for this exercise I work with shells but with one-dimensional beams (they are in the single-dimensional case).
the program does not give me the sigma of von mises I have to be me to calculate it and as told by Roman lightning the ideal sigma is given by a combination or the main sigma or sigma and tau in any reference system.
well (previously I apply the de saint venant theory as monodimensional and therefore I have a sigma and 2 tau) I since I know that straus7 provides me the values indicated above as axial stress.... and following in the plans related to the local coordinate system (1,2,3) now assumed that axial stress I have to take it into consideration stress bending or shear stress? or both?

 

[Fulvio Romano]

I don't know what stress bending and stress shear are probably bending and cutting, but they should represent a distribution of tensions in a section, and not a single dot tension.
However both, the sigma of von mises in one point should be worth sqr(s1^2 + s2^2 + s3^2 + 3t1^2 + 3t2^2 + 3t3^2), but check the formula, I am not sure.

be careful that the sigma must be calculated at the same point, so if you have for example cutting and bending, the maximum cut is at the center of the section, the maximum traction at the end, then should not be added.

to be sure of the meaning of the terms, why don't you make a framed beam and compare the results with those of the de Saint Venant theory?