STEEL DESIGN - USER SECTION - Different Section properties database-analysis
No, no "factor". Closed = known formula is used to calculate such properties instead of taking them from database
Could anyone elaborate this......
Which is the known formula?
Formula for SHAPE_TYPE = 36 section , circular hollow section ("single tube")
Wply = Wplz = 4.0/3.0*(R*R*R-Ri*Ri*Ri);
where
R – ext radius
Ri – int radius
If you save section to database with "?" symbol (SHAPE_TYPE = 0) the database values will be considered.
Rafal Gaweda
I believe this has already been explained on the forum but I think it would be useful to write this again.
When you create a user defined section and this section is to be saved to the user section database you need to answer yourself a question: am I going to use this section in the steel design module?
- if no, you just do not have to care about the selection of the section type as this is irrelevant for calculation of the model itself
- if yes, then you have to be aware that Robot itself is not able to classify sections based on their shapes (channels, angles etc.) and this has to be done manually.
This decision influences section class (slender, semi-compact etc.) classification which is determined by wall height to thickness ratio that you provide after selecting the symbol type as well as the use of the verification formulas from the selected design code (including e.g. Wpl calculation). In case you select "?" (generic cross section; you may for better understanding of the situation assume this is a solid rectangle) all cross sectional properties are taken from the section database but as the section type is undetermined the code checking does not include such effects as LTB or section slenderness.
Hope this helps.
Artur Kosakowski
Assuming that you are about to calculate (verify) this section by hand what is be the verification procedure you would follow? In other words would you verify it as a tube, a box or just checked the stresses? Other?
Artur Kosakowski
In such case select the tube section. Typing the dimensions you may consider to enter h equal to the horizontal size of the entire compound section. The other possible approach is define the section (in the model) as 4 separate bars (each with the 'standard' tubular cross section) connected at certain spacing along their lengths with rigid links that cause them to work together. The idea is to distribute load to each of them and then design them following the standard code procedure for tubes.
Artur Kosakowski
As I wrote the key is to answer yourself a question how would you checked such section by hand. Knowing the answer you can make the decision how to assign parameters.
If I choose to save it as a tube and type as h the horizontal size of the compound section which should be the thickness then?
I think there are two options: 1. Set is as for a single tube. 2. Set is in such a way that the section class is as you would like it to be.
The second suggestion might be the most feasible but which is the most appropriate distance between the rigid links?Let's say it doesn't matter...
This depends on the way the tubes are connected together. If they are welded let's say each 3 m then it would be 3 m. If you have continuous welds than more often.
Would I have to brake the columns at this distance?
No. All you need is to have nodes along the bars.
How would I specify the buckling lenghts....?
Again this depends on the boundary conditions of this profile in the model. You can try to define them in the same way as you would do for the compound profile.
I'm very sorry but I'm not in the position to tell what would be the best - all I'm trying to do is to provide you with the list of the possible solutions I can think of. Perhaps the users of the forum have also faced this sort of the situation and can shear their experience with you?
Artur Kosakowski
