uniting surfaces for finite element analisys

[atomic_duck]

first of all hello

well, I'm not a frequent english speaker so the spelling can be wrong

I took a serious crash course in catia (2 wheeks and counting) because I needed to make this project until june.

I am using CATIA V5R17 to design a bicycle frame and ansys to analise it
I'm using thin tubes (surfaces) that i will later model as shell elements. I used the generative shape design and sweeped/revoluted surfaces. the surfaces are intersecting eachother but the intersections aren't recognised and the tubes are considered independent entitys (in catia and ansys-doesn't glue 'em-).
the tubes are created as separate parts and copyed in one part file
If I'm creating a shape fillet with both bodys trimmed it "magicaly" unites them......but if I'm trying to create the same fillet with only one of the supports trimmed (as it should be) it's not uniting the 2 surfaces.......
other surfaces splited and filleted to the tubes are also considered independent entitys (even after the fillet!).
I tried with join but the conexity check gives an error and even with the check off it doesn't recognises 'em as a single surface.
I tried with add too but, even so, it's moving the surfaces under the add command and not doing anything to them.
as I mentiond above I'm a newby in catia an I'm sorry if the question is trivial........
I attached the files in .igs and .model also

 

[andy.parrow]

I created a dune buggy frame once. I designed the whole thing drawing just the wireframe centerlines, then create solid tubes later and trimmed and filleted afterwards. Seemed to work pretty good. I think solid modeling is easier then surfacing.

I imagine the same thing could be done for a bike frame.

 

[atomic_duck]

thank you for the answer
well yes, I dit draw it (at first) as lines and then modelled them as beams but that was really only to determine the right geometry for a minimal imposed deflection.
finally I gave up, I created the solids and annalised it but the results on shells would have been much more accurate then the sollid elements on thin tubing.