Weld design for beams picked from skyciv

[rcfraz37]

Hello all,

I'm designing an octagonal steel cage which has several arms coming off of it which each hold a sail that catches the wind. This leads to high loading in storms (about 2000lb on some of the arms). The result stresses the beams which make up the octagon. I've run the system though skyciv and gotten what I think is some pretty good data. The problem is that the beams are under some odd combinations of loads that don't seem to translate well into the simple models of weld evaluations. Does anyone have any resources or suggestions for doing this? I'm way out of my depth.

One thing I did was grab the max stress in the beam from skyciv and evaluate the welds undergoing that stress, this leads to long thick welds and I think it is probably over designed.

Thanks

a big question i have is how do i evaluate the welds strength as all these take place.

 

[kingnero]

As always, wisely choose your axes, choose your load combinations, divide the combined stresses in their most basic components along those axes, and evaluate using the Von Mises model. Easily said, sometimes a bit more difficult to practise. But a good understanding/visualisation of those stresses should help you, the calcs are pretty straightforward once you set up a decent model.

 

[rcfraz37]

Thanks. Any advice on getting those stresses and loads out of the data? Taking the max stress like I mention above seems wrong, as I think that is actually elsewhere in the beam not at the weld.
The software sections the beam as part of its analysis and gives the length along the beam, the axial force, the shear in Y and Z, the torsion about x, and the moment about Y and Z. it feels like I've got all the information there but the way its segmented makes me think that cant simply be plugged in.

I've got to evaluate the normal shear, which should be bending component(the torsion) + axial load.

so torsion*r/polar moment of inertia + axial/area of the part.

then I have the shear and moments, which I thought I would only need the shear as the moments would create that shear.

then I'm not sure how to add these all together or if they need to be evaluated separately.

 

[human909]

Grab the moment from SkyCiv not the max stress and then work off first principles and suitable design guides for the section type, orientation and type of connection. Use FEA if you are competent with it.

A picture would greatly help here. Is this an octagonal from from flat bar, I-sections, C-section, box-sections, pipe, or something else?

From my experience with SkyCiv it is pretty good at something but is still a "work in progress" app. Which largely also applies to other cloud apps like ClearCalcs. All software you should use at your own risk, but these newer packages that applies even more so. (I use ClearCalcs for some things, but it isn't my workhorse.)

I'm designing an octagonal steel cage which has several arms coming off of it which each hold a sail that catches the wind.

So possibly some 'weird' section choices and almost certainly some 'weird' connections.

Ideastatica is the perfect software for analysing this. It costs a bomb but there is a free trial. It pretty much does everything you want it to do in a connection/weld design software package, I'd consider it pretty well developed. But always good to cross check with hand calcs if something is particularly weird.

 

[MintJulep]

This will be subject to reversing loads.

So it's a fatigue case.

You need to design weld joints that are suitable for fatigue and analyze them for fatigue performance.