Forces in members of three dimensional welding trestle 1

[Dinga17]

Hi all,

I've been doing some checking of some older fabricated trestles at work to check load ratings etc. See the attached image for a welding trestle. I have been using FEA so we have a report record etc. Anyways, so far all have been 2D planar members for legs - as in if you look at the end view of the trestle the legs are 2D so it would be simple statics to work out the force in each leg of the trestle.

One I checked today wasn't planar - the legs were angled out in the y and z direction, so if you look at the end view it's not 2D. If I wanted to calculate the force in each leg do I need to use vectors or is there a simpler method?
Trying to remember back to my statics days ...
It's easy enough to resolve a weight on the trestle to two point loads on top of each set of legs. What's the easiest method to use from there?

Cheers guys

 

[KootK]

I did this in 30s so do QC my work.

 

[rb1957]

3D frames = 3D forces, in fact the forces would be axial in the member, so the three components are related by the direction cosines of the member.

unless you can simplify the reactions of the frame (as KootK has done) ... but then I wonder how to determine the member loads (for these reactions) ... bending members ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Dinga17]

Yeah you could simplify it KootK but that's not entirely accurate.

Rb1957, I'm not sure either. I though the solution might be to use vectors and coordinates, like how you would have a mass hanging from three cables in a 3D co-ordinate. Not entirely sure though.

 

[KootK]

...but that's not entirely accurate.

In what sense is it inaccurate? Are you referring to moment frame behavior where both end frames participate to resist lateral / unbalanced loads?

For the FBD that I drew above, the moments within the frame can be determined by breaking it down into more straight forward FBD's.