FBD for tripod with crossmembers

[310toumad]

I'm trying to verify the stresses in the FEA simulation for this (shear stresses at joints, compression in tubes, etc.). The set up is three equally spaced legs (120 degrees apart) welded to a center tube with a load of 36,000 pounds on it. Three equally spaced, horizontal cross members are welded to each leg and to the tube for support. The feet are resting on the foundation. Could someone give me assistance on what the FBD would look like? Most statics problems just represent structures as simplified with pinned joints which do not transmit shear/moments. Attached are the FEA, and my attempt at the FBD for one leg. Does each welded connection have a moment associated with it? There just seems like too many unknowns to solve for.

 

[310toumad]

Here is the FEA result.

 

[BUGGAR]

This structure may be sensitive to foundation settlement.

 

[rabendt]

Your FEA model could be simplified by using beam elements to determine member axial, shear and moment forces. Also, you need to consider your connection design before creating the FEA model. If three angled tubes are welded to the vertical member, how will angled tubes be machined? And the welded joints will have substantial moments on them. BUGGAR is correct that the design concept is asking for problems with the foundation. I'd suggest buying a camera tripod and studying how it is constructed.