Risa 3D - Equipment Anchor Design

[ChangeOrder]

I am designing an equipment foundation and anchors for a piece of equipment. In Risa 3D, I have located the anchors and drawn a vertical rigid link from center of foundation to top of concrete distance, using a fixed end condition at the node which would be at the center of the foundation. There is a total of 6 anchors. From the top of the vertical rigid links representing the anchor bolts, i have drawn rigid links all to the center of gravity of the equipment where i would add a single nodal load for DL, LL, Wind Load, etc.
My question is, will all the rigid links have fixed ends, creating a completely rigid frame? I plan on using the reactions at the anchor nodes. I have tried pin connections for the rigid links to the center of gravity, but get much larger shear reactions at the anchors, so i believe a completely rigid frame would make more sense. I will transfer the model into Risa Foundation to do the concrete design.

 

[dold]

I'd delete the "anchor" rigid links and just apply a pinned boundary condition to the "to-center-of-mass" rigid links. I've actually done this before for this exact situation and it matches hand calcs fairly close. If your BC's are all pinned then that end of the rigid link will have to be fixed-end. Or vice-versa. Fixed BC's and release ends of members. Might want to just experiment and see if there's any difference. Probably will be. Or just do it by hand hah.

 

[bones206]

I've done it this way before also. One thing to watch out for is overconstraining the model with too many rigid links and fixed conditions. You can end up with some unexpected results due to the high degree of indeterminacy. Like dold suggested, experiment with different boundary conditions until the reactions match what you would expect by hand-calc analysis.