boundary condition for a flange with grounded bolt connections

[Anonymous]

Hi

I have a general question regarding boundary condtions which  helps novice users like me.

The attached image is a bolted flange and it is bolted to the ground.A moment load is applied as shown.model will be in 3d and meshed with brick elements.

Now In ASIM, I can use bolt generator and use grounded bolts, which essentially the one end node of the bolt is fixed.

Obviously, one side of the bolts in the pattern will be in tension and other will be in compression

Now in realty the ground resists displacement of nodes on the bottom surface of the flange which in turn effects the loads in the bolts.

 so my question is what REASONABLE boundary condtion can be assumed IN ASIM for the bottom surface of flange OTHER THAN USING GAP ELEMENTS. Can we use spring elements? if so how the stiffness must be calculated.

thanks

flange with grounded bolt connection

[John_Holtz]

Hi madg1,

I think the answer depends on what assumption you want to make.

1) If the flange will remain in contact with the ground over the entire surface, then use general constraints.

2) If the flange will lift up, then you need to use contact.

If you know the stiffness of "the ground", then you will need to distribute that stiffness to the N constraints or gap elements using the law of equivalent stiffness for parallel springs. (1 known stiffness somehow equals N springs working in parallel.)

Naturally, option 1 is the fastest solution, and the reaction forces would indicate whether any of the nodes are trying to lift off of the ground (but are being restrained).

Be sure to apply the preload to the bolts; otherwise, the flange will be lifting off of the ground.