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# Strain compatibility method using joint constraints to obtain base plate anchor forces

## Strain compatibility method using joint constraints to obtain base plate anchor forces

(OP)
Hi everyone,

I am currently trying to model a base plate in order to obtain forces at the anchors. The assumption is that the plate is rigid, therefore only the stiffness of the concrete foundation and the anchors come into play. I have successfully modelled the plate with shells and applied the compression-only subgrade reaction. I have used 1-joint non-linear "hook" links to model the anchors with their stiffness. In order to make the plate rigid, I have used the "body" joint constraints and applied this property to all joints. The attachment shows a 3D view of the plate.

After creating a non-linear load case, applying moments at the load introduction node (centre of the plate)and running the analysis, I am achieving the expected tensile forces in the anchors, as well as the compression forces in the concrete. However, if I apply a shear force instead of a moment, my expectation would be to obtain an even distribution of shear forces amongst the anchor group, but this isn't happening. Instead, I don't get any reactions at all? I should have mentioned that the "hook" link is fixed in the X-Y horizontal plane.

Any ideas of what's going on? I think I may be modelling the plate incorrectly for shear...

Many thanks to all.

Emilio

Replies continue below

### RE: Strain compatibility method using joint constraints to obtain base plate anchor forces

I've never modeled a structure (or any of it's elements) that may needs fancy support condition such as body constraint or non linear links. Thus, you may not find my response very helpful.

Still I'm curious about the following.

#### Quote:

In order to make the plate rigid, I have used the "body" joint constraints and applied this property to all joints.
My question is If you wanted to model a rigid plate than why didn't you use "thick" plate option when defining the shell element? This seems less complicated than the body constraint boundary condition.

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