RigidDiaphragm at base, analysis error

[serggg]

I'm working on a nonlinear model and looking to investigate the effect of applied rotational accelerations at the base. My idea in to how to input the rotations is to generate a master node at the base, fix it, and generate a rigidDiaphragm constraining all of the nodes at the base level. I'd like to use a rigidDiaphragm and apply the rotation as a ground motion to the master node to account for the rigid body rotation. A very broad summary of the code.

# Master node
node 1 $x $y $z
fix 1 1 1 1 1 1 1
rigidDiaphragm 3 1 $slaveNode1 $slaveNode2 ...

There are several slaveNodes (50+), all on the same plane XY as the master node, and all without any fixed conditions.

Once I try to perform a gravity analysis, I get a instability error, stating that a diagonal entry is zero. I'm using a Transformation constraint handler, a SparseSYM system, and an RCM numberer.

If I avoid defining the master node, and the rigid diaphragm, and instead fix all the slave nodes, I can perform the gravity analysis without any issue.

Is there something I'm missing, is it even possible to define a rigidDiaphragm to a fully fixed node?

Any help is kindly appreciated

[mhscott]

Rigid diaphragm does not enforce constraints among all DOFs from primary node to secondary nodes.

You can define rotational acceleration anyway without doing the rigid diaphragm: https://portwooddigital.com/2021/11/12/openseesaw/

[serggg]

Thank you very much!