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Modelling Rigid Diaphragm in ABAQUS

Hi Everyone 

I have a question in using kinematic constraint to
model rigid diaphragm in ABAQUS? For example i define a RP(reference
point) at each story level and constraint three dof (U1,U2,UR2)(2
translational and 1 vertical rotational dof) of the Coupling Node to the
RP. However i think because of using the Kinematic constraint, The dof of
RP is now activated which means that the dof that i am not constraint
(U2,UR1,UR3) to can be free to translate and rotate, so i'm starting to
get error due to the singularity problems. I try to fix the problem by
providing a boundary condition to the unconstrained dof of the RP, however
my result start to get ugly because the extra boundary that i specified. 

I was just wondering if you have any thought to my problems. 

Many Thanks.

Peter

Based on your description, let me assume your coordinate system.

X, Y axes are in the plane , and Z is parallel to the surface normal of diaphragm.

(You may be clear about it)The diaphragm constraint restricts the motion of a group of nodes (lying on a plane) to more rigidly in the plane but are free to move independently out of plane. Therefore, you should constrain the dofs responsible for inplane movement (i.e., U1, U2 and UR3). 

Creating a reference node and constraining it with other nodes, activates all 6 dofs on the reference node. Therefore, one easy solution for you would be to use one node from the diaphragm set as the reference node for the kinematic constraints. This way you don't need to define any additional bc, and the constraint is imposed on all other nodes lying the plane. 

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