degree of freedom

Hi,

I got a simple 2D problem (a rectangular shell, static general, CPS4R element), with 557 nodes, each of them have 2 DOFs (U1 and U2), according to the data file. But when I print out the ELEMENT STIFFNESS MATRIX, for each element it is a 12x12 matrix which means the rotational DOF about z axis is also taken into account. How can I omit this 3rd DOF? Can I?

Thank you.

Hello Experts,

I have written a uel subroutine where I have totally 12 degree of freedom. Among these 12 degree of freedom, 6 are standard abaqus degree of freedom (3 Displacements and 3 Rotations) and another 6 are User defined degree of freedom. 

I assign these these degree of freedom in following way.

*USER ELEMENT,TYPE =U9, NODES=9,PROPERTIES=24,coordinates=3
1,2,3,4,5,6
9,1,2,3,4,5,6,7,8,9,10,11,12

Dear All,

I have much problem when modelling my project with ANSYS, one of problem that I met always like this 

 *** ERROR ***                           CP =     296.828   TIME= 14:56:15
 A small negative equation solver pivot term has been encountered at the
 ROTZ degree of freedom of node 11758.  Check for an insufficiently     
 constrained model.