NON-CONFORMING MODES STABILIZATION OF A 9-NODE STRESS-RESULTANT DEGENERATED SHELL ELEMENT WITH DRILLING FREEDOM

A nine-node degenerate stress-resultant shell element with 6 dof at each node is presented. The geometry of the element is defined in a manner which would allow the Jacobian to be assumed constant through the thickness without violating the rigid body rotation criterion; and the penalty function method is used to incorporate the sixth dof. A non-conforming mode stabilization procedure is used in the design of the new element. The non-conforming modes were derived by removing one or a number of nodes from the original element. The stabilization procedure involves careful combining of components of the stiffness matrices of the parent and the reduced element. The performance of the new element in an extensive number of problems supports this formulation.