How to integrate with 6 tying points (TP) for transverse shear and 4 TP for in-plane shear, in case of Assumed Natural Strain?

Hi Experts,


I am presently working with a 9-node shell element and understood that there were many rigid body modes available even with reduced integration.

Thus, I am planning to implement Assumed Natural Strain and found out that there will be 6 integration points for transverse shear strains gamma_xz and gamma_yz and  nominal strain while there are only 4 typing points in-plane shear strain.

Attached Images
(1)  ANS Strain integration, (2) Tying points

While please be noted that I am using material non-linearity (plasticity) which is designed to get integrated at the same integration point for stress update or during stiffness calculation. Generally, I am using 2x2 integration points for 9-noded element.

Can you please guide me, how this integration can be achieved at a common integration point in the case of Assumed Natural Strain Method.

Please let me know if you require any further information in this regards.


Thanks


Best regards,

Maharshi.