The analysis model contains several nonlinearities, among them contacts between plates. The contacts are very strong in compression and extremely weak in tension.
However, some stiffness is necessary even in tension to ensure the numerical stability of the model. There were several very rare cases with a large contact area and a large deformation in tension where the tension in contacts consumed a significant portion of set loading.
The contact model was improved to maintain the stability of the numerical analysis and limit tensile force in contact to a negligible level.
Available in Expert and Enhanced edition.