Defining Element Foundation Behavior
Foundation pressures act normal to the element faces on which they are applied. In large-displacement analysis the direction of action of the foundation is based on the deformed configuration; foundations rotate with the element sides.
Convergence difficulties may arise with large-deformation problems since no corresponding foundation load stiffness terms are included in the element stiffness matrices.
To define the foundation behavior, you specify the foundation stiffness per unit area (per unit length for beams).