Membrane type area elements transfer shear only with no moments whereas shell type area elements transfer shears and moments. Alternatively, you could assign area stiffness modifiers to reduce or eliminate stiffness in different directions
stressed is correct. Do that through stiffness modifier. However, read the SAP2000 manual for how each component(direction) is defined since that could be confusing for first time user. A lot of times it is the opposite way than you think it is.
Moment curvature analysis,reinforced concrete column design and prestressed concrete pile design at