Beam with hinges elements - Scott and Fenves

[marcellosabene]

Hy to everyone,
I have a problem with Scott and Fenves' finite element, which i am using to model beams/columns
members in a 2D Frame in OpenSees.
I've evaluated the Plastic Hinge Length "Lp" using Paulay and Priestley (1992) formulation,
but in this way i found a high axial deformability of the element even for gravitational loads only.

In Opensees wiki example: Pushover Analysis of 2-Story Moment Frame,
0.004*(Element Length) is used to evaluate the same Plastic Hinge Length.
In this way you obtain a smaller plastic hinge lenght (one order of magnitude) than that calculated with Paulay and Priestley (1992) formulation.

My questions are:

1) Which of the two formulations is more appropriate?
2) How can I neglect the axial stiffness using Scott and Fenves' finite element?

Thanks in advance for your reply and for your availability.