Current earthquake-resistant procedures prescribe generic values for the response reductions factors, regardless
of the configurational characteristics of the designed buildings. It is well know that these response reduction factors
values reflect the expected behavior of the structures when they are under strong ground motions, being this seismic
behavior usually evaluated through ductility and over-strength. In this work calculated values of the ductility of special
moment-resisting steel frames with different span lengths and designed according the Ecuadorian Construction Code
are presented. Results show that the buildings’ ductility is strongly influenced by the spans length and they would reach
inadequate values if the second-order effect P-Δ occur, and then indicating that the structures are more vulnerable than structures
not affected by P-Δ effect.