A Comparison of the Krawinkler and Scissors Models for Including Beam Column Joint Deformations in the Analysis of Moment Resisting Steel Frames

Current codes and specifications require that the flexibility of the beam-column joint region of moment resisting frames be included in structural analysis. The two most popular analytical models for modeling the joint are the Krawinkler model and the Scissors model. Each of these models represent a mechanical analog of the joint, with the joint being represented as an assembly of rigid links and rotational springs. This paper provides a complete derivation for the nonlinear spring properties to be used in the Krawinkler and Scissors models, and through nonlinear static and dynamic analysis, shows that the models, when properly used, produce similar but not identical results. It is further shown that the properties for the two models are not interchangeable; the spring properties derived for the Krawinkler model may not be used directly in the Scissors model. Unfortunately, several references that recommend the use of the Scissors model erroneously suggests that the spring properties for this model are the same as those derived for the Krawinkler model. This paper quantifies the effect that this assumption has on the computed nonlinear static and dynamic response of a moment frame, and shows that the result of the error may have a negative impact on the economy of steel moment frames.