Story-based effective length factors for unbraced PR frames

Abstract

This paper proposes a practical method to evaluate the effective length factor K for compressive members in unbraced partially-restrained frames under elastic buckling. In light of story-based buckling and the introduction of the end-fixity factor to characterize the beam-to-column connections of partially-restrained frames, the lateral stiffness of columns with consideration of the effect of axial load is derived. The formulations and procedure of calculating story-based column effective length factors are presented. Numerical examples are then presented to illustrate the effectiveness of the proposed procedure. With the adoption of the end-fixity factor, different member end rotational conditions can be readily modelled by derived formulations. Therefore, the proposed approach is comprehensive and can be applied for both unbraced partially and fully-restrained frames.