Modified Approaches for Calculation of Effective Length Factor of Frames

Abstract

As a crucial factor for stability calculation of frames, the effective length factor is generally determined by the traditional approaches in most current design codes, but some assumptions imposed do not reflect the real frame buckling behaviors. In this paper modified approaches are proposed based on the change of some unreasonable assumptions of the traditional approaches mainly in two aspects. Firstly, the premise that all frame columns buckle simultaneously is changed into an individual column buckling mode in braced frames, or story buckling mode in both braced and unbraced frames. Secondly, actual distribution of axial forces of columns is taken into account, so that the stability functions of columns may not be identical. Moreover, approximate formulas for calculation of the effective length factor are obtained based on the modified approaches, by which a series of numerical analysis is carried out. Numerical analysis results demonstrate that the modified approaches improve the accuracy well compared with the traditional ones.

Part I: Modified Buckling Factor for Columns in Braced and Unbraced Frames with Composite Girders

“…On the basis of the modified approaches, approximate formulae for calculating the effective length factor are derived by changing some of the old approaches' inappropriate assumptions [9]. Furthermore, the modified G factor used in US code alignment charts was determined using the stiffness parameter calculated for girders on elastic foundations with different far end conditions in braced and unbraced frames [1].…”

Numerical investigation of the design of single‐span steel portal frames using the effective length and direct analysis methods

“…In addition, Chen and Chuan [13] asserted that the effective length method mainly applies to the determination of elastic critical loads in frame structures. Far et al [14] agreed with Surovek and Ziemian [8] by saying that an advanced analysis is required in complex and irregular structures in which the second-order effects are significant.…”