Modification for French rules equations for effective length factors of steel compression members

Abstract EN

In most current codes of design steel members and frames, specifications for the design of compression columns or of beam-column use the effective length factor; K.

the effective length factor is employed to facilitate the design of framed members by transforming an end-restrained compressive member to an equivalent pinned-ended member.

The effective length factor is obtained by solving the exact equations numerically which require many routine calculations or by using a pair of alignment charts for the two cases of braced frames and sway frames.

The accuracy of these charts depends on the size of chart and the reader’s sharpness of vision.

Instead of using complicated equations or charts, simple equations are required to determine the effective length factor directly as a function of the rotational resistant at column ends (GA, GB).

better equations have been available in the French design rules for steel structures since 1966, and have been included in the European recommendations of 1978.

In this paper, modification to the French design rules equations for effective length factors are presented using multiple regressions for tabulated exact values corresponding to different practical values of the rotational resistance at column ends (GA, GB).

The investigated equations are more accurate than current French rules equations that recommended in some steel constructions codes.

Comparisons between the results of the present equations and those obtained by current equations with those obtained by exact solutions are given also in this paper.