The Structural Engineer's Corner

Eng. Onorio Francesco Salvatore

The Form Factor for local buckling as per Australian Standard 4100

Written By: Lexatus - Sep• 12•13

Buckling - Onorio

The form factor (kf) is defined in Clause 6.2.2 of AS 4100. Kf is used to determine the design section capacity of a concentrically loaded compression member (φNs).

The calculation of kf indicates the degree to which the plate elements which make up the column section will buckle locally before squashing (i.e. yielding). kf represents the proportion of the section that is effective in compression and is based on the effective width of each element in the section (i.e. kf = 1.0 signifies a column section which will yield rather than buckle locally in a short or stub column test). Hence, the formula is:

kf = Ae / Ag

Ae = the effective area of the section;

Ag = the gross area.

The effective area can be calculated considering the effective widths, as per clause 6.2.4.

The evaluation of kf is also important when designing to the higher tier provisions for members subject to combined actions as noted in Section 8 of AS 4100.

For any issues or questions, you can contact the author at:

Eng. Onorio Francesco Salvatore

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