4.6Frame Buckling Analysis

4.6.2.1 Regular non-sway frames (see 4.1.2)

In a rectangular non-sway frame with regular loading and negligible axial forces in the beams, the Euler buckling stress $f_{\mathrm{cc}}$ for each column shall be determined in accordance with 7.1.2.1. The elastic buckling load factor $\left(\lambda_{\mathrm{cr}}\right)$ for the whole frame shall be taken as the lowest of the ratio of $\left(f_{\mathrm{cc}} / f_{\mathrm{cd}}\right)$ for all the columns, where

$f_{\mathrm{cd}}$ is the axial compressive stress in the column from the factored load analysis.

4.6.2.2 Regular sway frames

In a rectangular sway frame with regular loading and negligible axial forces in the beams, the buckling load, $P_{\mathrm{cc}}$, for each column shall be determined as $P_{\mathrm{cc}}=A f_{\mathrm{cc}}$ where $f_{\mathrm{cc}}$ is the elastic buckling stress of the column in the plane of frame, obtained in accordance with 7.1.2.1. The elastic buckling load factor $\lambda_{\mathrm{cr}}$ for the whole frame shall be taken as the lowest of all the ratios, $\lambda_{\mathrm{scr}}$, calculated for each storey of the building, as given below:

$\lambda_{\mathrm{ser}}=\frac{\sum\left(P_{\mathrm{cc}} / L\right)}{\sum(P / L)}$

where

• $\begin{aligned} P & =\text { member axial force from the factored load } \\ & \text { analysis, with tension taken as negative; and }\end{aligned}$
• $\begin{aligned} L & =\text { column length and the summation includes } \\ & \text { all columns in the plane frame within a } \\ & \text { storey. }\end{aligned}$