11.3Compression Members

11.3.1 Actual Compressive Stress

The actual compressive stress, $f_{\mathrm{c}}$ at working (service) load, $P_{\mathrm{s}}$ of a compression member shall be less than or equal to the permissible compressive stress, $f_{\mathrm{ac}}$ as given below:

Actual compressive stress, $f_{\mathrm{c}}=P_{\mathrm{s}} / A_{\mathrm{c}}$

The permissible compressive stress, $f_{\mathrm{ac}}=0.60 f_{\mathrm{cd}}$ where

• $\begin{aligned} A_{\mathrm{e}} & =\text { effective sectional area as defined in } 7.3 .2 \\ & \text { and }\end{aligned}$
• $\begin{aligned} f_{\mathrm{cd}} & =\text { design compressive stress as defined in } \\ & 7.1 .2 .1 \text { (for angles see } 7.5 .1 .2\end{aligned}$.

11.3.2 Design Details

Design of the compression members shall conform to 7.3.

11.3.3 Column Bases

The provisions of 7.4 shall be followed for the design of column bases, except that the thickness of a simple column base, $t_{\mathrm{s}}$ shall be calculated as:

$t_{s}=\sqrt{3 w\left(a^{2}-0.3 b^{2}\right) / f_{\mathrm{bs}}}$

where

• $\begin{aligned} w & =\text { uniform pressure from below on the slab } \\ & \text { base due to axial compression; }\end{aligned}$

• $\begin{aligned} a, b & =\text { larger and smaller projection of the slab base } \\ & \text { beyond the rectangle circumscribing the } \\ & \text { column, respectively; and }\end{aligned}$

• $\begin{aligned} f_{\mathrm{bs}} & =\text { permissible bending stress in column base } \\ & \text { equal to } 0.75 f_{y} .\end{aligned}$

11.3.4 Angle Struts

Provisions of 7.5 shall be used for design of angle struts, except that the limiting actual stresses shall be calculated in accordance with 11.3.1.

11.3.5 Laced and Battened Columns

The laced and battened columns shall be designed in accordance with 7.6 and 7.7, except that the actual stresses shall be less than the permissible stresses given in 11.3.1.