Estimating sizes

Simplified procedures can be used to estimate the required size of column section.

It may not be necessary to perform detailed calculations to determine column sizes, and simpler methods can be adopted. These include rules of thumb which enable a simple estimate of approximate section sizes, and safe load tables which provide a more rigorous approach to estimating column sizes.

Rules of thumb provide an estimate of the required cross-section in relation to function and position within the building.

A typical structural frame for a multi-storey building may require column sizes which vary depending on the number of storeys supported. Thus the columns on the top storey supporting the roof only are likely to be much smaller than those on the ground floor which support all of the intermediate floors.

Safe load tables provide more rigorous guidance on required sizes.

The compressive strength of a column is related primarily to its cross-sectional area and slenderness ratio, and the material strength. Because of the importance of slenderness ratio in relation to buckling, it is not possible to calculate the maximum compressive strength for any cross-section, unless this is related to the effective length of the column. However, by assuming a range of different values, the compressive strength can be published as a function of effective length. Such tables enable the section size required for a given axial load and effective length to be read directly.