Effective lengths of columns in braced multi-storey frames

In several design codes and specifications, simplified formulae, nomographs or charts are given for determining the effective lengths of frame columns. It is shown that these simplified approaches may yield rather erroneous results in most of the cases. This is due to the fact that, the code formulae utilize only local stiffness distributions, thus ignoring the general behaviour of the system. In this paper, a simplified procedure for determining approximate values for the effective lengths of braced multi-storey frame columns is developed. The procedure utilizes a simple average calculation and yields errors less than 10 %, which may be considered suitable for practical purposes. The proposed procedure is applied to several numerical examples and it is shown that all the errors are in the acceptable range.