Fuzzy logic based estimation of effective lengths of columns in partially braced multi-storey frames

Columns in multi-storey frames are presently categorized as either braced or unbraced, usually by means of the stability index criterion, for estimating their effective length ratios by design aids such as `alignment charts'. This procedure, however, ignores the transition in buckling behaviour between the braced condition and the unbraced one. Hence, this results in either an overestimation or an underestimation of effective length estimates of columns in frames that are in fact `partially braced'. It is shown in this paper that the transitional behaviour is gradual, and can be approximately modelled by means of a `fuzzy logic' based technique. The proposed technique is simple and intuitively agreeable. It fills the existing gap between the braced and unbraced conditions in present codal provisions.