Stability of unbraced frames under non-proportional loading

This paper discusses the elastic stability of unbraced frames under non-proportional loadingbased on the concept of storey-based buckling. Unlike the case of proportional loading, in which the loadpattern is predefined, load patterns for non-proportional loading are unknown, and there may be variousload patterns that will correspond to different critical buckling loads of the frame. The problem ofdetermining elastic critical loads of unbraced frames under non-proportional loading is expressed as theminimization and maximization problem with subject to stability constraints and is solved by a linearprogramming method. The minimum and maximum loads represent the lower and upper bounds of criticalloads for unbraced frames and provide realistic estimation of stability capacities of the frame underextreme load cases. The proposed approach of evaluating the stability of unbraced frames under non-proportionalloading has taken into account the variability of magnitudes and patterns of loads, therefore,it is recommended for the design practice.