Stability of unbraced frames under non-proportional loading

This paper discusses the elastic stability of unbraced frames under non-pro portional loading based on the concept of storey-based buckling. Unlike the case of proportional loading, in which the load pattern is predefined, loa d patterns for non-proportional loading are unknown, and there may be vario us load patterns that will correspond to different critical buckling loads of the frame. The problem of determining elastic critical loads of unbraced frames under non-proportional loading is expressed as the minimization and maximization problem with subject to stability constraints and is solved b y a linear programming method. The minimum and maximum loads represent the lower and upper bounds of critical loads for unbraced frames and provide re alistic estimation of stability capacities of the frame under extreme load cases. The proposed approach of evaluating the stability of unbraced frames under nonproportional loading has taken into account the variability of ma gnitudes and patterns of loads, therefore, it is recommended for the design practice.