Stability of unbraced frames under non-proportional loading

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