| A comprehensive study of the inelastic stability of steel beam-columns and frames subjected to nonproportional loads is conducted. A set of materially nonlinear differential equations of equilibrium for planar and biaxially loaded beam-columns are first formulated including sidesway. The analysis includes the effect of flexible connections, and initial imperfections in the form of member crookedness and residual stresses. Also, hollow rectangular sections are adopted for the study. First, an iterative numerical solution procedure is formulated for sway beam-columns utilizing central finite-differences with second-order truncation errors. Next, using the beam-column analysis, an inelastic frame analysis procedure is formulated by a conversion of the governing equations to a system of three-dimensional inelastic slope-deflection equations. The three-dimensional frame analysis is verified experimentally by conducting a rigorous test on a 15-foot high three-story single-bay structural steel space frame. The experimental results are in good agreement with the theoretical predictions. The strength of beam-columns, and plane and space frames with flexible connections is found to be load path dependent. |
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