Load History Effects on Structural Members

Strength determination in usual structural engineering practice is based on failure under monotonically increasing, proportional loadings. The effects of nonproportional load sequences are largely ignored. Specificallyrinformation on column behavior in steel building frames is generally obtarrted from analyses under proportionally increasing axial loads and bending moment, although the former, largely due to gravity loads, are likely to precede the latter, which are primarily caused by lateral loads. To explore these effects, the investigation in this paper proceeds in the following steps. Based on measurements of strains during uniaxial cyclic tests of mild steel specimens, a cyclic stress‐strain law is formulated, and verified against test results. Secondly, this stress‐strain law is incorporated into an analysis to predict the response‐of structural steel sections under arbitrary applied axial load and moment sequences. The results of this analysis are again verified by comparison with test data. Finally the section analysis is used to explore the effect of different axial load‐momenrfustories on the response of column sections, and it is concluded that column deformations are insensitive to sequence of load application.