Axial-moment interaction and load path dependency for steel columns
This paper discusses the effect of out-of-straightness direction, major-minor moment interaction and path dependency for steel columns. This has been undertaken by using the Extended Direct Analysis (EDA) method which has been developed for analysing a simple low-rise 3D steel frame structure under 3D biaxial loadings in arbitrary load-paths from first principles. It takes into account non-ideal conditions, residual stresses, member out-of-straightness, statistical variation in capacities, plasticity, and second-order geometric effects. It was found steel columns are path dependant, with the plastic capacity reducing by up to 18% when the loading occurs in the major and minor axis at the same time. By completing bi-directional loading on a simple 3D frame it was found that the maximum critical load on the major and minor axes reduced by 10% when compared to the 2D EDA method which does not consider major-minor moment interaction. Therefore it is concluded that the tangent modulus is a function of axial load, moment and load path. Further research is required to account for torsional effects and shear before this method can be used for design.