Steel member design sign conventions

The steel member design module deals only with the member cross section axes. The longitudinal local x-axis of the member is of no relevance.

If the cross section is not transposed (the usual case) then the steel member design module treats the local z-axis of the member as the cross section's major axis. If it is transposed then it treats the local y-axis as the major axis.

If Imajor < Iminor then the steel member design module will display an error message.

If the cross section has been rotated or mirrored in the shape builder then you can’t use it in the steel member design module. If you want to rotate the cross section and still use it in a steel member design then you should do it as a direction angle, direction node or direction axis in the member properties.

For most section types, steel member design input and output data always relates to the major and minor principal cross section axes. The only exception is for single angle sections where the effective lengths and flange restraints must be input relative to the non-principal axes (the axes parallel to the angle legs) for all design codes.

During the design phase, the data for single angle sections (except for the bending effective lengths) is converted to the principal axes for AS4100, BS5950, NZS3404, AS4600, AISC-LRFD and AISC-ASD. Output reports for those codes also show the data in principal axes for single angle sections.