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For columns, wall studs, and CLT wall panels, the program implements interaction equations for combined axial and bending resistance or both axial tension and axial compression loads when combined with lateral forces due either side loading or to or the moment due to eccentric axial loads.
For sawn lumber, glulam and SCL design, refer to NDS 3.9 - Combined Bending and Axial Loading, and Biaxial Bending for more details.
For CLT, refer to Axial Design for CLT Wall Panels and NDS C15.4 - CLT Combined Axial and Bending .
The following give design interpretations not addressed in the design standards:
Load Combinations In Each Direction
Sizer constructs load combinations for both directions of loading, axial and lateral, using all the load types on the member, even if some of those load types do not apply to that direction of loading. The effects on moment and shear in the lateral direction due to eccentric axial loading are also considered. The program relies on both the CD factor and the fact that some loads will be of zero magnitude in one direction or the other, to discard load combinations during design that are not appropriate to the direction of loading. The complete analysis is too complex to present here.
Load Duration Factor CD
For both tension and compression design, the progam applies the same duration factor CD to both bending strength Fb' and the axial strength Fc' or Ft' derived from the shortest duration of loads (highest factor) for either direction of stress. In other words, the program examines a load combination for combined design, and uses the load duration factor corresponding to that combination for both axial and bending resistance, regardless of which load types within the combination contribute to axial and to bending stress.
For example, for a column under concentric compressive dead load and lateral live load the program uses CD factor of 1.0 for both axial Fc' and lateral Fb'.