This check is used for Class 1, 2 and 3 Plastic, Compact and Semi-compact rolled I- and H-sections with equal flanges (Class 4 Slender sections and Effective Class 2 sections are not included in this release).

Three formulae are provided in clause 4.8.3.3.2 (c) to cover the combined effects of major and minor axis moment and axial force. These are used irrespective of whether all three forces / moments exist. Clause 4.9 deals with biaxial moment in the absence of axial force, clause 4.8.3.3.2 (c) can also be used in such cases by setting the axial force to zero.

All three formulae in clause 4.8.3.3.2 (c) are checked; the second is calculated twice – once for Face A and once for Face C.

Only one value of F is used, the worst anywhere in the length being checked. If the axial load is tensile, then F is taken as zero.

To identify Faces A and C for an individual column, see Steel member orientation.

Important Note

Clause 4.8.3.3.4 defines the various equivalent uniform moment factors. The last three paragraphs deal with modifications to these depending upon the method used to allow for the effects of sway. This requires that for sway sensitive frames the uniform moment factors, m_x, m_y and m_xy, should be applied to the non-sway moments only. In this release there is no mechanism to separate the sway and non-sway moments, Tekla Structural Designer adopts the only conservative approach and sets these “m” factors equal to 1.0 if the frame is sway sensitive (in either direction). This is doubly conservative for sway-sensitive unbraced frames since it is likely that all the loads in a design combination and not just the lateral loads will be amplified. In such a case, both the sway and non-sway moments are increased by kamp and neither are reduced by the above “m” factors. The calculation of m_LT is unaffected by this approach, and thus if the second equation of clause 4.8.3.3.2 (c) governs, then the results are not affected.