There are numerous parameters that can affect the effective length of a member subject to axial load. The criteria are set in the dialog shown by selecting Criteria-Effective Length, or on a member-by-member basis using the Assign menu.

For columns, the engineer can specify an appropriate effective length factor per Table 24 in BS 5950. Otherwise, the engineer can specify that the effective length be calculated according to the requirements of Appendix E. This appendix considers the members framing into the column, and whether a section is sway-sensitive or non-sway (See Post-Processing Criteria above for making this designation) to calculate the effective length of the column. The equations used to calculate the Le/L factor are taken from Annex E in the Draft Amendments for BS 5950, dated April 1998. The structure is assumed to be comprised of rigid joints where moment connected, and is either fully braced against sidesway (k3=infinity) or has unrestricted sidesway (k3=0), no partial lateral support is considered. The effective length factor used to calculate the axial capacity of the column is also used to calculate the lateral torsional buckling capacity for the beam when subject to bending. The following assumptions are made in implementing Appendix E:

A column pinned top and bottom (or where all beams and columns framing into the column in question are pinned) will be assigned an effective length factor of 1.0. This is true even when the column is indicated as being subject to sidesway.

• A column fixed at the foundation will be assigned a k2 value of 0.5 per BS 5950, Clause 5.1.2.4. (a).
• A column pinned at the foundation will be assigned a k2 based on a base stiffness equal to 10% of the column itself. This is according to BS 5950, Clause 5.1.2.4. (b) and results in a k factor of 0.909.
• Any other columns, which are continuous but have no rigid connected beams framing into the joint will be assigned a k value of 0.909, similar to the factor at a pin support per BS 5950 Clause 5.1.2.4.
• A beam designated as composite is assumed to carry a concrete slab and the relevant beam stiffness kb is taken equal to I/L. Per Appendix E.4.1, the beam stiffness for non-composite beams is taken as 0.5I/L if braced against sidesway and as 1.5I/L if not braced against sidesway.

Knee brace columns are assigned a Le/L value of 1.0 in the direction of the knee brace.

The effective length factor for brace members subject to axial load is provided by the engineer for all shapes except double angles. For double angles, the connection detail must be provided and the effective length factor is then determined according to Clause 4.7.10.3 of BS 5950. Single angles are not currently accommodated in the structural system. Capacity of T-Section struts is computed per section 4.7.10. As described in table 4.15 the capacity of the T-Section is affected by the connection configuration. To specify the appropriate connection type for the T-Section select the Criteria-Effective Length Command and choose the appropriate option in the dialog that appears as shown below The Le/L factor used to calculate the axial capacity is also used in the calculation of bending capacity lateral torsional buckling where a brace is subject to end moments.

The compression capacity of I-section and RHS beams subject to axial load is calculated using the effective length factors provided by the engineer. For channels, the end connection details are used to determine the effective length factor according to Section 4.7.10.4 of BS 5950. Double channels are not currently accommodated in the structural system. In calculating the bending capacity of an unbraced beam the effect of end fixity on the lateral torsional buckling (LTB) capacity of the section is considered. Loads are assumed to be normal loads (applied at the shear center). For a segment continuous through brace points, the Le is equal to the unbraced length. Where a beam is continuous through a column or supporting girder an effective length factor of 0.7 is assigned to that end of the segment. This is indicative of the column providing the beam a measure of restraint for bending about the minor axis. Where a beam is pinned at a support, or where a cantilever tip occurs, the effective length factor is taken as the value provided by the engineer in the Criteria-Effective Length dialog. The effective length factor for an unbraced segment is taken as the average of the factors at the segment ends (Refer to Table 10). For I and RHS struts the minor axis effective length factor can be the same as the effective length calculated for the segment for lateral torsional buckling if the engineer indicates as such in the Effective Length dialog described previously.