Compression resistance (Beams: BS 5950)
For most structures, all the members resisting axial compression need checking to ensure adequate resistance to buckling about both the major- and minor-axis. Since the axial force can vary throughout the member and the buckling lengths in the two planes do not necessarily coincide, both are checked. Because of the general nature of a beam, it may not always be safe to assume that the combined buckling check will always govern. Hence the compression resistance check is performed independently from the other strength and buckling checks.
Effective lengths
The value of effective length factor is entirely at your choice. The default value is 1.0 for “normal” loads and 1.2 for “destabilizing loads”. Different values can apply in the major and minor axis.
Beams are less affected by sway than columns but the effectiveness of the incoming members to restrain the beam in both position and direction is generally less than for columns. Hence, it is less likely that effective length factors greater than 1.0 will be required but equally factors less than 1.0 may not easily be justified. Nevertheless, it is your responsibility to adjust the value from 1.0 and to justify such a change.
Please note that the requirements for slenderness limits in (for example l/r ≤ 180) are no longer included in BS 5950-1: 2000. Consequently Tekla Structural Designer does not carry out such checks. Accordingly, for lightly loaded members you should ensure that the slenderness ratio is within reasonable bounds to permit handling and erection and to provide a reasonable level of robustness.