Steel Design - New Patterning of Eccentricity Moments

Since the very first release of Tekla Structural Designer, additional “eccentricity moments” - resulting from the eccentricity of supported beam reactions - have automatically been calculated and considered in steel column design. For more on this feature see the Help topic Steel column connection eccentricity moments. In this release the feature is enhanced with the option to consider patterning of eccentricity moments, resulting from different permutations of loading of the supported beams producing unbalanced load and hence potentially increased moments. Five patterns are considered as illustrated in the picture below, in which the ✔ indicates full loading of the beam connected to that face of the column and the ✕ reduced load. The analysis of patterned eccentricity moments applies to all Head Codes, while they are considered by design in the Eurocode and US Head Codes.

The feature is fully automatic and requires no additional modeling or loading. To activate it, as shown in the pictures below, simply:
- Check on the new “Use patterning of eccentricity moments…” option ( in Home > Settings > Loading > General for Global Settings and new models, and the same location in Home > Model Settings for an existing open model)
- Check on the “Pattern Eccentricity Moments” for the Imposed (Live) Load case(s) in the Loading dialog (no other load types can be patterned)
  - (Note that the default for both settings is Off)

Key aspects of this new feature are:
- The inferred ecc. moment profile assumes the same pattern at the top and bottom of a stack e.g. it is not possible to have P1 at the top and P4 at the bottom of a stack.
- Patterned ecc. moments are combined with ‘real’ moments in the same way as in previous releases (which essentially considered only P0).
- Axial force; this is reduced (by patterns P1-4) at the current level while that from floors above is from P0 (which is a conservative assumption)
- All design checks apart from ‘Shear’ can be affected by patterning
  - Note that, in this and all previous releases, there is no rigorous implementation of ‘Simple Construction’ in which load patterning is explicitly ignored (per BS 5950 Clause 4.7.7)
- Eccentricity moments are determined by a post-analysis process which applies to all Head Codes.
  - The Load Analysis View is also enhanced to enable the viewing of results for patterns to see how they affect the major and minor moments, and axial force. The picture below shows the effect on the major axis moment. A pattern number drop-down list is added allowing the results of a specific pattern to be selected (the eccentricity moments are denoted by a dashed line).
- The eccentricity moments are considered by the steel column design process for the Eurocode (all country NA’s) and US Head Codes.
  - To keep the design details to a manageable level, results for every pattern are not listed; the pattern which produces the governing design forces is listed in the check combination and location tree and details heading, as shown in the picture below.