Design Using Tekla Portal Frame Designer - Improvements for Class 4 Haunches - Eurocode

Tekla Structural Designer
Tekla Structural Designer

Design Using Tekla Portal Frame Designer - Improvements for Class 4 Haunches - Eurocode

For those designing steel portal frames to the Eurocode (UK and Irish NA’s) in Tekla Structural Designer 2021, there is a new companion release of Tekla Portal Frame Designer which features significant enhancements to the classification of haunches, in accordance with customer feedback. The Eurocode introduced tighter rules for section classification on the Class 3/ Class 4 boundary which resulted in many haunches that were adequate to BS 5950 being Class 4 at the deep end to the Eurocode. This resulted in a 'Fail' because Class 4 sections are not dealt with in Tekla Portal Frame designer. A number of improvements to the classification rules and equations are made in the new release to mitigate the occurrence of Class 4 haunches. For full details please see the Tekla Portal Frame Design 21 Release notes and Improvements to classification of haunched rafters to EC3. Briefly the enhancements are:

  • Haunch Web Slenderness - calculation of the slenderness ratio c/tw now includes the rolled section root radius thus reducing slenderness e.g. for a 405x140x46 section c/tw reduces from 56.0 to 53.0

  • Strength Check - Strength is checked at five positions with the first position now accounting for the end plate thickness.

  • Classification of moment + axial - the combined compressive stress is ‘normalised’ to fy, by increasing the bending stress while axial stress remains constant.

  • Class 4 Design Status - when the haunch web is still Class 4 this is accorded a Warning rather than Fail status (note this applies only to the haunch web not that of the rafter). The design process is completed assuming the section is Class 3 - the designer can discuss this circumstance with the checking authority.

  • Cross-section Strength Checks - classification now includes the more favourable provisions of Cl. 5.5.2(9) in which calculation of ε is based on the actual stress rather than that of grade S235.

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