AD 403: Steel strengths for fabricated haunches
This AD is a simple reminder that the steel strength selected for haunches must match that assumed in the design calculations. As S355 is now the common steel strength for rolled sections, it is highly likely that the calculations for the haunch have also assumed S355 steel – it is important that rolled sections or plate used for the haunch matches the higher grade, unless design calculations have verified a lower strength steel.
In the UK, S275 rolled sections are no longer readily available, with S355 being the common steel strength. For the design of portal frames, the increase in strength is not always beneficial – the opportunity to select smaller sections means that deflections will increase and second order effects (which are calculated based on deflections) will be more significant.
Most haunches are cut from rolled sections, so will normally be the higher grade steel. The potential for a mistake is increased with haunches fabricated from plate. Plate (particularly in the form of flats) is available in S275 steel, so connection designers need to be careful to specify the appropriate steel strength clearly.
Contact: Richard Henderson