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  1. johannes17

    Portal frame rafter LTB

    Hi Kootk Thanks for the great advice! I think it's a good idea to not try to reinvent the wheel for now, so I'll stick with the traditional approach then. As for the reference on LTB restraint via stiffeners and rigid purlin connections - I haven't seen that being used in practice although it...
  2. johannes17

    Portal frame rafter LTB

    Hi KootK Are you saying that if I were to omit all kneebracing and apex beam (i.e. no actual bottom flange restraints) a conservative approach would be to take the effective length for LTB as the full sloped distance of rafters between columns? What about the additional stiffness that the...
  3. johannes17

    Portal frame rafter LTB

    What would the effective length be for LTB if no flybracing is used at all? I've seen many portal frames in South Africa that do not use it, although I think some engineers simply up the rafter size and don't really care much about optimizing the structure. The use of flybracing can result in...
  4. johannes17

    Portal frame rafter LTB

    Hi all This question is similar to a previous one of mine, but with some difference. I am designing a standard steel portal frame (elastic analysis) with the following details: 1. Total clear span = 12m (duo pitch portal with 15 degree roof slope) 2. Haunches at the eaves and apex (ex IPE 180...
  5. johannes17

    Portal rafter effective lengths

    Thanks KootK, much appreciated!
  6. johannes17

    Portal rafter effective lengths

    Hi everyone I am doing a design check on a steel portal frame using the Combined Stresses module from Prokon's Frame Analysis. I have tried to replicate an old portal design from a textbook to check if my understanding of the theory is correct, but I have come across some differences when...

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