Steel portal frame: unequal columns.
Steel portal frame: unequal columns.
(OP)
Hi guys,
Client needs a 6-bay extension to an existing shed, with the roof line continued, but with a narrower internal width; frames will be at approx 5.5m centres. This presents two problems;
1) one side of the frame will be higher than the other, and I can't find any design info. on this situation;
2) client wants the extended roof at the side to form a canopy over a loading bay. Is it best to run the rafter continuous over the column, or could the canopy be a separate element, though presumably with a hefty moment-connection at the column?
Snow load is not great, and no seismic issues, but I'm concerned about wind loading in particular, and how to approach this structure in general.
Section diagram with approx. dimensions attached.
Any advice appreciated.
Client needs a 6-bay extension to an existing shed, with the roof line continued, but with a narrower internal width; frames will be at approx 5.5m centres. This presents two problems;
1) one side of the frame will be higher than the other, and I can't find any design info. on this situation;
2) client wants the extended roof at the side to form a canopy over a loading bay. Is it best to run the rafter continuous over the column, or could the canopy be a separate element, though presumably with a hefty moment-connection at the column?
Snow load is not great, and no seismic issues, but I'm concerned about wind loading in particular, and how to approach this structure in general.
Section diagram with approx. dimensions attached.
Any advice appreciated.






RE: Steel portal frame: unequal columns.
2) It could be done either way. My choice would be to run the roof beam continuous over the column.
BA
RE: Steel portal frame: unequal columns.
Keep a close eye on LTB bracing requirements, particularly if your going to be designing plastically.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Steel portal frame: unequal columns.
I agree with BA, run the beams over the columns. That canti. moment connection to the column is a real dog to do well and properly. Let that moment run right through the beam. Maybe put a kicker from the middle of the canti. span back and down to the column. Assemble them on the ground and tip them up.
RE: Steel portal frame: unequal columns.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: Steel portal frame: unequal columns.
TBH I don't often do portals as they're not in my usual line. I end up doing them by hand, and have perhaps been over-concerned about different column heights on this one.
The suggestions to continue the rafter over the column is of course sound - (can't think why I would have suggested a separate cantilever!).
And I will watch out for LTB, and wind uplift.
Thanks again.