×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Steel portal frame: unequal columns.

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.

RE: Steel portal frame: unequal columns.

1) What kind of design info are you expecting to find? These frames are usually analyzed by computer.

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.

Other than the fact that your solution may be asymmetric, like your columns, I don't see that the unequal column lengths bring any new challenges into play. I like everything pretty much the way that you're showing it. At the cantilever condition, you could throw a bolted splice plate on top to moment connect the two top flanges. And, of course, stiffeners where your need them. AISC has design guides for both bolted moment connections and tapered members. Both of those documents are geared towards this kind of structure. If you're not already familiar with them, you may find them useful.

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.

Tony1851:
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.

I agree with the others, continue the beam, particularly if you have a wind uplift greater than your dead load. That canopy picks up full pressure underneath and suction on top and might put the bottom flange in tension. It could be awkward designing the haunches to handle that situation.

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.

(OP)
Many thanks for the responses fellas.
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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources