×
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

Welded Truss Connections

Welded Truss Connections

Welded Truss Connections

(OP)
If a truss is defined by having pinned connections and therefore theoretically its members only carry axial load, why are so many trusses welded in real life? Would a welded connection not mean that they are also transferring moment?

I realize some moment and shear has to be developed in these members since they are not weightless but ultimately aren't welded connections considered a "fully fixed" or moment resisting connection? If I were to analyze a welded steel truss should I not analyze it with moment connections (which would ultimately make it a frame)?

Thanks

RE: Welded Truss Connections

Your question may be answered (with opinions, it seems) in an old thread here: Link

Yes, it does transfer moment, but the members of the truss will barely change as a result of fixing the web members versus pinning them. However, idealizing the truss with pinned-pinned connections for the web members will simplify analysis, which is why it is done in school, but I don't agree with it for practice. This was the way it was done in the past. With computers, you can simply model everything as truly built. Fix those connections and be sure to design the connections considering the moments transfer.

RE: Welded Truss Connections

There's nothing perfect out there so a practical definition of a truss is a frame in which load is predominantly resisted via axial loading of the members. Welded joints usually increase joint fixity but don't necessarily change the balance all that much. And bolted joints can add significant fixity too. The choice of welded versus bolted connections usually has more to do with wconomics and aesthetics than it does with a desire to control behaviour.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Welded Truss Connections

Amirfa - In accordance with Coty and KootK's comments, there is a famous 1909 technical paper that revolutionized design of truss joints, for the reason you are questioning. The paper is by Mr. E.W. Pittman and is attached below. In essence, he recommended increasing thickness of gussets plates to permit use of smaller gusset plates with fewer (but more heavily loaded) rivets. Smaller gusset plates result in lower secondary stresses. Same principle applies for both bolted and welded joints.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

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