×
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

K-value AISC 13th edition help

K-value AISC 13th edition help

K-value AISC 13th edition help

(OP)
I am currently using 13th edition. however i found a large  values for K compared to 9th edition of AISC. this is because the moment for each beam is considered. Does this happens to all of you when designing the steel? I am doubtful that I'm at the wrong track since my K-value is large. can anybody tell me how to do this quickly and easily but correctly.


thanks in advance
alphaxy

RE: K-value AISC 13th edition help

The method should be the same when calc'ing k for the 9th edition or the 13th edition.  Are you sure you're using the same nomograph (sway frame vs. non-sway frame) when comparing values from the 9th vs. the 13th editions?
Also, I don't think the moments in the members contribute to the calculation of the k value, only the stiffness of the members.
If you have a sway frame, k will always be greater than 1.0.  If you have a non-sway frame, k will always be less than or equal to 1.

RE: K-value AISC 13th edition help

(OP)
thank you StructuralEIT..your comment about 9th edition the way it should be is entirely correct, but it seems the method for calculating k-value in 13th edition is different although it uses the same nomograph. the stiffness of a member for sway frames rely on a modified length which considers the moment in beams which is used to calculate Ga & Gb for beams = I/L then the same way for columns = I/L. Im confused with this method. should i use modified length only for beams = I/L or also for columns = I/L???

thanks in advance

RE: K-value AISC 13th edition help

Yes, I realize exactly what you are saying now.  I looked at this pretty intensively because we do a lot of Flexible Wind Connection buildings which means the leeward connection is a pin under lateral loads. For sway frames, the introduction of the Mf and Mn is an attempt to incorporate the actual fixity of the beams as opposed to called it fixed or pinned.  I would definitely take this into account since anything less than 100% fixity will increase the effective length of the girders (and reduce the stiffness they contribute to teh column).  This will essentially increase the k value, so it would be unconservative to ignore it.
I hope that helps.  If I failed to answer your question, let me know.

RE: K-value AISC 13th edition help

Um, why are you even using the K value?  Based on Chapter C and Appendix 7 in the 13th edition you should be able to eliminate the need for the K value almost completely.  

Eliminating the use of K values is actually one of the real benefits of using the 13th edition.

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