×
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

Conservative K value for partially braced frame?

Conservative K value for partially braced frame?

RE: Conservative K value for partially braced frame?

I would call the chevron braced portion rigid, and use K=1.2 (assuming the base is fixed as shown) for the unbraced segment. If the base is pinned you could conservatively say K=2

RE: Conservative K value for partially braced frame?

I agree with canwesteng but I'm wondering why the columns are not rotated 90o so that the major axis is resisting the frame bending moments.

BA

RE: Conservative K value for partially braced frame?

You could calculate G and use sidesway uninhibited alignment chart. Conservatively ignore the braces and the strut.

RE: Conservative K value for partially braced frame?

2.0 with L being taken from the point of the lower strut to the foundation would be conservative in my book.

RE: Conservative K value for partially braced frame?

Pinned base = 2X distance between base pl and truss CL. Fixed base = 1/2 that. These are upper bound approximations that assume sway frame action and members of infinite axial rigidity. The real values will be less than these approximations but more than 2X/1x the base plate to low strut distance which serve as lower bound approximations. I think this is as good as it gets without diving deep into the math. I’d also temper these values with a judgement factor as we do with other effective length situations where we know our assumptions are imperfect.

You could also use the alignment chart with the column length taken to truss CL and the truss stiffness subbed in for the girder stiffness. This is effectively column and girder with a wildly stiff girder.


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: Conservative K value for partially braced frame?

Using the direct analysis method K is always 1.0. The direct analysis method involves using a reduction on E, second order analysis and notional loads (minimum horizontal loads). It looks like you are using RISA. They have very good online videos and customer service to help you figure this out. See the following link for an explanation of the direct analysis method.
https://www.youtube.com/watch?v=dcKQ0SD-rp8

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