×
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

Short column buckling theory

Short column buckling theory

Short column buckling theory

(OP)
My Canadian colleague is taking me to task for not being familiar with Johnston column buckling theory. After some poking around it looks like Johnston developed a tangent modulus theory to describe the inelastic buckling of columns. I also see a single reference to his name in my 1000 page university text. It's not something that I see very often but I think AISC uses a less conservative method of reduced modulus. Does anyone know any background on this and why one is used over the other when you are outside the elastic/Euler range?

Also just as a refresher, what are some design scenarios where inelastic column buckling modes are common?

TIA

RE: Short column buckling theory

Is your colleague speaking of Bruce G. Johnston? He helped to form the Column Research Council (CRC), the precursor to today's Structural Stability Research Council (SSRC). In that capacity, his fingerprints were all over AISC column equations from the 1940's to 1960's. I don't believe there is a particular equation attributed to Johnston (e.g., the "Johnston equation/theory") but, again, he played a significant role in the development of the CRC column curves that formed the basis for the AISC allowable stress column design requirements. Mr. Johnston also served as editor of "Design Criteria for Metal Compression Members", the predecessor to the current "Guide to Stability Design Criteria for Metal Structures", published by SSRC and now in its sixth edition.

RE: Short column buckling theory

Short columns don't buckle, so the thread title is misleading. Long columns buckle elastically using the Euler theory. Short columns fail be crushing of the material. Intermediate columns fail by inelastic buckling. If you are using the Canadian code, this is taken into account by the formulas given in CSA S16-01.

This article sheds some light on the subject:

http://www.efunda.com/formulae/solid_mechanics/col...

BA

RE: Short column buckling theory


Also just as a refresher, what are some design scenarios where inelastic column buckling modes are common?

Almost all design scenarios actually. Using BA's definitions, which are the right ones, it's pretty rare to have either long or short columns. A short column suggests inefficiency; a long column suggests a high slenderness ratio and perhaps madness.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Short column buckling theory

In the Canadian code, Unit Factored Compressive Resistances Cr/A have been calculated and listed for KL/r values from 1 to 200 which includes the entire gamut of short, intermediate and slender columns, all of which are permitted under CSA S16-01. I agree that columns near both ends of the scale are not common, but they do occasionally occur.

BA

RE: Short column buckling theory

Well, I understood what he meant by short column buckling. Columns that are too short to buckle via euler buckling and which instead buckle via inelastic buckling.

Inelastic buckling is probably the most common scenario for steel buildings. If you look at AISC 14th edition, equation E3-3 is based on Euler buckling. But, equation E3-2 is based on inelastic buckling.

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