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Re: damaged columns

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Steve Kramer wrote:

<< I have a single story industrial building with 8 inch diameter schedule
20
columns 21 feet high.  Many of the columns have been stuck by forklift
trucks and have varying degrees of damage.  Does anyone know of any
criteria to evaluate how much damage is acceptable before repair is
required?  For example, if the wall was dented reducing the diameter by 1/2
inch, would repair be required? >>


For long columns subject to elastic (Euler) buckling, the effect of local
buckling on overall column strength is negligible.  In other words, if
lamda-sub-c times SQRT Q is greater than 1.5 in LRFD or if KL/r is greater
than C-sub-c in ASD, the local buckling caused by the forklift doesn't
reduce your overall column strength.  Salmon & Johnson, Chapter 6 has some
good background theory.

My calculations indicates that you have a short column subject to inelastic
buckling.  Therefore you need to evaluate your overall column strength,
reduced by a form factor "Q".

Q-sub-s for your pipe section equals 1.0.  Q-sub-a for your pipe section
(stiffened element) equals the effective area divided by the actual area.
One logical approach would be to evaluate your pipe column at the "dent" by
considering only the undented perimeter as effective.  Q-sub-a equals
undented perimeter divided by total perimeter of the pipe cross-section.  Q
equals Q-sub-s times Q-sub-a equals Q-sub-a.

See ASD or LRFD Appendix B for what to do with Q.

Hope this helps,

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA




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