Strehgthening of Existing Steel Column

[strucguy]

When enhancing the capacity of the existing wide flange steel columns by welding plates flush with the flanges of the column, do I need to consider any reduction in KL/R of the stiffened section for calulation of Fcr?? I am not sure as to whether the modified KL/R equation for built-up members is applicable in this case. Any guidance in this regard is greatly appreciated. Thank you.

 

[JedClampett]

Short answer:
Yes

 

[strucguy]

JedClampett -

Thanks for the clarification. Now, for the evaluation of separation ratio to be used in the calculation of modified KL/R, what does the term "h" mean. Is it the distance between the centroids of the plates being welded??

 

[BAretired]

If you add plates flush with the flanges, R_x increases so KL/R_x decreases. You may consider it, but are safe to ignore it.

Depending on the size of added plate, R_y could increase or decrease. If it decreases, KL/R increases and you need to consider it.

Perhaps it is best to provide a sketch showing what you intend to do.

BA

 

[strucguy]

Apologize for the typo....I actually meant "modification of KL/R" when I said "reduction of KL/R". My question was regarding modification of KL/R of the stiffened section for not providing contiouous weld. Thanks again.

 

[strucguy]

I intend to add plates flush with the flanges and use stitch welds instead of providing continous weld.

 

[JedClampett]

I was assuming your r would go down and kl/r would go up. If kl/r lower you probably shouldn't change your allowables. If it gets higher, use the lower allowables.

 

[msquared48]

With only stitch welding, I would definitely use the lower allowables.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[delagina]

question about stitch welding plates on column,

is this applicable also regardless of the failure axial or moment?

the way i understand it if it's axial failure it should be continues weld to have continues increase in area

 

[strucguy]

Thanks for the responses.


delagina-

That's where the modified KL/R comes into picture. The KL/R calulated based on the assumption that the whole section acts as a single unit is modified for welds not being continuous. This is addressed in the "Compression of built-up sections" part of the AISC manual. That is where I am stuck now....having hard time interpreting the term "alpha" in the equation E6-2. The AISC manual calls it separation ratio.

 

[BAretired]

Equation E6-2 is attached. The terms are all defined below.

BA