Strengthening of Steel Column
Strengthening of Steel Column
(OP)
I am looking for some guidance on strengthening existing steel columns for a major renovation project. All columns are A992 Gr. 50 steel and will be reinforced with A36 grade plates welded to the flanges. But, I am having hard time estimating the compressive strength of the stiffened member. Is there any guidance available on estimating Fcr for a member that uses two different grades of steel? Your thoughts are greatly appreciated. Thanks in advance.






RE: Strengthening of Steel Column
"Reinforcing Loaded Steel Compression Members" by J.H. Brown.
I can't find my copy of it.
I know it is available through AISC for free for members and for $10 otherwise.
Not sure if it covers different materials.
RE: Strengthening of Steel Column
Here is the paper you're talking about.
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
I did go through the papers...but, I couldn't find a case where two different material strengths are addressed.
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Strengthening of Steel Column
The KL/r for the column isn't big enough for stresses to be in the elastic range.
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
You are right. But, the KL/r isn't large enough for the column to fail because of inelastic buckling.
RE: Strengthening of Steel Column
"....fail because of elastic buckling"
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
I have read the second paper your posted in the past and I'm not sure I'd ever go that route. The whole process seems way too academic to me.
Thoughts?
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
I could definitely do what you said. But, wouldn't that be conservative and force me into using thicker plates? I just wanted to know if there is any other rational approach to the problem, and get away with a little additional steel as possible.
RE: Strengthening of Steel Column
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Strengthening of Steel Column
Use the new kl/r to get the allowable stresses in the plates only (call fa1). Use the new kl/r to get the allowable for the WF only (call fa2), then subtract the existing stress from the WF (call fe). Use the difference (call fa3 = fa2-fe).
Hopefully fa3 is close to fa1 so that you don't need to have different strains in different parts of the column to reach full capacity. I would probably use the lower of fa3 and fa1 on the entire section. I don't think I would want to get any more refined than that.
My biggest concern is that if the plates yield while the WF is still elastic, they are going to soften and effectively reduce the E of those plates. That would have detrimental effects on the overall column. I would limit fa3 above to no more than fa1.
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
24 Aug 10 15:31
"Sounds like a good article for next quarters Engineering Journal."
Start writing!
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Strengthening of Steel Column
I cannot see any way around that.
RE: Strengthening of Steel Column
If the column is already loaded, you can have a strain correlated to 14 ksi already in the column (just for talking purposes). If you now add 36 ksi plates, you have 36 ksi left to yield in the 50ksi column which provides for strain compatibility with the 36 ksi plates. That is a rare condition, which is why I noted above to use the lesser of fa1 and fa3 - I agree with you 100% on the strain compatibility issue.
RE: Strengthening of Steel Column
Not saying its not possible, just not sure how it could be achieved outside a laboratory.
RE: Strengthening of Steel Column
Also, I think as long as you are primarily using longitudinal welds and not welding across the column web or flanges welding under load can be done.
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
RE: Strengthening of Steel Column
Technically it is a stepped column but if the ends of the plates are close enough to the top and bottom then it shouldnt make a difference.
RE: Strengthening of Steel Column
Tensile strength of A36 is 58 ksi
Tensile strength of A992 is 65 ksi.
Not really all that much different, is it? Don't over-complicate the analysis.