A 53 Grade A Steel Pipe Axial Load

[lgsabr]

We have salvaged some pipe to be used for temporary falsework. The pipe is good and straight (for the most part) and has no defects. We were told it was A53 Grade B, but a tensil test has revealed that it may actually be A53 Grade A (or similar to A252 Grade 1). The unbraced length of the pipe is tall enough that the allowable stress is controlled by Elastic Buckling and not the material strength. Therefore, under this condition, using Euler's formula, there is no difference in Grade A (fy=30ksi) or Grade B (fy=36ksi) in allowable stress. Does anyone see an issue with using this pipe under an axial load? Additionally, is it possible for the Modulus of Elasticity to be lower in some pipe than others?

 

[ATSE]

Using pipe with a high kL/r (above 160) is not advisable except for extremely light loads. If you're in the elastic range of the buckling curve, you may want to reconsider pipe diameter vs. height. Since the pipe is used, it will likely have a larger out-of-plane curvature than what the steel buckling curves are based on. Couple that with high kL/r and you have statistics working against you.
Modulus of Elasticity is uniform for structural steel and does not vary based on yield or tensile.

 

[lgsabr]

Thank you for your response. Just to give you the parameters:
kl/r = 150 (h = 78', 18" pipe w 3/8" wall r = 6.23in). Using Eulers with a factor of safety of 2.12 (per AASHTO) I get Fa = 6ksi. I have also considered combined axial and bending for an out of plumb tolerence of 1". So am still coming up with an allowable load of 110kips. Do you disagree?

 

[ATSE]

I get your numbers (roughly), but don't use those numbers.
1" out-of-plumb initial sweep for a 78' tall pipe is unrealistic, especially for used pipe.
Chances are, 78' long pipe has been welded. Not a structural problem, but likely a straightness problem.
For pipe, permissible straightness = 0.025" per foot length. That is, about 2" delta for your condition (if it was new). Use a stringline on a few different planes to check the actual sweep of the used pipe. Probably more than 3".
Since the code buckling equations are based on a lower initial out-of-straightness, you may be better off running a P-Delta analysis and more conservative reduction factors than trying to use code equations.

 

[MJCronin]

Isn't this question posted in the wrong forum..???

I suggest that you post in the Structural engineering Forum ..

 

[rmw]

MJC,

When this post first appeared I had the same thought and then looked back at the forum title and noticed that it was the STEEL and SS eng forum, so I didn't comment. I think it does fit on that basis.

rmw