Grade of Steel

[priya15]

I am evaluating an existing steel structure for current loads. I modeled the structure only to realize that the whole structure is failing, while in reality the structure is doing just fine. There is not explicit note on the drawings saying it is Fy=50 ksi structural steel and hence, I modeled it with 36ksi steel. Are there any tests out there that I can tell the owner to perform to confirm the grade of steel? Please let me know your thoughts on this subject.

 

[Ron]

Pick an ASTM standard, such as A572 and test to that standard. It will require removing a coupon specimen from the structure, but that can be done without compromising the structure.

 

[MiketheEngineer]

And don't forget that real loads versus code loads are often quite different. Code loads are based on at least a 50 year building life cycle. In other words - the building MAY only see those loads once in fifty years..

 

[JStephen]

A lot of the 36 ksi materials will have 50 ksi yield strengths, so I don't know that you could tell for sure with cutting samples out.

 

[Lion06]

In addition to the higher strength that is likely there, and the probability of the lack of the building seeing the design loads (as noted by Mike), there are also other built-in "conservatisms" that we neglect - there is some end restraint at simple connections. Even if it's only 5% at each end, that going to help the midspan moment. Non-composite beams will often behave in a composite manner for non-ultimate loads due to deck welding and friction. Even if it does see the full design service LL, there is still a F.S. of roughly 1.67. Our stick models use length of beam as center to center of column when it's actually face to face of column (for beams not going to column web) - this can cut down on the length of the beam by a foot, typically.
I'm sure there are more that others will point out, but you get the picture.

 

[BAretired]

It would be unwise to assume that the steel is any better than A36. A better evaluation, in my mind, would be to tell the owner that the structure is adequate to sustain gravity, wind and seismic loads of x, y and z psf respectively based on your calculations.

Why should you assume responsibility for certifying material properties which you cannot confirm? Unless, of course you enjoy the exhilaration of retaining lawyers, preparing statements of defense, giving evidence at examinations for discovery, appearing at court and finally, convincing the judge who hasn't the faintest idea of what you are talking about that you really were justified in assuming the steel had a yield of 50 ksi or more.

BA

 

[hokie66]

It might help to know how the useage has changed, and a better description of the structure. We know it is steel, but that doesn't tell us much.

 

[JHanson717]

Rolling mills often identify the shapes on the web as they are rolled, you might start there...

 

[StructuralEd]

And could it even be A7?
I might start by considering what was available and most widely used during the era of the date on the drawings.
It would seem that something out of the ordinary would have been so noted.