1970 Structural Steel Grade

[EngineeringEric]

Hello All,

Wondering what your opinion is on the grade of structural steel in 1970 Construction. We are doing some work on a 280 ft steel truss above a sports arena. We are not doing much in terms of loading so testing is out of the question. I do however have to check some elements for incidental loading.

The plans do not state grades, but the members are 12WF16 and 12WF27. Would the grades be equivalent to todays A992 or would it be more like A36?

I have one member that fails by 1% when fully loaded with a conservative load (100psf on a limited access walkway) so by judgment i'd say it is adequate... I can use load reduction factors but I am curious what you all think.

 

[Archie264]

Absent documentation that it's Grade 50 it would have been A36. (Right, others?)

1% on one member is not significant. My opinion only.

 

[EngineeringEric]

With 1% I would not look twice, but I have to submit calcs and they (the owners/client) look at the calcs in depth and may not be as OK as an Engineer would be.

 

[JedClampett]

I worked on a lot of structures that were built during that time and we always assumed (and specified A36) steel. There's a remote possibility that it's Corten, which has a 50 ksi yield, but that's definitely not a default. If the steel is uncoated with a red rusty pateen, it might be Corten.
I would explain to the owner that 36 ksi steel usually has a yield point near 48 to 50 ksi, so the 1% is strictly a calculated value, not a real reflection of the building strength. If they're still worried, they should test it.

 

[msquared48]

In the AISC 6th edition (my copy is 1967), the steel in the beam tables for allowable moments in beams was only for A-36 material. Column capacities were listed for 36, 42 and 50 ksi materials.

Unless you have other information from drawings, calculations, or lab testing of the steel, I would conservatively material.

If your results are consistently over by a large amount, I would consider testing the critical members.

Mike McCann
MMC Engineering

 

[EngineeringEric]

Thanks gentlemen. Ill add a comment on my over stress and if needed i can easily defend the value over a phone call.

 

[msquared48]

Unless you have other information from drawings, calculations, or lab testing of the steel, I would conservatively use A-36 material.

Sorry...

Mike McCann
MMC Engineering

 

[Archie264]

Eric,

A thought: if they do not realize that a 1% overage into the considerable safety factor on one member out of many, with conservative assumptions, is insignificant perhaps they shouldn't be requesting calculations in the first place, since they are obviously unable to grasp their significance. I know we can't control our clients but honestly, some bureaucrats out there just want to check things off their to-do list with no thought as to reality, it would seem. But why would they ask to see them if you can't understand them anyway? (Rhetorical question, of course.)

 

[BAretired]

In Canada, the 1967 Canadian Steel Handbook shows that the prevalent structural steel was G40.21 which is listed as having a yield of 44ksi but ASTM A36 and ASTM A441 were also available at that time.

BA

 

[bridgebuster]

Go with A36 unless you're going to take coupons. Don't lose sleep over 1%.

When I started working in the late 70's the use of 50ksi steel was the exception not the rule; no one wanted to spend the extra $.05/lb.

 

[Archie264]

Eric,

Are you submitting calculations in STAAD, or a similar software package, perhaps? If so then I understand the dilemma: the failure of one member, even by a small margin, fails the whole system. And it's not good for repeat business to submit calculations that say "FAILURE" on them. Is that the case? If so there are probably some means to address that.

 

[EngineeringEric]

Archie,

I am not using STAAD as it is not that complex. I am however using software to run most of my beam clacs and the member in question does state FAILS on it. the entity that reviews calcs means well but they are not engineers, they are Building Code Officials (the special ones are Master Building Code Officials ). They flagged me once for not showing a calc of a 5" weld that was only loaded with 1kip shear... so i know they actually follow the loads but don't have enough sense to understand it all. I once had to teach them about modes of failures for beams and lateral bracing.

And we are trying to get more business with them so submitting failures never looks good as you mentioned. And to muddy the waters, the reviewer is the client and the owner of the existing building, just different departments.

I plan on just adding notes onto the calcs stating why the overage is deemed acceptable.

 

[Archie264]

I see. And I was going to then suggest you do exactly what you mentioned in your last sentence. In general it seems to me that people are willing to accept things if they are documented and explained...that helps them feel comfortable, I suppose. If I were preparing it I might focus on the safety factor. I.e., point out that that it went from 1.50 to 1.49, or whatever, on one member, with conservative load assumptions and that the load assumptions are not within 1% accuracy anyway...well, maybe not that last part as it might confuse them but that type of thing. It sounds like you have it well in hand. Good luck.

 

[EngineeringEric]

Thanks again for your guys input as always!

 

[dik]

If American, then there's a really good likelihood that it is A36... If Canadian then likely Grade 44... They were common grades back then.

Dik