Historical practice for specifying A7-39 Steel

[curvbridger]

I am looking at a steel structure built in 1942 by American Bridge Company of Gary, IN. The steel specification has not been recorded in the available documents. The design drawings list design stresses as high as 19.8ksi in tension. The shop drawings list AASHO as the construction specification, which suggests an AASHO design specification and Fa = 18ksi = 0.55x33ksi yield

I assume based on age and location that the material is A7-39 Steel, which has Fu = 60ksi to 72ksi and a yield point of 1/2 Fu (not less than 33 ksi).

Would it have been possible for a procurer to specify that they wanted A7-39 steel WITH Fu = 72ksi, so that the higher yield could be used?

If the designer was going to have Fu = 72ksi material procured, then Fy would be 36ksi and Fa for net tension would be 0.55xFy =19.8ksi.

I will do some testing coupons, but I would feel better if I knew it might have been specified this way.

Any thoughts?

 

[JStephen]

In looking through the A7-1946 and AISC specification, it looks like the 60-72 ksi is the allowable range as produced, and you couldn't very well specify minimum 72 ksi and also maximum 72 ksi, so I would expect that properties were not normally specified in that way.

In the AISC spec, they just call for all steel to be A7, then say allowable tension/bending is 20,000 psi, etc., the tension/bending isn't given as a function of yield or tensile strength.

 

[SlideRuleEra]

Would it have been possible for a procurer to specify that they wanted A7-39 steel WITH Fu = 72ksi...

I doubt it, in 1942 World War II was underway. The structure must have been important for national defense for the project to have sufficient priority to get any structural steel at all.

Allowable stresses for building design were raised in late 1942 (until early 1946) to conserve structural steel.

Allowable stresses for bridge design supposedly remained unchanged (compared to values before WWII), but I expect design stresses were pushed to the limit for the same reason.

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[curvbridger]

Yes, the structure was "mission critical" for WWII.

Still puzzled why the designer straightforwardly published stresses up to 19.8ksi, rather than what I believe was the published allowable of 18ksi...

 

[SlideRuleEra]

ASTM A7-39 applied to both buildings and bridges. Allowable tensile & bending stress was 20 KSI, not 18 KSI.

AISC addresses this in Design Guide 15:

https://www.aisc.org/store/p-1751-d...ilitation-and-retrofit-guide-a-reference.aspx

Actually, there is a long-standing error in Design Guide 15 that does not affect your project. It applies only to buildings from 1942 to 1946. I have notified AISC (I'm a member). Review / correction by AISC will probably take years. Here are links to information / documentation that I provided to AISC:

http://www.eng-tips.com/viewthread.cfm?qid=389036

However, this is really just of historical interest. AISC position on evaluation of steel furnished under old specifications includes the following statement:

"The steel does not know which specification it was designed under. The available strength of members and connections are permitted to be determined based on present specifications. It is preferable to use more current design methods when assessing existing structures."

This statement is taken from the July 2006 issue of AISC's "Modern Steel Construction" magazine:

http://msc.aisc.org/globalassets/modern-steel/steel-interchange/2006/072006_2006v07_si_web.pdf

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