Add A992 to existing A36 steel?

[FieldVerify]

A current power plant project was built in the mid 1970s entirely of A36 steel. I'm adding steel to support some new equipment. Are there any issues with adding steel that is A992 (Fy=50ksi) and welding it to new A36 angles or existing A36 steel? Also, is there an online resource/database that states if a particular steel shape is commonly available (in either A36 or A992)?

 

[jayrod12]

We've had this debate many times before. The actual welding of one to another is likely not an issue. However as a conservative route I generally design the new steel as if it was the old strength.

 

[dhengr]

FieldVerify:
I don’t quite agree with Jayrod12, but I suspect if he were teased to be more specific he wouldn’t disagree with me. Design the new members to their strength (A992), but then, you must pay attention to how the new members load and stress the old members ( at A36) and you certainly must pay attention to this strength difference, and design for it, at the connections. You’re not specific about the connections: if bolted, you must look at both strengths on the two halves of the connection, if welded, the same thing, A36 on its half of the connection and 50ksi on the A992 half of the connection. Use a welding rod/wire process which matches the A992 and you should be safe.

 

[TehMightyEngineer]

I went through this recently and ultimately came to the same conclusion as jayrod after talking with many people on this forum. Welding is likely not an issue but unless you 100% cannot get by without considering the additional strength from 36 to 50 ksi yield then ignore the added strength. You'll end up spending a lot of time for very little added benefit.

As for availability, assume all tee sections from wide flanges and all wide flanges are available in A992. For anything outside of that definitely call around to your local metal supply companies.

Maine EIT, Civil/Structural.

 

[KootK]

My colleagues are referring to this: Link

I believe that OP just wants to slip some new steel into the framing system, not reinforce exitsing members. If that is the case, there are no issues to be concerned about that I know of.

Most "least weight" wide flange beams are readily available if you have a steel manual handy

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dhengr]

Now comes the engineering experience and judgement aspect of the problem. You might discover that you could get by with two different size bolts or welds on the two halves (two strengths) of the connection, and it’s probably best not to do this for the potential of the steel worker getting it wrong, in the field. He’ll use one more welding rod to make the two welds the same size and you’ll sleep well, knowing it is less likely to be done wrong.

 

[jayrod12]

dhengr, correct, if I was more specific I do agree with you. A quick response would be just design for the lower strength steel in all cases. However as the few posters have noted, that is only really the case when designing reinforcing of the existing section or the connection to the existing framing.

The remaining design of new members you can absolutely use the higher strength, just ensure your connection to existing framing can provide the required resistance.

 

[wannabeSE]

For your second questions, AISC maintains a database of shapes produced by various mills. The webpage states; "Generally, where many producers are listed, it is an indication that the particular shape is commonly available". See

http://www.aisc.org/steel/searchForm.aspx?id=2044.

See the Steel Construction Manual table 2-4 or

http://msc.aisc.org/globalassets/modern-steel/archives/2009/01/2009v01_are_you_properly.pdf

for material specification and/or grade that are available for different shapes.