Steel Market Trend (A36 vs. A572 Gr. 50) 1

[JohnRwals]

Hi!

For precast concrete connection designs, generally A36 plates have been used.
Recently, I was told A572 Gr.50 was more popular in the steel market. Is it true?
Is it really difficult or no advantage to use A36 for connection design?
(Including logistics and cost comparison?)
When I substitute Gr. 50 and I can select thinner plates,
shouldn't there any concern about warping due to excessive welding heat?
(In the past, I sometimes heard complaints with A36 plates.)

Thanks!
_JRW

 

[271828]

In the latest AISC Manual, 16th ed.:

Table 2-4 lists A572 Gr. 50 as the preferred material for angles.

Table 2-5 lists A572 Gr. 50 as a preferred specification for most plates.

 

[JohnRwals]

Do you know what caused this change?
Is it really difficult to see A37 in the market?
A37 should be much easier to bend/cut and cheaper...

 

[271828]

From everything I've heard from fabricator friends, Grade 50 is readily available. Also, if they get A36, it'll typically qualify as 50 ksi anyway.

Similar with HSS. That's why A500 Gr. C is the preferred specification in Table 2-4.

 

[phamENG]

A36 steel has a minimum yield stress of 36ksi. It could be 100ksi and still be classified as A36. The fact is, steel manufacturing in the US has been steadily improving and the strength of the steel being produced generally exceeds those minimums. And since more and more domestic steel is recycled, we're reusing that high quality steel and improving on it. I worked in a plate mill for a short time. While I wasn't involved in the actual steel making, I got to know a few of the metallurgists. They're incredibly smart and talented scientists.

(Somebody feel free to fact check me on the following statement.) If you look at the rise of A992 steel, it came from the North Ridge Earthquake. A bunch of A36 steel was assumed to yield at something like 40ksi. But whoops...it was actually yielding well above 50ksi. So the predicted behavior was all wrong and a bunch of buildings failed because of it. A992 acknowledges that a lot of the steel shapes being fabricated already had yield stresses greater than 50ksi, but also set a cap on it to make predicting inelastic behavior a bit more accurate.

It's a similar story with plate. The switch to Gr. 50 isn't because a bunch of people decided they wanted it...the steel mills realized they were already producing it and could dual certify their product. So you can get steel plate that is both A36 AND A572 Gr. 50.

 

[dauwerda]

I work for a fabricator, and yes, we prefer A572 Gr. 50. If a drawing calls for A36 we will either ask to change it to A572 Gr. 50 or use dual certified material. A572 is readily available (as others noted it is now listed as the preferred material in AISC) and it keeps us from having to stock two different types of material (A36 and A572) for the same things.

Warping of plate due to welding should definitely be considered in your design. Using the thinnest plate the numbers show you need is not always the correct answer. If you think it should be thicker for ease of fabrication then make it thicker!

We don't see any price difference between A36 and A572 Grade 50 (and grade 65 is only a few cents more than grade 50 per pound).

 

[RattlinBog]

Call your local fabricators and check on availability. I work on the owner side as a structural engineer, and our main steel supplier currently stocks A36 plate and orders A572 Gr. 50 on a per-project basis. They don't currently have enough warehouse space to stock both grades for plate. I could see that changing as more designs specify A572 Gr. 50. The cost difference isn't massive, though. However, their angle, channel, and S-shapes are triple-graded as A36/A992/A529 Gr. 50. I imagine each supplier is a little different.

 

[JohnRwals]

Examples of current PCI design handbook and my (old)steel textbooks use Fy=36ksi.
I guess these examples are based on out-of-date market trend.
I am raising this discrepancy between actual material and design calculation data
as it can provide very conservative/unrealistic design experience.

 

[JStephen]

We go through no end of A36, so it's readily available, can't speak for the alternatives.