"Box Section" 1

[Althalus]

I'm looking at AISC Section B4 - 2.

The design wall thickness, t, shall be taken equal to the nominal thickness for box sections and HSS produced according to ASTM... For (other HSS),,, t, shall be taken equal to 0.93 times the nominal wall thickness

Rectangular and square HSS are also commonly called tube steel or box section.

Question: The phrasing seems ambiguous. Does it mean that ANY square/rectangular HSS can use the nominal thickness? Or just the box sections "that are also manufactured to" the listed ASTM specs?

I have a square HSS and I need to know the bolt bearing on a wall. Hence "t" is of great importance.

 

[271828]

If your HSS is A1085, then the design thickness equals the nominal thickness.

If it is A500, then the design thickness is 0.93 times the nominal.

 

[JoshPlumSE]

This is an ASTM thing. If your HSS was manufactured per A500 (i.e. the older HSS ASTM specs) the ASTM allowed too large of a tolerance with the thickness. The result was that most HSS manufactured per that spec was actually 7% thinner than the nominal thickness.

AISC corrected for that in their design specification.

Understanding the intent of the AISC provision, you can properly interpret this to mean that if the manufacturing process of the HSS (or box section) is such that you can be reasonable assured that the thickness is accurate, then you can use the nominal thickness. If not then you use the 93% value.

 

[JoshPlumSE]

Here is an article that elaborated on the subject in more detail. Though this was before the newer HSS specs.

https://www.aisc.org/globalassets/continuing-education/quiz-handouts/specifying-hss-article.pdf

This next article (from the Steel Tube Institute), talks about the newer spec:

https://steeltubeinstitute.org/wp-c...S1801-A1085-Specification-Brochure-030918.pdf

 

[Althalus]

I have to wonder why they even bothered to use the terminology "box sections". All "box sections" are HSS anyway.

So, why bother saying "box sections AND HSS"?

 

[271828]

I assume a "box section" would be built-up out of plates.

 

[JoshPlumSE]

Since AISC is based in the US, I think they are a bit biased towards the terminology we use here (whether colloquially or in ASTMs and such).

In the US, HSS are usually formed out of bent plate and welded at the seam. Whereas Box sections are usually built up out of welded plate.

 

[Althalus]

In the US, HSS are usually formed out of bent plate and welded at the seam. Whereas Box sections are usually built up out of welded plate.

That idea appears to disagree with the following statement I quoted above.

Rectangular and square HSS are also commonly called tube steel or box section.

I saw this same description from multiple sources.

 

[JoshPlumSE]

I was referring to the manufacturing process that is used to create HSS. All you have to do is look up any reference on HSS and they should have a description of it. This includes the AISC design guide on HSS connections (which supersedes the manual I quote below).

From AISC's "Hollow Structural Section, Connections Manual":

Page 1-7: Standard Mill Practice:
ERW and SAW Manufacturing Methods:
The transformation of a flat strip into an HSS is the result of a series of operations including forming, welding and sizing. Currently three traditional methods are being utilized for the manufacture of HSS in North America. These methods include the formed-from round process, the weld-square form-square process for ERW HSS and the SAW for larger size HSS.

The manual goes onto include details about each process.