AISC 15th vs 13th Edition - HSS 1

[sail7seas]

When comparing AISC 15th to 13th edition HSS beams.
15th Edition an HSS12x4x1/2 in Table 3-12 (p 3-136) for ASD X-Axix allowable bending is 117 kip-ft
13th Edition an HSS12x4x1/2 in Table 3-12 (p 3-140) for ASD X-Axix allowable bending is 107 kip-ft
The section properties are the same in both editions.
What accounts for the 9.35% difference between the two Editions?
Thank you in advance.
Chris

 

[neffers]

Is one table based on 46 ksi and the other 50 ksi?

 

[sail7seas]

Yes, that is probably the reason, thank you.
50ksi / 46ksi = 1.0870
117kip-ft / 107kip-ft = 1.0935

 

[WinelandV]

I don't have the 15th edition, but it's possible that the 15th ed is based on tubes manufactured to ASTM A1085 while the 13th edition (for certain) was using tubes manufactured to ASTM A500.

ASTM A500 tolerances allow for a wall thickness that is not greater than +/- 10% of the nominal value. Because the plate and strip from which electric-resistance-welded (ERW) HSS are produced to a much smaller thickness tolerance, manufacturers in the United States consistently produce ERW HSS with a wall thickness that is near the lower-bound wall thickness limit. Consequently, AISC and the Steel Tube Institute of North America (STI) recommend that 0.93 times the nominal wall thickness be used for calculations involving engineering design properties of ERW HSS.

If I recall correctly, ASTM A1085 produces shapes whose thickness matches the nominal thickness.

Too my knowledge, Grade 50 tubes are still a special order item.

 

[neffers]

I just looked at the (2) versions of the AISC manual. In the 13th on page 3-28 it lists that Table 3-12 is based on Fy=46 ksi (ASTM A500 Gr. B). In the 15th on page 3-12 it lists Table 3-12 is based on Fy=50 ksi (ASTM A500 Gr. C). The the yield strength used is also denoted at the the top of each table.

 

[EngineerEIT]

ASTM A500 GR C (50 ksi for square/rect, 46ksi for circular) is the preferred material for HSS per the 15th edition manual, hence the use of Fy=50 ksi in the 15th edition manual.

See the recent article from modern steel construction:

https://www.aisc.org/globalassets/m...2018/04/areyouproperlyspecifyingmaterials.pdf

 

[cal91]

Just to clarify, the tables are based on ASTM A500 Gr. C, NOT ASTM A1085.

Both grades are 50 ksi, but A500 Gr. C the nominal thickness is multiplied by 0.93 for design, whereas A1085 does used 1.0* nominal wall thickness for design.