New features of ASTM A1085 for Hollow Structural Sections (HSS) will save you money!

On April 11, 2013, The American Society for Testing and Materials (ASTM) announced a new specification, A1085, impacting the production of steel Hollow Structural Sections (HSS). This new specification provides for enhanced performance to make designing with HSS easier and more efficient for structural engineers and it has been officially adopted in AISC 360-16 specifications. Some of the benefits of the new specification include:

?Tighter material tolerances

? Single minimum yield stress of 50 ksi & maximum of 70 ksi and a higher tensile strength of 65 ksi

?Standard requirement for Charpy V-notch toughness

? Range defined for corner radius and smaller tolerance for wall thickness.

Both standards are limited to a maximum perimeter of 88” for cold formed welded manufacturing process with a wall thickness of less than 7/8”. However, ASTM A500 Gr. B has a wall thickness tolerance of +/- 10% while A1085 has a tolerance of +10%/-5% and the manufacturers usually try to be closer to the lower limits to save material. So the A1085 introduced a mass tolerance of -3.5%. So, HSS sections produced to ASTM A1085 will consist of additional features to make it a premium product with a higher level of performance. When compared to ASTM A500 Gr. B, more steel is required to produce the product, because of the tighter material tolerances. Regular testing is also required to satisfy the Charpy V-notch test. While the additional ASTM A1085 features lead to a price increase of $3/CWT or $60/ton for HSS produced, that is about a 6-7% increase over current pricing of HSS produced to A500. However, designing with HSS produced to ASTM A1085 can lead to better utilization of the material and potential cost savings. The savings result from higher yield strength and almost the full nominal area is available for strength calculations as you won’t need to use the 0.93 factor on nominal wall thickness per AISC manual 360-16 and also the reduced variation in the expected yield strength will lead to a smaller Ry & Rt values for connection design based on the AISC seismic provisions 341-16.

For example, a HSS column with an unbraced length of 15 ft has the following capacities:

HSS 8 x 8 x 3/8 (37.61 plf), A500, Grade B, has an axial capacity of 343 kips vs 390 kips for A1085

HSS 8 x 8 x ? (48.72 plf), A500, Grade B, has an axial capacity of 441 kips vs 500 kips for A1085

This is over a 13% increase in capacity with no increase in nominal weight and only a 6-7% increase in cost. You may also consider this as a weight savings of 23% to meet a demand of say a value between 343 and 390 Kips, where you could use HSS 8 x 8 x 3/8, A1085 in lieu of HSS 8 x 8 x ?, A500, Grade B.

Using ASTM A1085 HSS not only leads to better performance, but also has the potential to save you money.

NOTE: Very few service centers carry these and those that do have a limited range, price will be slightly higher – roughly $100 per ton. The US mills don't make sizes like HSS10 x 10 x ?” that are not shown in the AISC Manual. All built up tube sections, beyond the scope of the AISC manual can be designed and specified to ASTM A1065. A1065 is a specification for very large sections. One would typically specify this material for sections larger than 22 inch square or 24 inch by 12 inch rectangles. This ASTM covers sections up to 50 inch square and 60 inch by 40 inch rectangles with thicknesses of 1 inch or less. An A1065 section will have two seams in lieu of the more traditional standard A500 or A1085 section with single seam, because the section is produced by welding two C-shaped sections together with a partial-joint penetration weld.

Links:

Webinars:

General Steel Resource:

Steel Wise & Steel Interchange by AISC are excellent resources