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A New Standard for Hollow Structural Sections (HSS) - ASTM A1085
by Wayne Thompson, CTL Thompson
For those of you who don’t wait at the mailbox for the latest issue of Modern Steel Construction to arrive, you may have missed this. There is a new standard for HSS (Hollow Structural Sections), commonly known as tube steel. The new standard is ASTM A1085 (click here for aisc information)
What does this mean to the helical pile industry? Currently, most hollow shafts are constructed using ASTM A500 steel. A provision in the steel design specification requires a designer to take a 7% reduction in wall thickness when designing using ASTM A500 sections. That reduction is based on manufacturing tolerances for A500 steel. ASTM A1085 has stricter tolerances. Therefore, according to one of the articles in Modern Steel Construction, (click here for article) there is language being written that would allow designers to use full wall thickness for the design of members using ASTM A1085. Using a 3 ½” shaft as an example, quick calculations indicate that the design shaft bending strength would increase by roughly 6%, simply by being allowed to use the full wall thickness.
ASTM A1085 steel also has some tighter tolerances on strength. The minimum yield strength is 50 ksi, instead of the 42 ksi and 46 ksi values that we normally use with ASTM A500. Therefore, shaft design capacity can increase with the higher material strength.
So what’s the catch? Cost. For now. AISC (American Institute of Steel Construction) indicates that the cost of ASTM A1085 steel will likely be higher than A500 steel for a while. As demand rises, that may change. For now, check with your normal suppliers to see if they are making any changes to their product line. At our end, we will keep an eye on the proceedings regarding industry approval of using full design thickness, and we will also talk to ICC-ES about their opinions of the changes.
Feel free to contact us with questions.
CTL I Thompson, Inc.
351 Linden St., Suite 140
Fort Collins, CO 80524
Ph # 970-206-9455