In April 2013, the American Society for Testing and Materials (ASTM) adopted the new HSS tubing specification ASTM A1085 as (what is being marketed as) an alternate to and potential replacement for ASTM A500. Long story short, as the American Institute of Steel Construction (AISC) updated material requirements to reflect modern advancements in engineering seismic resistant structures (much as they did in the late 1990’s when the WF beam specification ASTM A992 was designed) engineers were seeing that our beloved A500 just wasn’t cutting the structural mustard. As a colaborative effort between AISC engineers and the major US tube manufacturers, ASTM A1085 promises to bring the necessary structural and economic benefits modern structures demand.
There are three main benefits ASTM A1085 offers over ASTM A500:
Tighter tolerances and a single minimum yield
The tighter wall tolerances (+10% -5%) and new mass tolerance (-3.5%) allows engineers to use nominal wall thicknesses in their designs using HSS material…as opposed to needing to adjust for materials being rolled light.
ASTM A500B had a minimum yield of 42 KSI for rounds, and 46 KSI for square/rec. ASTM A1085 has a universal minimum yield of 50 KSI. This higher minimum yield and increased strength to weight ratio will allow for more economical and efficient structural design.
Maximum specified yield stress
The 70 KSI maximum yield will result in a lower expected yeild strength and reduce capacity design requirements and column required strengths.
A minimum charpy v-notch (CVN) value of 25 ft-lb at 40 degrees fahrenheit.
So how much will this cost, and how much will this help…I’m glad I asked. General opinion among the mills is that due to the extra steel needed to manufacture ASTM A1085 will raise its price 6-8% relative to ASTM A500…but here is the benefit:
8” x 8” x 1/2” A500B 15’ long has an axial capacity of 441 KIP (a KIP = 1,000 LBS of force)
8” x 8” x 1/2” A1085 15’ long has an axial capacity of 500 KIP
This is a 13% increase in capacity with no increase in weight
Say you had a structure with a load demand of 380 KPS…
8” x 8” x ½” A500B 15’ long has an axial capacity of 441 KIP.
8” x 8” x 3/8” A500B 15’ long has an axial capacity of 343 KIP.
8” x 8” x 3/8” A1085 15’ long has an axial capacity of 390 KIP.
Here you see that the ASTM A1085 product has a 23% weight savings relative to an 8% increase in cost.