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More Thoughts on A1085
In last month's HSS eNews we shared the announcement of a new ASTM specification for HSS, A1085. (In
case you missed the article you can access it here. A1085 provides for enhanced performance to make designing
with HSS easier and more efficient for structural engineers, with explicit opportunities in seismic and dynamic
applications. As a follow-up to that announcement, Kim Olson of FORSE Consulting provides thoughts
on how the new specification impacts seismic member design. She also outlines the need for prequalified
moment connections to help make HSS a preferred structural member type for seismic applications, and gives
a preview of how STI will be addressing this need.
Those of us who have been practicing engineering for some time remember when seismic design was only a
West Coast concern. Today, more than half the buildings designed in the United States require some level of
seismic detailing. For example, the New Madrid fault line in Missouri and the South Carolina fault zone are
two high seismic regions that have design requirements equal to those areas we typically think of as a seismic
zone.
The Northridge and Kobe earthquakes in the mid-1990's spurred a major overhaul of the seismic design codes
resulting in higher performance requirements. These requirements led to the addition of A992 specification
for wide-flange shapes (WF) in the early 2000's. But nothing changed for HSS members....until now. With
ASTM's announcement in April of A1085, HSS now has a specification with a maximum yield stress of 70 ksi.
This reduces capacity design requirements and column required strengths in seismic designs. A1085 is the
only specification used in North America or Europe that limits the maximum yield stress in HSS.
As you well know, when designing for gravity or wind, engineers must design for a minimum capacity that
structural members must meet. Seismic codes, however, dictate that we engineers design for the expected
maximum capacity of a member to try to force a ductile failure. To do so, a Ry factor is multiplied by the capacity
of a member. This factor is 1.1 for A992 (WF) and 1.4 for A500 (HSS). This discrepancy in Ry factor is
due to A992 having a very small range of yield strengths while A500 material can carry a yield strength anywhere
from 46 ksi up to 75 ksi and beyond. As you can easily see, this poses a challenge when attempting to
specify HSS in applications governed by seismic codes.
We are hopeful that will now change with the announcement of A1085. Given that A1085 has an upper and
lower bound on the yield strength, Fy, it is reasonable to expect the Ry factor will decrease for A1085. We are
awaiting specific AISC guidance on reducing the Ry factor for A1085 usage.
A second benefit of A1085 is a specified range with lower and upper bounds for corner radius. During testing,
some cold formed square (or rectangular) hollow sections were prone to fracture in their corners even if they
were not very slender (low b/t ratio).

This has resulted in engineers shying away from specifying square hollow sections as bracing in lieu of pipe or
WF sections which produce a more desirable gradual buckling deformation. The new material, plus the specification
of a minimum corner radius, will work to minimize these fractures.
A1085 will obviously improve ease of use of HSS for structural members. But what about the impact on connection
design One area of explicit need is prequalified moment connections for HSS now that A1085 has
been released. Because of the past design challenges surrounding A500 as a true option for moment frames,
moment connections for HSS have never been fully scoped. Now that A1085 will be a viable option for seismic
and dynamic applications, documentation of moment connections to resist seismic loads is an obvious need.
We at STI realize the lack of such documentation and know it is vital to aid in the adoption of A1085. In coming
months, a number of us who serve as technical advisors to STI will be working with connection experts
in the industry to meet this need. Be looking for a Part II to this article providing you with an update on our
progress come late summer or early fall.
Until then, we encourage engineers to continue learning about A1085 by monitoring news from STI and
AISC. Should you have questions you’d like addressed in future issues of HSS eNews -- or to inquire about
using A1085 in a specific design or application -- feel free to connect with us via email at
hssinfo@steeltubeinstitute.org.