A new specification addresses performance issues for design professionals
Hollow structural sections (HSS) are structural steel shapes used for bolted and welded construction and have numerous benefits for design professionals. Made from hot-rolled steel coil, HSS is produced by cold-forming the coil into square, round and rectangular shapes. HSS is used in a number of different applications including buildings, bridges, stadiums, exposed applications and trusses-just to name a few.
HSS is a popular choice for use in steel construction for a variety of different reasons. The number one reason that HSS is used is aesthetics-the clean look of the tube provides a fresh, appealing style that makes them a popular choice for exposed sections and for creating unique architectural features.
HSS also has a high strength-to-weight ratio, meaning it can carry more load per pound. This and the closed shape lead to greater unbraced lengths and longer spans using less material. For example, as a tall column, HSS can carry more axial load on a given cross-sectional area over a longer distance. This increased, more efficient load-carrying capacity can lead to HSS being more cost effective.
Reasons for the New HSS Spec
In the second quarter of 2013, a new standard for HSS was published by ASTM (American Society of Testing and Materials): ASTM A1085. Developed by a committee comprised of members of AISC
(American Institute of Steel Construction), HSS producers, professors and engineers, the new specification was envisioned to address specific performance issues that design professionals had identified with ASTM A500: the prevalent standard specification for HSS.
The committee determined it was important to address three major areas for the new spec:
1) Performance issues in fatigue-related applications such as seismic load-resisting systems and bridges.
2) Performance issues related to the high variability of mechanical properties of HSS produced to ASTM A500.
3) HSS must be made economical and efficient.
After several years, the committee developed the specification that eventually would become the new ASTM A1085.
Benefits and Advantages of ASTM A1085
ASTM A1085 HSS provides a host of benefits and advantages above and beyond HSS produced to the standard ASTM A500:
• Improved performance related to low-cycle fatigue applications
• Tighter material tolerances allow for nominal sections properties for added structural capacity
• A single minimum yield stress of 50 ksi
• Maximum yield stress of 70 ksi to better predict and control the overstrength factors for seismic design
• A standard requirement for Charpy v-notch toughness consistent with the American Association of State Highway and Transportation Officials bridge design specification
With all of these new benefits, and improving the performance issues related to ASTM A500, ASTM A1085 is undoubtedly a superior product. Add that to the potential for cost savings, and there is no excuse for design professionals to use anything but A1085 for steel construction!
Brad Fletcher is senior sales engineer, Atlas Tube, Chicago. For more information, go to www.atlastube.com.
Sidebar: Additional resources
If you would like any additional information on the new A1085 spec, the following are excellent industry resources:
• AISC: The American Institute of Steel Construction provides shape dimensions and section properties for the new A1085 spec, as well as documents showing available strength in axial compression. A producer availability survey is also available, indicating the sections and sizes of A1085 being produced by domestic producers.
• STI: The Steel Tube Institute website features a recorded webinar discussing A1085-how it differs from A500 and the design opportunities that the spec provides, especially in seismic applications. The webinar also discusses design examples and discussion of material availability for the new spec. A new HSS design manual is also available to professional members of the Steel Tube Institute.
• Atlas Tube: Atlas Tube, one of the largest domestic manufacturers of A1085, provides a properties chart for the new spec on their website. There is also a customer information kit available for download detailing further benefits and advantages of the new spec for industry professionals.