HSS continues to gain popularity in structural steel design — from column grids in commercial buildings to bridge components in seismic zones. With multiple specifications governing their production, choosing the right spec for a given application is crucial for success in designing with HSS. 

This article is for structural engineers who need a clear, current reference on the most common HSS specifications in use across North America. We’ll explore: 

• What distinguishes ASTM A500, ASTM A1085, and CSA G40.21 from each other 

• How key properties like yield strength, wall thickness tolerances, and fracture toughness affect design decisions 

• How spec selection connects to design efficiency, code compliance, and total project value 

What Is HSS and Why Do Engineers Use It? 

HSS is a cold-formed, welded steel tube produced in square, rectangular, and round profiles. Domestic manufacturers make HSS primarily using the electric resistance welded (ERW) process. Structural engineers use HSS across a wide range of applications like load-bearing columns, moment frames, truss chords, beams, and architecturally exposed elements. 

The appeal of HSS comes from several well-documented advantages: 

• High strength-to-weight ratio — for the same footprint, HSS can support up to 30% more axial load with 50% less surface area than wide flange sections in many column applications, which can reduce the total steel tonnage on a project 

• Uniform strength in all directions — beneficial for members under biaxial bending or torsion 

• Torsional stiffness — closed sections resist twisting more efficiently than open sections 

• Aesthetic versatility — clean lines make HSS a practical choice for architecturally exposed structural steel (AESS) 

• Domestic availability — HSS is available from a variety of North American producers with short lead times 

Historically called tube steel (TS), HSS is now specified to several ASTM (USA) and CSA (Canada) standards. Understanding the practical differences between those standards is where design efficiency starts. 

HSS is an ideal choice for aesthetically pleasing ambitious designs that require a high strength-to-weight ratio. 

The Three Most Common HSS Specifications in North America 

ASTM A500 — The U.S. Standard Baseline 

ASTM A500 is the most widely specified standard for structural HSS in the United States. It covers cold-formed, welded carbon steel tubing in rounds, squares, and rectangles for structural applications including load-bearing columns. 

The most produced grade is Grade C, which has a minimum yield strength of 50 ksi for rounds and 46 ksi for shaped (square and rectangular) sections. That distinction matters: the yield strength for shaped sections is lower, which engineers need to account for when designing mixed-profile structures. 

A500 provides a broad production framework, but it does carry some limitations that are worth knowing: 

• Wall thickness tolerances are relatively wide — up to ±10% on wall thickness, which can affect section properties in practice 

• No standard Charpy V-Notch (CVN) fracture toughness requirement — unless it is specified separately 

• No seismic yield cap — actual yield stress can exceed the minimum, which affects expected strength calculations in seismic design 

For standard building applications without demanding seismic or fracture requirements, A500 Grade C is a cost-effective and readily available option.

ASTM A1085 — The Higher-Performance Option 

ASTM A1085 was developed to address several of A500’s limitations. It uses the same ERW manufacturing process but imposes tighter controls that make it better suited for performance-critical applications. 

Key differences from A500: 

• Single minimum yield point of 50 ksi for all shapes — rounds, squares, and rectangles — simplifying design calculations and reducing the risk of under-designing shaped sections 

• Tighter wall thickness tolerances — A1085 limits wall thickness variation to approximately half that allowed under A500, meaning section properties are more predictable and align more closely with tabulated values 

• Standard CVN fracture toughness — meets AASHTO Zone 2 Fracture Critical Element requirements, eliminating the need to specify supplemental testing 

• Maximum yield cap of 70 ksi — actual yield stress cannot exceed this value, which supports more accurate expected strength calculations in seismic design and enables ductile behavior in accordance with AISC Seismic Provisions 

• Differences in availability — A500 is the most popular specification produced in the USA. Typically, A1085 is produced on an as-needed basis and requires fairly large minimum order quantities. 

A1085 is particularly well-suited for bridge structures, seismically active regions, and any application where fracture critical performance is a design requirement. The tighter tolerances of A1085 also reduce uncertainty during design checks, which can streamline the review process.

The 50ksi minimum yield strength of square Jumbo™ HSS made the spire of this Manhattan office building possible. (Photo by Max Touhey) 

CSA G40.21 — The Canadian Standard 

In Canada, HSS production is governed by CSA G40.21, which functions as a broadly comparable standard to ASTM A500 with some meaningful distinctions. 

Wall thickness tolerances under CSA G40.21 are tighter than A500 — consistent with A1085 levels — giving Canadian-spec HSS more predictable section properties by default. 

CSA G40.21 also introduces two product classes: 

• Class C — standard cold-formed and welded HSS, equivalent in process to A500 Grade C 

• Class H — heat-treated HSS, where the section is passed through a furnace after forming to relieve residual stresses from the cold-forming process 

The Class H designation carries a specific design benefit under the CSA S16 steel design standard: engineers can use a different column curve when calculating axial capacity for Class H sections. That alternate curve accounts for reduced residual stresses and results in higher allowable axial loads — often leading to more economical column designs without increasing the section size. 

For Canadian projects where column efficiency is a priority, evaluating Class H availability against the potential design savings is worth the time. 

How Spec Selection Affects Design Efficiency and Project Value

Choosing between these HSS specifications has downstream effects on design, fabrication, and project cost. 

Yield strength consistency directly impacts how conservative a design needs to be. A500’s lower minimum yield for shaped sections (46 ksi vs. 50 ksi for rounds) can lead to larger sections than necessary if engineers are working from combined tables. A1085 and CSA G40.21 Class C can eliminate that variable in some situations. 

Wall thickness tolerances affect both structural calculations and connection design. Looser tolerances introduce variability in actual section properties versus tabulated values. When tolerances are tighter, as in A1085 and G40.21, the gap between calculated and as-built performance narrows — which matters for connections, especially in high-load applications. 

Fracture toughness requirements become critical for bridge work, crane runway girders, and fracture critical members. Specifying A1085 upfront can help avoid supplemental CVN testing, which adds cost and procurement time. 

Seismic design compliance under AISC Seismic Provisions requires specific expected strength and ductility criteria. A1085’s 70 ksi yield cap is particularly useful here — it reduces the overstrength factor that engineers would otherwise need to account for with A500 material. 

Getting the HSS specification right from the start means fewer RFIs, fewer material substitutions mid-project, and a design that holds up through the submittal and review process. 

ASTM A500, ASTM 1085, CSA G40.21 C/H Comparison Table 

Property	ASTM A500 (Grade C)	ASTM A1085	CSA G40.21 (Class C / Class H)
Min. yield (shaped)	46 ksi	50 ksi	~50 ksi
Min. yield (round)	50 ksi	50 ksi	~50 ksi
Wall thickness tolerance	±10%	~±5%	~±5%
CVN fracture toughness	Not standard	AASHTO Zone 2 standard	Not standard
Seismic yield cap	None	70 ksi max	Varies by class
Heat-treated option	No	No	Yes (Class H)

Selecting the Right Specification for the Job

Selecting the right HSS specification is a straightforward decision once you understand what each standard requires. ASTM A500 remains a practical baseline for most building applications. ASTM A1085 offers meaningful advantages for seismic applications and fracture-critical work. CSA G40.21 — particularly Class H — provides Canadian engineers with additional design efficiency tools for column-heavy structures. 

Choosing the right specification reduces design uncertainty, supports code compliance, and can contribute to lower total steel tonnage on a project. 

If you want to go deeper on HSS specifications — including how they interact with connection design, seismic provisions, and fabrication requirements — Atlas Tube’s Engineering Experts team offers no-cost HSS design consultations. You can also explore the HSS Connections Hub™’s complimentary Typical HSS Details and Connection Calculators to better leverage Atlas Tube’s 100% domestic size range, including Jumbo HSS.