Steel and Metal Selection for Engineering Design: Rolled Steel Sections

Rolled Sections, Wire Gages, and Sheet-Metal Standards Every Engineer Must Master

A wrong gage number cost the practitioner's fabrication shop 40,000 units of currency and three months of rework. Here is how you make sure that never happens to you.

the practitioner had run his structural fabrication shop for eleven years without a single major specification error. His crew bent angles, welded wide-flange beams, and cut sheet metal with the kind of precision that earned repeat contracts from construction firms across two continents.

Then came the Harborview Tower project.

The specs called for galvanized sheet steel at 16 gage. the practitioner's purchasing manager — new to the role, fresh from a shop that worked exclusively with aluminum — ordered material using the a legacy wire-gage reference Wire Gage instead of the Manufacturers' Standard Gage for Sheet Steel. The difference? A 16-gage under the Steel Gage is 0.0598 inches. A 16-gage under the a legacy wire-gage reference system is 0.0508 inches. That is a 15% difference in thickness.

Twelve thousand sheets arrived. The wrong sheets. Too thin for the structural cladding they were supposed to become. The material could not be returned. The project timeline slipped. The penalties mounted.

the practitioner learned a lesson that day that every engineer, fabricator, and procurement specialist must internalize: gage numbers are not universal, steel section designations have specific rules, and the difference between "close enough" and "exactly right" is the difference between profit and catastrophe.

This guide exists so you never have to learn that lesson the hard way.

What This Guide Covers — and Why Every Section Matters

This is not a surface-level overview. This is a comprehensive technical reference covering every major category of rolled steel sections and metal gaging systems used in structural engineering, fabrication, and manufacturing worldwide. You will find:

• Rolled Steel Sections — Angles bent to circular shapes, hot-rolled structural designations, wide-flange (W) sections, S sections, channels, equal-leg angles, unequal-leg angles, and aluminum structural shapes
• Wire Gages — Every major wire gage system with decimal equivalents
• Sheet-Metal Gages — Steel, Birmingham, galvanized, and zinc gage systems
• Tubing Wall Thicknesses — Gage systems for seamless and brazed tubing
• Flat Metal Products — Preferred thicknesses for uncoated metals
• Preferred Metric Thicknesses — The ANSI/ASME standard for global metric sizing

Bookmark this. Print it. Keep it at your workstation. You will need it.

Rolled Steel Sections

The Language of Structural Steel

Before you can select, specify, or order a single piece of structural steel, you need to speak its language. Through a joint effort, the American Iron and Steel Institute (AISI) and the American Institute of Steel Construction (AISC) standardized the designations for hot-rolled structural steel shapes. These designations are the standard for steel producing and fabricating industries and should be used when designing, detailing, and ordering steel.

Here is how the modern system works — and how it replaced the older, more confusing nomenclature.

Hot-Rolled Structural Steel Shape Designations (AISI and AISC)

Key Insight: If you encounter old drawings or specifications using the previous designations, this table is your Rosetta Stone. Misreading "24 WF 76" as anything other than "W 24 × 76" will cascade errors through your entire project.

How to Read a Steel Section Designation

Every designation follows a logical pattern:

• Section Letter → Identifies the shape type (W, S, M, C, L, etc.)
• Nominal Depth → The approximate depth of the member in inches
• Nominal Weight → The weight in pounds per linear foot

Example:

$$\text{W 18} \times 64$$

This tells you: Wide-flange shape, approximately 18 inches deep, weighing 64 pounds per foot.

The actual depth will differ slightly from the nominal depth. For a W 18 × 64, the actual depth might be 18.35 inches, not exactly 18. Always verify actual geometry from section property tables.

Angles Bent to Circular Shape

When you need to bend an angle-iron to fit around a circular structure — a standpipe, smokestack, tank, or cylindrical column — you cannot simply multiply the diameter by π and call it done. The angle's cross-section shifts the neutral axis, and the required length depends on whether the angle sits inside or outside the circular surface.

The Method:

1. Calculate the circumference of the circle in inches
2. Find the constant for your specific angle size from the table below
3. Inside placement: Subtract the constant from the circumference
4. Outside placement: Add the constant to the circumference

Worked Example:

A stand-pipe, 20 feet inside diameter, uses a 3 × 3 × 3⁄8 inch angle-iron on the inside at the top.

• Circumference = 20 × 12 × π = 754 inches
• Constant for 3 × 3 × 3⁄8 angle = 4.319
• Length of angle = 754 − 4.319 = 749.681 inches

If the angle were on the outside: 754 + 4.319 = 758.319 inches

Constants for Angles Bent to Circular Shape

Visual Strategy: A diagram showing a circular cross-section with an angle-iron placed on the inside vs. outside would clarify the add/subtract logic. Show the neutral axis offset and how it changes the effective circumference.

Steel Wide-Flange Sections (W Shapes)

The Workhorse of Structural Steel

Wide-flange sections are the most commonly specified structural steel shapes in the world. They carry bending loads efficiently, resist lateral buckling, and come in a range that covers everything from light framing to heavy column applications.

Symbols used throughout this section:

• I = Moment of inertia (in.⁴)
• S = Section modulus (in.³)
• r = Radius of gyration (in.)
• A = Cross-sectional area (in.²)
• d = Depth (in.)
• bf = Flange width (in.)
• tf = Flange thickness (in.)
• tw = Web thickness (in.)

Why These Properties Matter

Every number in a section property table tells you something critical about how a beam will perform:

• Moment of Inertia (I): Measures resistance to bending. Higher I = less deflection under load.
• Section Modulus (S): Directly determines bending stress. Your allowable bending moment = S × allowable stress.
• Radius of Gyration (r): Controls buckling behavior. Critical for column design where slenderness ratio (L/r) determines capacity.

The formula connecting them:

$$S = \frac{I}{c}$$

Where c is the distance from the neutral axis to the extreme fiber (half the depth for symmetric sections).

And:

$$r = \sqrt{\frac{I}{A}}$$

Steel Wide-Flange Sections — Heavy and Deep (W 27 through W 18)

Note: Consult the AISC Manual for W shapes having nominal depths greater than 27 inches.

Steel Wide-Flange Sections — Medium Depth (W 16 through W 14)

Important Note on W 14: The W 14 family is enormous — it ranges from the ultra-heavy W 14 × 730 (used as building columns in skyscrapers) down to the lightweight W 14 × 22 (used in light framing). The heaviest W 14 shapes have actual depths exceeding 22 inches despite the "14" nominal designation.

W 14 — Heavy Column Sections

W 14 — Standard Beam Sections

Practical Note: Look at the W 14 × 730. Its actual depth is 22.42 inches — more than 8 inches deeper than its nominal "14-inch" designation. This is because the heavy W 14 column sections were designed to maintain a consistent nominal flange width (around 16–17 inches) while adding material to increase capacity, which increases the overall depth significantly.