8.1 Structural Steel Shapes, Framing & Erection Stability
Key Takeaways
- A W-shape designation gives nominal depth and weight per foot.
- Erection planning must maintain stability at every temporary stage.
- Column bases require the OSHA minimum anchor arrangement and approved repairs for damaged anchors.
8.1 Structural Steel Shapes, Framing & Erection Stability
Commercial general contractors in Georgia must master the engineering standards, fabrication tolerances, connection mechanics, and safety mandates governing structural steel construction. Structural steel framing systems form the primary gravity-load-resisting and lateral-force-resisting superstructure for commercial mid-rise, high-rise, industrial, and institutional facilities. Construction execution requires strict adherence to the American Institute of Steel Construction (AISC) specifications, ASTM International material standards, the American Welding Society (AWS) D1.1 Structural Welding Code, and OSHA 29 CFR 1926 Subpart R safety regulations.
AISC Structural Steel Shapes & Designations
Structural steel members are hot-rolled or cold-formed into standardized cross-sectional profiles. AISC establishes standard nomenclature identifying the geometric profile, nominal dimensions, and weight per linear foot of each structural shape.
| Structural Shape | AISC Designation Example | Geometric Profile & Structural Application |
|---|---|---|
| Wide-Flange Shapes (W-Shapes) | W12x26 | I-shaped cross-section with parallel inner and outer flange surfaces. W12x26 designates a member with a nominal depth of 12 inches and a weight of 26 pounds per linear foot. Standard structural choice for primary beams, girders, and building columns. |
| American Standard Beams (S-Shapes) | S12x35 | I-shaped cross-section with relatively narrow flanges featuring an inside flange slope of 16.67% (2 on 12). Primarily used in crane runways, monorails, and specialized industrial framing. |
| Standard Channels (C-Shapes) | C10x30 | C-shaped profile with flanges extending from one side of the web, with sloped inner flange faces. Common in stair stringers, roof purlins, wall framing girts, and built-up truss chords. |
| Structural Angles (L-Shapes) | L4x4x1/2 or L6x4x3/8 | L-shaped profile with two perpendicular legs. Designated by leg lengths and metal thickness (e.g., L6x4x3/8 has a 6" leg, a 4" leg, and a 3/8" thickness). Used for diagonal bracing, truss web members, shelf lintels, and connection clip angles. |
| Hollow Structural Sections (HSS) | HSS8x8x1/2 (Square), HSS10x6x3/8 (Rectangular), HSS8.625x0.500 (Round) | Tubular cross-sections with uniform wall thickness produced by electric resistance welding or seamless forming. Excellent torsional resistance and bi-axial buckling capacity; widely used for exposed architectural columns, long-span trusses, and exterior bracings. |
| Structural Tees (WT-Shapes) | WT6x13 | T-shaped member produced by splitting a wide-flange beam down its longitudinal centerline. A WT6x13 is cut from a W12x26; commonly utilized as chords in welded roof trusses and stiffener elements. |
| Steel Plates & Flat Bars (PL) | PL 1/2 x 12 | Rectangular flat rolled steel designated by thickness followed by width. Used for column base plates, splice plates, gusset plates, and shear tabs. |
ASTM Structural Steel Grades & Mechanical Metallurgy
Structural steel performance is dictated by its metallurgical composition, yield strength ($F_y$), tensile strength ($F_u$), and ductility. Modern building codes require specific ASTM steel grades tailored to member geometry and structural demands.
STRUCTURAL STEEL GRADES
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ASTM A36 (CARBON) ASTM A992 (HSLA) ASTM A500 (TUBING)
• Fy = 36 ksi (Min) • Fy = 50 ksi (Min) • Grade B: 46 ksi (Shapes)
• Fu = 58–80 ksi • Fu = 65 ksi (Min) • Grade C: 50 ksi (Shapes)
• Angles, Plates, Base Plates • Fy / Fu Ratio ≤ 0.85 • Cold-Formed Square, Rect,
• Excellent Weldability • Standard for W-Shapes and Round HSS Members
- ASTM A36: The traditional carbon steel standard with a minimum yield strength of 36 ksi (36,000 psi) and tensile strength of 58–80 ksi. It remains the predominant specification for base plates, gusset plates, angles, channels, and miscellaneous steel fabrications due to exceptional ductility and ease of field welding.
- ASTM A992: The universal standard for wide-flange (W) beams and columns. Engineered with a minimum yield strength of 50 ksi and tensile strength of 65 ksi. Crucially, ASTM A992 enforces strict chemical and mechanical controls, including a maximum yield-to-tensile ratio ($F_y / F_u \le 0.85$) and a maximum carbon equivalent ($CE \le 0.45%$), ensuring predictable plastic deformation during seismic and cyclic wind events.
- ASTM A572 Grade 50: High-strength low-alloy (HSLA) columbium-vanadium structural steel offering 50 ksi yield strength. Frequently specified for heavy plates, built-up plate girders, and structural shapes where A992 is not applicable.
- ASTM A500 (Grades B and C): Cold-formed welded and seamless carbon steel structural tubing (HSS). Grade B provides a minimum yield of 46 ksi for rectangular/square shapes (42 ksi for rounds); Grade C provides 50 ksi for shapes (46 ksi for rounds).
- ASTM A588: Atmospheric corrosion-resistant high-strength low-alloy steel ("weathering steel" / Corten) with a 50 ksi yield strength. Develops a dense, protective copper-phosphorus oxide patina when exposed to outdoor wet-dry cycles, eliminating the need for protective paint systems in exterior pedestrian bridges and exposed canopies.
Under AISC structural steel shape nomenclature, what are the precise physical characteristics designated by the label W12x26?
Under OSHA 29 CFR 1926 Subpart R (Steel Erection), what is the minimum number of anchor bolts required for a structural column base plate assembly?