American standard H-beams, governed by ASTM standards (e.g., ASTM A6/A6M), are primarily classified into three main series: W-shapes (Wide Flange), S-shapes (American Standard I-Beams, often called "junior beams"), and M-shapes (Miscellaneous Shapes). These classifications are defined by their cross-sectional dimensions, weight per foot, and structural intent, ensuring compatibility with North American construction practices.
W-shapes (Wide Flange H-Beams) are the most common, designed for heavy structural loads. Their size range is extensive:
Height (depth): From 4 inches (102 mm) to 44 inches (1118 mm). For example, the W4×13 (4 inches tall, 13 lb/ft) is a small W-shape used in light framing, while the W44×335 (44 inches tall, 335 lb/ft) is a massive beam for skyscraper columns.
Flange width: Ranges from 3.98 inches (101 mm) for the W4×13 to 17.9 inches (455 mm) for the W44×335.
Web thickness: Typically 0.28 inches (7 mm) for small W-shapes to 1.83 inches (46 mm) for large ones.
Flange thickness: Varies from 0.43 inches (11 mm) to 3.0 inches (76 mm), with thicker flanges in heavier beams to enhance load-bearing capacity.
S-shapes have narrower flanges than W-shapes, making them suitable for medium-duty applications. Their dimensions include:
Height: 3 inches (76 mm) to 24 inches (610 mm), e.g., S3×5.7 (3 inches tall, 5.7 lb/ft) to S24×121 (24 inches tall, 121 lb/ft).
Flange width: Generally 2.33 inches (59 mm) to 8.06 inches (205 mm), narrower than W-shapes to reduce weight in non-critical loads.
M-shapes are specialized, with dimensions that don't fit W or S classifications. They range in height from 6 inches (152 mm) to 14 inches (356 mm) and are used in niche applications like industrial machinery frames.
Each size is labeled with a designation: the first number indicates height in inches, followed by weight per linear foot (lb/ft). For example, a W10×49 has a 10-inch height and weighs 49 lb/ft. This standardized labeling simplifies specification in engineering drawings, ensuring consistency across projects.
The size diversity of American standard H-beams allows engineers to select precise dimensions for specific loads. A W14×90, for instance, is commonly used in mid-rise building columns, balancing strength (with a flange width of 14.1 inches and web thickness of 0.52 inches) and material efficiency, while a W24×104 is preferred for bridge girders, where its 24-inch height and 12-inch flange width provide exceptional spanning capability.