Structural Steel I-Beams (AISC W-Shapes & S-Shapes)
Direct Answer
Structural steel I-beams standardized under the American Institute of Steel Construction (AISC 360) and ASTM A6 / ASTM A992 are hot-rolled load-bearing beams. Classified into Wide Flange W-Shapes (parallel inner and outer flange faces) and American Standard S-Shapes (tapered 16.67% inner flange slope), beam callouts designate nominal depth and weight in pounds per foot (e.g., W12×50).
Source: AISC 360-16 / ASTM A992 (Standard Specification for Structural Steel Shapes)
Specs
| Governing Standards | AISC 360 / ASTM A6 / ASTM A992 (Grade 50 steel: 50 ksi yield / 65 ksi tensile) |
| Standard Callout Format | W [Nominal Depth in inches] × [Weight in lbs per linear foot] |
| Example: W8×24 Dimensions | Actual Depth: 7.93" (201 mm) | Flange Width: 6.49" (165 mm) | Weight: 24 lb/ft |
| Example: W12×50 Dimensions | Actual Depth: 12.19" (310 mm) | Flange Width: 8.08" (205 mm) | Weight: 50 lb/ft |
| Example: W14×90 Dimensions | Actual Depth: 14.02" (356 mm) | Flange Width: 14.52" (369 mm) | Weight: 90 lb/ft |
| W-Shape Flange Profile | Parallel inner and outer surfaces (0° slope, square flanges) |
| S-Shape Flange Profile | 16.67% (1:6 or 9° 28') tapered inner flange slope |
Decoding AISC Beam Designations (W, S, HP, C)
In AISC structural engineering drawings, beam callouts provide immediate geometric and load metrics:
- $W12 \times 50$: A Wide Flange (W) beam with a nominal depth of $12\text{ inches}$ weighing exactly $50\text{ pounds per linear foot}$ ($74.4\text{ kg/m}$).
- $S12 \times 35$: An American Standard (S) I-beam with a $12\text{-inch}$ depth weighing $35\text{ lb/ft}$.
- $HP14 \times 89$: A Bearing Pile (HP) shape where the flange width and beam depth are identical ($14\times 14\text{ in}$) and flanges and webs share uniform thickness to resist axial pile driving loads.
Wide Flange (W) vs American Standard (S) Flange Geometry
The critical difference between modern $W\text{-Shapes}$ and legacy $S\text{-Beams}$ is flange surface parallelism:
- $W\text{-Shapes}$ (Wide Flange): The top and bottom surfaces of the flanges are completely parallel ($0^\circ$ slope). This allows structural bolts (A325/A490) to be torqued against flat surfaces without specialized beveled washers.
- $S\text{-Shapes}$ (Standard I-Beam): The inner surface of the flange has a $1:6$ ($16.67\%$) slope, requiring square beveled washers (ASTM F436 Type 1) under bolt heads to maintain axial tension.