W8×31 vs W16×31
A side-by-side comparison of two AISC wide-flange beams, 16th Edition. Detailing dimensions to the nearest 1/16 in.
W8×31 and W16×31 both weigh 31 lb per foot, so the choice comes down to depth and stiffness rather than weight.
W16×31 is the deeper section at a nominal 16 in., versus 8 in.
W16×31 has the greater bending strength: section modulus Sx of 47.2 in³ versus 27.5, about 72% more.
| Property | W8×31 | W16×31 |
|---|---|---|
| Weight | 31 lb/ft | 31 lb/ft |
| Depth (d) | 8" | 15 7/8" |
| Flange width (bf) | 8" | 5 1/2" |
| Web thickness (tw) | 5/16" | 1/4" |
| Flange thickness (tf) | 7/16" | 7/16" |
| Area (A) | 9.13 in² | 9.13 in² |
| Moment of inertia (Ix) | 110 in⁴ | 375 in⁴ |
| Section modulus (Sx) | 27.5 in³ | 47.2 in³ |
| Plastic modulus (Zx) | 30.4 in³ | 54 in³ |
Open W8×31 in the interactive size chart →
Full detail: W8×31 · W16×31. Verify critical dimensions against the current AISC Steel Construction Manual before fabrication.
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