W21×147 Steel Beam
A W21×147 is a wide flange steel beam 22.1 inches deep with 12.5-inch flanges, weighing 147 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 1,399 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 477 kips.
Design a W21×147 beam Opens a 33 ft span in the free beam designer.
W21×147 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 22.1 in |
| Flange width, bf | 12.5 in |
| Flange thickness, tf | 1.15 in |
| Web thickness, tw | 0.720 in |
| Distance to web toe of fillet, kdes | 1.65 in |
| Distance between flange centroids, ho | 20.95 in |
| Cross-sectional area, A | 43.2 in2 |
| Weight | 147 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W21×147 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 3630 in4 | 376 in4 |
| Elastic section modulus, S | 329 in3 | 60.1 in3 |
| Plastic section modulus, Z | 373 in3 | 92.6 in3 |
| Radius of gyration, r | 9.17 in | 2.95 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 15.4 in4 |
| Warping constant, Cw | 41100 in6 |
| Effective radius of gyration, rts | 3.46 in |
| Flange slenderness, bf/2tf | 5.44 |
| Web slenderness, h/tw | 26.1 |
W21×147 bending and shear strength
For ASTM A992 steel (Fy = 50 ksi, E = 29,000 ksi) per AISC 360-16. Its flanges and web are compact for bending, so with its compression flange braced it reaches its full plastic moment.
| Strength | LRFD | ASD |
|---|---|---|
| Bending, compression flange braced | φMn = 1,399 kip-ft | Mn/Ω = 931 kip-ft |
| Shear | φVn = 477 kips | Vn/Ω = 318 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 10.4 ft between braces it keeps its full strength; past Lr = 36.3 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 1,399 kip-ft | 931 kip-ft |
| 10 ft | 1,399 kip-ft | 931 kip-ft |
| 10.4 ft (Lp) | 1,399 kip-ft | 931 kip-ft |
| 20 ft | 1,201 kip-ft | 799 kip-ft |
| 30 ft | 994 kip-ft | 661 kip-ft |
| 36.3 ft (Lr) | 863 kip-ft | 574 kip-ft |
| 40 ft | 765 kip-ft | 509 kip-ft |
| 50 ft | 586 kip-ft | 390 kip-ft |
| 60 ft | 476 kip-ft | 317 kip-ft |
| 70 ft | 402 kip-ft | 267 kip-ft |
A beam with a uniform load between braces has Cb above 1.0 (1.14 for a simple span braced only at its ends), so these values are conservative. The beam designer works out Cb for every segment between braces.
W21×147 load table by span
The largest uniform load a simply supported W21×147 can carry, in kips per foot, with its compression flange braced along its length (by a floor or roof deck, for example). The loads include the beam's own weight of 0.147 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 11 ft | 86.8* | 57.9* | 117.2 | 175.8 |
| 13 ft | 66.2 | 44.1 | 71.0 | 106.5 |
| 15 ft | 49.7 | 33.1 | 46.2 | 69.3 |
| 17 ft | 38.7 | 25.8 | 31.7 | 47.6 |
| 19 ft | 31.0 | 20.6 | 22.7 | 34.1 |
| 21 ft | 25.4 | 16.9 | 16.8 | 25.3 |
| 23 ft | 21.2 | 14.1 | 12.8 | 19.2 |
| 25 ft | 17.9 | 11.9 | 9.98 | 15.0 |
| 27 ft | 15.3 | 10.2 | 7.92 | 11.9 |
| 29 ft | 13.3 | 8.85 | 6.39 | 9.59 |
| 31 ft | 11.6 | 7.75 | 5.23 | 7.85 |
| 33 ft | 10.3 | 6.84 | 4.34 | 6.51 |
| 35 ft | 9.13 | 6.08 | 3.64 | 5.46 |
| 37 ft | 8.17 | 5.44 | 3.08 | 4.62 |
| 39 ft | 7.36 | 4.89 | 2.63 | 3.94 |
| 41 ft | 6.66 | 4.43 | 2.26 | 3.39 |
| 43 ft | 6.05 | 4.03 | 1.96 | 2.94 |
| 45 ft | 5.53 | 3.68 | 1.71 | 2.57 |
| 47 ft | 5.07 | 3.37 | 1.50 | 2.25 |
| 49 ft | 4.66 | 3.10 | 1.33 | 1.99 |
| 51 ft | 4.30 | 2.86 | 1.18 | 1.76 |
| 53 ft | 3.98 | 2.65 | 1.05 | 1.57 |
| 55 ft | 3.70 | 2.46 | 0.94 | 1.41 |
- Factored and allowable loads are limited by bending, or by shear where marked *.
- The deflection columns are the service loads that make the beam sag span/360 or span/240. Compare span/360 with the live load alone and span/240 with dead plus live load, the usual floor limits in IBC Table 1604.3.
Reading the table
At a 33 ft span, a W21×147 carries a factored load of 10.3 kips per foot (LRFD) or an allowable load of 6.84 kips per foot (ASD). A live load of 4.34 kips per foot would deflect it span/360, which is 1.10 in. The beam works if the factored load is under the first number and the live and total loads are under the deflection numbers. For other spans, supports or loads, open it in the beam designer, or follow the steel beam design guide to check one by hand.
W21×147 questions
What does W21×147 mean?
W means a wide flange shape. 21 is its nominal depth in inches (the actual depth is 22.1 in) and 147 is its weight in pounds per foot.
How much does a W21×147 weigh?
147 pounds per foot, so a 20 ft W21×147 weighs about 2,940 pounds.
How far can a W21×147 span?
It depends on the load. Braced along its length, it carries 86.8 kips per foot of factored load at 11 ft and 3.70 kips per foot at 55 ft; the load table has the spans in between. Floor beams are often 33 to 44 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W21×147 a compact section?
Yes. Its flanges (bf/2tf = 5.44) and web (h/tw = 26.1) are both compact for bending in 50 ksi steel.