W21×101 Steel Beam
A W21×101 is a wide flange steel beam 21.4 inches deep with 12.3-inch flanges, weighing 101 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 949 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 321 kips.
Design a W21×101 beam Opens a 33 ft span in the free beam designer.
W21×101 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 21.4 in |
| Flange width, bf | 12.3 in |
| Flange thickness, tf | 0.800 in |
| Web thickness, tw | 0.500 in |
| Distance to web toe of fillet, kdes | 1.30 in |
| Distance between flange centroids, ho | 20.60 in |
| Cross-sectional area, A | 29.8 in2 |
| Weight | 101 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W21×101 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 2420 in4 | 248 in4 |
| Elastic section modulus, S | 227 in3 | 40.3 in3 |
| Plastic section modulus, Z | 253 in3 | 61.7 in3 |
| Radius of gyration, r | 9.02 in | 2.89 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 5.21 in4 |
| Warping constant, Cw | 26200 in6 |
| Effective radius of gyration, rts | 3.35 in |
| Flange slenderness, bf/2tf | 7.68 |
| Web slenderness, h/tw | 37.5 |
W21×101 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 = 949 kip-ft | Mn/Ω = 631 kip-ft |
| Shear | φVn = 321 kips | Vn/Ω = 214 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 10.2 ft between braces it keeps its full strength; past Lr = 30.1 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 949 kip-ft | 631 kip-ft |
| 10 ft | 949 kip-ft | 631 kip-ft |
| 10.2 ft (Lp) | 949 kip-ft | 631 kip-ft |
| 20 ft | 775 kip-ft | 516 kip-ft |
| 30 ft (Lr) | 597 kip-ft | 397 kip-ft |
| 30.1 ft (Lr) | 595 kip-ft | 396 kip-ft |
| 40 ft | 396 kip-ft | 264 kip-ft |
| 50 ft | 296 kip-ft | 197 kip-ft |
| 60 ft | 236 kip-ft | 157 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.
W21×101 load table by span
The largest uniform load a simply supported W21×101 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 0.101 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 11 ft | 58.4* | 38.9* | 78.1 | 117.2 |
| 13 ft | 44.9 | 29.9 | 47.3 | 71.0 |
| 15 ft | 33.7 | 22.4 | 30.8 | 46.2 |
| 17 ft | 26.3 | 17.5 | 21.2 | 31.7 |
| 19 ft | 21.0 | 14.0 | 15.2 | 22.7 |
| 21 ft | 17.2 | 11.5 | 11.2 | 16.8 |
| 23 ft | 14.3 | 9.55 | 8.55 | 12.8 |
| 25 ft | 12.1 | 8.08 | 6.65 | 9.98 |
| 27 ft | 10.4 | 6.93 | 5.28 | 7.92 |
| 29 ft | 9.02 | 6.00 | 4.26 | 6.39 |
| 31 ft | 7.90 | 5.25 | 3.49 | 5.23 |
| 33 ft | 6.97 | 4.64 | 2.89 | 4.34 |
| 35 ft | 6.20 | 4.12 | 2.42 | 3.64 |
| 37 ft | 5.54 | 3.69 | 2.05 | 3.08 |
| 39 ft | 4.99 | 3.32 | 1.75 | 2.63 |
| 41 ft | 4.52 | 3.00 | 1.51 | 2.26 |
| 43 ft | 4.10 | 2.73 | 1.31 | 1.96 |
| 45 ft | 3.75 | 2.49 | 1.14 | 1.71 |
| 47 ft | 3.44 | 2.29 | 1.00 | 1.50 |
| 49 ft | 3.16 | 2.10 | 0.88 | 1.33 |
| 51 ft | 2.92 | 1.94 | 0.78 | 1.18 |
| 53 ft | 2.70 | 1.80 | 0.70 | 1.05 |
- 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 W21×101 carries a factored load of 6.97 kips per foot (LRFD) or an allowable load of 4.64 kips per foot (ASD). A live load of 2.89 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.
W21×101 questions
What does W21×101 mean?
W means a wide flange shape. 21 is its nominal depth in inches (the actual depth is 21.4 in) and 101 is its weight in pounds per foot.
How much does a W21×101 weigh?
101 pounds per foot, so a 20 ft W21×101 weighs about 2,020 pounds.
How far can a W21×101 span?
It depends on the load. Braced along its length, it carries 58.4 kips per foot of factored load at 11 ft and 2.70 kips per foot at 53 ft; the load table has the spans in between. Floor beams are often 32 to 43 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W21×101 a compact section?
Yes. Its flanges (bf/2tf = 7.68) and web (h/tw = 37.5) are both compact for bending in 50 ksi steel.