W12×120 Steel Beam
A W12×120 is a wide flange steel beam 13.1 inches deep with 12.3-inch flanges, weighing 120 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 698 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 279 kips.
Design a W12×120 beam Opens a 21 ft span in the free beam designer.
W12×120 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 13.1 in |
| Flange width, bf | 12.3 in |
| Flange thickness, tf | 1.11 in |
| Web thickness, tw | 0.710 in |
| Distance to web toe of fillet, kdes | 1.70 in |
| Distance between flange centroids, ho | 11.99 in |
| Cross-sectional area, A | 35.3 in2 |
| Weight | 120 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W12×120 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 1070 in4 | 345 in4 |
| Elastic section modulus, S | 163 in3 | 56.0 in3 |
| Plastic section modulus, Z | 186 in3 | 85.4 in3 |
| Radius of gyration, r | 5.51 in | 3.13 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 12.9 in4 |
| Warping constant, Cw | 12400 in6 |
| Effective radius of gyration, rts | 3.56 in |
| Flange slenderness, bf/2tf | 5.57 |
| Web slenderness, h/tw | 13.7 |
W12×120 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 = 698 kip-ft | Mn/Ω = 464 kip-ft |
| Shear | φVn = 279 kips | Vn/Ω = 186 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 11.1 ft between braces it keeps its full strength; past Lr = 56.6 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 698 kip-ft | 464 kip-ft |
| 10 ft | 698 kip-ft | 464 kip-ft |
| 11.1 ft (Lp) | 697 kip-ft | 464 kip-ft |
| 20 ft | 645 kip-ft | 429 kip-ft |
| 30 ft | 585 kip-ft | 389 kip-ft |
| 40 ft | 526 kip-ft | 350 kip-ft |
| 50 ft | 467 kip-ft | 311 kip-ft |
| 56.6 ft (Lr) | 428 kip-ft | 285 kip-ft |
| 60 ft | 402 kip-ft | 267 kip-ft |
| 70 ft | 343 kip-ft | 228 kip-ft |
| 80 ft | 299 kip-ft | 199 kip-ft |
| 90 ft | 265 kip-ft | 176 kip-ft |
| 100 ft | 238 kip-ft | 158 kip-ft |
| 110 ft | 216 kip-ft | 144 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.
W12×120 load table by span
The largest uniform load a simply supported W12×120 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 0.120 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 7 ft | 79.7* | 53.1* | 134.0 | 201.0 |
| 9 ft | 62.0* | 41.3* | 63.1 | 94.6 |
| 11 ft | 46.1 | 30.7 | 34.5 | 51.8 |
| 13 ft | 33.0 | 22.0 | 20.9 | 31.4 |
| 15 ft | 24.8 | 16.5 | 13.6 | 20.4 |
| 17 ft | 19.3 | 12.8 | 9.36 | 14.0 |
| 19 ft | 15.5 | 10.3 | 6.70 | 10.1 |
| 21 ft | 12.7 | 8.42 | 4.96 | 7.45 |
| 23 ft | 10.5 | 7.02 | 3.78 | 5.67 |
| 25 ft | 8.93 | 5.94 | 2.94 | 4.41 |
| 27 ft | 7.65 | 5.09 | 2.34 | 3.50 |
| 29 ft | 6.63 | 4.41 | 1.88 | 2.83 |
| 31 ft | 5.81 | 3.86 | 1.54 | 2.31 |
| 33 ft | 5.12 | 3.41 | 1.28 | 1.92 |
- 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 21 ft span, a W12×120 carries a factored load of 12.7 kips per foot (LRFD) or an allowable load of 8.42 kips per foot (ASD). A live load of 4.96 kips per foot would deflect it span/360, which is 0.70 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.
W12×120 questions
What does W12×120 mean?
W means a wide flange shape. 12 is its nominal depth in inches (the actual depth is 13.1 in) and 120 is its weight in pounds per foot.
How much does a W12×120 weigh?
120 pounds per foot, so a 20 ft W12×120 weighs about 2,400 pounds.
How far can a W12×120 span?
It depends on the load. Braced along its length, it carries 79.7 kips per foot of factored load at 7 ft and 5.12 kips per foot at 33 ft; the load table has the spans in between. Floor beams are often 20 to 26 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W12×120 a compact section?
Yes. Its flanges (bf/2tf = 5.57) and web (h/tw = 13.7) are both compact for bending in 50 ksi steel.