W12×279 Steel Beam
A W12×279 is a wide flange steel beam 15.9 inches deep with 13.1-inch flanges, weighing 279 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 1,804 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 730 kips.
Design a W12×279 beam Opens a 24 ft span in the free beam designer.
W12×279 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 15.9 in |
| Flange width, bf | 13.1 in |
| Flange thickness, tf | 2.47 in |
| Web thickness, tw | 1.53 in |
| Distance to web toe of fillet, kdes | 3.07 in |
| Distance between flange centroids, ho | 13.43 in |
| Cross-sectional area, A | 81.9 in2 |
| Weight | 279 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W12×279 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 3110 in4 | 937 in4 |
| Elastic section modulus, S | 393 in3 | 143 in3 |
| Plastic section modulus, Z | 481 in3 | 220 in3 |
| Radius of gyration, r | 6.16 in | 3.38 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 143 in4 |
| Warping constant, Cw | 42000 in6 |
| Effective radius of gyration, rts | 4.00 in |
| Flange slenderness, bf/2tf | 2.66 |
| Web slenderness, h/tw | 6.35 |
W12×279 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 = 1,804 kip-ft | Mn/Ω = 1,200 kip-ft |
| Shear | φVn = 730 kips | Vn/Ω = 487 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 11.9 ft between braces it keeps its full strength; past Lr = 125.4 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 1,804 kip-ft | 1,200 kip-ft |
| 10 ft | 1,804 kip-ft | 1,200 kip-ft |
| 11.9 ft (Lp) | 1,804 kip-ft | 1,200 kip-ft |
| 20 ft | 1,749 kip-ft | 1,164 kip-ft |
| 30 ft | 1,681 kip-ft | 1,118 kip-ft |
| 40 ft | 1,613 kip-ft | 1,073 kip-ft |
| 50 ft | 1,545 kip-ft | 1,028 kip-ft |
| 60 ft | 1,477 kip-ft | 983 kip-ft |
| 70 ft | 1,409 kip-ft | 937 kip-ft |
| 80 ft | 1,341 kip-ft | 892 kip-ft |
| 90 ft | 1,273 kip-ft | 847 kip-ft |
| 100 ft | 1,205 kip-ft | 801 kip-ft |
| 110 ft | 1,137 kip-ft | 756 kip-ft |
| 125.4 ft (Lr) | 1,032 kip-ft | 686 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.
W12×279 load table by span
The largest uniform load a simply supported W12×279 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 0.279 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 8 ft | 182.5* | 121.6* | 261.0 | 391.4 |
| 10 ft | 144.3 | 96.0 | 133.6 | 200.4 |
| 12 ft | 100.2 | 66.7 | 77.3 | 116.0 |
| 14 ft | 73.6 | 49.0 | 48.7 | 73.0 |
| 16 ft | 56.4 | 37.5 | 32.6 | 48.9 |
| 18 ft | 44.5 | 29.6 | 22.9 | 34.4 |
| 20 ft | 36.1 | 24.0 | 16.7 | 25.1 |
| 22 ft | 29.8 | 19.8 | 12.5 | 18.8 |
| 24 ft | 25.1 | 16.7 | 9.67 | 14.5 |
| 26 ft | 21.3 | 14.2 | 7.60 | 11.4 |
| 28 ft | 18.4 | 12.2 | 6.09 | 9.13 |
| 30 ft | 16.0 | 10.7 | 4.95 | 7.42 |
| 32 ft | 14.1 | 9.38 | 4.08 | 6.12 |
| 34 ft | 12.5 | 8.31 | 3.40 | 5.10 |
| 36 ft | 11.1 | 7.41 | 2.86 | 4.30 |
| 38 ft | 9.99 | 6.65 | 2.44 | 3.65 |
| 40 ft | 9.02 | 6.00 | 2.09 | 3.13 |
- 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 24 ft span, a W12×279 carries a factored load of 25.1 kips per foot (LRFD) or an allowable load of 16.7 kips per foot (ASD). A live load of 9.67 kips per foot would deflect it span/360, which is 0.80 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.
W12×279 questions
What does W12×279 mean?
W means a wide flange shape. 12 is its nominal depth in inches (the actual depth is 15.9 in) and 279 is its weight in pounds per foot.
How much does a W12×279 weigh?
279 pounds per foot, so a 20 ft W12×279 weighs about 5,580 pounds.
How far can a W12×279 span?
It depends on the load. Braced along its length, it carries 182.5 kips per foot of factored load at 8 ft and 9.02 kips per foot at 40 ft; the load table has the spans in between. Floor beams are often 24 to 32 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W12×279 a compact section?
Yes. Its flanges (bf/2tf = 2.66) and web (h/tw = 6.35) are both compact for bending in 50 ksi steel.