W12×170 Steel Beam
A W12×170 is a wide flange steel beam 14 inches deep with 12.6-inch flanges, weighing 170 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 1,031 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 403 kips.
Design a W12×170 beam Opens a 21 ft span in the free beam designer.
W12×170 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 14.0 in |
| Flange width, bf | 12.6 in |
| Flange thickness, tf | 1.56 in |
| Web thickness, tw | 0.960 in |
| Distance to web toe of fillet, kdes | 2.16 in |
| Distance between flange centroids, ho | 12.44 in |
| Cross-sectional area, A | 50.0 in2 |
| Weight | 170 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W12×170 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 1650 in4 | 517 in4 |
| Elastic section modulus, S | 235 in3 | 82.3 in3 |
| Plastic section modulus, Z | 275 in3 | 126 in3 |
| Radius of gyration, r | 5.74 in | 3.22 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 35.6 in4 |
| Warping constant, Cw | 20100 in6 |
| Effective radius of gyration, rts | 3.70 in |
| Flange slenderness, bf/2tf | 4.03 |
| Web slenderness, h/tw | 10.1 |
W12×170 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 = 1,031 kip-ft | Mn/Ω = 686 kip-ft |
| Shear | φVn = 403 kips | Vn/Ω = 269 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 11.4 ft between braces it keeps its full strength; past Lr = 78.5 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 1,031 kip-ft | 686 kip-ft |
| 10 ft | 1,031 kip-ft | 686 kip-ft |
| 11.4 ft (Lp) | 1,031 kip-ft | 686 kip-ft |
| 20 ft | 978 kip-ft | 651 kip-ft |
| 30 ft | 916 kip-ft | 610 kip-ft |
| 40 ft | 854 kip-ft | 568 kip-ft |
| 50 ft | 793 kip-ft | 527 kip-ft |
| 60 ft | 731 kip-ft | 486 kip-ft |
| 70 ft | 669 kip-ft | 445 kip-ft |
| 78.5 ft (Lr) | 617 kip-ft | 410 kip-ft |
| 80 ft | 605 kip-ft | 402 kip-ft |
| 90 ft | 536 kip-ft | 357 kip-ft |
| 100 ft | 482 kip-ft | 321 kip-ft |
| 110 ft | 438 kip-ft | 291 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.
W12×170 load table by span
The largest uniform load a simply supported W12×170 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 0.170 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 7 ft | 115.2* | 76.8* | 206.7 | 310.0 |
| 9 ft | 89.6* | 59.7* | 97.2 | 145.9 |
| 11 ft | 68.2 | 45.4 | 53.3 | 79.9 |
| 13 ft | 48.8 | 32.5 | 32.3 | 48.4 |
| 15 ft | 36.7 | 24.4 | 21.0 | 31.5 |
| 17 ft | 28.5 | 19.0 | 14.4 | 21.6 |
| 19 ft | 22.9 | 15.2 | 10.3 | 15.5 |
| 21 ft | 18.7 | 12.4 | 7.65 | 11.5 |
| 23 ft | 15.6 | 10.4 | 5.83 | 8.74 |
| 25 ft | 13.2 | 8.78 | 4.54 | 6.81 |
| 27 ft | 11.3 | 7.53 | 3.60 | 5.40 |
| 29 ft | 9.81 | 6.53 | 2.91 | 4.36 |
| 31 ft | 8.58 | 5.71 | 2.38 | 3.57 |
| 33 ft | 7.58 | 5.04 | 1.97 | 2.96 |
| 35 ft | 6.73 | 4.48 | 1.65 | 2.48 |
- 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 W12×170 carries a factored load of 18.7 kips per foot (LRFD) or an allowable load of 12.4 kips per foot (ASD). A live load of 7.65 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.
W12×170 questions
What does W12×170 mean?
W means a wide flange shape. 12 is its nominal depth in inches (the actual depth is 14.0 in) and 170 is its weight in pounds per foot.
How much does a W12×170 weigh?
170 pounds per foot, so a 20 ft W12×170 weighs about 3,400 pounds.
How far can a W12×170 span?
It depends on the load. Braced along its length, it carries 115.2 kips per foot of factored load at 7 ft and 6.73 kips per foot at 35 ft; the load table has the spans in between. Floor beams are often 21 to 28 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W12×170 a compact section?
Yes. Its flanges (bf/2tf = 4.03) and web (h/tw = 10.1) are both compact for bending in 50 ksi steel.