W18×175 Steel Beam
A W18×175 is a wide flange steel beam 20 inches deep with 11.4-inch flanges, weighing 175 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 1,493 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 534 kips.
Design a W18×175 beam Opens a 30 ft span in the free beam designer.
W18×175 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 20.0 in |
| Flange width, bf | 11.4 in |
| Flange thickness, tf | 1.59 in |
| Web thickness, tw | 0.890 in |
| Distance to web toe of fillet, kdes | 1.99 in |
| Distance between flange centroids, ho | 18.41 in |
| Cross-sectional area, A | 51.3 in2 |
| Weight | 175 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W18×175 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 3450 in4 | 391 in4 |
| Elastic section modulus, S | 344 in3 | 68.8 in3 |
| Plastic section modulus, Z | 398 in3 | 106 in3 |
| Radius of gyration, r | 8.20 in | 2.76 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 33.8 in4 |
| Warping constant, Cw | 33300 in6 |
| Effective radius of gyration, rts | 3.24 in |
| Flange slenderness, bf/2tf | 3.58 |
| Web slenderness, h/tw | 18.0 |
W18×175 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 = 1,493 kip-ft | Mn/Ω = 993 kip-ft |
| Shear | φVn = 534 kips | Vn/Ω = 356 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 9.7 ft between braces it keeps its full strength; past Lr = 46.8 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 1,493 kip-ft | 993 kip-ft |
| 9.8 ft (Lp) | 1,492 kip-ft | 993 kip-ft |
| 10 ft | 1,489 kip-ft | 990 kip-ft |
| 20 ft | 1,329 kip-ft | 885 kip-ft |
| 30 ft | 1,170 kip-ft | 779 kip-ft |
| 40 ft | 1,011 kip-ft | 673 kip-ft |
| 46.8 ft (Lr) | 903 kip-ft | 601 kip-ft |
| 50 ft | 841 kip-ft | 560 kip-ft |
| 60 ft | 694 kip-ft | 462 kip-ft |
| 70 ft | 591 kip-ft | 393 kip-ft |
| 80 ft | 515 kip-ft | 343 kip-ft |
| 90 ft | 457 kip-ft | 304 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.
W18×175 load table by span
The largest uniform load a simply supported W18×175 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 0.175 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 10 ft | 106.8* | 71.2* | 148.2 | 222.3 |
| 12 ft | 82.9 | 55.2 | 85.8 | 128.7 |
| 14 ft | 60.9 | 40.5 | 54.0 | 81.0 |
| 16 ft | 46.6 | 31.0 | 36.2 | 54.3 |
| 18 ft | 36.9 | 24.5 | 25.4 | 38.1 |
| 20 ft | 29.8 | 19.9 | 18.5 | 27.8 |
| 22 ft | 24.7 | 16.4 | 13.9 | 20.9 |
| 24 ft | 20.7 | 13.8 | 10.7 | 16.1 |
| 26 ft | 17.7 | 11.8 | 8.43 | 12.6 |
| 28 ft | 15.2 | 10.1 | 6.75 | 10.1 |
| 30 ft | 13.3 | 8.83 | 5.49 | 8.23 |
| 32 ft | 11.7 | 7.76 | 4.52 | 6.79 |
| 34 ft | 10.3 | 6.87 | 3.77 | 5.66 |
| 36 ft | 9.21 | 6.13 | 3.18 | 4.77 |
| 38 ft | 8.27 | 5.50 | 2.70 | 4.05 |
| 40 ft | 7.46 | 4.97 | 2.32 | 3.47 |
| 42 ft | 6.77 | 4.50 | 2.00 | 3.00 |
| 44 ft | 6.17 | 4.10 | 1.74 | 2.61 |
| 46 ft | 5.64 | 3.75 | 1.52 | 2.28 |
| 48 ft | 5.18 | 3.45 | 1.34 | 2.01 |
| 50 ft | 4.78 | 3.18 | 1.19 | 1.78 |
- 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 30 ft span, a W18×175 carries a factored load of 13.3 kips per foot (LRFD) or an allowable load of 8.83 kips per foot (ASD). A live load of 5.49 kips per foot would deflect it span/360, which is 1.00 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.
W18×175 questions
What does W18×175 mean?
W means a wide flange shape. 18 is its nominal depth in inches (the actual depth is 20.0 in) and 175 is its weight in pounds per foot.
How much does a W18×175 weigh?
175 pounds per foot, so a 20 ft W18×175 weighs about 3,500 pounds.
How far can a W18×175 span?
It depends on the load. Braced along its length, it carries 106.8 kips per foot of factored load at 10 ft and 4.78 kips per foot at 50 ft; the load table has the spans in between. Floor beams are often 30 to 40 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W18×175 a compact section?
Yes. Its flanges (bf/2tf = 3.58) and web (h/tw = 18.0) are both compact for bending in 50 ksi steel.