W18×283 Steel Beam
A W18×283 is a wide flange steel beam 21.9 inches deep with 11.9-inch flanges, weighing 283 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 2,535 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 920 kips.
Design a W18×283 beam Opens a 33 ft span in the free beam designer.
W18×283 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 21.9 in |
| Flange width, bf | 11.9 in |
| Flange thickness, tf | 2.50 in |
| Web thickness, tw | 1.40 in |
| Distance to web toe of fillet, kdes | 3.00 in |
| Distance between flange centroids, ho | 19.40 in |
| Cross-sectional area, A | 83.3 in2 |
| Weight | 283 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W18×283 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 6170 in4 | 704 in4 |
| Elastic section modulus, S | 565 in3 | 118 in3 |
| Plastic section modulus, Z | 676 in3 | 185 in3 |
| Radius of gyration, r | 8.61 in | 2.91 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 134 in4 |
| Warping constant, Cw | 65900 in6 |
| Effective radius of gyration, rts | 3.47 in |
| Flange slenderness, bf/2tf | 2.38 |
| Web slenderness, h/tw | 11.3 |
W18×283 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 = 2,535 kip-ft | Mn/Ω = 1,687 kip-ft |
| Shear | φVn = 920 kips | Vn/Ω = 613 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 10.3 ft between braces it keeps its full strength; past Lr = 73.7 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 2,535 kip-ft | 1,687 kip-ft |
| 10 ft | 2,535 kip-ft | 1,687 kip-ft |
| 10.3 ft (Lp) | 2,535 kip-ft | 1,687 kip-ft |
| 20 ft | 2,374 kip-ft | 1,579 kip-ft |
| 30 ft | 2,208 kip-ft | 1,469 kip-ft |
| 40 ft | 2,042 kip-ft | 1,359 kip-ft |
| 50 ft | 1,876 kip-ft | 1,248 kip-ft |
| 60 ft | 1,710 kip-ft | 1,138 kip-ft |
| 70 ft | 1,544 kip-ft | 1,027 kip-ft |
| 73.7 ft (Lr) | 1,482 kip-ft | 986 kip-ft |
| 80 ft | 1,364 kip-ft | 907 kip-ft |
| 90 ft | 1,211 kip-ft | 805 kip-ft |
| 100 ft | 1,088 kip-ft | 724 kip-ft |
| 110 ft | 989 kip-ft | 658 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.
W18×283 load table by span
The largest uniform load a simply supported W18×283 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 0.283 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 11 ft | 167.2* | 111.5* | 199.2 | 298.7 |
| 13 ft | 120.0 | 79.8 | 120.7 | 181.0 |
| 15 ft | 90.1 | 60.0 | 78.5 | 117.8 |
| 17 ft | 70.2 | 46.7 | 54.0 | 80.9 |
| 19 ft | 56.2 | 37.4 | 38.6 | 58.0 |
| 21 ft | 46.0 | 30.6 | 28.6 | 42.9 |
| 23 ft | 38.3 | 25.5 | 21.8 | 32.7 |
| 25 ft | 32.4 | 21.6 | 17.0 | 25.4 |
| 27 ft | 27.8 | 18.5 | 13.5 | 20.2 |
| 29 ft | 24.1 | 16.0 | 10.9 | 16.3 |
| 31 ft | 21.1 | 14.0 | 8.90 | 13.3 |
| 33 ft | 18.6 | 12.4 | 7.38 | 11.1 |
| 35 ft | 16.6 | 11.0 | 6.18 | 9.27 |
| 37 ft | 14.8 | 9.86 | 5.23 | 7.85 |
| 39 ft | 13.3 | 8.87 | 4.47 | 6.70 |
| 41 ft | 12.1 | 8.03 | 3.85 | 5.77 |
| 43 ft | 11.0 | 7.30 | 3.33 | 5.00 |
| 45 ft | 10.0 | 6.66 | 2.91 | 4.36 |
| 47 ft | 9.18 | 6.11 | 2.55 | 3.83 |
| 49 ft | 8.45 | 5.62 | 2.25 | 3.38 |
| 51 ft | 7.80 | 5.19 | 2.00 | 3.00 |
| 53 ft | 7.22 | 4.80 | 1.78 | 2.67 |
| 55 ft | 6.70 | 4.46 | 1.59 | 2.39 |
- 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 W18×283 carries a factored load of 18.6 kips per foot (LRFD) or an allowable load of 12.4 kips per foot (ASD). A live load of 7.38 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.
W18×283 questions
What does W18×283 mean?
W means a wide flange shape. 18 is its nominal depth in inches (the actual depth is 21.9 in) and 283 is its weight in pounds per foot.
How much does a W18×283 weigh?
283 pounds per foot, so a 20 ft W18×283 weighs about 5,660 pounds.
How far can a W18×283 span?
It depends on the load. Braced along its length, it carries 167.2 kips per foot of factored load at 11 ft and 6.70 kips per foot at 55 ft; the load table has the spans in between. Floor beams are often 33 to 44 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W18×283 a compact section?
Yes. Its flanges (bf/2tf = 2.38) and web (h/tw = 11.3) are both compact for bending in 50 ksi steel.