W18×106 Steel Beam
A W18×106 is a wide flange steel beam 18.7 inches deep with 11.2-inch flanges, weighing 106 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 863 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 331 kips.
Design a W18×106 beam Opens a 29 ft span in the free beam designer.
W18×106 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 18.7 in |
| Flange width, bf | 11.2 in |
| Flange thickness, tf | 0.940 in |
| Web thickness, tw | 0.590 in |
| Distance to web toe of fillet, kdes | 1.34 in |
| Distance between flange centroids, ho | 17.76 in |
| Cross-sectional area, A | 31.1 in2 |
| Weight | 106 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W18×106 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 1910 in4 | 220 in4 |
| Elastic section modulus, S | 204 in3 | 39.4 in3 |
| Plastic section modulus, Z | 230 in3 | 60.5 in3 |
| Radius of gyration, r | 7.84 in | 2.66 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 7.48 in4 |
| Warping constant, Cw | 17400 in6 |
| Effective radius of gyration, rts | 3.10 in |
| Flange slenderness, bf/2tf | 5.96 |
| Web slenderness, h/tw | 27.2 |
W18×106 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 = 863 kip-ft | Mn/Ω = 574 kip-ft |
| Shear | φVn = 331 kips | Vn/Ω = 221 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 9.4 ft between braces it keeps its full strength; past Lr = 31.8 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 863 kip-ft | 574 kip-ft |
| 9.4 ft (Lp) | 862 kip-ft | 574 kip-ft |
| 10 ft | 854 kip-ft | 568 kip-ft |
| 20 ft | 708 kip-ft | 471 kip-ft |
| 30 ft | 562 kip-ft | 374 kip-ft |
| 31.8 ft (Lr) | 536 kip-ft | 356 kip-ft |
| 40 ft | 402 kip-ft | 268 kip-ft |
| 50 ft | 310 kip-ft | 206 kip-ft |
| 60 ft | 252 kip-ft | 168 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.
W18×106 load table by span
The largest uniform load a simply supported W18×106 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 0.106 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 9 ft | 73.6* | 49.0* | 112.6 | 168.8 |
| 11 ft | 57.0 | 37.9 | 61.7 | 92.5 |
| 13 ft | 40.8 | 27.2 | 37.4 | 56.0 |
| 15 ft | 30.7 | 20.4 | 24.3 | 36.5 |
| 17 ft | 23.9 | 15.9 | 16.7 | 25.1 |
| 19 ft | 19.1 | 12.7 | 12.0 | 17.9 |
| 21 ft | 15.6 | 10.4 | 8.86 | 13.3 |
| 23 ft | 13.0 | 8.68 | 6.74 | 10.1 |
| 25 ft | 11.0 | 7.35 | 5.25 | 7.88 |
| 27 ft | 9.47 | 6.30 | 4.17 | 6.25 |
| 29 ft | 8.20 | 5.46 | 3.36 | 5.05 |
| 31 ft | 7.18 | 4.78 | 2.75 | 4.13 |
| 33 ft | 6.34 | 4.22 | 2.28 | 3.43 |
| 35 ft | 5.63 | 3.75 | 1.91 | 2.87 |
| 37 ft | 5.04 | 3.35 | 1.62 | 2.43 |
| 39 ft | 4.54 | 3.02 | 1.38 | 2.08 |
| 41 ft | 4.10 | 2.73 | 1.19 | 1.79 |
| 43 ft | 3.73 | 2.48 | 1.03 | 1.55 |
| 45 ft | 3.41 | 2.27 | 0.90 | 1.35 |
| 47 ft | 3.12 | 2.08 | 0.79 | 1.19 |
- 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 29 ft span, a W18×106 carries a factored load of 8.20 kips per foot (LRFD) or an allowable load of 5.46 kips per foot (ASD). A live load of 3.36 kips per foot would deflect it span/360, which is 0.97 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.
W18×106 questions
What does W18×106 mean?
W means a wide flange shape. 18 is its nominal depth in inches (the actual depth is 18.7 in) and 106 is its weight in pounds per foot.
How much does a W18×106 weigh?
106 pounds per foot, so a 20 ft W18×106 weighs about 2,120 pounds.
How far can a W18×106 span?
It depends on the load. Braced along its length, it carries 73.6 kips per foot of factored load at 9 ft and 3.12 kips per foot at 47 ft; the load table has the spans in between. Floor beams are often 28 to 37 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W18×106 a compact section?
Yes. Its flanges (bf/2tf = 5.96) and web (h/tw = 27.2) are both compact for bending in 50 ksi steel.