W18×86 Steel Beam
A W18×86 is a wide flange steel beam 18.4 inches deep with 11.1-inch flanges, weighing 86 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 698 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 265 kips.
Design a W18×86 beam Opens a 27 ft span in the free beam designer.
W18×86 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 18.4 in |
| Flange width, bf | 11.1 in |
| Flange thickness, tf | 0.770 in |
| Web thickness, tw | 0.480 in |
| Distance to web toe of fillet, kdes | 1.17 in |
| Distance between flange centroids, ho | 17.63 in |
| Cross-sectional area, A | 25.3 in2 |
| Weight | 86 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W18×86 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 1530 in4 | 175 in4 |
| Elastic section modulus, S | 166 in3 | 31.6 in3 |
| Plastic section modulus, Z | 186 in3 | 48.4 in3 |
| Radius of gyration, r | 7.77 in | 2.63 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 4.10 in4 |
| Warping constant, Cw | 13600 in6 |
| Effective radius of gyration, rts | 3.05 in |
| Flange slenderness, bf/2tf | 7.20 |
| Web slenderness, h/tw | 33.4 |
W18×86 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 = 698 kip-ft | Mn/Ω = 464 kip-ft |
| Shear | φVn = 265 kips | Vn/Ω = 177 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 9.3 ft between braces it keeps its full strength; past Lr = 28.5 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 698 kip-ft | 464 kip-ft |
| 5 ft | 698 kip-ft | 464 kip-ft |
| 9.3 ft (Lp) | 697 kip-ft | 464 kip-ft |
| 10 ft | 688 kip-ft | 458 kip-ft |
| 15 ft | 620 kip-ft | 412 kip-ft |
| 20 ft | 552 kip-ft | 367 kip-ft |
| 25 ft | 484 kip-ft | 322 kip-ft |
| 28.6 ft (Lr) | 435 kip-ft | 290 kip-ft |
| 30 ft | 406 kip-ft | 270 kip-ft |
| 35 ft | 329 kip-ft | 219 kip-ft |
| 40 ft | 277 kip-ft | 184 kip-ft |
| 45 ft | 239 kip-ft | 159 kip-ft |
| 50 ft | 210 kip-ft | 140 kip-ft |
| 55 ft | 188 kip-ft | 125 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.
W18×86 load table by span
The largest uniform load a simply supported W18×86 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 0.086 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 9 ft | 58.9* | 39.3* | 90.2 | 135.3 |
| 11 ft | 46.1 | 30.7 | 49.4 | 74.1 |
| 13 ft | 33.0 | 22.0 | 29.9 | 44.9 |
| 15 ft | 24.8 | 16.5 | 19.5 | 29.2 |
| 17 ft | 19.3 | 12.8 | 13.4 | 20.1 |
| 19 ft | 15.5 | 10.3 | 9.58 | 14.4 |
| 21 ft | 12.7 | 8.42 | 7.10 | 10.6 |
| 23 ft | 10.5 | 7.02 | 5.40 | 8.10 |
| 25 ft | 8.93 | 5.94 | 4.21 | 6.31 |
| 27 ft | 7.65 | 5.09 | 3.34 | 5.01 |
| 29 ft | 6.63 | 4.41 | 2.70 | 4.04 |
| 31 ft | 5.81 | 3.86 | 2.21 | 3.31 |
| 33 ft | 5.12 | 3.41 | 1.83 | 2.74 |
| 35 ft | 4.56 | 3.03 | 1.53 | 2.30 |
| 37 ft | 4.08 | 2.71 | 1.30 | 1.95 |
| 39 ft | 3.67 | 2.44 | 1.11 | 1.66 |
| 41 ft | 3.32 | 2.21 | 0.95 | 1.43 |
| 43 ft | 3.02 | 2.01 | 0.83 | 1.24 |
| 45 ft | 2.76 | 1.83 | 0.72 | 1.08 |
- 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 27 ft span, a W18×86 carries a factored load of 7.65 kips per foot (LRFD) or an allowable load of 5.09 kips per foot (ASD). A live load of 3.34 kips per foot would deflect it span/360, which is 0.90 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.
W18×86 questions
What does W18×86 mean?
W means a wide flange shape. 18 is its nominal depth in inches (the actual depth is 18.4 in) and 86 is its weight in pounds per foot.
How much does a W18×86 weigh?
86 pounds per foot, so a 20 ft W18×86 weighs about 1,720 pounds.
How far can a W18×86 span?
It depends on the load. Braced along its length, it carries 58.9 kips per foot of factored load at 9 ft and 2.76 kips per foot at 45 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 W18×86 a compact section?
Yes. Its flanges (bf/2tf = 7.20) and web (h/tw = 33.4) are both compact for bending in 50 ksi steel.