W18×158 Steel Beam
A W18×158 is a wide flange steel beam 19.7 inches deep with 11.3-inch flanges, weighing 158 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 1,335 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 479 kips.
Design a W18×158 beam Opens a 30 ft span in the free beam designer.
W18×158 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 19.7 in |
| Flange width, bf | 11.3 in |
| Flange thickness, tf | 1.44 in |
| Web thickness, tw | 0.810 in |
| Distance to web toe of fillet, kdes | 1.84 in |
| Distance between flange centroids, ho | 18.26 in |
| Cross-sectional area, A | 46.3 in2 |
| Weight | 158 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W18×158 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 3060 in4 | 347 in4 |
| Elastic section modulus, S | 310 in3 | 61.4 in3 |
| Plastic section modulus, Z | 356 in3 | 94.8 in3 |
| Radius of gyration, r | 8.12 in | 2.74 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 25.2 in4 |
| Warping constant, Cw | 29000 in6 |
| Effective radius of gyration, rts | 3.20 in |
| Flange slenderness, bf/2tf | 3.92 |
| Web slenderness, h/tw | 19.8 |
W18×158 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 = 1,335 kip-ft | Mn/Ω = 888 kip-ft |
| Shear | φVn = 479 kips | Vn/Ω = 319 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 = 42.9 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 1,335 kip-ft | 888 kip-ft |
| 9.7 ft (Lp) | 1,335 kip-ft | 888 kip-ft |
| 10 ft | 1,330 kip-ft | 885 kip-ft |
| 20 ft | 1,173 kip-ft | 780 kip-ft |
| 30 ft | 1,016 kip-ft | 676 kip-ft |
| 40 ft | 859 kip-ft | 571 kip-ft |
| 42.9 ft (Lr) | 814 kip-ft | 541 kip-ft |
| 50 ft | 688 kip-ft | 458 kip-ft |
| 60 ft | 566 kip-ft | 377 kip-ft |
| 70 ft | 482 kip-ft | 321 kip-ft |
| 80 ft | 420 kip-ft | 279 kip-ft |
| 90 ft | 372 kip-ft | 247 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.
W18×158 load table by span
The largest uniform load a simply supported W18×158 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 0.158 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 10 ft | 95.7* | 63.8* | 131.5 | 197.2 |
| 12 ft | 74.2 | 49.3 | 76.1 | 114.1 |
| 14 ft | 54.5 | 36.3 | 47.9 | 71.9 |
| 16 ft | 41.7 | 27.8 | 32.1 | 48.1 |
| 18 ft | 33.0 | 21.9 | 22.5 | 33.8 |
| 20 ft | 26.7 | 17.8 | 16.4 | 24.7 |
| 22 ft | 22.1 | 14.7 | 12.3 | 18.5 |
| 24 ft | 18.5 | 12.3 | 9.51 | 14.3 |
| 26 ft | 15.8 | 10.5 | 7.48 | 11.2 |
| 28 ft | 13.6 | 9.06 | 5.99 | 8.98 |
| 30 ft | 11.9 | 7.90 | 4.87 | 7.30 |
| 32 ft | 10.4 | 6.94 | 4.01 | 6.02 |
| 34 ft | 9.24 | 6.15 | 3.34 | 5.02 |
| 36 ft | 8.24 | 5.48 | 2.82 | 4.23 |
| 38 ft | 7.40 | 4.92 | 2.40 | 3.59 |
| 40 ft | 6.68 | 4.44 | 2.05 | 3.08 |
| 42 ft | 6.05 | 4.03 | 1.77 | 2.66 |
| 44 ft | 5.52 | 3.67 | 1.54 | 2.31 |
| 46 ft | 5.05 | 3.36 | 1.35 | 2.03 |
| 48 ft | 4.64 | 3.08 | 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 W18×158 carries a factored load of 11.9 kips per foot (LRFD) or an allowable load of 7.90 kips per foot (ASD). A live load of 4.87 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.
W18×158 questions
What does W18×158 mean?
W means a wide flange shape. 18 is its nominal depth in inches (the actual depth is 19.7 in) and 158 is its weight in pounds per foot.
How much does a W18×158 weigh?
158 pounds per foot, so a 20 ft W18×158 weighs about 3,160 pounds.
How far can a W18×158 span?
It depends on the load. Braced along its length, it carries 95.7 kips per foot of factored load at 10 ft and 4.64 kips per foot at 48 ft; the load table has the spans in between. Floor beams are often 30 to 39 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W18×158 a compact section?
Yes. Its flanges (bf/2tf = 3.92) and web (h/tw = 19.8) are both compact for bending in 50 ksi steel.