W18×258 Steel Beam
A W18×258 is a wide flange steel beam 21.5 inches deep with 11.8-inch flanges, weighing 258 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 2,291 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 826 kips.
Design a W18×258 beam Opens a 33 ft span in the free beam designer.
W18×258 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 21.5 in |
| Flange width, bf | 11.8 in |
| Flange thickness, tf | 2.30 in |
| Web thickness, tw | 1.28 in |
| Distance to web toe of fillet, kdes | 2.70 in |
| Distance between flange centroids, ho | 19.20 in |
| Cross-sectional area, A | 75.9 in2 |
| Weight | 258 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W18×258 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 5510 in4 | 628 in4 |
| Elastic section modulus, S | 514 in3 | 107 in3 |
| Plastic section modulus, Z | 611 in3 | 166 in3 |
| Radius of gyration, r | 8.53 in | 2.88 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 103 in4 |
| Warping constant, Cw | 57600 in6 |
| Effective radius of gyration, rts | 3.42 in |
| Flange slenderness, bf/2tf | 2.56 |
| Web slenderness, h/tw | 12.5 |
W18×258 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 = 2,291 kip-ft | Mn/Ω = 1,524 kip-ft |
| Shear | φVn = 826 kips | Vn/Ω = 550 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 10.2 ft between braces it keeps its full strength; past Lr = 67.3 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 2,291 kip-ft | 1,524 kip-ft |
| 10 ft | 2,291 kip-ft | 1,524 kip-ft |
| 10.2 ft (Lp) | 2,291 kip-ft | 1,524 kip-ft |
| 20 ft | 2,129 kip-ft | 1,417 kip-ft |
| 30 ft | 1,964 kip-ft | 1,307 kip-ft |
| 40 ft | 1,799 kip-ft | 1,197 kip-ft |
| 50 ft | 1,634 kip-ft | 1,087 kip-ft |
| 60 ft | 1,469 kip-ft | 978 kip-ft |
| 67.3 ft (Lr) | 1,349 kip-ft | 898 kip-ft |
| 70 ft | 1,295 kip-ft | 862 kip-ft |
| 80 ft | 1,130 kip-ft | 752 kip-ft |
| 90 ft | 1,003 kip-ft | 667 kip-ft |
| 100 ft | 902 kip-ft | 600 kip-ft |
| 110 ft | 819 kip-ft | 545 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.
W18×258 load table by span
The largest uniform load a simply supported W18×258 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 0.258 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 11 ft | 150.1* | 100.1* | 177.9 | 266.8 |
| 13 ft | 108.5 | 72.2 | 107.7 | 161.6 |
| 15 ft | 81.5 | 54.2 | 70.1 | 105.2 |
| 17 ft | 63.4 | 42.2 | 48.2 | 72.3 |
| 19 ft | 50.8 | 33.8 | 34.5 | 51.8 |
| 21 ft | 41.6 | 27.7 | 25.6 | 38.3 |
| 23 ft | 34.7 | 23.1 | 19.5 | 29.2 |
| 25 ft | 29.3 | 19.5 | 15.2 | 22.7 |
| 27 ft | 25.1 | 16.7 | 12.0 | 18.0 |
| 29 ft | 21.8 | 14.5 | 9.71 | 14.6 |
| 31 ft | 19.1 | 12.7 | 7.95 | 11.9 |
| 33 ft | 16.8 | 11.2 | 6.59 | 9.88 |
| 35 ft | 15.0 | 9.96 | 5.52 | 8.28 |
| 37 ft | 13.4 | 8.91 | 4.67 | 7.01 |
| 39 ft | 12.1 | 8.02 | 3.99 | 5.99 |
| 41 ft | 10.9 | 7.25 | 3.43 | 5.15 |
| 43 ft | 9.91 | 6.60 | 2.98 | 4.47 |
| 45 ft | 9.05 | 6.02 | 2.60 | 3.90 |
| 47 ft | 8.30 | 5.52 | 2.28 | 3.42 |
| 49 ft | 7.63 | 5.08 | 2.01 | 3.02 |
| 51 ft | 7.05 | 4.69 | 1.78 | 2.68 |
| 53 ft | 6.53 | 4.34 | 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 W18×258 carries a factored load of 16.8 kips per foot (LRFD) or an allowable load of 11.2 kips per foot (ASD). A live load of 6.59 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.
W18×258 questions
What does W18×258 mean?
W means a wide flange shape. 18 is its nominal depth in inches (the actual depth is 21.5 in) and 258 is its weight in pounds per foot.
How much does a W18×258 weigh?
258 pounds per foot, so a 20 ft W18×258 weighs about 5,160 pounds.
How far can a W18×258 span?
It depends on the load. Braced along its length, it carries 150.1 kips per foot of factored load at 11 ft and 6.53 kips per foot at 53 ft; the load table has the spans in between. Floor beams are often 32 to 43 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W18×258 a compact section?
Yes. Its flanges (bf/2tf = 2.56) and web (h/tw = 12.5) are both compact for bending in 50 ksi steel.