W33×318 Steel Beam
A W33×318 is a wide flange steel beam 35.2 inches deep with 16-inch flanges, weighing 318 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 4,763 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 1,098 kips.
Design a W33×318 beam Opens a 54 ft span in the free beam designer.
W33×318 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 35.2 in |
| Flange width, bf | 16.0 in |
| Flange thickness, tf | 1.89 in |
| Web thickness, tw | 1.04 in |
| Distance to web toe of fillet, kdes | 2.68 in |
| Distance between flange centroids, ho | 33.31 in |
| Cross-sectional area, A | 93.6 in2 |
| Weight | 318 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W33×318 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 19500 in4 | 1290 in4 |
| Elastic section modulus, S | 1110 in3 | 161 in3 |
| Plastic section modulus, Z | 1270 in3 | 250 in3 |
| Radius of gyration, r | 14.5 in | 3.71 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 84.4 in4 |
| Warping constant, Cw | 357000 in6 |
| Effective radius of gyration, rts | 4.40 in |
| Flange slenderness, bf/2tf | 4.23 |
| Web slenderness, h/tw | 28.7 |
W33×318 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 = 4,763 kip-ft | Mn/Ω = 3,169 kip-ft |
| Shear | φVn = 1,098 kips | Vn/Ω = 732 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 13.1 ft between braces it keeps its full strength; past Lr = 46.5 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 4,763 kip-ft | 3,169 kip-ft |
| 10 ft | 4,763 kip-ft | 3,169 kip-ft |
| 13.1 ft (Lp) | 4,763 kip-ft | 3,169 kip-ft |
| 20 ft | 4,381 kip-ft | 2,915 kip-ft |
| 30 ft | 3,827 kip-ft | 2,546 kip-ft |
| 40 ft | 3,273 kip-ft | 2,177 kip-ft |
| 46.5 ft (Lr) | 2,911 kip-ft | 1,937 kip-ft |
| 50 ft | 2,658 kip-ft | 1,769 kip-ft |
| 60 ft | 2,135 kip-ft | 1,421 kip-ft |
| 70 ft | 1,788 kip-ft | 1,189 kip-ft |
| 80 ft | 1,540 kip-ft | 1,024 kip-ft |
| 90 ft | 1,353 kip-ft | 900 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.
W33×318 load table by span
The largest uniform load a simply supported W33×318 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 0.318 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 18 ft | 117.6 | 78.2 | 143.7 | 215.5 |
| 20 ft | 95.3 | 63.4 | 104.7 | 157.1 |
| 22 ft | 78.7 | 52.4 | 78.7 | 118.0 |
| 24 ft | 66.1 | 44.0 | 60.6 | 90.9 |
| 26 ft | 56.4 | 37.5 | 47.7 | 71.5 |
| 28 ft | 48.6 | 32.3 | 38.2 | 57.2 |
| 30 ft | 42.3 | 28.2 | 31.0 | 46.5 |
| 32 ft | 37.2 | 24.8 | 25.6 | 38.4 |
| 34 ft | 33.0 | 21.9 | 21.3 | 32.0 |
| 36 ft | 29.4 | 19.6 | 18.0 | 26.9 |
| 38 ft | 26.4 | 17.6 | 15.3 | 22.9 |
| 40 ft | 23.8 | 15.8 | 13.1 | 19.6 |
| 42 ft | 21.6 | 14.4 | 11.3 | 17.0 |
| 44 ft | 19.7 | 13.1 | 9.83 | 14.8 |
| 46 ft | 18.0 | 12.0 | 8.61 | 12.9 |
| 48 ft | 16.5 | 11.0 | 7.58 | 11.4 |
| 50 ft | 15.2 | 10.1 | 6.70 | 10.1 |
| 52 ft | 14.1 | 9.37 | 5.96 | 8.94 |
| 54 ft | 13.1 | 8.69 | 5.32 | 7.98 |
| 56 ft | 12.1 | 8.08 | 4.77 | 7.16 |
| 58 ft | 11.3 | 7.54 | 4.29 | 6.44 |
| 60 ft | 10.6 | 7.04 | 3.88 | 5.82 |
| 62 ft | 9.91 | 6.59 | 3.52 | 5.27 |
| 64 ft | 9.30 | 6.19 | 3.20 | 4.79 |
| 66 ft | 8.75 | 5.82 | 2.91 | 4.37 |
| 68 ft | 8.24 | 5.48 | 2.66 | 4.00 |
| 70 ft | 7.78 | 5.17 | 2.44 | 3.66 |
| 72 ft | 7.35 | 4.89 | 2.24 | 3.37 |
| 74 ft | 6.96 | 4.63 | 2.07 | 3.10 |
| 76 ft | 6.60 | 4.39 | 1.91 | 2.86 |
| 78 ft | 6.26 | 4.17 | 1.77 | 2.65 |
| 80 ft | 5.95 | 3.96 | 1.64 | 2.45 |
| 82 ft | 5.67 | 3.77 | 1.52 | 2.28 |
| 84 ft | 5.40 | 3.59 | 1.41 | 2.12 |
| 86 ft | 5.15 | 3.43 | 1.32 | 1.98 |
| 88 ft | 4.92 | 3.27 | 1.23 | 1.84 |
- 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 54 ft span, a W33×318 carries a factored load of 13.1 kips per foot (LRFD) or an allowable load of 8.69 kips per foot (ASD). A live load of 5.32 kips per foot would deflect it span/360, which is 1.80 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.
W33×318 questions
What does W33×318 mean?
W means a wide flange shape. 33 is its nominal depth in inches (the actual depth is 35.2 in) and 318 is its weight in pounds per foot.
How much does a W33×318 weigh?
318 pounds per foot, so a 20 ft W33×318 weighs about 6,360 pounds.
How far can a W33×318 span?
It depends on the load. Braced along its length, it carries 117.6 kips per foot of factored load at 18 ft and 4.92 kips per foot at 88 ft; the load table has the spans in between. Floor beams are often 53 to 70 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W33×318 a compact section?
Yes. Its flanges (bf/2tf = 4.23) and web (h/tw = 28.7) are both compact for bending in 50 ksi steel.