W30×391 Steel Beam
A W30×391 is a wide flange steel beam 33.2 inches deep with 15.6-inch flanges, weighing 391 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 5,438 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 1,355 kips.
Design a W30×391 beam Opens a 51 ft span in the free beam designer.
W30×391 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 33.2 in |
| Flange width, bf | 15.6 in |
| Flange thickness, tf | 2.44 in |
| Web thickness, tw | 1.36 in |
| Distance to web toe of fillet, kdes | 3.23 in |
| Distance between flange centroids, ho | 30.76 in |
| Cross-sectional area, A | 115 in2 |
| Weight | 391 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W30×391 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 20700 in4 | 1550 in4 |
| Elastic section modulus, S | 1250 in3 | 198 in3 |
| Plastic section modulus, Z | 1450 in3 | 310 in3 |
| Radius of gyration, r | 13.4 in | 3.67 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 173 in4 |
| Warping constant, Cw | 366000 in6 |
| Effective radius of gyration, rts | 4.37 in |
| Flange slenderness, bf/2tf | 3.19 |
| Web slenderness, h/tw | 19.7 |
W30×391 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 = 5,438 kip-ft | Mn/Ω = 3,618 kip-ft |
| Shear | φVn = 1,355 kips | Vn/Ω = 903 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 13.0 ft between braces it keeps its full strength; past Lr = 58.7 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 5,438 kip-ft | 3,618 kip-ft |
| 10 ft | 5,438 kip-ft | 3,618 kip-ft |
| 13.0 ft (Lp) | 5,438 kip-ft | 3,618 kip-ft |
| 20 ft | 5,106 kip-ft | 3,397 kip-ft |
| 30 ft | 4,635 kip-ft | 3,084 kip-ft |
| 40 ft | 4,164 kip-ft | 2,770 kip-ft |
| 50 ft | 3,693 kip-ft | 2,457 kip-ft |
| 58.7 ft (Lr) | 3,279 kip-ft | 2,182 kip-ft |
| 60 ft | 3,203 kip-ft | 2,131 kip-ft |
| 70 ft | 2,711 kip-ft | 1,804 kip-ft |
| 80 ft | 2,352 kip-ft | 1,565 kip-ft |
| 90 ft | 2,078 kip-ft | 1,383 kip-ft |
| 100 ft | 1,863 kip-ft | 1,239 kip-ft |
| 110 ft | 1,688 kip-ft | 1,123 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.
W30×391 load table by span
The largest uniform load a simply supported W30×391 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 0.391 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 17 ft | 150.5 | 100.1 | 181.0 | 271.5 |
| 19 ft | 120.5 | 80.2 | 129.7 | 194.5 |
| 21 ft | 98.6 | 65.6 | 96.0 | 144.0 |
| 23 ft | 82.2 | 54.7 | 73.1 | 109.6 |
| 25 ft | 69.6 | 46.3 | 56.9 | 85.4 |
| 27 ft | 59.7 | 39.7 | 45.2 | 67.8 |
| 29 ft | 51.7 | 34.4 | 36.5 | 54.7 |
| 31 ft | 45.3 | 30.1 | 29.9 | 44.8 |
| 33 ft | 39.9 | 26.6 | 24.7 | 37.1 |
| 35 ft | 35.5 | 23.6 | 20.7 | 31.1 |
| 37 ft | 31.8 | 21.1 | 17.6 | 26.3 |
| 39 ft | 28.6 | 19.0 | 15.0 | 22.5 |
| 41 ft | 25.9 | 17.2 | 12.9 | 19.4 |
| 43 ft | 23.5 | 15.7 | 11.2 | 16.8 |
| 45 ft | 21.5 | 14.3 | 9.76 | 14.6 |
| 47 ft | 19.7 | 13.1 | 8.57 | 12.8 |
| 49 ft | 18.1 | 12.1 | 7.56 | 11.3 |
| 51 ft | 16.7 | 11.1 | 6.70 | 10.1 |
| 53 ft | 15.5 | 10.3 | 5.97 | 8.96 |
| 55 ft | 14.4 | 9.57 | 5.35 | 8.02 |
| 57 ft | 13.4 | 8.91 | 4.80 | 7.20 |
| 59 ft | 12.5 | 8.31 | 4.33 | 6.50 |
| 61 ft | 11.7 | 7.78 | 3.92 | 5.88 |
| 63 ft | 11.0 | 7.29 | 3.56 | 5.33 |
| 65 ft | 10.3 | 6.85 | 3.24 | 4.86 |
| 67 ft | 9.69 | 6.45 | 2.96 | 4.44 |
| 69 ft | 9.14 | 6.08 | 2.71 | 4.06 |
| 71 ft | 8.63 | 5.74 | 2.48 | 3.73 |
| 73 ft | 8.16 | 5.43 | 2.29 | 3.43 |
| 75 ft | 7.73 | 5.15 | 2.11 | 3.16 |
| 77 ft | 7.34 | 4.88 | 1.95 | 2.92 |
| 79 ft | 6.97 | 4.64 | 1.80 | 2.71 |
| 81 ft | 6.63 | 4.41 | 1.67 | 2.51 |
| 83 ft | 6.31 | 4.20 | 1.56 | 2.33 |
- 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 51 ft span, a W30×391 carries a factored load of 16.7 kips per foot (LRFD) or an allowable load of 11.1 kips per foot (ASD). A live load of 6.70 kips per foot would deflect it span/360, which is 1.70 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.
W30×391 questions
What does W30×391 mean?
W means a wide flange shape. 30 is its nominal depth in inches (the actual depth is 33.2 in) and 391 is its weight in pounds per foot.
How much does a W30×391 weigh?
391 pounds per foot, so a 20 ft W30×391 weighs about 7,820 pounds.
How far can a W30×391 span?
It depends on the load. Braced along its length, it carries 150.5 kips per foot of factored load at 17 ft and 6.31 kips per foot at 83 ft; the load table has the spans in between. Floor beams are often 50 to 66 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W30×391 a compact section?
Yes. Its flanges (bf/2tf = 3.19) and web (h/tw = 19.7) are both compact for bending in 50 ksi steel.