W18×143 Steel Beam
A W18×143 is a wide flange steel beam 19.5 inches deep with 11.2-inch flanges, weighing 143 pounds per foot. In ASTM A992 steel (Fy = 50 ksi) it has a design bending strength of 1,208 kip-ft (LRFD) when its compression flange is braced, and a design shear strength of 427 kips.
Design a W18×143 beam Opens a 30 ft span in the free beam designer.
W18×143 dimensions
| Dimension | Value |
|---|---|
| Depth, d | 19.5 in |
| Flange width, bf | 11.2 in |
| Flange thickness, tf | 1.32 in |
| Web thickness, tw | 0.730 in |
| Distance to web toe of fillet, kdes | 1.72 in |
| Distance between flange centroids, ho | 18.18 in |
| Cross-sectional area, A | 42.1 in2 |
| Weight | 143 lb/ft |
Dimensions are AISC design values. Detailing dimensions are rounded to the nearest 1/16 in.
W18×143 section properties
| Property | Strong axis (x) | Weak axis (y) |
|---|---|---|
| Moment of inertia, I | 2750 in4 | 311 in4 |
| Elastic section modulus, S | 282 in3 | 55.5 in3 |
| Plastic section modulus, Z | 322 in3 | 85.4 in3 |
| Radius of gyration, r | 8.09 in | 2.72 in |
| Torsion and slenderness | Value |
|---|---|
| Torsional constant, J | 19.2 in4 |
| Warping constant, Cw | 25700 in6 |
| Effective radius of gyration, rts | 3.17 in |
| Flange slenderness, bf/2tf | 4.25 |
| Web slenderness, h/tw | 22.0 |
W18×143 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 = 1,208 kip-ft | Mn/Ω = 803 kip-ft |
| Shear | φVn = 427 kips | Vn/Ω = 285 kips |
If the compression flange isn't braced, the beam can buckle sideways before it yields. Up to Lp = 9.6 ft between braces it keeps its full strength; past Lr = 39.6 ft it buckles elastically. With uniform moment between braces (Cb = 1.0):
| Unbraced length, Lb | φMn (LRFD) | Mn/Ω (ASD) |
|---|---|---|
| Braced | 1,208 kip-ft | 803 kip-ft |
| 9.6 ft (Lp) | 1,207 kip-ft | 803 kip-ft |
| 10 ft | 1,201 kip-ft | 799 kip-ft |
| 20 ft | 1,046 kip-ft | 696 kip-ft |
| 30 ft | 890 kip-ft | 592 kip-ft |
| 39.6 ft (Lr) | 740 kip-ft | 492 kip-ft |
| 40 ft | 732 kip-ft | 487 kip-ft |
| 50 ft | 571 kip-ft | 380 kip-ft |
| 60 ft | 470 kip-ft | 313 kip-ft |
| 70 ft | 399 kip-ft | 266 kip-ft |
| 80 ft | 348 kip-ft | 231 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.
W18×143 load table by span
The largest uniform load a simply supported W18×143 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 0.143 kips per foot.
| Span | Factored load (LRFD) | Allowable load (ASD) | Load at span/360 | Load at span/240 |
|---|---|---|---|---|
| 10 ft | 85.4* | 56.9* | 118.1 | 177.2 |
| 12 ft | 67.1 | 44.6 | 68.4 | 102.6 |
| 14 ft | 49.3 | 32.8 | 43.1 | 64.6 |
| 16 ft | 37.7 | 25.1 | 28.8 | 43.3 |
| 18 ft | 29.8 | 19.8 | 20.3 | 30.4 |
| 20 ft | 24.2 | 16.1 | 14.8 | 22.2 |
| 22 ft | 20.0 | 13.3 | 11.1 | 16.6 |
| 24 ft | 16.8 | 11.2 | 8.55 | 12.8 |
| 26 ft | 14.3 | 9.51 | 6.72 | 10.1 |
| 28 ft | 12.3 | 8.20 | 5.38 | 8.07 |
| 30 ft | 10.7 | 7.14 | 4.38 | 6.56 |
| 32 ft | 9.43 | 6.28 | 3.61 | 5.41 |
| 34 ft | 8.36 | 5.56 | 3.01 | 4.51 |
| 36 ft | 7.45 | 4.96 | 2.53 | 3.80 |
| 38 ft | 6.69 | 4.45 | 2.15 | 3.23 |
| 40 ft | 6.04 | 4.02 | 1.85 | 2.77 |
| 42 ft | 5.48 | 3.64 | 1.59 | 2.39 |
| 44 ft | 4.99 | 3.32 | 1.39 | 2.08 |
| 46 ft | 4.57 | 3.04 | 1.21 | 1.82 |
| 48 ft | 4.19 | 2.79 | 1.07 | 1.60 |
- 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 W18×143 carries a factored load of 10.7 kips per foot (LRFD) or an allowable load of 7.14 kips per foot (ASD). A live load of 4.38 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.
W18×143 questions
What does W18×143 mean?
W means a wide flange shape. 18 is its nominal depth in inches (the actual depth is 19.5 in) and 143 is its weight in pounds per foot.
How much does a W18×143 weigh?
143 pounds per foot, so a 20 ft W18×143 weighs about 2,860 pounds.
How far can a W18×143 span?
It depends on the load. Braced along its length, it carries 85.4 kips per foot of factored load at 10 ft and 4.19 kips per foot at 48 ft; the load table has the spans in between. Floor beams are often 29 to 39 ft for this depth (span-to-depth ratios of about 18 to 24), where deflection usually governs.
Is a W18×143 a compact section?
Yes. Its flanges (bf/2tf = 4.25) and web (h/tw = 22.0) are both compact for bending in 50 ksi steel.