Roof Beam Span Table

Loading: 40 psf total (20 dead + 20 live), tributary width 30 ft

Beam Max Span (ft) Governs Weight (lb/ft)
W12x19 22 Deflection 19
W12x22 24 Deflection 22
W14x22 25 Deflection 22
W14x26 27 Deflection 26
W16x26 29 Deflection 26
W16x31 31 Deflection 31
W18x35 34 Deflection 35
W18x40 36 Deflection 40
W21x44 39 Deflection 44
W21x50 41 Deflection 50
W24x55 44 Deflection 55
W24x62 46 Strength 62
W27x84 52 Strength 84

Composite Beam Span Table (With Shear Studs)

Composite beams (steel beam + concrete slab with shear studs) are 30-50% stronger than bare steel beams. Loading: 100 psf total, 30 ft tributary.

Beam Composite Span (ft) Bare Steel Span (ft) % Increase
W16x31 28 22 27%
W18x35 32 25 28%
W18x40 34 27 26%
W21x44 38 31 23%
W21x50 40 33 21%
W24x55 44 37 19%
W24x62 46 39 18%
W27x84 52 45 16%
W30x90 55 48 15%

Composite action provides the biggest benefit for smaller beams. As beams get deeper, the relative improvement decreases.

Typical Beam Selections by Application

Office Buildings

Span (ft) Typical Beam Depth (in) Loading Notes
20-25 W16x31 to W16x36 16 100 psf, 30 ft trib Floor framing
25-30 W18x40 to W18x50 18 100 psf, 30 ft trib Standard office bay
30-35 W21x50 to W21x62 21 100 psf, 30 ft trib Long-span office
35-40 W24x62 to W24x76 24 80-100 psf Open plan offices
40-50 W27x84 to W30x99 27-30 80 psf Atriums, large spaces

Industrial / Warehouse

Span (ft) Typical Beam Loading Notes
20-30 W18x35 to W18x50 150-250 psf Heavy storage
30-40 W24x55 to W24x76 100-150 psf Light manufacturing
40-50 W30x90 to W30x116 80-120 psf Warehouse, clear span
50-60 W33x118 to W36x150 60-100 psf Heavy industrial

Roof Purlins and Girts

Span (ft) Typical Beam Loading Notes
20-25 W12x16 to W12x22 30-40 psf Metal building roof
25-30 W14x22 to W14x26 30-40 psf Standard purlin
20-25 W8x10 to W10x12 20 psf Wall girt

Deflection Limits

Member Type Dead Load Live Load Total Load Source
Floor beams L/360 L/360 L/240 IBC Table 1604.3
Floor beams (sensitive) L/480 L/360 L/240 Strict criteria
Roof beams — L/360 L/240 IBC
Roof beams (LL only) — L/180 — Roof live load
Crane runway L/800 L/800 L/600 AISE criteria

Deflection is often the governing criterion for floor beams. A beam that satisfies strength may fail the L/360 live load deflection limit.

Quick Weight Estimates

For preliminary estimates, steel beam weight per square foot of floor area:

Span (ft) Bay Size Steel Weight (psf) Beam Depth
25 25 × 30 4-6 W16-W18
30 30 × 30 5-7 W18-W21
35 30 × 35 6-9 W21-W24
40 30 × 40 8-12 W24-W27
45 30 × 45 10-14 W27-W30

These weights are for beams only (not including columns, connections, or bracing). Total structural steel for a typical office building is 8-12 psf.

Frequently Asked Questions

How far can a W21x44 beam span? Under typical office loading (100 psf, 30 ft tributary), a W21x44 can span approximately 31 ft when fully laterally supported. With composite action (shear studs), the span increases to about 38 ft.

What is the longest span for a steel beam? Practically, W-shape beams span up to about 65-70 ft (W36x230 or larger). Beyond 65 ft, trusses, plate girders, or built-up sections become more economical. For spans over 100 ft, space frames or cable-stayed systems are used.

What governs beam span: strength or deflection? For typical floor beams, deflection (L/360 live load) often governs. Deeper beams (W21, W24) are more efficient for deflection control because moment of inertia increases with the cube of depth. Strength may govern for heavily loaded or short-span beams.

How does composite action increase span? Shear studs connect the concrete slab to the steel beam, creating a composite section. The slab acts as additional compression flange area, increasing the effective moment of inertia by 30-50%. This allows either longer spans for the same beam size or smaller beams for the same span.

Try it now: Check your beam span with our free Beam Span calculator →

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Disclaimer

This is a calculation tool, not a substitute for professional engineering certification. All results must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in construction, fabrication, or permit documents. The user is responsible for the accuracy of all inputs and the verification of all outputs.

Beam Design Methods

Lateral-Torsional Buckling

For beams that are not adequately braced against lateral movement and twist, the nominal moment capacity is governed by lateral-torsional buckling (LTB). The resistance depends on the unbraced length (Lb) relative to limit states:

Shear Design

Web shear strength depends on the panel aspect ratio and stiffener configuration. For unstiffened webs, the nominal shear capacity is:

Compact sections with low web slenderness (h/tw) can develop full shear yielding. Slender webs may require transverse stiffeners to develop adequate shear capacity.

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Frequently Asked Questions

What is the recommended design procedure for this structural element?

The standard design procedure follows: (1) establish design criteria including applicable code, material grade, and loading; (2) determine loads and applicable load combinations; (3) analyze the structure for internal forces; (4) check member strength for all applicable limit states; (5) verify serviceability requirements; and (6) detail connections. Computer analysis is recommended for complex structures, but hand calculations should be used for verification of critical elements.

How do different design codes compare for this calculation?

AISC 360 (US), EN 1993 (Eurocode), AS 4100 (Australia), and CSA S16 (Canada) follow similar limit states design philosophy but differ in specific resistance factors, slenderness limits, and partial safety factors. Generally, EN 1993 uses partial factors on both load and resistance sides (γM0 = 1.0, γM1 = 1.0, γM2 = 1.25), while AISC 360 uses a single resistance factor (φ). Engineers should verify which code is adopted in their jurisdiction.

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