---------------------------- | --------------------- | --------- | | Vertical impact (cab operated) | 1.25 | AISC DG7 | | Vertical impact (pendant operated) | 1.10 | AISC DG7 | | Lateral force (monorail) | 20% of load | AISC DG7 | | Lateral force (cab operated) | 10% of load | AS 1418 | | Longitudinal braking | 10% of max wheel load | AISC DG7 |

Fatigue Considerations

Crane runway beams are fatigue-critical. The number of loading cycles determines the fatigue category:

Fatigue must be checked at:

• Web-to-flange welds
• Bracket and connection details
• Rail contact surface
• Cope and re-entrant corners

Design Procedure

Step 1: Determine Factored Loads

Apply load combinations per ASCE 7 / AS/NZS 1170:

LRFD (AISC): 1.2D + 1.6(L_crane + impact)

AS 4100: 1.2G + 1.5Q_crane × impact_factor

Step 2: Select Trial Section

Typical runway beam sections:

Alternatively, US W-shapes:

Step 3: Bending Capacity Check

Strong axis (vertical):

φMnx = φ × Fy × Sx (elastic, for unbraced length > Lr) φMnx = φ × Fy × Zx (plastic, for compact sections with Lb ≤ Lp)

Weak axis (lateral):

The lateral load from the crane creates weak-axis bending. For a W-shape runway beam:

φMny = φ × Fy × Zy ≤ 1.6 × Fy × Sy

Combined check:

(Mux / φMnx) + (Muy / φMny) ≤ 1.0

Step 4: Shear Check

Check web shear capacity at supports and near wheel load points:

φVn = φ × 0.6 × Fy × Aw (for stocky webs)

where Aw = d × tw.

For slender webs, use the web shear buckling capacity per AISC Chapter G or AS 4100 Clause 5.11.

Step 5: Lateral-Torsional Buckling

Crane runway beams are vulnerable to LTB because the top flange is loaded laterally by the crane and may not be continuously braced.

Critical parameters:

• Lb: unbraced length of compression flange (between lateral braces)
• Lp: limiting laterally unbraced length for full plastic moment
• Lr: limiting laterally unbraced length for inelastic LTB

LTB capacity per AISC Chapter F:

• If Lb ≤ Lp: φMn = φFyZx
• If Lp < Lb ≤ Lr: φMn = Cb[1 - (Lb-Lp)/(Lr-Lp) × (1 - 0.7FySx/φMn)] × φFySx (simplified)
• If Lb > Lr: elastic LTB governs

The Cb factor (moment gradient modifier) helps for non-uniform moment diagrams. For crane loads, Cb is typically 1.0 to 1.3.

Step 6: Web Crippling and Yielding

Concentrated wheel loads can cripple the web. Check per AISC Chapter J10:

Web local yielding: Rn = Fyw × tw × (5k + N)

Web local crippling: Rn = 0.8 × t²w × √(E × Fyw / tw) × [1 + 3(N/d) × (tw/tf)^1.5] (for interior loads)

where:

• k = distance from outer face of flange to web toe of fillet
• N = bearing length (crane rail width)
• tf = flange thickness

If web crippling capacity is insufficient, add transverse stiffeners at wheel load locations.

Step 7: Deflection Check

Crane runway beams have strict deflection limits:

Vertical deflection for simply supported beam under wheel loads:

Use influence line analysis or superposition for moving point loads.

For a single wheel load P at midspan of span L:

Δ = PL³ / (48EI)

For two equal wheel loads at spacing s:

Δ = P × a² × (3L - 4a) / (6EI)

where a = (L - s) / 2 is the distance from support to the nearer wheel.

Step 8: Fatigue Check

Check fatigue at all stress concentrations using AISC Appendix 3 or AS 4100 Section 11.

Fatigue life per AISC:

The nominal stress range must not exceed the threshold stress range for the applicable fatigue category:

Design stress range: Δσ = σ_max - σ_min at the detail

Required: Δσ ≤ Δσ_threshold (for infinite life at N > 2×10⁶ cycles)

Rail-to-Beam Connection

The crane rail is attached to the top flange of the runway beam. Common methods:

1. Direct welding: Rail welded to flange. High fatigue category (E or E'). Not recommended for heavy cranes.
2. Bolted clips: Rail held by bolted clamp plates. Allows thermal movement. Most common for medium cranes.
3. Hook bolts: J-bolts hook over the rail flange. Simple but limited lateral capacity.
4. Punched rail: Rail has pre-drilled holes for direct bolting. Best for heavy cranes.

Rail pad (resilient layer between rail and beam) reduces impact and noise.

Frequently Asked Questions

What is the deflection limit for crane runway beams? AISC Design Guide 7 recommends L/800 for vertical deflection under live load and L/600 for total deflection. These are stricter than typical floor beams (L/360) because excessive deflection causes crane misalignment and rail wear.

How do I calculate crane wheel loads? The maximum wheel load occurs when the trolley is at the extreme position carrying the rated load. Obtain the wheel load from the crane manufacturer's data sheet, which provides the maximum wheel load for each crane configuration.

Do crane runway beams need fatigue checks? Yes. Crane runway beams are fatigue-critical members. The number of cycles over the design life (typically 25-50 years) determines the fatigue category and the allowable stress range at each detail.

What is the lateral force from an overhead crane? Per AISC Design Guide 7, the lateral force is 20% of the crane rated capacity for monorails and 10% for bridge cranes. This force acts at the rail level and creates weak-axis bending in the runway beam.

Can I use a standard W-shape for a crane runway beam? For light to moderate cranes (up to 20 tons), standard W-shapes are common. For heavier cranes or longer spans, built-up plate girders with heavier flanges and thicker webs are used.

What is web crippling in crane beams? Web crippling is a local buckling failure of the web under concentrated wheel loads. It occurs when the web is too slender to transfer the wheel load from the rail to the web without local buckling. Stiffeners can be added to increase capacity.

Try it now: Check your crane runway beam with our free Crane Runway Beam calculator →

Related Pages

• Crane Runway Beam Calculator — Automated crane beam design
• Beam Capacity Calculator — Flexure, shear, LTB checks
• Steel Beam Deflection Check — L/360, L/800 checks
• Steel Beam Sizes — W-shape, UB dimensions and properties
• Lateral-Torsional Buckling — LTB theory and checks
• Fatigue Design — Fatigue categories and stress ranges
• Beam Design Example — Worked beam design example

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), Chartered Professional Engineer (CPEng), or Structural Engineer before use in construction, fabrication, or permit documents. The user is responsible for the accuracy of all inputs and the verification of all outputs.

Design Resources

Calculator tools

• Beam Capacity Design Tool
• Steel Beam Deflection Check
• Beam Calculator — SFD, BMD & Reactions
• Beam Optimizer — Find Most Efficient Section
• Beam Span Table Tool

Design guides

• Steel Beam Calculator Guide
• Beam Capacity Worked Example
• Beam Deflection Worked Example
• Steel Beam Design Workflow
• Steel Beam Span Reference