| Overhead bridge — manual | 1.10 | Light-duty monorail | | Overhead bridge — electric | 1.25 | Standard industrial bridge crane | | Overhead bridge — cab | 1.25 | Cab-operated heavy bridge crane | | Monorail — electric | 1.20 | Electric hoist monorail | | Jib crane | 1.15 | Wall or column-mounted jib |

The impact factor accounts for: hoist acceleration, braking, and dynamic effects from load swing.

Lateral Load

Per CSA S16 Clause 8.3.3, lateral force at the top of the rail:

L_f = 0.20 × (C_c + C_h) / n_w (per wheel, acting laterally)

This represents 20% of the lifted load plus hoist weight applied as a lateral force at the rail head. The lateral force is resisted by the top flange in weak-axis bending or by a surge girder (horizontal truss) connecting the two runway beams.

Longitudinal Load

Per CSA S16 Clause 8.3.4, longitudinal (traction) force:

LONG_f = 0.10 × P_max (per wheel, acting along the runway)

This force is transferred through the rail to the runway beam and then to the building bracing system.

Deflection Limits

Per CSA S16:24 and the National Building Code of Canada:

Where L is the span of the runway beam between support columns.

Runway Beam Design Procedure

Step-by-Step

1. Determine wheel loads: Vertical, lateral, and longitudinal from crane data
2. Calculate bending moments: Maximum moment from moving wheel loads (influence line)
3. Select trial section: W-shape with channel cap if needed for lateral strength
4. Check strong-axis bending: M_fx ≤ M_rx per Clause 13.5
5. Check weak-axis bending: Lateral load on top flange, M_fy ≤ M_ry
6. Check shear: V_f ≤ V_r per Clause 13.4
7. Check deflection: delta_max ≤ L/600 (live load only)
8. Check fatigue: Stress range ≤ permissible per Clause 26
9. Check local flange bending: Wheel load on flange per Clause 14.3.4
10. Design connections: Runway beam splices, rail fasteners, support brackets

Influence Line for Maximum Moment

For two equal wheel loads P at spacing a, simply supported span L:

M_max = P × L / 2 (for a ≤ L/2 with one wheel at centre)

M_max = P × (2L - a)^2 / (8L) (for a > L/2, general case)

The critical position places the centre of gravity of the wheel group equidistant from the beam centreline and the nearest wheel.

Runway Beam Section Properties

Typical W-shapes for crane runway beams:

Note: M_rx and M_ry calculated for 350W steel, assuming full lateral support at compression flange for LTB check. For crane beams, the top flange is laterally supported by the rail (in friction) — but this is not relied upon for LTB design unless the rail is positively fastened.

Channel Cap Detail

For crane runway beams, a channel section is often welded to the top flange to:

1. Increase weak-axis bending strength for lateral loads
2. Provide a wider flange for rail fastening
3. Reduce local flange bending stress at the wheel load

Typical channel caps:

Worked Example — 10-Tonne Bridge Crane Runway

Given: 10-tonne (100 kN) capacity overhead bridge crane. Hoist + trolley weight = 30 kN. Bridge self-weight = 80 kN. Span of bridge = 15.0 m. Runway beam span = 9.0 m. 2 wheels per side at 3.6 m spacing. Electric operation (alpha = 1.25). 350W steel.

Step 1 — Wheel Loads:

Crane capacity portion per wheel: P_cap = 100 × 1.25 / 4 = 31.25 kN (vertical, hook load)

Hoist + trolley portion: P_hoist = 30 × 1.25 / 4 = 9.38 kN

Bridge self-weight portion: P_bridge = 80 × 1.25 / 4 = 25.0 kN (includes impact on bridge weight — conservatively)

Total maximum wheel load: P_max = 31.25 + 9.38 + 25.0 = 65.6 kN

Lateral load per wheel: L_f = 0.20 × (100 + 30) / 4 = 0.20 × 130 / 4 = 6.5 kN

Step 2 — Maximum Bending Moment:

Wheel spacing a = 3.6 m. Runway span L = 9.0 m. Two equal wheels P = 65.6 kN each.

For a = 3.6 m, L = 9.0 m: Position wheels so centre of gravity is equidistant from beam centreline: CG of wheel group is at mid-point between wheels = 1.8 m from each wheel. Place CG at midspan (4.5 m): wheels at 2.7 m and 6.3 m from left support.

R_left = 65.6 × (9.0 - 2.7)/9.0 + 65.6 × (9.0 - 6.3)/9.0 = 65.6 × 0.700 + 65.6 × 0.300 = 45.9 + 19.7 = 65.6 kN

M_max under left wheel (at 2.7 m): M = 65.6 × 2.7 - 65.6 × (2.7 - max(0, 2.7-2.7)) × 0.0 M = 65.6 × 2.7 = 177.1 kN·m

Moment from beam self-weight (assume W530×82, mass = 82 kg/m = 0.804 kN/m): M_sw = w × L² / 8 = 0.804 × 9.0² / 8 = 8.1 kN·m

M_fx_total = 1.25 × 177.1 + 1.25 × 8.1 = 185.2 kN·m (factored — dead load factor 1.25, live 1.5, but crane load already includes impact. Use load combination from NBCC.)

Crane load factor = 1.5 per NBCC Table 4.1.3.2. Dead load factor = 1.25: M_fx = 1.5 × 177.1 + 1.25 × 8.1 = 265.7 + 10.1 = 275.8 kN·m

Lateral moment under wheel: M_fy = 1.5 × (6.5/2) × 2.7 = 1.5 × 3.25 × 2.7 = 13.2 kN·m (lateral load shared by both runway beams via surge girder — conservatively apply full lateral moment to one beam)

Step 3 — Section Selection:

Try W460×68: M_rx (assuming fully braced) = 409 kN·m. M_ry = 35.9 kN·m.

Combined bending check per CSA S16 Clause 13.8: M_fx/M_rx + M_fy/M_ry = 275.8/409 + 13.2/35.9 = 0.674 + 0.368 = 1.042 > 1.0. NOT OK. (Ratio = 1.04)

Try W530×82: M_rx = 570 kN·m. M_ry = 50.4 kN·m.

275.8/570 + 13.2/50.4 = 0.484 + 0.262 = 0.746 ≤ 1.0. OK. (Ratio = 0.75)

Step 4 — Deflection Check:

Vertical deflection (live load only, serviceability — unfactored):

delta_max (two moving wheel loads, approximate): delta = P × L³ × K / (48 × E × I_x)

For two wheels at third points (conservative approximation): K ≈ 0.8 for a/L = 0.4

delta = 65.6 × 9,000³ × 0.8 / (48 × 200,000 × 477 × 10⁶) = 65.6 × 729 × 10⁹ × 0.8 / (48 × 200,000 × 477 × 10⁶) = 38.2 × 10¹² / 4,579 × 10⁹ = 8.34 mm

delta_allow = L/600 = 9,000/600 = 15.0 mm

delta = 8.34 ≤ 15.0 mm. OK. (Ratio = 0.56)

Step 5 — Fatigue Check:

Crane cycles per design life: Operating 8 hours/day, 250 days/year, 20 lifts/hour, 50-year life: N_design = 8 × 250 × 20 × 50 = 2,000,000 cycles

Stress range: delta_sigma = M_service / S_x = (0.8 × 177.1 × 10⁶) / 1,810,000 = 78.3 MPa

Detail at web-to-flange fillet weld: Category B, CAFL = 110 MPa. delta_sigma = 78.3 ≤ 110 MPa → Infinite fatigue life. OK.

Result: W530×82 crane runway beam satisfies CSA S16:24 requirements for strength (ratio 0.75), deflection (ratio 0.56), and fatigue (infinite life). Provide 20 mm rail with bolted clips at 600 mm centres. Lateral surge forces to be resisted by horizontal truss between paired runway beams.

Frequently Asked Questions

What is the vertical impact factor for crane runway design per CSA S16? Per CSA S16:24 Table 8.1, the vertical impact factor accounts for dynamic effects including hoist acceleration, load swing, and sudden load application. Standard values: 1.25 for electric overhead bridge cranes, 1.20 for electric monorails, 1.10 for manual cranes, and 1.15 for jib cranes. For cab-operated heavy bridge cranes (> 50 tonnes), manufacturers may specify higher impact factors based on dynamic analysis. The impact factor is applied to the lifted load only — not to the crane bridge or runway beam self-weight.

What deflection limit applies to crane runway beams? Per CSA S16 and industry practice: L/600 for the live load (crane + hook load) vertical deflection. For cranes requiring high positioning precision or cranes with capacity > 20 tonnes: L/800. For lateral deflection at the rail head: L/400, or L/600 for cranes > 20 tonnes. These limits are more stringent than typical floor beam deflection limits (L/360) because excessive deflection causes: (a) rail misalignment and binding of crane bridge wheels, (b) increased wear on wheels and rails, (c) difficulty in precise load positioning, and (d) dynamic amplification from "bump" effects at rail joints.

Do I need a channel cap on the runway beam? A channel cap (C-section welded to the top flange) is recommended when: (a) the lateral load from the crane exceeds the weak-axis bending capacity of the beam alone; (b) local flange bending under the wheel load exceeds 0.9 × Fy × b_f² / (4 × t_f²); (c) additional flange width is needed for rail fastening. The channel cap increases the weak-axis section modulus by 40-60% and effectively stiffens the top flange against local bending. The cap should be continuously welded to the beam flange with a 6 mm minimum fillet weld to develop composite action.

How do I account for fatigue in crane runway design? Per CSA S16:24 Clause 26, fatigue must be checked when cycles exceed 20,000 over the design life. For crane runway beams: (a) identify the critical detail category at each weld location (typically Category B at the web-to-flange fillet, Category C at stiffener terminations); (b) calculate the stress range from the maximum and minimum wheel positions (for simply supported beams, the minimum moment is zero between crane passes); (c) check against the CAFL (constant amplitude fatigue limit) — if delta_sigma ≤ CAFL, the detail has infinite life and no further checking is needed; (d) if delta_sigma > CAFL, check N_design ≤ N_allowed = C / delta_sigma³. For most industrial crane beams, fatigue governs at high cycle counts (> 500,000 cycles).

Related Pages

• Canadian Steel Fatigue Design
• CSA S16 Beam Design
• Canadian Lateral-Torsional Buckling
• CSA S16 Deflection Limits
• CSA S16 Weld Capacity
• Canadian Vibration Design
• All Canadian References

This page is for educational reference. Crane runway design per CSA S16:24 Clauses 8.3, 13.5, and 26. Crane loads, impact factors, fatigue assessment, and deflection limits must be verified by a licensed Professional Engineer for the specific crane data, duty classification (CMAA or CSA B167), and building configuration. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.

Design Resources

Reference pages

• CA Crane Support

Disclaimer: This content is for educational purposes only. Results must be verified by a licensed professional engineer. Steel Calculator provides preliminary design tools — NOT a substitute for professional engineering judgment.