overhead-crane

name	overhead-crane
description	Overhead crane design — CMAA 70/74 classification (service classes A–F), girder design (box/I-beam, deflection limits L/888), end truck, wheel load, fatigue (ASME B30.2 stress cycles), lifting mechanism (wire rope, drum, hook, load block), runway rail design, electrical classification (OSHA 1910.179), anti-sway control, ASME HST hoist standards, and seismic considerations.
metadata	{"priority":7,"promptSignals":{"phrases":["overhead crane","bridge crane","crane girder design","CMAA 70","crane fatigue","hoist design"],"minScore":3}}

Overhead Crane Design — Complete Skill

Classification

CMAA Service Classes

CMAA Specification 70 (Electric Overhead Traveling Cranes): Classifies cranes by loading spectrum and duty cycle

Class	Description	Example	Cycles/Year
A	Standby / infrequent	Powerhouse; maintenance	< 500
B	Light service	Light manufacturing; assembly	500–2,500
C	Moderate service	Machine shop; general manufacturing	2,500–10,000
D	Heavy service	Heavy manufacturing; steel mills	10,000–25,000
E	Severe service	Mill duty; continuous production	25,000–100,000
F	Continuous severe	Magnet service; ladle cranes	> 100,000

Load spectrum: Class A: frequently lifts maximum load (full rated capacity); single load bin Class D: Σ(n_i × (P_i/P_max)^3) loading spectrum; mixed loads; lower average

Impact factor φ (dynamic load factor): φ = 1.0 + 0.1 × v_hoist / √(H) [CMAA; v_hoist = hoist speed m/s; H = lift height m] Or simplified: φ = 1.15 (Class A/B); φ = 1.25 (Class C); φ = 1.33 (Class D–F) Applied to hook load: P_dynamic = φ × P_rated

FEA Group Classification (ISO 4301-1/FEM 1.001): M1–M8 mechanism groups; relates to classification factor m and spectrum factor k_Q ISO alternative to CMAA; internationally preferred

Structural Design — Bridge Girder

Girder Types

Box girder: Two webs + top/bottom flanges; high torsional stiffness; preferred for longer spans (> 15 m) and heavy cranes Built-up welded plate construction; webs and flanges from plate

Single-girder (I-beam or fabricated): Up to ~25 m span; lighter loads (Class A/B/C) Trolley runs on bottom flange or on rail on top flange

Twin-girder: Trolley rail on top of each girder; most common for heavy cranes

Girder Sizing

Deflection limit (CMAA 70): Vertical live load deflection: ΔL ≤ L/888 [L = girder span] Calculated for rated load + impact at center of span (simply supported)

Maximum live load deflection (simple beam with mid-span load P): Δ = P × L³ / (48 × E × I) [I = moment of inertia of girder cross-section] Required I: I_min = P × L³ / (48 × E × L/888) = P × L² × 888 / (48E) = 18.5 × P × L² / E

Example (P = 200 kN, L = 20 m, E = 200 GPa): I_min = 200,000 × 20² × 888 / (48 × 200,000,000) = 200,000 × 400 × 888 / (9.6×10⁹) = 7.4×10⁻⁴ m⁴ = 74,000 cm⁴

Bending stress check (CMAA 70 Section 3): f_b = M_max / S [S = section modulus] Allowable: F_b = 0.60 × F_y (Class A/B); F_b = 0.55 × F_y (Class C/D); F_b = 0.50 × F_y (Class E/F) F_y: typically 250 MPa (A36) or 345 MPa (A572 Gr. 50)

Maximum moment (trolley at mid-span): M_max = (P_dynamic + w_girder × L/2) × L / 4 [w_girder = girder self-weight per unit length]

Shear check: V_max at end truck ≈ (P_dynamic + W_trolley) + W_girder × L / 2 f_v = V_max / (A_web); allowable F_v = 0.40 × F_y

Web local buckling: h/t_w ≤ 300 (compact web; no longitudinal stiffeners required; A36) If h/t_w > 260: add transverse stiffeners (CMAA Table 3.2.6)

Crane Rail on Girder Top Flange

Rail selection: Rail type from wheel load: A.S.C.E. 20–135 lb/yard rails Wheel load P_wheel = P_dynamic / (N_wheels) [N_wheels = number of wheels per bridge end] Rail contact stress (Hertz): σ_contact = 0.418 × √(P_wheel × E_rail / r_wheel × (1 + r_wheel/L_rail))

Rail clips and holddowns: AIST Technical Report 6: rail fastener requirements; allow ±3 mm lateral float Rail welding: typically not welded (thermal expansion); clips at 400–800 mm spacing

End Truck and Runway

End Truck Design

End truck: Bridge end-beams + wheels + bearings; connects main girder to runway rail Wheel load = (bridge + trolley + load) / number_of_runway_wheels Runway wheel size: proportional to load; 200–800 mm diameter (AISI 1060 forged)

Runway alignment: Span tolerance: ±3 mm for crane rail span (CMAA 70 Section 7) Rail joint gap: < 3 mm; elevated joint heights < 1.5 mm (reduce wheel impact)

Buffer stops: Energy absorber at runway ends; absorb kinetic energy of crane impact E_impact = 0.5 × m_bridge × (v_travel)² × damping_factor Spring or hydraulic buffers; CMAA 70 Section 4

Runway Rail and Support Structure

Column caps and runway girder: Runway girder deflection limit: L/600 vertical; L/400 lateral (AISC/CMAA) Runway rail splice: butt joint with backing bar weld; no elevated joint Runway girder fatigue: AASHTO Category C at rail clip holes; Category B at welds

Hoist Mechanism

Wire Rope and Drum

Wire rope selection: Rope classification: 6×19 (general purpose); 6×36 (flexibility); 8×19 (flexible; lower fatigue life) Rope diameter: D_rope ≥ √(P_hook / (k × F_u_rope)) [k = safety factor = 5 minimum per ASME B30.2; F_u = rope breaking strength] Rope breaking strength (approximate): F_u ≈ 32.4 × D_rope² (kN; D in mm; 6×19 IWRC improved plow steel)

Drum design: Drum diameter: D_drum ≥ C₁ × D_rope [C₁ = drum/rope ratio; C₁ ≥ 18 for Class B; C₁ ≥ 30 for Class E/F per CMAA] Number of drum wraps: N_wraps = H / (π × D_drum) + 2 dead wraps Drum groove: spiral groove radius = D_rope/2 + 0.5 mm; helix angle < 4°

Fleet angle: Angle between rope and drum axis: ≤ 2° (groove; CMAA recommendation) Fleeting angle exceeds 2°: accelerated rope wear; install sheave compensator

Wire rope bending fatigue: Rope fatigue life reduces with D/d ratio (D = sheave/drum diameter; d = rope diameter) D/d < 16: very short life; D/d = 26: standard; D/d ≥ 40: high-cycle applications (Class E/F)

Rope end connection: Spelter socket (wedge and swaged): efficiency 100% (full breaking strength) Wire rope clip (U-bolt): efficiency 80%; requires 3 clips minimum Hook (open swaged eye): efficiency 90%

Hook and Load Block

Hook rating: Hook load = rated load × impact factor φ; hooks rated per load class ASME B30.10: hook design, marking, inspection Hook material: ASTM A668 Class F forging; proof load = 2× rated load Hook throat opening: minimum per load rating table

Block and sheave: Number of parts of rope: N_rope × F_pull = P_hook → N_rope = P_hook / F_pull (F_pull = hoist motor pull per rope) Block efficiency: η = (1 - f^N_rope) / (N_rope × (1-f)) [f = sheave friction factor ≈ 0.02–0.05 per sheave] Sheave diameter: same D/d requirement as drum

Hoist Motor and Brake

Motor power: P_motor = P_hook × v_hoist / η_mechanical [η_mech = gear + rope efficiency = 0.85–0.95] P_motor [kW] = (P_hook [N] × v_hoist [m/s]) / (1000 × η)

Motor class (NEMA or IEC): IEC duty class S4 (periodic duty) or S3 (intermittent) for hoist motor Service factor from CMAA classification: Class A → S.F. 1.0; Class F → S.F. 1.5

Brake: Hoist brake: spring-set electromagnetic brake; holds load when de-energized (fail-safe) Braking torque: T_brake ≥ 1.5 × rated motor torque (CMAA requirement) OSHA 1910.179: brake holding capacity ≥ 125% of rated load

Fatigue Design

Stress Cycles and CMAA

Fatigue stress calculation: Stress range ΔS = maximum stress - minimum stress (at connection or weld detail) Number of cycles N: from crane service class × design life

CMAA 70 fatigue categories: Class A/B cranes: rarely governs fatigue (low cycle count) Class D/E/F: fatigue governs; use AISC fatigue categories or ASME B30 criteria

AISC fatigue categories at welds: Category B: base metal at fillet-welded attachments; ΔF_n = 110 MPa (2×10⁶ cycles) Category C: shear connectors; web stiffener welds; ΔF_n = 69 MPa (2×10⁶ cycles) Category D: web copes; short attachment welds; ΔF_n = 48 MPa

Cumulative fatigue (Miner's rule): Σ n_i / N_i ≤ 1.0 [n_i = actual cycles at ΔS_i; N_i = allowable cycles at ΔS_i]

OSHA and Safety Standards

OSHA 1910.179 (Overhead and Gantry Cranes)

Required safeguards: Hoist limit switches: upper and lower travel limit End stops at runway ends; bumpers on crane bridge and runway Emergency stop accessible to operator Load testing: 125% proof test before first use; records maintained

Inspection requirements: Pre-shift inspection by operator (hooks, rope, controls, brakes) Periodic inspection (monthly/annually based on service class) Rope discard criteria: 6 broken wires in any rope lay; outside wire wear > 1/3 of original diameter; kinking

Rated load marking: Visible from ground; rated capacity in tons on both sides of crane bridge (ASME B30.2-3.1.7) No side-loading: crane designed for vertical lift only (no tipping)

ASME B30 Series

ASME B30.2: Overhead and Gantry Cranes (top-running bridge; single or multiple girder) ASME B30.16: Overhead Underhung Cranes (monorail, bottom-running) ASME B30.11: Monorails and Underhung Cranes ASME HST-4/HST-6: Electric/manual chain hoists

Anti-Sway Control

Load Pendulum Dynamics

Natural frequency of hanging load: f_n = (1/2π) × √(g/L) [L = rope length [m]; f_n in Hz] At L = 5 m: f_n = 0.22 Hz; At L = 20 m: f_n = 0.11 Hz

Sway angle from crane acceleration: θ_sway = arctan(a_crane / g) ≈ a_crane / g [for small angles; a_crane = bridge/trolley acceleration]

Anti-sway input shaping: Zero-vibration (ZV) input shaping: command pulse sequence timed to cancel residual sway ZV shaper: two impulses at t = 0 and t = T_n/2 with amplitudes A₁ = 1/(1+K); A₂ = K/(1+K) K = e^(-ζ × π / √(1-ζ²)); T_n = 1/f_n Results in zero sway at end of move if crane dynamics match model

Active sway control: Feedback of rope angle (sensor: encoder or camera) → modulate trolley velocity → close loop Available in modern PLCs: anti-sway function block

Standards and References

Standard	Scope
CMAA Specification 70	Electric overhead traveling cranes
CMAA Specification 74	Top-running bridge cranes (metric)
ASME B30.2	Overhead and gantry cranes
OSHA 29 CFR 1910.179	Overhead cranes (general industry)
ASME HST-4/-6	Hoist standards
AIST Technical Report 6	Crane runway systems
ISO 4301-1	Crane classification
FEM 1.001	European crane design rules

Output

Provide: crane type (single/double girder, top-running/underhung) and service class (A–F; CMAA 70), rated capacity [tons or kN] and span L [m], bridge girder (box or I-beam; cross-section: h/b/flange thickness/web thickness [mm]; I [cm⁴]; S [cm³]), deflection check: Δ_max [mm] vs. L/888 limit [mm], bending stress f_b [MPa] vs. allowable F_b [MPa], wheel load [kN] per runway wheel, dynamic impact factor φ, drum diameter [mm] and D/d ratio (rope), wire rope: diameter [mm], classification (6×19), safety factor (5.0 min), brake holding capacity [% of rated load], hoist motor power [kW], fatigue category (AISC) for critical weld detail and ΔS_n limit [MPa], compliance summary (OSHA 1910.179; ASME B30.2 limit switches; proof test 125%), and applicable standard (CMAA 70, ASME B30.2, OSHA 1910.179).