Design calculation sheet for 150-ton 20-meter double-girder gantry crane

Design Basis

1. National Standards
   • GB/T 14406-1993 “General Gantry Crane”
   • GB/T 3811-1983 “Crane Design Code”
2. Design Parameters
   • Rated Lifting Capacity: 150 tons (main hook)
   • Span: 20 meters
   • Lifting Height: Set as required (reference value: 15-22 meters)
   • Duty Class: A5 (Heavy Duty)
   • Main Girder Type: Welded Box Girder Structure

I. Main Girder Design and Calculation

1. Load Condition Analysis
   • Combined Loads: Deadweight (G), Lifting Load (Q), Wind Load (P), Inertia Force, etc.
     • Wind Load Calculation: According to GB/T 3811, wind pressure is 250 N/m², and windward area F = Ψ·A (Ψ is the fill factor).
   • Load Combination:
     • Case 1: 1.2G + 1.4Q (Normal Operation)
     • Case 2: 1.1G + 1.3Q + 1.3P (Extreme Wind Load).
2. Strength and Stiffness Calculation
   • Strength Verification.
   • Stiffness Control:
     • Vertical static deflection of the main beam at midspan ≤ L/800 (allowable deflection 25mm for a 20-meter span).
     • Deflection at the cantilever end ≤ L1/350 (if cantilever is used).

II. Outrigger Stability Calculation

1. Outrigger Type
   • A combination of rigid and flexible outriggers is used. The portal frame structure must resist overturning moments.
2. Stability Verification
   • Euler’s formula: Calculate the critical load Pcr = π²EI/(μL)², ensuring a safety factor ≥ 1.5. Overturning Moment:
     • Stabilizing Moment Mstab = G·B/2 (B is the distance between the outriggers).
     • Tipping Moment Mtip = Q·L/4 + P·H (H is the height at which the wind load acts).

III. Traveling Mechanism Design

1. Trolley Traveling Mechanism
   • Wheel Pressure Calculation: Maximum Static Wheel Pressure Pmax = (G+Q)/n + Mtip/B (n is the number of wheels).
   • Drive Motor Power: Select according to the operating resistance F = μ(G+Q), variable frequency stepless speed regulation (reference speed 20-32 m/min).
2. Trolley Design
   • Refer to the trolley calculation sheet for 5t-50t bridge cranes (pulley and wire rope specifications must be adjusted for a 150-ton load).

IV. Safety Device Selection

1. Brakes: The hoisting mechanism uses dual brakes with a braking torque ≥ 1.5 times the rated torque.
2. Wind and Slip Protection: Rail clamps or anchoring devices with an anti-slip force ≥ 1.2 times the wind load.
3. Limiter: A weight limiter is required for lifting capacities ≥ 10t.

V. Overall Performance Verification

1. Wheel Pressure to Ground Pressure Ratio:
   • Maximum wheel pressure ≤ track bearing capacity (reference value: ≤ 35t/wheel).
2. Anti-overturning stability:
   • Condition 1 (no wind): Mstab/Mtip ≥ 1.4
   • Condition 2 (windy): Mstab/Mtip ≥ 1.15.

Conclusion

This design meets the strength, rigidity, and stability requirements of a 150-ton, 20-meter double-girder gantry crane. The main girder utilizes a box-type welded structure, the outriggers are designed as a rigid-flexible combination, the operating mechanism is equipped with variable frequency speed regulation, and the safety devices meet national standards. Finite element analysis is required to further optimize local stress concentration areas.