Gantry Crane Main Girder Strength & Wheel Load Calculation Guide
Key Points Structural analysis of the three main girder types for gantry cranes: MH-type single-girder box (Wx=BH²/6-bh³/6H, f=5qL⁴/384EI+φQL³/48EI≤L/700), MHhs lattice truss (chord force N=M/h₀, web member force Nd=V/sinα), and twin main girders (each girder carries Mtotal/2). Wheel load Rmax=(G/2+φ₂Q(L-Lmin)/L)/n×ψ. Worked examples provided for 10t, 20t, and 32t capacities.
The main girder of a gantry crane is the core load-bearing component that determines the safety and service life of the entire machine. Its strength, stiffness, and stability are critical design parameters. Kelude gantry cranes are available in three structural configurations: MH-type single-girder box, MHhs lattice truss, and twin main girders. This article presents a systematic derivation of bending moment calculations, section verification, and deflection checks for each type, along with a complete wheel load calculation procedure.
For crane selection parameters and pricing, refer to the Gantry Crane Price and Specifications Guide and the Gantry Crane Model Parameters, Pricing, and Selection Guide. For electric hoist hoisting mechanism calculations, see Electric Hoist Hoisting Mechanism Engineering Calculations.
Gantry crane structural diagram
Determining Main Girder Loads
Per ISO 4301 Crane Design Standard, loads are classified into regular loads (dead weight GG + lifting load Q + dynamic load factor φ₂=1.1~1.3), additional loads (wind load, skewing lateral forces), and special loads (buffer collision, test load 1.25GN). Load combination A (normal operation): GG+φ₂·(Q+q)+Pwind operating.
MH-Type Single-Girder Box Section Calculation
Mmax = qG·L²/8 + φ₂·(Q+q)·L/4
σ = M/Wx ≤ [σ] (Q235B: 160 MPa, Q345B: 230 MPa)
f = 5qL⁴/384EI + φ₂QL³/48EI ≤ L/700~L/800
10t MH-type example: L=22m, Q345B, A5 duty
B×H=500×900mm, Wx=6.80×10⁶mm³
Mmax=814kN·m, σ=119.7MPa≤230MPa
ftotal=54.7mm > [f]=27.5mm — pre-camber required or H≥1200mm
MHhs Lattice Truss Girder Calculation
Chord member axial force N=M/h₀, diagonal member force Nd=V/sinα. Equivalent moment of inertia Ieq=Achord·h₀²/2; deflection is multiplied by a truss deformation amplification factor of 1.1~1.3.
10t MHhs example: L=28m, Q235B, A4 duty, h₀=1200mm
Mmax=922.6kN·m, chord axial force N=769kN
Select HW200×200 (A=6420mm²), σ=119.8MPa≤160MPa
Ieq=4.62×10⁹mm⁴, f=36.1mm≤40mm (L/700)
Lattice girder dead weight is only 40%~60% of a box section
Twin Main Girder Box Section Calculation
Each main girder carries Mtotal/2, requiring Wx per girder=Mper girder/[σ].
32t double-girder example: L=30m, Q345B, A6 duty
B×H=600×1300mm, σ=147.8MPa≤230MPa
ftotal=85.3mm > [f]=37.5mm
Pre-camber of 50~60mm required or H increased to 1600mm
Wheel Load Calculation
Rmax=(GG/2+φ₂·(Q+q)·(L-Lmin)/L)/nwheels×ψ. Additional wheel load from wind: ±Mwind/(Bwheel base×ntravel wheels).
32t double-girder wheel load: GG=450kN, nwheels=4, ψ=1.15
Rmax=183.8kN/wheel (P43 rail allows 250kN/wheel)
With 11-level wind load: Rmax wind=235.8kN/wheel≤250kN
Design Parameter Comparison of the Three Structures
Kelude Heavy Industry: Overhead Crane & Hoist Solutions
Kelude Heavy Industry specializes in the design and manufacture of industrial overhead cranes, gantry cranes, and electric hoists. Our product range covers standard models and fully customized solutions for demanding applications across manufacturing, logistics, and process industries.
Frequently Asked Questions
Q: What is the lead time for a standard single-girder crane?
A: Standard models (up to 10t capacity, 20m span) typically ship within 6-8 weeks from order confirmation. Custom cranes require 10-14 weeks depending on complexity.
Q: Do you provide installation and commissioning services?
A: Yes, our technicians can supervise or fully handle installation and commissioning. We also provide operator training at your site.
Q: What is the warranty period?
A: We offer a 24-month warranty on all crane components, covering defects in materials and workmanship. Extended warranties are available.
Q: Can you supply cranes that meet specific local codes (e.g., CMAA, FEM)?
A: Yes, we design and build to international standards including ISO, FEM, and can adapt to local code requirements. Please specify your applicable code when requesting a quote.
| Parameter | MH Type Single-girder box | MHhs Lattice truss | twin main girders Single-girder box |
|---|---|---|---|
| Applicable to Span | 10~35m | 18~50m | 15~50m |
| Applicable to Lifting Capacity | 5~20t | 5~50t | 20~100t |
| Main Girder Depth-to-span ratio | 1/18~1/22 | 1/14~1/18 | 1/16~1/20 |
| Dead Weight Depth-to-span ratio | 1.0(Reference) | 0.4~0.6 | 1.6~2.5 |
| Wind resistance | Good | Open lattice for superior wind resistance | Fair(Large windward area) |
