Overhead Crane Calculator
Preliminary design chain for a double-girder overhead crane — dead weight, wheel load, impact, girder moment and deflection, rope size, motor power, and wheel diameter.
When to use this calculator
Use for the preliminary sizing pass on a double-girder electric overhead travelling crane, or to sanity-check a supplier's proposal before it goes to detailed design. It runs the whole conventional hand-calculation chain in one place — from the dead weights and the rated load through to wheel load, impact load, girder design load, bending moment, and the deflection check against S/600 or S/800 — and then covers the drive-side items: hoist rope diameter, motor power, hook approach, and minimum wheel diameter. The load and deflection conventions follow IS 3177, IS 807, CMAA 70, and FEM 1.001.
Required inputs
- Safe working load and impact factor φ
- Dead weights: bridge, trolley, hoist, end carriages, miscellaneous
- Crane span S, number of wheels, girder E and I
- Deflection limit divisor — typically 600 or 800
- Rope safety factor and rope constant K; motor torque, speed, and efficiency; wheel constant K
Expected outputs
- Total dead weight, total load, and static wheel load
- Impact load, girder design load, and maximum bending moment
- Girder deflection against the S/600 and S/800 allowables, with pass or fail
- Rope minimum breaking load and approximate diameter
- Motor power required at the stated efficiency, hook approach, minimum wheel diameter
Formula overview
Metric throughout: loads entered in tonnes, dead weights in kg, span in m, E in N/mm², I in mm⁴, torque in N·m, speed in rpm. Deflection is worked in N, mm, N/mm², and mm⁴ so it comes out in mm.
Loads:
W_D = Σ dead weights total = SWL + W_D
W_L = total force / n_wheels static wheel load
impact load = (SWL + W_D) × φ
design load P = φ × W_L
Girder — trolley at mid-span, concentrated load:
M_max = P · S / 4
δ = W_L · S³ / (48·E·I) static load, no impact factor
allowable = S / 600 or S / 800
Drives (empirical design aids, not code equations):
MBL = SWL × SF rope d = K · ∛SWL
motor P = 2π·T·N / 60 000, required = P / η
hook approach A = 0.5·S min wheel D = K · √W_L, W_L in kNWorked example
SWL 10 t, four wheels, span S = 12 m, impact factor φ = 1.25.
Dead weights: bridge 4000, trolley 800, hoist 600, end carriages 700,
misc 200 kg → W_D = 6300 kg
Total load = 10 000 + 6300 = 16 300 kg = 159.8 kN
W_L = 159.8 / 4 = 39.96 kN per wheel
Design load P = 1.25 × 39.96 = 49.95 kN
M_max = 49.95 × 12 / 4 = 149.9 kN·m
Girder with E = 210 000 N/mm², I = 1.2 × 10⁹ mm⁴:
δ = 39 962 × 12 000³ / (48 × 210 000 × 1.2e9) = 5.7 mm
allowable S/800 = 12 000/800 = 15 mm → passCommon mistakes
- Using the distributed-load deflection formula for the trolley wheel load. The critical case is a concentrated load at mid-span, so δ = W_L·S³/(48·E·I) applies. Substituting the UDL form under-predicts deflection by a factor of 8/5 and can report a pass for a girder that actually fails.
- Applying the impact factor to the deflection check. Deflection limits are a stiffness criterion, so the check is made under the static wheel load. Impact belongs on the strength side — the girder design load and the bending moment.
- Treating the rope and wheel sizing as code results. The rope diameter and minimum wheel diameter formulas are empirical design aids carrying their own unit conventions; they give a starting size for selection from a manufacturer's table, not a certifiable answer.
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