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📘 What is Tandem Lifting?

Tandem lifting involves the simultaneous use of two or more cranes to lift a single load. It is used when the load:

  • Exceeds the capacity of a single crane
  • Must remain level during lifting
  • Is long or has an offset center of gravity (COG)

📐 Basic Load Distribution Formula

When two cranes lift an asymmetrical load, you use moment balancing to calculate how much each crane carries.

Formula:

Load_A * Distance_A = Load_B * Distance_B
Load_A + Load_B = Total Load

Example:

  • Total Load = 20,000 kg
  • Distance from Crane A to COG = 5 m
  • Distance from Crane B to COG = 7 m

Step 1: Moment balance

Load_A * 5 = Load_B * 7

Step 2: Total load

Load_A + Load_B = 20000

Solving gives:

  • Load_A = 11,667 kg
  • Load_B = 8,333 kg

🏗️ Crane Configuration Example

CraneModelMax CapacityDistance to COGLoad Share
AZoomlion QY-30V30,000 kg5 m11,667 kg
BLiebherr LTM104040,000 kg7 m8,333 kg

🖼️ Diagram (Top View)

      Crane A (Zoomlion)              Crane B (Liebherr)
         |------5m------[COG]------7m------|
               |<------ 20,000 kg ------>|

🧮 Auto Calculation Formula (Excel)

Use the following cell formulas in Excel:

Total_Weight: 20000 (Cell B2)
Distance_A: 5 (Cell B3)
Distance_B: 7 (Cell B4)

Crane B Load = (Distance_A / (Distance_A + Distance_B)) * Total_Weight
Crane A Load = Total_Weight - Crane B Load

Excel Cell Formula:

Crane_B_Load = =B3/(B3+B4)*B2
Crane_A_Load = =B2-Crane_B_Load

✅ Safety Checklist

  • Cranes positioned on level ground
  • Rigging inspected and matched
  • Clear communication established
  • Load path and COG confirmed
  • Lift plan reviewed and signed off

📥 Resources