Multi-Crane (Tandem) Lifts
When one crane can't lift a load, two cranes may share it. Tandem lifts handle long beams, large vessels and heavy equipment, but they are among the riskiest operations in rigging. The load and the share on each crane change as the cranes move, and a small mistake can overload one crane and collapse it. They need a written plan, one person in charge and flawless coordination.
- Crane Operators
- Lift Directors
- Riggers
- Engineers
- Signal Persons
Why tandem lifts are different
- Each crane carries only part of the load, and the share changes if either crane's hook height, radius or speed differs.
- If one crane moves faster, tilts the load or swings differently, the other crane can be overloaded or pulled sideways, and the rigging can shock-load.
- Two operators must coordinate without seeing each other's controls.
- Tandem lifts are normally treated as critical lifts. See Lift Planning.
What OSHA requires
OSHA's construction crane rule includes supplemental requirements for lifts with more than one crane or derrick (29 CFR 1926.1432). In general:
- The lift must be planned in a written plan developed by a qualified person.
- The plan must be reviewed in a meeting with all employees involved, including operators, signal persons and riggers, before the lift.
- A competent and qualified person (the lift director) must be responsible for the operation and be at the lift site, giving direction and stopping the lift if needed. Many companies require the lift director to be on the ground and in radio contact with both operators.
- The plan must ensure that the load on each crane stays within its rated capacity for all movements and configurations.
- If a qualified person cannot ensure this, an engineer must be consulted. Many companies set conservative limits for the share each crane may carry, often well below 100 percent of rated capacity. Follow your company's engineering standard.
- See Crane Basics, Load Charts and Qualified Riggers.
Planning the lift
- Determine the exact weight and center of gravity of the load and rigging. See Estimating Load Weight.
- Choose cranes of similar type and boom setup where possible, and calculate the share each carries at the pick, during travel and at the set.
- Plan the rigging: spreader or equalizer beams, sling angles, hooks and attachment points, with designs approved by an engineer if the load is unusual. See Below-the-Hook Devices.
- Plan the site: ground bearing, mats, outriggers, swing clearances, power lines and overhead obstructions, and the travel path.
- Set wind and weather limits lower than normal, since wind affects a large load. See Lift Wind Limits.
- Plan communication: one signal person or the lift director directs both cranes by radio, with agreed words for "stop." Test radios.
- Plan for emergencies and how to land the load if one crane fails.
During the lift
- Hold the pre-lift meeting and make sure everyone understands the plan, roles and limits.
- Both operators raise slowly to take up the load, then pause to check hook loads, boom angles, level and rigging.
- Move together at slow, matched speeds. Keep hooks plumb and watch for load tilt. One person gives the signals.
- Use load monitoring (load cells or the crane's load moment indicator) on each crane where available.
- Keep everyone out from under the load and out of the swing and travel areas.
- Any person can call "stop." Land the load and re-evaluate.
Tandem lift checklist
- A written plan by a qualified person is reviewed with the whole crew
- A lift director is in charge and in radio contact with both operators
- Each crane's share is within its chart at every point of the lift
- Ground, wind, power lines and rigging are checked
- Both cranes move slowly and together; anyone can call stop
Standards & references
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