14.3 Multiple crane lifts
14.3.1 Safety measures for multiple crane lifts
14.3.2 Calculated share of the load
14.3.3 Principles for multiple crane lifting
Lifting a load with two or more cranes requires greater attention to planning and supervision, because the effects of the relative motion between the cranes may create additional loadings on the cranes, the load and the lifting gear in place.
14.3.1 Safety measures for multiple crane lifts
Where possible, avoid hoisting a load with more than one crane. However, where it is necessary to lift a load using more than one crane, the following steps should be taken:
- A person certificated to work as an intermediate rigger should be in overall control of the lift.
- Make an accurate assessment of:
- the share of the load which is to be carried by each crane;
- how the load sharing is to be proportioned; and
- how the proportioning is to be maintained.
- Make sure the instructions to each crane operator and other persons involved are clear, and rehearse the operation wherever possible.
- Use cranes of equal capacity and similar characteristics, where practicable.
- Make sure that both cranes are aligned in the same direction when using non-slewing type cranes in the pick-and-carry mode.
- Use luffing up in preference to luffing down.
Dual lifts are not to be undertaken unless all cranes are fitted with a load indicator. Section 7.5 of this code requires load indicators to be fitted to all mobile cranes with a maximum rated capacity of more than three tonnes.
14.3.2 Calculated share of the load
Where multiple hoisting operations are carried out, the following minimum capacity requirements for each crane will apply:
- for two cranes—20% greater than the calculated share of the load;
- for three cranes—33% greater than the calculated share of the load;
- for four or more cranes—50% greater than the calculated share of the load.
If it is not possible to comply with the minimum capacity requirements stated above, then an engineer must check and certify the lifting procedure. The lifting procedure must be documented.
14.3.3 Principles for multiple crane lifting
The following factors are to be considered when planning for multiple crane lifts:
- mass of the load;
- position of the centre of gravity;
- mass of the lifting gear;
- safe working capacity of the lifting gear; and
- synchronisation of crane motions.
Ensure the total mass of the load and its distribution is either known or calculated. Where the information is taken from a technical drawing, ensure allowances are made for manufacturing tolerances.
Position of the centre of gravity
Due to the variable effect of manufacturing tolerances and rolling margins, the position of the centre of gravity may not be accurately known. Accordingly, the proportion of the load being carried by each crane may therefore be uncertain.
Ensure the mass of the lifting gear and its distribution are accurately known and included as part of the calculated load on the cranes. Where heavy or awkwardly shaped loads are handled, the deduction from the safe working loads of the cranes to allow for the weight of the lifting gear may be quite significant.
Safe working capacity of the lifting gear
Ensure the distribution of the forces within the lifting gear which will arise during the lifting operation is established. The lifting gear should have a safe working capacity margin in excess of that needed for its proportioned load. Determine whether special lifting gear is required to suit the maximum variation in distribution and direction of applied loads and forces which may occur during multiple lifting.
Synchronisation of crane motions
Minimise the variation in the direction and magnitude of forces acting on the cranes by synchronising the cranes’ motions. Where possible, ensure cranes of equal capacity and similar operating characteristics are used. However, in practice, there will always be some variation due to differences in response to the activation of the motion controller and the setting and efficiency of the braking system.
As it is unlikely that the motions of the cranes will be accurately synchronised, ensure that an assessment of the effect of variation in plumb of the hoist ropes, which may arise from inequalities of speed, and the means for keeping such inequalities to a minimum, is made. To allow for these inequalities, the lifting operation should be performed at low speeds with extreme care to ensure the hoist ropes are kept as close as possible to vertical.
The rated capacity of a crane is calculated on the assumption that the load will be raised and lowered in a vertical plane. The crane boom has limited strength in the lateral plane.
Last updated June 9, 2006