Learn more about how the tandem lifting scheme works – the best option for effective economy

Learn more about how the tandem lifting scheme works – the best option for effective economy
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In certain situations, tandem lift may be more expedient than to rent two mobile cranes at once. This article considers the rent of truck cranes: not one, but two at once. We will talk about such a service as the twin mode of operation of two cranes.

The work of a truck crane with large, heavy, unbalanced loads can cause certain difficulties, both organizational and financial. If it is necessary to conduct such reloading operations permanently, enterprises usually acquire special grippers, manufacture unique load-handling devices, traverses, and leasing reloading equipment with the appropriate characteristics and heavy lifting capacity.

If you do not need to constantly order a crane to handle large, heavy, unbalanced loads, then the increased price of renting a heavy crane and the high cost of manufacturing special devices for loading and unloading work will be impractical.

As a rule, it is cheaper and easier to rent two mobile cranes with the appropriate technical characteristics that will allow you to unload or load a heavy, bulky cargo at no additional cost.

Using 10-t and 14-t cranes in tandem is an economically more advantageous solution than renting one crane with a large load capacity. In addition, the two cranes provide greater stability of the lifted cargo, which has an additional convenience when mounting the wheels.

Before ordering the services of mobile cranes for work in twin mode, you need to make sure that:

  • the total lifting capacity of the two cranes at the required reach of the boom exceeds the weight of the loaded cargo (the weight of the load and the traverse if a traverse is used)
  • the weight of the load can be distributed evenly between the cranes
  • the cranes will be operated only by experienced operators (truck crane drivers).

The latter condition is very important, as when truck cranes are working in tandem, the main success factors are the skill and consistency of the movements performed by the two cranes simultaneously.

For the performance of work in the coupled mode, it is recommended to rent the same type of boom cranes with the same lifting capacity.

It is possible to apply two variants of lifting and moving cargo by cranes: by means of a traverse and without a crossbeam. The use of the traverse is designed to promote a uniform weight distribution between the cranes. When the load is lifted by means of a traverse, the following requirements must be met:

  • the size and lifting capacity of the traverse must correspond to the dimensions and weight of the lifted load and the distance between the hooks of the cranes
  • the weight of the traverse is added to the weight of the lifted load
  • when lifting and moving the load, the ropes of the cranes should remain in a vertical position and the traverse must remain horizontal.

When working without a traverse, it is necessary to monitor the even distribution of load on the cranes, the horizontal position of the load, the possibility of moving it above objects encountered on the way (at least 0.5 m higher) and the vertical position of the ropes of the cranes. The work should be supervised by a specialist responsible for the safe conducting of loading and unloading operations.

What are the safety requirements when lifting cargo with two cranes?

In accordance with the Rules for the Arrangement and Safe Operation of Cranes (PB 10-38200), in certain cases lifting and moving cargo by two cranes and more is permitted.

The work is carried out in accordance with the project in which the schemes of slinging and moving the cargo with the indication of the sequence of operations, the position of the cargo ropes, as well as the requirements for the state of the track, and other instructions for the safe movement of cargo should be given.

When lifting and moving the load by several cranes, the load per each of them must not exceed the crane’s load capacity. Work on the movement of goods by several cranes is carried out under the direct supervision of the person responsible for the safe manufacture of cranes.

For work, one should use the same type of cranes or sets of rigging means of the same load capacity, having equal speeds of working movements. To ensure even distribution of the workload between load-lifting machines, balancing traverses must be used.

Uneven distribution of load and rocking of the load can lead to overloading of one of the cranes, spontaneous unloading, etc.

The work of bridge cranes in tandem

The work of bridge cranes in tandem is used for joint work with more than one load-lifting device. This mode is applicable for two or more cranes installed on certain crane tracks. An important advantage is that the crane operator can control the cranes and all their lifting mechanisms from one control panel.

The work of overhead cranes in tandem allows you to reach:

  • synchronous movement of cranes
  • synchronous movement of cargo trolleys of cranes
  • synchronous lifting and lowering of loads
  • canting of goods by cranes on weight (using two-link cranes).

As a part of a large project to build a road in the north of England, the Scottish company Weldex with the help of two crawler cranes Liebherr copes with the central construction site. Both cranes install a heavy arch of a bridge weighing about 560 tons above the Erwell River in Manchester in tandem lifting.

Before announcing the start of the work, the crane model was used actively for six months. In this case, a massive construction was used to work on the lower part of the bridge (for construction) at an altitude of about 90 meters. To make this possible, the company used to build small sections of the structure then assembling them to make a full-fledged completed project.