Tower cranes are a fairly common sight in larger cities, around larger and medium-sized construction sites. Colloquially they are called construction cranes or simply construction cranes. They are a lifting device, classified as one of the largest working machines. The components of this type of lifting device include a vertical mast (called a tower) mounted on a suitable ground. This substrate can be stationary or mobile. There are two types of running ground - rail and tracked. Another component of the tower crane is one of two types of jib - tilting or horizontal. The swing boom has a tractor at its end. The tractor is nothing more than a device whose task is to mix solid objects by means of chain or linear strands with the use of a hitch - most often a hook or a grapple. In the case of a horizontal boom, the tractor moves on it.
Application of construction cranes
The work performed by the tower crane is lifting and moving loads, usually on a hook, which is lowered onto a rope from the jib. The crane moves the load horizontally by turning it around its axis, and also in vertical movement by lifting or lowering the attached load. Cranes of this type are used in both residential and industrial construction, in the transport of various types of materials, as well as in the assembly of steel structures. The undoubted advantage of this type of machine is the large reach of the jib that allows you to operate on a large surface, which gives them an advantage over mobile mobile cranes. They are perfect for operation on large construction sites. Along with the development of the development industry and the construction of new housing estates, office buildings and public utility buildings, they become irreplaceable equipment.
Parameters of construction cranes
- Nominal capacity - this is the maximum load weight that can be lifted by the crane during its operation, maintaining all strength, safety and stability requirements. It is a parameter with a variable value - it depends on the increasing or decreasing crane reach. In order to choose the right machine for the job, you need to know the weight of the heaviest load.
- Boom length - it is one of the most important technical parameters of construction cranes. Greater outreach results in the possibility of passing the load further. The jib length should be selected according to the size of the object under construction, thanks to which the crane operator will be able to deliver the load to each of the designated places.
- Useful height lifting - this is the maximum height at which the crane can lift the load attached to the hook. This distance is measured vertically, starting from the ground level, ending with the axis of the hook, which is the highest point at the current projection. The value of this parameter is also variable, as it depends on the number of installed tower members.
- Working moment - is a constant value. It is the product of the crane by its extension.
- Crane tipping moment - the value is calculated in relation to the hypothetical tipping edge and is a component of various moments - fixing and capsizing of the crane.
Moreover, each such machine is equipped with several drives. The most common are electric drives, each of which is responsible for one movement. Examples of such movements are: boom tilting, undercarriage travel, boom rotation, hook lifting or plunger movement. The jib length of the largest crane currently produced is 100 m, and its maximum lifting capacity is 240,000 kg with a reach of 44 m, and also 120,000 kg with a reach of 82 m. The maximum height of the hook in this model is 86 m.
Classification of tower cranes
Breakdown of construction cranes can be made due to several important attributes. Taking into account the type of boom, the following cranes are distinguished:
- with a trailing jib (extraction and without extraction)
- with a swing boom (called cantilever).
In the case of the mounting method:
- quick assembly (no need for an auxiliary crane)
- assembled in units (requires the use of an auxiliary crane)
Due to the type of base, the following can be distinguished:
- stationary cranes (anchored to the foundation)
- mobile cranes (rail, crawler)
The last classification depends on the place where the rotation mechanism is located, cranes are distinguished here:
- top swivel (the swivel mechanism is at the top of the turret, it rotates the jib, while the turret remains stationary)
- bottom swivel (the swivel mechanism is at the bottom of the tower, the boom rotates with the tower)
The course of the assembly of tower cranes
The assembly of such machines is a responsible and relatively demanding task. In this activity, it is important to properly plan the work and precisely adjust individual elements. These machines, due to their large size, are folded only at the place of their work. The tower crane assembly process should begin with the placement of the crane base on the ground. There are two types of bases - cross and foundation anchor. It must be anchored in a suitable ground (compact and load-bearing). It is necessary to properly stabilize and level such a base, and the anchor must be poured into the cement foundation. Further construction elements belonging to the tower set are placed on the base prepared in such a way.
In the case of the assembly of a bottom swivel crane, work begins with placing the legs. The next step is to level the base and set the tower vertically. Then the counterweight is placed and the assembly of the tower and boom begins. The boom and the tower are assembled in two ways:
- hydraulically - actuators are used here. There are two elements per tower, connected with each other with a hinge, they are unfolded with an actuator. Unfortunately, using this option, you cannot change the height of the tower. The projection is folded out like the tower. And in this case, it is possible to attach the jib while transporting the load while avoiding an obstacle (it is worth remembering, however, that at this time the lead must be in the part of the jib that is not folded)
- mechanically - i.e. telescopically using ropes and pulleys
A mobile crane is used to prepare the top-slewing cranes. The tower is assembled from successive structural elements on a specially prepared base. The next step is to place the central ballast, then mount the turntable and the counter-overhang. The last phase is folding the boom on the ground, lifting it completely and mounting it on the turntable.
Qualifications required to operate the tower crane
Anyone over 18 years of age can become the operator of such a crane. It is also necessary to have a valid medical certificate, which will state the absence of any contraindications to work as a construction crane operator and a valid qualification certificate issued by the Technical Inspection Office of UDT, TDT or WDT (it entitles you to service construction cranes). According to the currently applicable regulations, such a certificate is valid for 5 years. There are many specialized Vocational Training Centers they organize tower crane operator courses. The training is divided into two parts - theoretical and practical. Such a course ends with an examination before the Technical Inspection Committee. After passing the exam, the student receives a certificate of qualifications that entitles him to operate the crane. It is also worth mentioning that the indefinite qualification certificates of the Technical Inspection are valid until January 1, 2024. In order to extend the validity of the rights, you should report to the authority that issued the certificate with a special application, preferably 3 months before this date.