Construction jacks: characteristics and selection rules

Any modern construction at the stage of erection of monolithic structures requires the use of all kinds of devices that can facilitate the work and contribute to an increase in the overall level of the casting performed, and, consequently, of the entire object. Among the main elements of the formwork that are used in monolithic construction, it is necessary to highlight the support posts or, as they are also called, jacks, the value of which is difficult to overestimate.... It is about them that will be discussed in our material.

The construction jack is used during the installation of monolithic slab formwork. It consists of several structural elements:

• supports - upper or lower;
• nuts;
• retainer;
• unvilka.

Bottom part such a rack, as a rule, is static and does not move, it ends with a support, the dimensions of which are sufficient to ensure maximum stability of the structure. Top part, on the contrary, it is retractable, it is also equipped with a support that interacts with the details of the formwork system, for example, with an I-beam.

Pull-out section of the rack is considered the basic element with which you can adjust the entire structure in height. The inner tube has technological holes, it is inserted into them retainer. Due to the design features of this unit, the product is adjusted in height.

With full movement of the inner tube the maximum rack height is 5 m. To fill the ceilings placed at high heights, a telescopic stand is used and reinforced with a tripod - it also allows high-quality centering of the entire structure. In general, the installation of a jack for construction formwork is not a particularly difficult technical process.

In order to carry out the lifting of the load during the implementation of construction and installation and repair and finishing works, in addition to the hoists themselves, jacks are widespread. They are especially relevant in cases where a low lifting height is technologically required. In construction practice they use jack of screw, rack and pinion, as well as hydraulic or pneumatic types... Such equipment is used for vertical transportation of goods or holding large-sized items, structures and even buildings during any technological and construction operations.

The most primitive screw jack includes a body with trapezoidal or rectangular threads. On the upper part of it there is a head, which is responsible for maintaining the raised soil. The ratchet wheel fixes the head, the screw covered by the clamp is set in motion by the handle and the double-sided pawl fixed on the axle. In this position of the pawl, a spring fixed to the handle is fixed.

All screw jacks are adjustable and self-braking systems, so their lifting angle, as a rule, does not exceed 5 degrees. The lifting capacity of typical construction jacks ranges from 15 to 20 tons, while the lifting height is 0.25-0.35 m.In structures where an additional gear for the rotation of the screw is provided, the lifting capacity can be 50 tons.

Rack jacks are needed for lifting loads weighing up to 6 tons. A toothed rack with a swivel load head and a foot for lifting low-lying loads moves in the body. This rack moves in the housing with the help of a rack gear, and that, in turn, receives rotation from the handle through one or two pairs of gears. In order to keep the load in a raised position, a ratchet with a pawl is attached to the handle shaft.

Hydraulic installations have a lifting capacity of up to 200 tons, they are indispensable for the installation of heavy construction and production equipment, as well as metal structures. In this case, the lift height reaches 0.15-0.2 m. The piston in them moves in the functional cylinder under the action of the hydraulic fluid, during its movement from the chamber to the cylinder under the action of the piston and gear pump. The piston lift is controlled through the spool valve of the distributor or some other device; for lowering the piston, a channel is provided that connects the working cylinder to the chamber.

When lifting loads weighing several thousand tons, usually several such jacks are connected at once into a common battery, feeding them from one common pump. In recent years, hydraulic jacks of this special design have been widely used for tensioning reinforcement during the manufacture of stress-reinforced concrete products.

Pneumatic installations are a symbiosis of a compressor, as well as a membrane elastic container, in which compressed air is supplied. Such installations are in demand in the course of emergency and rescue operations, they are used when dismantling debris, in traffic accidents and in other emergencies.

The use of a jack in the construction of monolithic buildings is explained by the action of multidirectional loads. This mechanism is indispensable in almost all formwork systems that are used to fill horizontal, vertical, and volumetric structures. The basic function of the jack in this case is to ensure maximum stability of the entire structure. In addition, it can be used for alignment, fixing and separation of the formwork system during the pouring of the slabs. Only in horizontal structures all the functionality of construction jacks is revealed to the maximum extent.

When choosing any construction jack, first of all, the following factors matter:

• minimum pick-up height,
• maximum lifting height,
• loading capacity of the device.

A parameter such as minimum pick-up height, shows the starting working height. The lower this parameter is, the more versatile the jack itself will be, which means that it can be used for a wide range of construction projects.

Maximum lifting height is also considered one of the most important parameters that you need to pay attention to when buying a construction jack. For most devices, this parameter is in the range from 30 to 50 cm. As a rule, this is quite enough to create conditions for access to a particular building surface and move it to the level of the scaffolding.

In the next video, you will learn how to choose the right jack.