Creating a solid foundation is one of the most important steps in building a house. The designs of the carrier base may vary, but the solution of problems of mechanical reinforcement in one form or another implies any technology. The most common operations to support the foundation are the laying and knitting of reinforcement, the rods of which penetrate and strengthen the structure of the foundation.
Target parts to strengthen
In modern construction, reinforced concrete structures in buildings are rarely dispensed with. Usually the frame contains several elements, the main of which are the foundation and basement levels. They can be monolithic or prefabricated, but the integration of reinforcing bars will in any case be mandatory. Also, the over-foundation structure involves metal reinforcement. In this part, load-bearing beams, ceilings, lintels and pillars are constructed. Moreover, depending on the design solution, reinforcing rods can monolithically move from one level to another. For example, knitting reinforcement underthe strip foundation from the installed lower tier goes to the grillage, the first floor and the walls.
In the choice of specific means of reinforcement, much will depend on the target design. The length, diameter, type and shape of the rods - these and other parameters are determined by the installation site. For example, a monolithic foundation block involves the introduction of thick rods with ribs, and for a cement screed in the first floor, thin rods and even wire are used.
Laying the lower reinforcing belt
At this stage, the basis of the frame is formed to strengthen the foundation. As a rule, a tape structure is used, the shape of which must repeat the reinforcing skeleton. Laying is carried out on a prepared multi-layer "pillow" of sand, gravel and special insulation in the form of geotextiles. From the lower belt to the very sole of the foundation, a gap of 5 cm should be maintained. For example, these can be 3 rods with a diameter of 16 mm. Reinforcement should be knitted with a distance of 1 step, using cross bars from smaller bars. It is necessary to calculate the parameters of the frame so that after pouring it completely remains in the structure of the foundation. Moreover, it is desirable to keep a protective layer of 3-4 cm in the form of a spade over the edges of the frame. At the slightest sign of destruction, insufficiently closed corners of the reinforcing structure may undergo corrosion, which over time will negatively affect the entire carrier platform.
Installation of vertical reinforcement
After laying the horizontal linereinforcing frame, you can proceed with the installation of rods along the entire height of the foundation. For this, 10 mm metal rods are used. They should be located at the corners of the structure and along the sides, retreating an average of 1.5 m. And again, it should be borne in mind that the rods after pouring should receive a protective sheath with a spade from the edges up to 3-4 cm. produced both internally and externally. Only in rare cases, when building small objects with thin walls, it is allowed to place load-bearing reinforcement racks in the center in one line.
Large houses at the foundation level additionally receive a reinforcing vertical mesh with 10x10 cm cells. For such flooring, a wire about 4 mm thick is used. During operation, this grid will perform the function of a compensator for horizontal stresses at the ground level. It is mounted on the inside and outside of the trench, fixing to pre-installed vertical posts.
Reinforcement at the corners
The configuration of the joints at the corners has its own characteristics, which must be taken into account in the knitting process. In these parts of the reinforcement cage, the maximum load is expected due to high stress, which will affect the stability of the structure. Simply making an overlap joint or using one long rod with bends at the corners are unacceptable installation tactics. Knots are made according to the L- or U-shaped scheme. The reinforcement lines to be connected must be different:one rod enters and refracts into a small segment of the girth, and the second one continues the contour, in turn, leaving the end for fastening. It is desirable that the reinforcement in the corners be knitted with additional support from longitudinal metal plates. But it is also undesirable to oversaturate the structure in this zone, since the loose structure of concrete is more prone to destruction.
What kind of wire is used for knitting?
The issue of selecting consumables for fastening different reinforcing lines is fundamental, since the reliability of the structure as a whole will depend on it. The most common use of galvanized and mild steel wire. The material is distinguished by high protective qualities, which are provided by hot-dip galvanizing technology. The thickness of the coating may vary, but in average calculations, you can focus on 85-90 g/m2 in a wire with a diameter of 6 mm. You can also add reliability structures by knitting reinforcement with copper-nickel alloy wire, but the cost of the consumable in this case will increase by 15-20%.
The type of hardening should also be taken into account. Allocate unheated material, and subjected to special annealing. In the second case, the knitting wire is heated in a blast furnace to high temperatures, which makes it possible to relieve the internal stress of the structure. Industrial annealing gives the material strength and elasticity. But even in this case, you need to prepare for an increase in the cost of the consumable.
Knitting toolfittings
The process of connecting bars is carried out either with a special gun or with a hook. The first option is more advantageous, since the performer saves time for the operation, providing high-quality fastening. On average, one node takes 1-2 seconds. When choosing this device, you should take into account the traction force, the size of the wire suitable for maintenance and the battery capacity, on which the operating time on a single charge depends. For example, a medium-sized rebar tying gun provides a force of up to 85 Nm, working with wire up to 1.5 mm thick.
As for the knitting hooks, they are used for manual connection. These are small devices, the quality of work with which will largely depend on the master himself. There are also more technologically advanced automatic hooks, the principle of which is based on the translational movements of the working gripping part.
Pistol knitting technique
The design of the device provides a special store in which there is a block with wound wire. The user only needs to load the coil, check the battery charge and adjust the operating parameters of the device. In particular, the tension force and the length of the twisted wire are set. A standard rebar tying gun of medium power allows you to make about 200-250 knots in one continuous session. To perform each connection, the operator needs to position the working head of the device in the area of the intersection of two rods and press the start button. Behindfor a couple of moments, the wrapped connection will be reinforced with wire.
Pistols are recommended for professional builders working with large volumes of knitting material. For example, on foundation sites with a frame covered with a mesh, such an apparatus can replace 10 workers with hooks. However, hand knitting devices have their advantages.
Crochet reinforcing bars
The same wire with a thickness of 0.8-1.5 mm can be used in the work. With hands without a hook, the master threads it along the capture line so that a loop is formed at the junction. That is, it is necessary in advance to bend the wire twice or four times, not forgetting the acceptable degree of material rigidity. Next, a hook is taken for knitting reinforcement, with the sting of which you will need to grab the loop. After that, the knot is twisted to the desired level, but the wire should not be tightened too much, as it will simply burst if it is overstressed. The number of turns around the girth can be different - it depends on the reinforced structure, the format of the wire itself and the operating conditions. As for the advantages of this knitting technique, it is low-cost and almost universal. The hook costs about 200-300 rubles, does not require special maintenance and power supply.
General workflow guidelines
Strengthening the foundation involves taking into account many technological nuances that appear depending on the working conditions. The most common of them include the following points.
- Problems with finding fittings that meet design requirements are a fairly common situation. There are parameters in which the discharge is allowed, but there are also strict characteristics to comply with. For example, you cannot change smooth rods to ribbed ones (and vice versa), use a different grade of steel, etc.
- The surface of the rods must not be rusty or painted. If a gun or automatic hook is used for tying rebar, they should also be degreased.
- It is forbidden to connect reinforcing bars in places of tension of a bent concrete structure. These are critical areas, in which there should be no mounting points.
- To exclude voids (the so-called shells) in the foundation, the gaps between reinforcement lines should be balanced over the entire area.
Advantages of tying rebar before welding
Many mistakenly choose the welding method of connection due to higher reliability. This is partly true, but studies show that the method of knitting does not matter after concreting. The fastening itself is used as a means of maintaining the frame structure for the installation period. Therefore, it is quite possible to knit the reinforcement with your own hands, even with the help of plastic clamps - the main thing is that they do not burst in the process of transferring the structure to the formwork. Wire connections are beneficial in that they are completed faster, require less financial costs, and also do without connecting additional equipment such as weldingdevices, inverters and transformers.
Conclusion
The process of laying and knitting rebars is recommended to be performed in dry weather and immediately before pouring concrete. This will maintain optimal performance of the material and make timely technical corrections to the frame if errors are detected at the time of the installation of the supporting structure.
As for the connection methods, it will be optimal to knit reinforcement with a gun. The user will spend less time on installation operations, but will perform the task with high quality. The hook should be chosen by those who build the foundation in a one-time order. Nevertheless, a knitting gun costs an average of 20-30 thousand rubles, so buying it for domestic use is hardly justified.
