Creating a solid foundation is one of the most critical stages of building a house. The design of the carrier base may vary, but the solution of the problems of mechanical reinforcement in one form or another implies any technology. The most common operations to support the foundation are laying and knitting reinforcement, the rods of which penetrate and strengthen the foundation structure.
Target parts for strengthening
In modern construction, rarely do without reinforced concrete structures in buildings. Typically, 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 rods in any case will be required. Also, the over-foundation structure involves metal reinforcement. In this part, supporting beams, floors, lintels and poles are constructed. Moreover, depending on the design solution, the reinforcing rods can seamlessly move from one level to another. For example, knitting reinforcement under the strip foundation from the installed lower tier is sent to the grillage, the first ceiling and walls.
In the choice of specific means of amplification, 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 location. 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 base of the frame is formed to strengthen the foundation. As a rule, a tape structure is used, the shape of which must be repeated by the reinforcing skeleton. Laying is done on a prepared multilayer “pillow” of sand, gravel and special insulation in the form of geotextiles. From the lower zone to the very bottom of the foundation, a gap of 5 cm should be maintained. For example, these can be 3 rods with a diameter of 16 mm. The reinforcement should be knitted with a distance of 1 step, using cross-sections from smaller rods. The parameters of the frame must be calculated so that after pouring it completely remains in the foundation structure. Moreover, it is desirable to maintain a protective layer of 3-4 cm in the form of a protrusion beyond the edges of the frame. At the slightest sign of destruction, insufficiently closed corners of the reinforcing structure may corrode, which over time will negatively affect the entire supporting platform.
Installation of vertical fittings
After laying the horizontal line of the reinforcing 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 on average 1.5 m. And again, it should be borne in mind that the bars after pouring should receive a protective shell with a spacing from the edges up to 3-4 cm. Moreover, the reinforcement is knitted under the foundation with a tape type design It is made both from the outside, and from the inside. Only in rare cases when constructing small objects with thin walls is it possible to place load-bearing reinforcing posts 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 of about 4 mm thickness is used. During operation, this grid will perform the function of a horizontal voltage compensator at ground level. It is mounted on the inside and outside of the trench, fixing to pre-installed vertical racks.
Corner reinforcement
The configuration of the joints in the corners has its own characteristics that must be taken into account during the knitting process. In these parts of the reinforcing cage, the maximum load is assumed due to the high voltage, which will affect the stability of the structure. Just doing a joint like overlap or applying one long rod with bends in the corners - invalid mounting tactics. Nodes are performed according to the G- or U-shaped scheme. The connected lines of reinforcement should be different: one rod enters and refracts over a small segment of the girth, and the second continues the contour, in turn, leaving the end for fastening. It is desirable that the knitting of the reinforcement in the corners is carried out with the additional support of longitudinal metal plates. But it is undesirable to oversaturate the structure in this zone, since a loose structure of concrete is more susceptible to destruction.
What wire is used for knitting?
The issue of selecting consumables for fastening different reinforcing lines is a matter of principle, since the reliability of the structure as a whole will depend on it. The most common use is galvanized and low carbon steel wire. The material is characterized by high protective qualities, which are provided by the technology of hot galvanizing. The coating thickness may be different, but in average calculations it is possible to focus on 85-90 g / m 2 in a wire with a diameter of 6 mm. You can add reliability designs by knitting the reinforcement with a wire made of a copper-nickel alloy, but the cost of the consumable in this case will increase by 15-20%.
Consideration should be given to the type of hardening. Material that has not undergone heat treatment is isolated and subjected to special annealing. In the second case, the knitting wire is heated in a blast furnace to high temperatures, which allows you to remove the internal stress of the structure. Industrial annealing gives the material strength and elasticity. But in this case, you need to prepare for an increase in the cost of the consumable.
Rebar Knitting Tool
The process of connecting the rods is carried out either with a special gun or with a hook. The first option is more advantageous, since the contractor saves time on the operation, providing high-quality fastening. One node takes an average of 1-2 seconds. When choosing this device, one should take into account the traction force, the size suitable for servicing the wire and the battery capacity, on which the operating time on one charge depends. So, the average pistol for reinforcing knitting provides a force of up to 85 Nm, working with wire up to 1.5 mm thick.
As for the crochet hooks, they are used to make a manual connection. These are small devices, the quality of work with which will largely depend on the master himself. There are also more technological automatic hooks, the principle of which is based on the translational movements of the working exciting part.
Knitting Technique
The design of the device provides a special store in which there is a unit with a wound wire. All that is required of the user is 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 gun for knitting medium power fittings allows for one continuous operation to make about 200-250 knots. To make each connection, the operator needs to position the working head of the device in the zone of intersection of the two rods and press the start button. In a couple of moments, the hooked connection will be reinforced with wire.
Pistols are recommended for professional builders working with large volumes of knitting material. For example, on foundation platforms with a wire mesh frame, such a device can replace 10 workers with hooks. However, the devices for hand knitting have their advantages.
Crochet reinforcing bars
In the work, the same wire with a thickness of 0.8-1.5 mm can be used. With his hands without a hook, the master passes it along the capture line so that a loop forms at the junction. That is, in advance it is necessary to bend the wire twice or four times, not forgetting about the acceptable degree of stiffness of the material. Next, a hook for knitting reinforcement is taken, the sting of which will need to grab the loop. After this, the assembly is twisted to the desired level, but the wire should not be tightened too much, since it will simply burst if the voltage is excessive. The number of turns in girth may be different - it depends on the reinforced structure, the format of the wire itself and operating conditions. As for the advantages of this knitting technique, it is low-cost and almost universal. The hook costs about 200-300 rubles. It does not require special maintenance and power supply.
General workflow guidelines
Strengthening the foundation involves taking into account the many technological nuances that manifest themselves depending on the working conditions. The most common of them include the following points.
- Problems with finding fittings that meet design requirements is a fairly common situation. There are parameters in which departure is allowed, but strict specifications are present for compliance. For example, you cannot change smooth rods to ribbed ones (and vice versa), use steel of a different grade, etc.
- The surface of the rods should not be rusty or painted. If a gun or automatic hook is used to knit fittings, they should also be degreased.
- In places of tension of a bent concrete structure, it is prohibited to connect reinforcing bars. These are critical areas where any mounting points should be absent.
- To exclude voids (the so-called shells) in the foundation, the gaps between the reinforcement lines should be balanced to calculate over the entire area.
Advantages of knitting reinforcement before welding
Many people mistakenly choose the welding method of connection due to their higher reliability. This is partly true, but studies show that the method of mating does not matter after concreting. The bond itself is used as a means of maintaining the structure of the frame 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 during the transfer of the structure to the formwork. Wire connections are advantageous in that they are faster to complete, require less financial expense, and also do without connecting additional equipment like welding machines, inverters and transformers.
Conclusion
The laying and knitting of reinforcing bars is recommended to be carried out in dry weather and immediately before pouring concrete. This will allow to maintain optimal performance characteristics of the material and timely make technical corrections to the frame when errors are detected at the time of the load-bearing structure.
As for the connection methods, it will be optimal to knit the reinforcement with a gun. The user will spend less time on installation operations, but will qualitatively fulfill the task. The hook is worth choosing for those who build the foundation in a single order. Nevertheless, a knitting gun costs an average of 20-30 thousand rubles, so its purchase for domestic use is unlikely to pay off.