Building rebar is a steel rod, which during the construction process is connected into a frame, contributing to the creation of the strength of all elements of the building.
This is most often an auxiliary structure, which helps to distribute loads, increase the bearing capacity of the structure. It is used in the construction of reinforced concrete buildings and in the foundation.
Strengthens the properties of concrete, does not allow it to crack. It has all the common properties: strength, ductility, frost and heat resistance, corrosion resistance.
Steel rebar is hot-rolled rod and cold-rolled (cold drawn) wire. The most widely used hot rolled steel rebar having a long pipe with a smooth or periodic profile (in other words, with a smooth or ribbed surface).
The rebar of a periodic profile are in great demand since has better contact with concrete. However, a periodic profile is a specific determinant of the tension and strength of steel. Therefore, if adhesion to concrete is not required, use a material with a smooth surface. The rods are produced with a diameter of 10 to 57 mm.
Rod rebar are made of alloy steel. Silicone and manganese. Chromium and titanium are sometimes added.
An easy way to introduce into the printout of additional substances that improve the physical and mechanical properties of steel. Stainless steel products, resistant to corrosion, wear resistance. In the manufacture of the frame, the rebar rods are welded or connected by knitting using a knitting wire.
Cold drawn wire rebar has a diameter of 3 to 13 mm. It is made of low-carbon steel (high-strength wire of class B-II) or carbon steel (high-strength wire of class B-II). There are also smooth and grooved (class BP-I or BP-II). I use class B-wire for non-tensile rebar. Class B-II – for prestressed. High-strength wire rebar is a quality product, but it is less in demand than steel rods. Firstly, the cost of wire is higher. Secondly, it requires the use of heavy-duty, high-quality concrete.
They can be made of several (3-19) wires with a smooth surface. The most common are seven-wire, manufactured using six spiral wires with a diameter of 1.5 to 5 mm around a straight cylindrical wire.
Installing rebar under the foundation yourself
For installing reba, you need a minimal set:
- the rebar itself;
- knitting wire;
- knitting gun or pliers;
- time and patience.
The required strength of the foundation is achieved due to the concrete grade and the correctly selected diameter of the rods. The most reliable, but also more costly option will be products with the largest possible diameter.
|Linear Mass Density||Nominal diameter||Nominal area|
|#3||No.10||0.376||0.560||0.375 = 3⁄8||9.53||0.11||71|
|#4||No.13||0.668||0.994||0.500 = 1⁄2||12.7||0.20||129|
|#5||No.16||1.043||1.552||0.625 = 5⁄8||15.9||0.31||200|
|#6||No.19||1.502||2.235||0.750 = 3⁄4||19.1||0.44||284|
|#7||No.22||2.044||3.042||0.875 = 7⁄8||22.2||0.60||387|
|#8||No.25||2.670||3.973||1.000 = 8⁄8||25.4||0.79||510|
|#9||No.29||3.400||5.060||1.128 ≈ 9⁄8||28.7||1.00||645|
|#10||No.32||4.303||6.404||1.270 ≈ 10⁄8||32.3||1.27||819|
|#11||No.36||5.313||7.907||1.410 ≈ 11⁄8||35.8||1.56||1,006|
|#14||No.43||7.650||11.384||1.693 ≈ 14⁄8||43.0||2.25||1,452|
|#18||No.57||13.60||20.239||2.257 ≈ 18⁄8||57.3||4.00||2,581|
- Typically, 10-13 mm thick rods are selected for work. This indicator is quite enough for the construction of buildings with a high degree of load. But if it is planned to equip the base at a shallow depth, then such an overspending of the material is not justified.
- In the calculations, you can be guided by the following proportion: the cross section of the rebar should be equal to 0.1% of the foundation area.
- One of the rational methods is to select the thickness of the rebar based on its location. For a longitudinal arrangement, products with a diameter of 10 mm and a maximum length of 3 m are taken. In this case, the transverse rods may have a diameter of 10 mm.
- If it is planned to use rebar of greater length, that is, more than 3 m, then the recommended diameter will be 13 mm. Consequently, the transverse rods may be 10 mm thick.
- Regarding composite materials, it should be said that the diameter of fiberglass rods equal to 10 mm is similar to the diameter of metal products in 10-13 mm, respectively.
Calculation of rebar under the foundation
In order not to have to suspend construction with a lack of reinforcing material, and at the same time not to pay extra for the second delivery, it is necessary to draw a foundation diagram and calculate the number of rods.
For a good example, take a house 9 by 12 m with two load-bearing walls 9 and 6 m long. The structure will be built on the basis of the tape type. As a rule, for such a scheme, a rod with a diameter of 13 mm is used. In a longitudinal arrangement, 4 pieces are placed.
- First, calculate the perimeter of the building: (9 + 12) * 2 = 216 (m).
- The length of the base under the supporting walls is added to the result: 216 + 9 + 6 = 231 (m).
- The resulting length is multiplied by the number of rods: 231 * 4 = 924 (m).
- If it was not possible to purchase the rods of the required length, then take into account additional meters of rebar for dressing, where the overlap should be at least 1 m.
- Suppose the project provides one connection on the longitudinal bars, then the number of reinforcing rods according to the scheme is multiplied by the number of walls. The result should be: 4 * 6 = 24 (m). The obtained result adds to the previous value: 924 + 24 = 948 (m).
- Now we will calculate the smoothbore rebar necessary for transverse laying, where the width of the strip foundation will be 0.5 m. For the step between the crossbars we will take 0.3 m.
- 231 / 0.3 * 0.5 = 385 (m).
- It is quite difficult to take into account all the trimmings and overlaps in preliminary calculations. Therefore, experts recommend adding 10% to the final result.
Rebar device under the foundation
Without diving deeply into the calculations and physicotechnical characteristics of the materials used in the construction of the foundation, we can say the following:
- concrete has high compressive strength, but low tensile strength, while steel and composite products quietly withstand large tensile loads;
- the lower part of the base of the structure takes tensile forces, and the upper part takes on compression loads. Thus, combining reinforcing elements and concrete, it is possible to achieve the optimal ratio of resistance to various types of exposure;
Based on the above theses, we can conclude that only the lower part of the base needs rebar. But, in addition to the loads produced by the walls of buildings and other structural elements, it is necessary to take into account the influence on the stability by the forces of frost heaving of the soil.
Angles require special attention. It is these points that are affected by maximum loads, so you can not save on material in any case.
Some useful tips
- Longitudinally spaced rods are taken with a diameter of 10-13 mm. The higher the perimeter of a standing building, the larger the diameter should be. For better adhesion to the concrete mass, it is better to purchase products with a ribbed surface.
- The rods should not lie on the bottom of the trench, should be located close to the surface (but also not deepen much) or in contact with the walls of the formwork. They must be reliably “hidden” in the thickness of concrete.
- Cross and vertically placed products carry less load. In this connection, smooth products of a smaller diameter (10 mm) are used for such work.
A layer of sand is poured into the prepared formwork, the walls of which are reliably protected by a waterproofing material. The substrate is moistened and rammed. On top of it lay pieces of broken brick or stone. They will serve as a support for the rods and will not allow them to touch the bottom. The distance between the walls of the formwork and the reinforcing frame should be at least 5 cm.
To achieve maximum strength and reliability of the structure, rods of maximum length are used. Thus, it will be possible to avoid a large number of compounds, and at the same time reduce material consumption due to the absence of overlaps.
For a standard base, a width of no more than half a meter, 4 longitudinal elements arranged in 2 rows (2 pieces above and below) are enough. The use of 3 or 4 products is relevant for a wider foundation or for the construction of a house on poorly bearing soil.
The rods are driven vertically into the ground, the lower horizontal row of rebar is tied to them. By means of a special gun a bunch of elements is produced. A crochet hook will speed up and facilitate the whole process of work. The number of turns is determined by experience – in the end you should get a tight knot.
With a small amount of work, ordinary pliers are used. A wire about 30 cm long is bent in half so that a loop forms on one side. Grasping a piece of wire with two connected rods, the second end of the wire is threaded into the eye. Then both ends rotate several times with rotational movements, tightening tightly into a knot. It is important here not to overdo it or cut off the wire at the connection point.
The fastening of metal elements can be carried out by a welding machine. This method will allow you to quickly and reliably combine them into a single bundle. However, strength can play against. During frosts, the soil begins to “walk” and the foundation has to adapt to it.
The wire just provides the necessary clearance for stretching. In addition, before welding, you should make sure that the metal product is marked C. Other products simply lose some of the strength at the connection points.
After the lower horizontal rods go to the upper row. It should be located 50-60 mm from the edge of the trench, regardless of the depth of the foundation.
Corners are reinforced using rebars. You can’t just lay a double row of rods at such points. Angular contact should be as strong as possible, this can be achieved by adding additional transverse and vertical elements. The same rules apply when arranging T-shaped crosshairs (the places where the internal bearing walls enter the external capital walls).
The use of rebar in the construction of concrete structures is not a new technique. However, bright minds could not come up with better technology. In order to protect the foundation of the house from destruction, do not neglect these works, extend the operation of the house for a longer period.