Reinforcement of strip foundation and calculation of reinforcement

The foundation is the foundation of any building, which is erected in the first place and takes on not only the load of the entire structure, but also the load from the soil during seasonal heaving, excessive precipitation and temperature changes. In this case, the main compressive load is assumed by the concrete component, and the tensile load is assumed by the steel reinforcement. And therefore, in order to improve the solidity of the building, a technology called "reinforcement of the strip foundation" is used.

It is the strip foundation that is most often used in the construction of buildings made of logs, glued beams, cinder blocks or bricks with a small number of storeys (usually 2-3 floors). The tape-type base has the appearance of a closed contour, precisely distributed along the perimeter of the building in accordance with the plan of the house. That is, such a foundation is mounted under each of the bearing walls of the building, where the goal is to evenly distribute the load from the house to the ground.

Important: incorrectly executed reinforcement of the strip foundation can soon lead to the destruction of not only the entire contour, but also the built building. That is why the reinforcement of the building foundation requires a careful and balanced approach, as well as compliance with the technologies regulated by SNiP.

Reinforcement technology

Reinforcement of the strip foundation is carried out at the initial stages of construction, namely, before pouring the concrete solution into the formwork. To strengthen the contour of the foundation, steel elements are used, which are assembled into a lattice structure with specified parameters. In this case, the calculation of the parameters of the reinforcing crate is carried out taking into account the height, length and width of the base tape.

The reinforcing grid is erected at the stage of formwork installation, after which it is poured with concrete in layers using a construction vibrator. Such a device allows you to better expel air bubbles from the structure of the solution and make it more dense and strong after drying. Lastly, waterproofing of the reinforced base is performed using special mastic and roofing material.

Types of rod for reliable reinforcement

In order for the reinforcement of the strip foundation by reinforcement to be reliable, it is necessary to use high-quality steel elements of a certain class. So, professionals suggest using for longitudinal reinforcement a rod marked with class A-III (today - A400) with a herringbone-type surface or simply with a ribbed top. The diameter of such steel should be from 10 to 22 mm, depending on the width and height of the base. Such frame elements will be the basis for the entire frame. That is why they are stacked in the amount of four pieces on each side of the foundation tape, two from the bottom and two from the top, creating a frame with the help of short longitudinal corner rods.

For transverse and vertical reinforcement, steel of a smaller section of class A-I (today A240) is most often used, which have a smooth surface. The diameter of such elements is from 4 to 10 mm, since the load on them is not as colossal as on rods for longitudinal laying.

Important: the spacing of the transverse and vertical angles during the installation of the crate varies from 30 to 50 cm, depending on the width and length of the base tape. At the same time, the upper longitudinal elements of the crate should not go deeper into the solution by more than 5 cm. Otherwise, the benefit of reinforcing the foundation from the side of the load-bearing walls will be minimal.

Calculation of the amount of reinforcement

You can also use our online calculator for calculating strip foundation reinforcement.

To carry out high-quality reinforcement at the stage of material procurement, it is necessary to calculate its quantity. In order to understand how many rods will be needed to complete the installation work, you can use the reinforcement weight coefficient used by professionals for many years.

Important: for reinforcing the foundation tape for low-rise houses (private construction), over the years, the weight of the reinforcement necessary for arranging 1 m3 of foundation has been taken out and accepted as the building norm. This value is 80 kg.

Thus, in order to calculate the required weight of reinforcement for a particular foundation, it remains to calculate the amount of concrete consumed for the construction of the foundation. To do this, it is enough to know the perimeter of the future house, the length of the bearing walls, the height and width of the foundation.

Example: with a concrete quantity of 20m3, the weight of the required reinforcement should be 1600 kg, that is, 20x80=1600.

• It is necessary to draw a general reinforcement scheme and calculate the number of linear meters of the rod required to equip the entire crate, knowing all the parameters of the foundation. To the result you need to add another 5-10%, which may be used for trimming.
• Now it is necessary to find out the weight per linear meter of the steel frame elements of the longitudinal and transverse / vertical arrangement.
• It remains to multiply the linear meters obtained when drawing the scheme by the weight of the rods for a specific purpose.

Important: if you don’t undertake to carry out the correct calculation yourself, then it’s better to entrust this stage of work to professionals.

Assembly of the crate

At the stage of installation of the reinforcing lattice, it is necessary to go through the stage of knitting steel rods into a single structure. To do this, use a steel wire with a cross section of 2 mm.

Important: welding during the installation of a reinforcing lattice is completely prohibited, since the steel loses its strength characteristics during the welding process, which means that the erected house will not be reliable. Welding is allowed by SNiP only if steel marked C is used for the frame. For example, A500C steel bar. This letter indicates that the material is suitable for welding.

Reinforcement is knitted using a special construction hook, which facilitates the formation of steel loops.

Reinforcement is knitted as follows:

• A piece about 30 cm long is cut from a common coil of wire;
• It is folded in half and applied to two rods that will be connected;
• Now the hook is threaded into the existing loop of wire and one free end is captured, passed into the loop and bent around the steel element;
• The second end of the wire is wrapped around the second rod in the same way through a loop, fastening them together at an angle of 90 degrees.

Thus, all structural elements are knitted.

Important: you can also use a special nozzle for a screwdriver or electric hooks to assemble the frame.

The distance of the rods in the crate according to SNiP

In SNiP 52-01-2003, the indentation from one element of the reinforcing frame to another is clearly regulated, thanks to which both professionals and private craftsmen can comply with the strip foundation technology.

So, the rules of SNiP are as follows:

• The minimum distance of the transverse steel bars from each other in the reinforcing crate depends entirely on the diameter of the elements, the size of the aggregate fractions for concrete, the location of the frame elements in relation to the direction of pouring the mortar and the method of laying the walls, but not less than 25 cm.
• The distance between the longitudinal elements of the frame is calculated taking into account the type of future structure (the presence of bay windows, balconies, columns, etc.), the height and width of the foundation tape. But at the same time, the distance between the longitudinal rods must either correspond to half of its height, or be from 30 to 50 cm.

Corner reinforcement technology

An important element in the construction of a steel bar crate is the reinforcement of the corners of the foundation. A big mistake is to assemble the structure from separate rods at an angle of 90 degrees. Even a securely connected structure in this case does not give any guarantee of the reliability of the foundation, since the frame elements in this case do not represent a reliable rigid frame and can be compressed and stretched. As a result, cracks and chips will appear at the corners of the foundation, which will subsequently lead to the destruction of the house.

Important: when reinforcing corners, only bent rods are used, which are then knitted with longitudinally arranged elements at a distance of 50-70 cm from the very corner of the foundation.

Reinforcement of bay windows and ledges

Often, for the beauty of the future building, the project provides for ledges under the veranda or the so-called bay window. A foundation is also poured under it, associated with a tape one.

In this case, it is also necessary to use the technology of bending the rod in the form of an obtuse angle.

The reinforcement technology will look like this:

• The bent steel is placed on the ledge of the foundation, and its edges lead to the outer longitudinal elements;
• Now the internal rods of the longitudinal arrangement are passed through the bent frame and connected together;
• Then the outer longitudinal frame elements are also bent after their junction with the curved element and brought to the inner ones;
• And to strengthen the structure, rods bent in the form of G and a sufficient number of clamps are used.

Several rules for high-quality reinforcement

In order to prevent a possible violation of the structure of the foundation and the subsequent destruction of the building, when reinforcing, it is also necessary to adhere to certain rules prescribed in SNiP:

• When installing a steel crate for reinforcement, it is necessary to avoid possible contact of the steel bar with the ground or formwork. This can subsequently lead to corrosion of the metal and a decrease in its technological characteristics. Therefore, it is very important to reliably deepen all frame elements into concrete. On all sides, steel should be buried in concrete by no more than 50-80 mm.
• To reinforce the corners of the foundation, you can use both L-shaped bent rods and U-shaped ones. In both cases, the structural elements are connected to the longitudinal ones using clamps.