How to reinforce a strip foundation with your own hands. Strip foundation reinforcement: meaning and features

The consumption of reinforcement must be determined at the foundation design stage in order to subsequently know exactly the amount of material purchased. Let's look at how to calculate reinforcement for a strip foundation using the example of a shallow foundation 70 cm high and 40 cm thick.

1.2 Reinforcement of a strip foundation (video)

2 Work technology

After the amount of reinforcement has been determined, a strip foundation reinforcement scheme must be selected, according to which the reinforced frame will be assembled. Straight sections of the structure are made of solid rods, while in corner areas additional reinforcement is required with reinforcement curved in a U or L-shape. The use of perpendicular overlap of individual reinforcement bars at corners and junctions is not permitted.

The correct reinforcement of the corners of a strip foundation is shown in the diagram:

Scheme of reinforcement of strip foundations at junctions:

Reinforcing a strip foundation with your own hands involves assembling the frame in a convenient place and then placing it inside the formwork. The technology requires bending reinforcement into rectangular clamps, which can be easily done at home using a homemade device.

On the 20th channel, you need to cut out grooves with a grinder, into which the reinforcement is subsequently inserted, and a section of steel pipe is placed on the rod, which is used as a lever. The finished rings must be fastened by welding or tied with wire. For rods with a diameter of 10-15 mm, 1.2-1.5 mm wire is used.

A strip foundation is one of the simplest and most reliable types of foundations that you can think of. One construction publication stated that a strip foundation, albeit with reinforcement, can last at least 200 years. How they calculated this and by what kind of chronometer is unknown, but it is a fact that a reinforced strip foundation is reliable. The main thing is to perform the reinforcement correctly, which is what we will do now.

Why and how to reinforce a strip foundation

If we could know for sure what loads our foundation would be subject to in a year, two, ten or twenty years, maybe it wouldn’t be worth reinforcing it. The fact is that the calculation is rather conditional. We bought a piano for our home - the load changed, the forces and vectors of influence changed. A new underground current has arisen - the same story. The foundation sank in some places and rose in others. Therefore, in order not to depend on the purchase of pianos and broken neighboring water pipes, the foundation must be reinforced.

Concrete itself does not have such plasticity to respond to any changes in loads. For this purpose, there is steel that holds the entire base structure together and can be plastic, while maintaining the rigidity that a strip foundation should have. Reinforcement, drawings and diagrams of which we will present on the page, will help maintain the strength of the base, impart plasticity and prevent cracking.

Foundation reinforcement. Which is better?

There is no special choice in structural reinforcement products, and it is not needed. Standard rolled rods do an excellent job of reinforcing any foundation, and their thickness and arrangement are selected depending on the design features of the foundation. Whatever the reinforcement is, it is laid only according to two schemes:

longitudinal reinforcement occurs when it is necessary to minimize tensile loads; such reinforcement is placed below and above the foundation screed, for this

• use a rod of grade A3 with a relief surface;
• Longitudinal-transverse reinforcement is performed when everything is expected from the foundation, and especially in cases where its height exceeds 1.5 m at least in some places.

In the second case, more powerful reinforcement of class A1 from a rolled rod is used, connecting the longitudinal with transverse knitting wire. Welding is not used in this case.

Calculation of reinforcement for strip foundations

Everything is simple here. GOSTs and SNiPs will not allow you to fantasize, but it is imperative to take into account the standards. Before pouring a strip foundation, you need to check the standards, and the standards state that the relative position of the reinforcement bars depends on what brand of concrete is used and on the aggregate fractions. The method of laying and compaction is also of great importance. The recommended distance between the reinforcement bars for a foundation width of 40 cm is about 10 cm, provided that four bars with a diameter of 8-10 mm are laid. GOST recommends placing horizontal rods at a distance of 30 cm with the same foundation width.

When tying reinforcement, it is very important to maintain the distance to the outer surfaces of the foundation, to the formwork and cushion. There are several ways to control this, but the easiest way is with bricks. It is necessary to ensure that the metal rods do not touch the ground, otherwise corrosion will negate all reinforcement efforts. The minimum distance from the rod to the ground should be at least 6-8cm. Only after this can you fill the pillow.

How to make reinforcement for a monolithic strip foundation

This is the simplest and most academic case, when reinforcement passes only along the bottom of the foundation. This is explained by the fact that a foundation buried to the freezing depth is built when the soil is stable and the building does not require a second floor. In this case, the reinforcement is rather of an insurance nature. In this case, A3 reinforcement and smooth A1 reinforcement are used for cross-linking. All dimensions specified in the standards remain valid in this case.

In the event that the soil on which construction is being carried out is unreliable and the load on the foundation is higher, more serious measures should be taken to strengthen the foundation. In these cases, the width of the foundation is taken to be one and a half to two times larger, and when reinforcing, the transverse rods are set to be equal in diameter to the longitudinal ones. In this case, the entire structure is connected with knitting wire; the use of welding is also not encouraged here. It is also recommended to increase the number of horizontal rods, reducing the distance between them to 20 cm.

We looked at the simplest reinforcement schemes for buried foundations, which are perfect for a fence on a strip foundation, for lightweight structures and outbuildings with the prospect of increasing the load.

Many believe that the cross-section and number of metal rods in the laid foundation does not play a special role, and they use everything that comes to hand, from knitting wire to metal pipes. But such connivance can have a bad impact in the future, both for the foundation itself and for the house standing on it.

In order for your future home to serve you for many years, it is necessary that the foundation of this house be strong enough and durable, and the correct calculation of the reinforcement for the foundation plays a huge role in this.

In this article we will calculate metal reinforcement; if you need to calculate fiberglass reinforcement, then you will need to take into account its features.

Calculating reinforcement for a strip foundation of a private house is not as complicated as it seems at first glance, and comes down to just determining the required diameter of the reinforcement and its quantity.

Strip foundation reinforcement scheme

To correctly calculate the reinforcement in a reinforced concrete strip, it is necessary to consider typical reinforcement schemes for strip foundations.

For private low-rise buildings, two reinforcement schemes are mainly used:

• four rods
• six rods

Which reinforcement scheme to choose? Everything is very simple:

According to SP 52-101-2003, the maximum distance between adjacent reinforcement bars located in the same row should be no more than 40 cm (400 mm). The distance between the extreme longitudinal reinforcement and the side wall of the foundation should be 5-7 cm (50-70 mm).
In this case, with the width of the foundation more than 50cm, it is advisable to use six-bar reinforcement scheme.

And so, depending on the width of the strip foundation, we have chosen a reinforcement scheme; now we need to select the diameter of the reinforcement.

Calculation of reinforcement diameter for foundation

Calculation of the diameter of transverse and vertical reinforcement

The diameter of transverse and vertical reinforcement must be selected according to the table:

In the construction of one- or two-story private houses, as a rule, rods with a diameter of 8 mm are used as vertical and transverse reinforcement, and this is usually quite sufficient for strip foundations of low-rise private buildings.

Calculation of the diameter of longitudinal reinforcement

According to SNiP 52-01-2003, the minimum cross-sectional area of ​​longitudinal reinforcement in a strip foundation should be 0,1% from the total cross-section of the reinforced concrete strip. This rule must be taken as a starting point when choosing the diameter of the reinforcement for the foundation.

Everything is clear with the cross-sectional area of ​​the reinforced concrete strip; it is necessary to multiply the width of the foundation by its height, i.e. Let's say your tape width is 40 cm, and the height 100 cm(1 m), then the cross-sectional area will be 4000 cm 2 .

The cross-sectional area of ​​the reinforcement should be 0,1% from the cross-sectional area of ​​the foundation, therefore the resulting area is necessary 4000 cm 2 / 1000 = 4 cm 2 .

In order not to calculate the cross-sectional area of ​​each reinforcement rod, you can use a simple plate. Using it you can easily select the required diameter of the reinforcement for the foundation.

There are very minor inaccuracies in the table due to rounding of numbers, please ignore them.

Important: If the length of the tape is less than 3 m, the minimum diameter of the longitudinal reinforcement bars must be 10 mm.
When the length of the tape is more than 3 m, the minimum diameter of the longitudinal reinforcement should be 12 mm.

And so, we have a minimum calculated cross-sectional area of ​​the reinforcement in the section of the strip foundation, which is equal to 4 cm 2 (this takes into account the number of longitudinal rods).

With a foundation width of 40 cm, it is enough for us to use a reinforcement scheme with four rods. We return to the table and look in the column where the values ​​for 4 reinforcement bars are given, and select the most suitable value.

Thus, we determine that for our foundation 40 cm wide, 1 m high, with a reinforcement scheme of four rods, the most suitable reinforcement with a diameter of 12 mm, since 4 rods of this diameter will have a cross-sectional area of ​​4.52 cm 2.

Calculation of the diameter of the reinforcement for a frame with six bars is carried out in a similar way, only the values ​​are already taken from the column with six bars.

It should be noted that the longitudinal reinforcement for a strip foundation must be of the same diameter. If for some reason your reinforcement is of different diameters, then rods of larger diameter must be used in the bottom row.

Calculation of the amount of reinforcement for the foundation

It often happens that the reinforcement was brought to the construction site, and when they begin to knit the frame, it turns out that it is missing. You have to buy more and pay for delivery, and these are additional expenses that are not at all desirable in the construction of a private house.

To prevent this from happening, it is necessary to correctly calculate the amount of reinforcement for the foundation.

Let's say we have the following foundation diagram:

Calculation of the amount of longitudinal reinforcement

First you need to find the length of all the foundation walls, in our case it will be:

6 * 3 + 12 * 2 = 42 m

Since we have a 4-rod reinforcement scheme, we need to multiply the resulting value by 4:

42 * 4 = 168 m

We have obtained the length of all longitudinal reinforcement bars, but do not forget that:

When calculating the amount of longitudinal reinforcement, it is necessary to take into account the launch of the reinforcement during joining, because it very often happens that the reinforcement is delivered to a section of a 4-6 m long rod, and in order to get the required 12 m, we will have to join several rods. The reinforcement bars must be joined with an overlap, as shown in the diagram below; the start of the reinforcement must be at least 30 diameters, i.e. when using fittings with a diameter of 12 mm, the minimum launch should be 12 * 30 = 360 mm (36 cm).

In order to take this launch into account, there are two ways:

• Draw up a diagram of the arrangement of rods and calculate the number of such joints
• Add about 10-15% to the resulting figure, as a rule, this is enough.

Let's use the second option and in order to calculate the amount of longitudinal reinforcement for the foundation, we need to add 10% to 168 m:

168 + 168 * 0.1 = 184.8m

We have calculated the number of only longitudinal reinforcement with a diameter of 12 mm, now let's calculate the number of transverse and vertical rods in meters.

Calculation of the amount of transverse and vertical reinforcement for a strip foundation

To calculate the amount of transverse and vertical reinforcement, let us again turn to the diagram, from which it can be seen that it will take one “rectangle”:

0.35 * 2 + 0.90 * 2 = 2.5 m.

I specifically took with a margin not 0.3 and 0.8, but 0.35 and 0.90 so that the transverse and vertical reinforcement would extend slightly beyond the resulting rectangle.

Important: Very often, when assembling a frame in an already dug trench, vertical reinforcement is placed at the bottom of the trench, and sometimes it is also driven a little into the ground for better stability of the frame. So this will need to be taken into account, and then it will be necessary to take into account not the 0.9 m length of vertical reinforcement, but increase it by about 10-20 cm.

Now let's count the number of such “rectangles” in the entire frame, taking into account that there will be 2 such “rectangles” at the corners and at the junction of the walls of the strip foundation.

In order not to suffer with calculations and not to get confused in a bunch of numbers, you can simply draw a diagram of the foundation and mark on it where your “rectangles” will be located, then count them.

Let's first take the longest side (12 m) and count the amount of transverse and vertical reinforcement on it.

As you can see from the diagram, on the 12 m side we have 6 of our “rectangles” and two parts of the wall of 5.4 m each, on which another 10 lintels will be located.

Thus, we get:

6 + 10 + 10 = 26 pcs.

26 “rectangles” on one side of 12 m. Similarly, we count the lintels on a 6 m wall and find that there will be 10 lintels on one six-meter strip foundation wall.

Since we have two 12-meter walls, and 3 6-meter walls, then

26 * 2 + 10 * 3 = 82 pieces.

Remember, according to our calculations, each rectangle had 2.5 m of reinforcement:

2.5 * 82 = 205 m.

Final calculation of the amount of reinforcement

We determined that we need longitudinal reinforcement with a diameter of 12 mm, and transverse and vertical reinforcement will have a diameter of 8 mm.

From previous calculations, we found out that we need 184.8 m of longitudinal reinforcement, and 205 m of transverse and vertical reinforcement.

It often happens that there are a lot of pieces of small-sized reinforcement left that won’t fit anywhere. Taking this into account, it is necessary to buy reinforcement a little more than what was calculated.

Following the above rule, we need to buy 190 – 200 m fittings with a diameter of 12 mm and 210-220 m fittings with a diameter of 8 mm.

If the reinforcement remains, don’t worry, you will need it more than once during the construction process.

Every building and structure requires a reliable foundation. In low-rise construction, strip foundation reinforcement is used for strengthening, the construction of which is one of the most important and costly stages.

You should not skimp on the quantity and quality of material, since neglecting technology and rules will lead to disastrous consequences.

The foundation is constructed in the following sequence:

1. Sampling of soil from the trench in accordance with the drawings for reinforcing the strip foundation.
2. Making a sand cushion with a tamper.
3. Installation of a frame made of steel reinforcement.
4. When the outside temperature is below five degrees, the concrete should be heated.
5. Fastening the formwork.
6. Pouring concrete.

Before properly reinforcing the foundation, you should find out the properties of the soil, draw up a diagram, calculate the amount of material and purchase it.

Reinforcement of strip foundations according to GOST 5781

When drawing up a project, in addition to the linear parameters of the concrete strip, the reinforcement characteristics are also indicated:

• what diameter of reinforcement is needed for the foundation;
• number of rods;
• their location.

If you plan to independently construct and reinforce a strip foundation for a house or garage, then they adhere to certain rules in accordance with current SNiP and GOST 5781-82. The latter presents the classification and assortment of hot-rolled round steel of periodic and smooth profiles, intended for the reinforcement of conventional and prestressed reinforced concrete structures (reinforcing steel). And also indicated:

• technical requirements;
• packaging, labeling;
• transportation and storage.

Before reinforcing a strip foundation, you should familiarize yourself with the classification of reinforcement. The rods are either smooth or have a periodic profile, that is, corrugated.

Maximum contact with poured concrete can only be achieved by using reinforcement with a profile surface.

Reflection can be:

• ring;
• sickle-shaped;
• mixed.

Also, reinforcement is divided into classes A1-A6 depending on the grade and physical and mechanical properties of the steel used: from low-carbon to almost alloyed.

When independently reinforcing a strip foundation, it is not at all necessary to know all the parameters and characteristics of the classes. It is enough to familiarize yourself with:

• steel grade;
• rod diameters;
• permissible bending angles in a cold state;
• radii of curvature during bending.

These parameters can be given in the price list when purchasing materials. They are presented in the table below:

The values ​​from the last column are important in the manufacture of bent elements (clamps, legs, inserts), since an increase in the angle or a decrease in the bending radius will lead to a loss of the strength properties of the reinforcement.

To make a strip foundation yourself, you usually take a corrugated rod of class A3 or A2, with a diameter of 10 mm or more. For bent elements - smooth reinforcement A1 with a diameter of 6-8 mm.

How to place fittings correctly

The location of the reinforcement in the strip foundation affects the strength and load-bearing capacity of the foundation. These parameters directly depend on:

• reinforcement thickness;
• frame length and width;
• rod shapes;
• knitting method.

During use, the foundation is subject to constant loads as a result of soil movement due to frost heaving, subsidence, the presence of karsts and seismicity, and finally, from the weight of the building itself. Thus, the top of the base experiences mainly a compressive load, and the bottom - a tensile load. There is practically no load in the middle. Therefore, it makes no sense to reinforce it.

In the reinforcement scheme, the tiers of the frame are located longitudinally along the top and bottom of the tape. If it is necessary to strengthen the foundation, identified during the calculation, additional tiers are installed.

When the base height exceeds 15 cm, vertical transverse reinforcement made of smooth rods is used.

It’s faster and more convenient to make a frame from separate contours made in advance. To do this, the rods are bent according to specified parameters, forming a rectangle. They should be made identical, without allowing deviations. You will need quite a lot of such elements. The work is quite labor-intensive, but in the trench things will go quickly.

Transverse reinforcement in the foundation is installed taking into account the loads that act transverse to the axis of the foundation. It secures longitudinal rods in a given design position and prevents the occurrence and development of cracks. The distance between the rods depends on the brand, method of laying and compacting concrete, the diameter of the reinforcement and its placement in the direction of concreting. Also, we should not forget that the foundation frame should be located 5-8 cm from the top pouring level and the edges of the formwork.

When connecting the rods, a knitting wire and a special hook are used. Welding is permissible only for fittings marked with the letter “C”. The frame is assembled using rods and clamps that connect it into a single structure. The pitch of reinforcement in a strip foundation should be 3/8 of its height, but not more than 30 cm.

Sole reinforcement

For a one-story house and in good soil conditions, the foundation is buried to the depth of soil freezing. In this case, the reinforcement of the base of the strip foundation serves rather as an insurance function. It is made by placing a grid of rods at the bottom of the base. The relative position in this case does not matter. The main thing is that the concrete layer is no more than 35 cm.

On soft soils or with a large design load, the foundation may need to have a wider base. Then longitudinal reinforcement is used, as in the first case, and for transverse reinforcement a separate calculation is required.

How to reinforce corners

Junctions and corners at the bases are places where multidirectional stress is concentrated. Incorrect joining of reinforcement in these problem areas will lead to the formation of transverse cracks, spalling and delamination.

Reinforcement of the corners of a strip foundation is carried out according to certain rules:

1. The rod is bent so that one end goes deep into one wall of the base, the other into the other.
2. The minimum allowance for a rod on another wall is 40 reinforcement diameters.
3. Simple linked crosshairs are not used. Only with the use of additional vertical and transverse rods.
4. If the length of the rod does not allow bending to another wall, then an L-shaped profile is used to connect them.
5. One clamp from another in the frame should be located at a distance half as great as in the tape.

To ensure that the loads in the corners of the strip base are distributed evenly, a rigid connection of external and internal longitudinal reinforcement is made.

How to calculate reinforcement

The calculation of the reinforcement of a strip foundation is carried out taking into account possible stresses during the construction and operation of the structure. For example, longitudinal tension caused by this design: vertical and transverse rods in long and relatively narrow channels have almost no effect on the distribution of loads, but act as fastening elements.

To calculate how much reinforcement to put in the foundation, you need to decide on its dimensions. For a narrow base of 40 cm, four longitudinal rods will be enough - two at the top and two at the bottom. If you plan to make a foundation measuring 6 x 6 m, then for one side of the frame you will need 4 x 6 = 24 m. Then the total amount of longitudinal reinforcement will be 24 x 4 = 96 m. It is convenient to calculate it when independently drawing up a drawing of the layout of the reinforcement.

If you cannot buy rods of the required length, then they can be overlapped (more than a meter) with each other.

The cost of the foundation consists of the price of the materials used and the amount of work. When making calculations, it is better to use a project with the specified depth and width of the base. The cost is also affected by the remoteness of the construction site and related work, such as:

• waterproofing;
• insulation;
• blind area;
• storm drain

All this adds up to the final price. Although for a small building the foundation can be done even with your own hands. The most difficult and time-consuming part of constructing a foundation strip is its reinforcement, but you can do it alone. Of course, if you have two or three assistants, the work is easier and safer.

Video about reinforcement of monolithic strip foundations

The foundation is the most vulnerable part of the structure. Due to the fact that the upper part of the building is subject to compressive loads and the lower part is subject to tensile loads, proper foundation laying plays an important role. To perform the correct reinforcement of a strip foundation with your own hands, you need to perform a calculation according to the diagram.

Such a base is, in fact, a reinforced concrete strip running along the outer part of the building and under the load-bearing walls inside.

In compression, concrete structures can withstand 50 times more than in tension.. Both the upper and lower parts of the structure experience overloads, so it is necessary to reinforce both parts. There is almost no load on the middle part. Metal fittings help solve these problems.

To ensure the strength, reliability, durability of the building, any foundation must be reinforced. After all, the foundation is subject to various loads. This includes the weight of the entire house and various movements of the soil. The reinforcement scheme for a strip foundation resembles the skeleton of a structure, which is assembled from steel rods. In order to choose the necessary scheme for it, you need to understand what it is.

Reinforcement of a strip foundation can be easily done with your own hands, without the involvement of specialists. It is important, first of all, to correctly select the required diameter of the reinforcement

Reinforcing material

The choice of material is a fairly important step. To reinforce a strip foundation with your own hands, use steel rods of different sections or fiberglass reinforcement. But most often metal is used.

The main horizontal reinforcement has a cross-section of rods from 12 to 24 mm. The rods that will be positioned vertically are auxiliary. That's why usually the cross-section of vertical rods is from 4 to 12 mm. Such a large difference is due to the variation in loads on the foundation and is directly dependent on the type of soil and the weight of the structure.

Auxiliary vertical rods are installed if the height of the foundation exceeds 15 cm. In this case, reinforcement with a cross section of 6-8 mm of class A1 is used. The frame is assembled from rods and clamps, cleaning them from rust. If necessary, the rods are straightened and cut. Knitting wire and a hook are used to connect the rods. Welding work can be performed if the rods are marked “C”.

The choice of diameter is influenced by the number of horizontal levels and the reinforcement scheme of the strip foundation.

Calculation of strip foundation reinforcement

The number of reinforcement elements must be calculated based on the size of the base. For foundations whose width is 40 cm, 4 longitudinal rods are sufficient - two at the top and two at the bottom. To install a row of frames in a strip base measuring 6x6 m, you will need, on average, 24 m of reinforcement. If you lay 4 rods at a time, you will need 96 m of longitudinal rods.

For transverse and vertical reinforcement of a foundation, the width of which is 0.3 m and the height of 1.9 m for each fastening at a distance of 5 cm from the surface, according to the concrete calculator, it is necessary (30-5-5)x2+(190-5-5)x2= 400 cm or 4 m of smooth shaped reinforcement elements.

If the mounting step of the clamps is 0.5 m, the number of connections will be: 24/0.5+1=49 pcs. This means, based on the calculations, you will need 4x49 = 196 m of transverse and vertical rods.

The total cross-sectional area of ​​the reinforcement and its weight, based on the diameter of the rods, can be calculated from the table:

The minimum area of ​​foundation reinforcement is regulated by regulatory documents, and the strength of the foundation depends on this

Which scheme is better to choose?

There are two main reinforcement schemes that are most often used to strengthen the foundation for low-rise buildings:

• four rods;
• six rods.

In accordance with SNiP 52-101-2003, adjacent reinforcement bars should be located at a distance of 40 cm (400 mm) in one row. The extreme longitudinal reinforcement should be at a distance of 5-7 cm (50-70 mm) from the side walls of the base. That's why, if the width of the base is more than 50 cm, then it is better to use a reinforcement scheme with six rods.

Depending on this, the diameter of the steel rods is selected.

Typically, for a strip base, the rods are laid “in a cage.” In this case, all the rods are attached at an angle of 90°. For longitudinal arrangement, reinforcing materials of class A3, having a round shape, are used.

How to reinforce corners

The corners bear a lot of load. Therefore, when reinforcing, care must be taken to strengthen them.

AtThe following rules must be taken into account:

• the rod must be bent so that one side of it is buried in one wall of the foundation, and the other in the other wall;
• if the rod is not long enough to make a bend, then L-shaped profiles can be used to fasten the rods at the corner.

Most often, class A3 fittings are used for this.

How to do reinforcement yourself

To do this, take a square or rectangle as a basis.

Before installing the frame, a sand cushion 1 m deep must be laid on the bottom of the trench.

The frame is installed as follows:

• bricks are laid at the bottom of the trench, the height of which is 5 cm (in order to create a gap between the lower part of the base and the frame);
• to install rack rods, it is necessary to make a sample in advance, according to which the rods will be cut;
• longitudinally shaped rods are laid on the bricks;
• Horizontal jumpers with a length slightly less than the thickness of the base (approximately 5 cm on each side) are tied to the longitudinal rods in increments of 50 cm using knitting wire;
• rods are attached vertically to the corners of the formed cells, 10 cm long less than the height of the base;
• the upper longitudinal rods are mounted to the vertical reinforcement;
• The upper transverse rods are tied to the resulting corners.

When reinforcing a strip foundation, it is necessary to adhere to the requirements of SNiP 52-01-2003

Basic provisions of SNiP 52-01-2003

The main provisions of SNiP 52-01-2003 concern the distance between the horizontal ribs of the steel frame and the diameter of the reinforcement. So, between the longitudinal rods should not be less than 25 cm and more than 40 cm.

The cross-section of the rods is selected according to the number of longitudinal rods. For a strip foundation, it must be at least 0.1% of the working sectional area of ​​the base. For example, if the height of the foundation is 1 m and the width is 0.5 m, the cross-sectional area should be approximately 500 mm2.

You can see the minimum diameter of the reinforcement more clearly in the table of examples:

Reinforcing a strip foundation is easy to do with your own hands; all you need to do is follow the technology and perform the calculations correctly. If it is difficult to do this on your own, it is better to seek the help of professionals. After all, a reliable and solid foundation is the price and guarantee of the stability of the entire building.

More information about reinforcing a strip foundation with your own hands can be seen in the video:

Books on the topic:

The fitter - Galina Kupriyanova - 621 rubles - link to book review
Foundations and foundations - Mikhail Berlinov - RUB 2,121 - link to book review
Shallow foundations. Rational designs and device technologies - Vitaly Krutov - 728 rubles - link to book review
Calculation of foundations on subsidence soils - Vladimir Krutov - 250 rubles - link to book review

Reinforcement of a strip foundation significantly increases its strength characteristics and allows you to create stable structures while reducing weight.

Strip foundation reinforcement

Calculations of reinforcement and reinforcement schemes are carried out in accordance with the provisions of the current SNiP 52-01-2003. The document has detailed requirements for calculations, provides footnotes to regulatory documents and codes of practice.

SP 63.13330.2012 Concrete and reinforced concrete structures. Basic provisions. Updated version of SNiP 52-01-2003. File for download

SNiP 52-01-2003

The strip foundation must meet the requirements for durability, reliability, resistance to various climatic factors and mechanical loads.

Concrete requirements

The main characteristics of the strength of concrete structures are the resistance to axial compression (Rb,n), tensile strength (Rbt,n) and transverse fracture. Depending on the normative standard indicators of concrete, its specific brand and class are selected. Taking into account the responsibility of the design, reliability correction factors can be used, which range from 1.0 to 1.5.

Diagram of bending moments

Requirements for fittings

During the reinforcement of strip foundations, the type and controlled values ​​of the quality of the reinforcement are established. The standards allow for the use of hot-rolled construction reinforcement of periodic profile, heat-treated reinforcement or mechanically strengthened reinforcement.

Construction fittings

The class of reinforcement is selected taking into account the guaranteed value of the yield strength at maximum loads. In addition to tensile characteristics, ductility, corrosion resistance, weldability, resistance to negative temperatures, relaxation resistance and permissible elongation before the onset of destructive processes are standardized.

Table of reinforcement classes and steel grades

The calculation of the strip foundation is carried out in accordance with the recommendations of GOST 27751, the indicators of limiting loaded states are calculated by group.

The first group includes conditions that lead to complete unsuitability of the foundation, the second group includes conditions that lead to partial loss of stability, complicating the normal and safe operation of buildings. According to the maximum permissible states of the second group, the following are produced:

• calculations for the appearance of primary cracks on the surface of a strip foundation;
• calculations based on the time period of increase in cracks formed in concrete structures;
• calculations of linear deformations of strip foundations.

The main indicators for resistance to deformation and strength of building reinforcement include maximum tensile or compressive strength, determined in laboratory conditions on special test benches. The technology and test methods are prescribed in state standards. In some cases, the manufacturer may use regulatory and technical documentation developed by the enterprise. At the same time, regulatory and technical documentation must be approved by regulatory authorities.

For concrete structures, these values ​​may be limited by the maximum rates of change in concrete linearity. Actual diagrams of the state of reinforcement under short-term one-sided exposure to design standard loads are taken as generalized indicators. The nature of the state diagrams of building reinforcement is established taking into account its specific type and brand. During the engineering calculation of a reinforced foundation, the state diagram is determined after replacing the standard indicators with actual ones.

Reinforcement requirements

Reinforcement cage - photo

1. Requirements for the dimensions of reinforced concrete structures. The geometric dimensions of the foundation should not interfere with the correct spatial placement of reinforcement.
2. The protective layer must provide joint resistance to the loads of reinforcement and concrete, protect against the influence of the external environment and ensure the stability of the structure.
3. The minimum distance between individual reinforcement bars should guarantee its joint work with concrete, allow for correct joining and ensure correct technological pouring of concrete.

Reinforced strip foundation diagram

For reinforcement, only high-quality reinforcement can be used; mesh knitting is carried out taking into account the calculated design parameters. Deviations from the values ​​cannot exceed the tolerance fields regulated by SNiP 3.03.01. Special construction measures must ensure reliable fixation of the reinforcing mesh in accordance with existing rules.

Reinforcement frame for strip foundation

SNiP 3.03.01-87. Load-bearing and enclosing structures. Building regulations. File for download

SNiP 3.03.01

When bending reinforcement, you need to use special devices; the minimum bending radius depends on the diameter and specific physical characteristics of the building reinforcement.

Video - Manual machine for bending reinforcement, video instructions

Video - How to bend reinforcement. Working on a homemade machine

The reinforcement is inserted into the formwork; the manufacture of the formwork should be carried out taking into account the requirements of GOST 25781 and GOST 23478.

STEEL MOLDS FOR THE PRODUCTION OF REINFORCED CONCRETE PRODUCTS. Technical conditions. File for download

Formwork for the construction of monolithic concrete and reinforced concrete structures. Classification and general technical requirements

Calculation of the quantity and diameter of reinforcement

For strip foundations of baths, construction reinforcement with a periodic profile Ø 6÷12 mm is used.

Periodic profile reinforcement Ø 10 mm

Current government regulations regulate the minimum number of rods in concrete to give it maximum strength characteristics. The minimum total cross-section of longitudinal reinforcement bars cannot be ≤ 0.1% of the cross-sectional area of ​​the foundation strip. For example, if the strip foundation has a cross-section of 12000×500 mm (sectional area is 600000 mm2), then the total area of ​​all longitudinal rods must be at least 600000×0.01% = 600 mm2. In practice, developers rarely maintain this indicator; the weight of the bathhouse, the nature of the soil and the specific brand of concrete are also taken into account. This calculated value can be considered approximate; deviations from the recommended values ​​should not exceed ≈20% downwards.

The amount of reinforcement is calculated mathematically

To calculate the amount of reinforcement, you need to know the cross-sectional area of ​​the foundation strip and the cross-sectional area of ​​the reinforcing bar. To make the calculations easier, we present to your attention a ready-made table.

Now calculations are greatly simplified. For example, to reinforce a strip foundation you use eight rows of reinforcement with a diameter of 10 mm. According to the table, the total area of ​​the rods is 628 mm. Such a frame can work with a concrete strip 120 cm deep and 50 cm wide. A few extra square millimeters can be ignored; they will be additional insurance in case of violation of the knitting technology or production of low-quality concrete.

In addition to these indicators, you need to decide on the diameters of the rods for the foundations. These indicators depend on many components; for simplified calculations, you can use the proposed table.

Permissible diameters of fittings

Using this table, you can easily select the recommended reinforcement diameter for a strip foundation.

Rules for reinforcing strip foundations

There are several patterns for tying reinforcement; each developer can use the one that is most convenient for himself. The choice of scheme must be made taking into account the size of the foundation and its load-bearing characteristics.

Reinforcement tying patterns

The reinforcement can be knitted separately, and then the finished structural elements are lowered into the foundation trench and connected to each other, or they can be knitted directly in the trench. Both methods are almost equivalent, but there is a slight difference. On the ground, all the main straight elements can be done independently; when working in a trench, an assistant is required. To knit, you need to make a special hook; the connection is made with soft wire with a diameter of ≈0.5 mm.

Crochet reinforcement

Crochet reinforcement

In some articles you can find advice to use a hand-held electric drill while knitting - do not pay attention to them. This can be written by those who have no idea about work.

Drill with hook

Firstly, a drill will tire your hand much more and faster than a light hook. Secondly, cables will always get tangled under your feet, cling to the ends of the fittings, etc. Thirdly, not all construction sites have electrical energy. And, fourthly, your wire knots will always be either loose or torn.

For tying reinforcement, thin soft wire is used, but it has low strength. Stretch the wire well; strong tying should occur within two to three turns of the hook. Otherwise, labor productivity decreases significantly and fatigue increases. There are also options for welding reinforcement, we will talk about them in the next section of the article.

How to knit reinforcement mesh yourself

We have already said above that in this way you can knit reinforcement on the ground. Only straight sections of the mesh are made, the corners are tied after they are lowered into the trench.

Step 1. Prepare pieces of reinforcement. The standard length of the rods is six meters; if possible, there is no need to touch them. If you are afraid that such dina will be difficult to work with, cut them in half.

Rebar cutting

We advise you to start knitting reinforcement for the shortest section of the strip foundation; this will give you the opportunity to gain a little experience and be more confident in handling long rods. It is not recommended to cut them; this increases metal consumption and reduces the strength of the foundation. Let's consider the dimensions of the blanks using the example of a strip foundation 120 cm high and 40 cm wide.

The reinforcement must be filled with concrete on all sides with a thickness of at least 5 centimeters. These are the initial conditions. Taking into account such indicators, the net dimensions of the reinforcement frame should be no more than 110 cm in height (minus 5 cm on each side) and 30 cm in width (minus 5 cm on each side). To knit, you need to add two centimeters on each side for the overlap. This means that the blanks for horizontal jumpers should have a length of 34 cm, the blanks for vertical jumpers should have a length of 144 cm. But you shouldn’t make the frame so high, it’s enough to have a height of 80 cm.

How to knit reinforcement correctly

Step 2. Choose a flat area, lay two long rods, and trim their ends.

Step 3. At a distance of ≈ 20 cm from the ends, tie horizontal spacers on both extreme sides. For knitting you need a wire approximately 20 centimeters long. Fold it in half, slide it under the tying point and tighten the wire with the usual twist of a crochet hook. Do not overdo it with force, the wire may not withstand it. The amount of twisting force is determined experimentally.

Step 3. At a distance of approximately 50 centimeters, tie all the remaining horizontal struts one by one. Everything is ready - set the structure aside in a free space and make another frame element in the same way. You have the top and bottom parts, now you need to fasten them together.

Step 4. Next, you should adapt stops for two parts of the mesh; you can rest them on any object. The main thing is that the connected elements occupy a stable lateral position; the distance between them should be equal to the height of the knitted reinforcement.

Knitting reinforced frame

Step 5. Attach two vertical spacers at the ends; you already know the dimensions. When the frame begins to more or less resemble the finished product, tie all the other pieces. Take your time and check all sizes. Even though your pieces are the same length, checking the dimensions won't hurt.

Step 6. Using the same algorithm, you need to connect all the straight sections of the frame on the ground.

Step 7 Place pads at least five centimeters high at the bottom of the foundation trench; the lower mesh bars will lie on them. Place side supports and set the net in the correct position.

Reinforcement (frame installed in formwork)

Step 8 Take measurements of unknitted corners and joints, prepare pieces of reinforcement to connect the frame into a single structure. Keep in mind that the overlap of the ends of the reinforcement must be at least fifty bar diameters.

Step 9 Tie the bottom turn, then the vertical posts and the top one to them. Check the reinforcement distance to all formwork surfaces.

Knitting reinforcement in corners

The reinforcement is ready, you can start pouring the foundation with concrete.

Knitting reinforcement using a special device

To make the device, you will need several boards approximately 20 mm thick; the quality of the lumber can be arbitrary. Making a template is not difficult, and it will simplify the work significantly.

Step 1. Cut four boards along the length of the reinforcement, connect them two at a time at the spacing of the vertical posts. You should end up with two identical templates. Carefully ensure that the markings of the distance between the slats are the same, otherwise there will be no vertical position of the connecting elements.

Step 2. Make two vertical supports; the height of the supports should correspond to the height of the reinforcing mesh. The supports must have side corner stops to prevent them from tipping over. All knitting work must be carried out on a level area. Check the stability of the assembled device and eliminate the possibility of it tipping over during work.

Step 3. Place the legs of the stops on two knocked down boards, place the two upper boards on the top shelf of the stops. Fix their position in any way.

Scheme of tying reinforcement using clamps

You have now created a model of the reinforcement mesh; now the work can be done quickly and without outside help. Install the prepared vertical reinforcement struts at the marked places; first, use nails to temporarily fix their position. Place a reinforcement bar on each horizontal metal jumper. This operation should be repeated on all sides of the frame. Check their position again. That's right - take the wire and hook and start knitting. It is advisable to make the device if you have many identical sections of mesh made of reinforcement.

Video - How to knit reinforcement using a device

How to knit reinforced mesh in a trench

Working in a trench is much more difficult due to cramped conditions. You need to think carefully about the knitting pattern of individual elements so that you don’t have to crawl between the reinforcement bars later. In addition, you won’t be able to knit the mesh yourself; you need to work with an assistant.

Step 1. Place stones or bricks at least five centimeters high at the bottom of the trench; they will lift the metal from the ground and allow the concrete to cover the reinforcement on all sides. The distance between the stones should be equal to the width of the mesh.

In the photo - a retainer for the reinforced frame

Step 2. Longitudinal rods must be placed on the stones. Horizontal and vertical rods should already be cut to size, as we have already told you how to measure them.

Step 3. Start forming the skeleton of the frame on one side of the foundation. If you first tie horizontal struts to the lying rods, the work will be easier. An assistant must hold the ends of the rods until they are locked in the desired position.

Reinforcement work

Step 4. Continue knitting the reinforcement one by one, the distance between the spacers should be approximately fifty centimeters.

Step 5. Using the same algorithm, tie the reinforcement on all straight sections of the foundation tape.

Step 6. Check the dimensions and spatial position of the frame; if necessary, you need to correct the position and prevent metal parts from touching the formwork.

Foundation reinforcement

Step 7 Now it's time to work on the corners of the foundation. The picture shows a rather complex version of knitting in the corners, you can come up with an easier one for yourself. The main thing is to maintain the length of the overlaps. And one more note. In corners, the foundation works not only for bending, but also for vertical discontinuity. These forces hold the vertical bars of construction reinforcement; do not forget to install them. To guarantee, reinforcement with a larger diameter can be used for these purposes.

Welding fittings for reinforcement

You need to know that any welding worsens the physical characteristics of the strength of the reinforcement; this method should be used only in extreme cases.

Welding fittings for reinforcement

If you still have to use welding, then do everything possible to put a minimum number of seams in one place, shift the fixation step of the horizontal and vertical stops by a few centimeters. During welding, accurately maintain the optimal current strength and electrode diameter. The metal in the places where the seam is applied should not overheat.

Welding reinforcement - photo

And the most important thing is that only special fittings are suitable for welding; brands of such fittings are designated by the letter “C”. By the way, this fittings are significantly more expensive than ordinary ones.

Strip foundation reinforcement scheme

There are several ways in which you can speed up and facilitate the knitting process and at the same time improve the quality of the design and reduce material consumption.

For spacers, bend the reinforcement into a “P” shape. To do this, you can make a basic machine in a couple of hours, and it will be useful not only for bending rods. First you need to bend one sample, check its dimensions and only then, using the sample as a template, prepare all the connections. Such spacers are much easier to knit; they immediately hold the desired size of the structure. Another plus is that the consumption of expensive material is reduced. At first glance, the savings seem insignificant, a maximum of ten centimeters per connection. But if you multiply ten centimeters by the number of pieces and the price of the fittings, you get a very “pleasant” amount.

Homemade machine for bending reinforcement

Bent reinforcement mesh

For spacers, you can use reinforcement of a smaller diameter and not necessarily expensive construction reinforcement of a periodic profile. Even metal rods or wire rod of the appropriate diameter will do.

If you do not have any experience in performing such work, then it is better not to do it yourself. Having an assistant makes the process much easier and safer.

The price of a reinforced foundation is much more expensive than an ordinary one; use this method of strengthening architectural structures in extreme cases. There are many cheaper ways to increase the load-bearing characteristics of a strip foundation. True, they cannot always be used; it all depends on the specifics of the bathhouse design, the characteristics of the soil and landscape.

A few words can be said about preloaded reinforcement. This is a complex method that allows you to significantly improve all the indicators of a strip foundation without increasing the amount of reinforcement. The essence of the method is to preload the rods with forces opposite to those that will act on the structure during operation of the foundation. For example, if the rod will work in tension, then it is pre-compressed, etc.

Video - Reinforcement of monolithic shallow strip foundations

Video - Do-it-yourself foundation reinforcement

Strip foundations are most common in the construction of private, low-rise buildings. Easy to implement, no special equipment or complex equipment required. All work can be done independently. The most important and difficult thing is to correctly reinforce the strip foundation with a width of 40 cm. We will consider what this is and how it affects the service life of the building in more detail below.

The strip foundation is the basis of the building. Its durability determines its service life, the need for repairs or additional strengthening. In order not to discover distortions in the walls in a year, two or five, not to watch how cracks “grow” under the windows, you should not neglect the reinforcement. This article will tell you how to do it correctly, what requirements need to be met.

How is reinforcement performed?

Before starting construction, you must familiarize yourself with the requirements of SNiP 2.03.01-84. It contains a direct indication that a strip foundation for a residential building cannot be without reinforcement. The width and height of the base and building do not matter.

There are two components at its core:

• concrete. Resistant to compression loads. But when the bending or tensile moment increases, the strip foundation is destroyed;
• reinforcement frame. Reduces the load on the concrete mass under the influence of bending or tensile forces. It consists of longitudinal tiers connected into a single structure by jumpers: transverse and vertical.

The number of tiers or belts directly depends on the height of the strip foundation:

• for shallow depths up to 1 meter high, 2 are enough;
• if the height exceeds 120 cm, an intermediate reinforcement belt is added.

Expert opinion

Sergey Yurievich

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The width of the base is not taken into account. You don't have to look at her.

For longitudinal belts and lintels, the optimal material is corrugated reinforcement with a diameter of 12-16 mm. Smooth, 8-10 mm in diameter, recommended only as lintels if a strip foundation is being installed

Expert opinion

Sergey Yurievich

Construction of houses, extensions, terraces and verandas.

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For dressing, a special knitting wire with a diameter of 1-2 mm is used. Welding is not recommended: the metal gets very hot, and “weak” spots appear at the joints, which need to be looked after especially carefully during the process of pouring concrete. If damaged, the reinforcement will not perform its function. At the same time, wire ligation is a complex and lengthy process that requires special skills. Welding is much faster.

Reinforcing frame configuration

When calculating reinforcement, the requirements of SNiP 2.03.01-84 “Manual for designing foundations for buildings and structures” must be taken into account:

• elements of the longitudinal frame of the strip base are located at a distance of 10 cm or less;
• between tiers of the frame - 50 cm or less;
• transverse vertical jumpers are located at a distance of 30 cm or less;
• from the lintels, frame contour to the formwork - at least 5 cm. Otherwise, the destruction of the concrete belt and the release of reinforcement to the surface of the strip foundation is possible;
• The lower belt should not lie on the ground. If a backfill of sand and crushed stone has not been made beforehand, a single brick or special plastic stands are placed under the tier, depending on the condition of the soil and its homogeneity.

Calculation of reinforcement for reinforcing a strip foundation 40 cm wide

It is better to calculate the required volumes before starting work, so as not to stop and look for where to urgently buy several rods or a coil of wire. In the above calculation, a conditional strip foundation with the following parameters is taken as a basis: height 70 cm, width 40 cm. The perimeter of the building is 50 meters.

Expert opinion

Sergey Yurievich

Construction of houses, extensions, terraces and verandas.

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For a base 70 cm high, two reinforcing belts are sufficient.

Each tier has 3 rods. For connection, reinforcement with a diameter of 12 mm is used, the pitch is 30 cm.

Quantity calculations:

1. laying 3 rods in 2 tiers will require 300 meters;
2. 167 jumpers are planned for the entire house, placed in increments of 30 cm;
3. for a vertical jumper the length is 60 cm, for a transverse one - 30 cm. Each joint requires 2 vertical and 2 horizontal jumpers.

Total: for vertical lintels you will have to purchase 200.4 meters of reinforcement, for horizontal ones - 100.2 meters. In total, the building requires at least 600.6 meters of reinforcing bars with a diameter of 12 mm. This number is not final. When placing an order, please provide a reserve in case of defects and reinforcement of corners. Take into account such parameters as the length and width of the facade, the number of meters in one rod. If possible, purchase rods that are pre-cut to size to reduce waste.

How is reinforcement performed?

For straight sections, it is important to choose whole rods. The fewer joints and connections, the stronger the strip foundation. When forming corners, overlapping of elements located perpendicularly is not allowed. The reinforcement should be bent in a “P” or “G” shape.

The frame can be assembled both directly on site, in the pit, and outside it. The first may not be very convenient due to the small space. In the second case, it is important to accurately observe all the dimensions, so as not to subsequently have to rework the frame for the strip foundation.

It is difficult, but possible, to bend the reinforcement at the required angles at home. To do this, you will need a section of channel in which holes are cut with a grinder strictly on the same line. The reinforcement rod is placed in the grooves. A steel pipe is placed on the long end and used as a lever. Bending requires a lot of effort, but allows you to do without purchasing a sheet bender. The ligation of the rods is done with wire.

The rods prepared for reinforcement are laid in the trench in accordance with the requirements described above after the formwork is installed. The tiers are strictly horizontal to the ground. At the next stage, when all the belts are installed and tied, you can proceed to pouring concrete. It is important to ensure that the reinforcement remains in place and does not move. For a private low-rise building, the optimal grade of concrete is M200. After curing in accordance with building regulations, the strip foundation will gain strength and will be ready for further use. Concrete should be covered with an opaque film for 28 days, protected from direct sunlight and periodically moistened with water.

Expert opinion

Sergey Yurievich

Construction of houses, extensions, terraces and verandas.

Ask a question to an expert

To avoid problems associated with soil heaving, before reinforcement, the bottom of the trench is filled with layers of sand and crushed stone of at least 10 cm each. Otherwise, the strip foundation will not withstand numerous freezing/thawing cycles.

Video about reinforcing strip foundations

Reinforcement is a construction process that is used to enhance the durability of a structure and increase its service life. It represents the formation of a prefabricated skeleton, acting as a protective component that resists the impact of soil on the walls of the structure.

To achieve maximum results, you should clearly calculate how much reinforcement is needed, as well as accurately reinforce the building’s foundation.

Correct reinforcement of a strip foundation with your own hands

At the base of the foundation, the primary component is a concrete mixture formed from cement, sifted sand and clean water. Since this solution does not have sufficient physical characteristics that can provide a guarantee against various types of deformations in the foundation of the structure, metal is additionally used.

It allows you to increase the degree of resistance to base shifts, sudden temperature changes and other negatively affecting factors. The metal itself is plastic, but it is capable of providing decent fixation, so reinforcement is an important and necessary process in the entire construction complex.

Reinforcement should be carried out only in places where there is a high degree of vulnerability to tension. Most often it occurs on the surface, so it is imperative to reinforce the upper level of the base. In order to avoid corrosion of the material, it should be protected with a layer of concrete mortar.

The acceptable distance of the reinforcing belt from the surface should be about 5 cm.

Possible deformation zones:

• the lower part, when there is a downward bending of its middle;
• the upper part is the arching of the frame upward.

For the middle level of the base, reinforcement is not necessary, since there is practically no tension in this zone.

Taking into account possible deformation options, it is imperative to reinforce the bottom and top using reinforcement with a ribbed surface and a diameter in the range of 10–12 mm. In this option, the closest contact with the concrete solution is observed. Other skeletal elements may be small in diameter and have a smooth surface.

If a foundation with a width of up to 40 cm is being reinforced, 4 reinforcement rods with a diameter of 10–16 mm are used, which are connected into a frame with a diameter of 8 mm.

The long-length tape type of base has a relatively small width, which is why it can only contain longitudinal stretches without transverse ones. Therefore, in this situation, it is best to use smooth and thin rods to form a frame, and not to carry heavy loads on the base.

Most attention should be paid to the reinforcement of corners, since in many cases deformations occur in this part of the structure. Reinforcement of the corners of the structure must be carried out so that one of the ends of the bent metal goes into one wall, and the other into another. Since not every reinforcement material can be welded, it is better to fasten the elements together using wire.

Rules for correct reinforcement of a strip foundation:

1. The work begins with the installation of formwork, which is lined with parchment on the inside. This procedure allows you to quickly disassemble the created structure in the future.
2. Then you should drive the reinforcing bars into the ground trenches at a distance of 5 cm from the formwork and in increments of 40–60 cm. The length of the rods should be equal to the depth of the foundation.
3. A stand measuring 8–10 cm is placed at the bottom of the trench, and 2 or 3 threads of a row of reinforcement are formed on top of it. As a stand, you can use an ordinary brick laid on its edge.
4. Upper and lower chord made of reinforcement with cross connections attached to vertical rods.
5. In places where elements intersect, it is necessary to fasten with wire or welding.

Be sure to maintain the distance to the future surface of the foundation; you can use bricks for this.

1. Installing the fittings, ventilation holes should be made and concrete should be poured.

The presence of ventilation holes and holes increases shock absorption and prevents the occurrence of rot.

The ideal option is to use a diagram for a strip foundation, consisting of primitive geometric shapes, such as a square or rectangle, then the frame is easier to mount correctly, and the resulting foundation is more reliable and strong.

Basic mistakes in reinforcing strip foundations

The most famous and frequently made mistakes:

1. Angles. The main problem and mistake is to lay the corner rods crosswise. Due to such installation, cracks very often occur in the foundation.
2. Waterproofing material. Very often, when creating formwork, they forget about using waterproofing, as a result of which water washes out the cement and makes the concrete less stable and durable. This also contributes to the occurrence of shrinkage cracks. The waterproofing layer should be very well and carefully attached to the formwork to eliminate the formation of unwanted folds and depressions in the foundation.
3. Pouring concrete. Filling the strip foundation with concrete mixture in height very often does not reach the edges, and topping up is carried out only after a couple of days. This type of technology is no longer a monolithic structure; it is similar to two ordinary beams with single-layer reinforcement, which are connected by bonding layers of concrete mixture and transverse reinforcement. Pouring concrete when creating the foundation should be continuous, and the maximum allowable interval for a break should be no more than two hours.
4. Ventilation. A huge mistake is made when installing and during operation of the products necessary for ventilation of a cold underground. They are made from pipes with a diameter of 10 cm. The minimum area required for ventilation should be about 0.05 m2 (approximately 20x25 cm).

It is forbidden to close the vents for the winter, as this leads to a lack of ventilation and rotting of the structure.

Why do you need reinforcement in a strip foundation?

Over time, any house will experience subsidence, as the soil under the base yields to pressure from above and becomes compacted. The more pressure is put on it, the stronger and faster it compacts. If the resulting pressure is distributed evenly over the entire area of ​​the strip foundation, then this is not a particular problem.

As a rule, in real conditions the pressure on the foundation is not symmetrical, which is why the building settles unevenly. To avoid such a problem, tapes of various widths are used in the foundation, but even this technique does not always help eliminate and equalize the pressure on the foundation.

Uneven settlement of the foundation is caused by:

1. Various soil inclusions.
2. Uneven and inconsistent humidity.
3. Various additions and extensions.
4. Leakage of water-carrying communications.
5. Absence of a blind area on any side, etc.

Under the influence of these causes of settlement, the soil surface under the foundation becomes curved relative to the vertical direction of the building. The corners of the structure and areas with large load differences are most affected.

In such a situation, internal tension arises in the foundation strip, which contributes to the occurrence of bending moments and cracks. To eliminate unwanted pressure on the foundation and reduce the number of cracks and bends, reinforcement is added inside the foundation.

What reinforcement is needed for the foundation?

There are two options used in the construction of reinforcement:

1. Steel, which is divided into:
   • core;
   • wire
2. Composite reinforcement. It is used relatively rarely due to its characteristic disadvantages.

To reinforce a strip-type foundation, rod reinforcement is used as the main (working) material and smooth reinforcement as an additional one.

The main property for working reinforcement is the ability to quickly and well adhere to concrete. This type of reinforcement is produced with a periodic profile, dividing it into classes according to strength indicators.

According to GOST, which existed during the USSR period, for private types of construction, class A-ΙΙΙ reinforcement or an analogue of A400 (according to modern GOST) is used. For transverse reinforcement, a smooth rod of class A-Ι or A240 (modern GOST) is used.

There is a difference between the old and modern fittings in the form of a modified crescent-shaped profile; in other aspects there are no differences.

To choose the right reinforcement for the foundation in the store, you just need to pay attention to the designations:

• Index C indicates that the reinforcing bars are weldable;
• Index K indicates that the reinforcement is resistant to corrosion cracking processes that arise due to pressure on the foundation.

If these indices are not on the packaging, it is better not to buy such similar material.

Structural requirements for strip foundations and their reinforcement

Due to the inability to accurately calculate the diameter for a strip foundation, special design requirements for its reinforcement were developed:

1. At working rods must have a diameter of at least 12 mm.
2. Number of longitudinal rods should be at least 4, preferably 6.
3. Longitudinal rods are connected to each other into a spatial frame by wire knitting or welding.
4. Step for transverse reinforcement should be 20–60 cm, and the diameter of the reinforcement 6–8 mm.
5. Places with the highest possible precipitation, as well as T-shaped intersections require reinforced reinforcement using reinforcing tabs or haunches with a diameter equal to that used for longitudinal bars.
6. Thickness of tape type base, as a rule, is about 30 cm.

How much reinforcement is needed for a strip foundation?

For the foundation, reinforcement with a small diameter is used, for example, for low-rise construction, reinforcement with a diameter of 10–12 mm is used, somewhat less often - 14 mm.

Regardless of the height of the base for reinforcement, you will need to make two belts of class A3 ribbed reinforcement at a distance of 5 cm from the bottom and top of the foundation. Transverse and vertical rods can be made of smooth type A1 class reinforcement.

For a foundation width of about 40 cm, it is sufficient to use 4 longitudinal reinforcement bars, of which two are located at the bottom and two at the top. If the width of the foundation is more than 40 cm or construction is carried out on moving soils, more rods should be used, approximately 3 - 4 for the upper and the same number for the lower chord.

To calculate the amount of required reinforcement, there are two methods:

Self-calculation

Example. The length of the foundation for a 6 by 10 m building with two walls will be 48 meters (6+10+6+10+6+10=48m).

If the width of the base is 60 cm, and the reinforcement consists of 6 longitudinal rods, then their length will be 288 meters (6*48=248m).

The step between the transverse and vertical rods is maintained at 0.5 m, the width of the foundation is 60 cm, the height is 1.9 m, the distances of the rods from the frame are 5 cm.

In this case, the length of smooth reinforcement with a diameter of 6 mm for each connection is 640 cm or 6.4 m ((60-5-5)*2+(190-5-5)*3=640 cm), and the connections will be 97 pieces (48/0.5+1=97 pieces), they will require 620.8 meters of reinforcement (97*6.4=620.8 m).

Each connection requires 6 crossings for tying reinforcement and approximately 12 pieces of tying wire. One bundle requires 30 cm of wire. Based on these data, the total wire consumption will be 349.2 m (0.3*12*97=349.2 m).

Use of reinforcement factor

For buildings with a small number of storeys, there is an indicator for the amount of reinforcement already established by the builders, which is 80 kg/m3.

Example. If 20 m3 of concrete solution is needed for the foundation, then 20*80=1600 kg of reinforcement will be needed. Calculating concrete is not difficult, you just need to know the perimeter of the house, the length of the internal walls, set the height of the tape to 30 cm and multiply it by the width.

To make the calculation more economical, it is best to make a more accurate calculation of the required amount of reinforcement by drawing a reinforcement diagram. And then, having calculated the moldings for longitudinal and transverse reinforcement, vut, and also adding to this approximately 10%, which will be spent on trimmings, multiply the result by the weight of a linear meter for each of the reinforcement diameters used.

Reinforcement of a strip foundation - knit or weld?

Metal rods can be connected to each other into a frame by knitting or welding. Each option has its own positive and negative qualities.

The main disadvantage of welding is the inability to make a high-quality transverse connection using a hand electrode. In factories, frames and meshes are connected using contact rather than arc welding.

In this regard, insufficiently strong connections (lack of penetration) or weakening of the longitudinal rod (undercut) are very often observed. Also, a big disadvantage of welding is that not all materials can be welded, for example, class A3 reinforcement is made from 35GS steel, which cannot be welded.