Strip foundation reinforcement drawings

Any building, regardless of its purpose, is unthinkable without a reliable foundation. The construction of the foundation is one of the most important and natural tasks of the entire construction cycle as a whole, and this stage, by the way, is often one of the most time-consuming and costly - often up to a third of the estimate is spent on it. But at the same time, any simplifications, unreasonable savings on the quality and quantity of the necessary materials, disregard for the current rules and technological recommendations should be absolutely excluded here.

Of all the variety of foundation structures, tape is the most popular, as the most versatile, suitable for most houses and outbuildings being built in the field of private construction. Such a base is highly reliable, but, of course, with its high-quality performance. And the key condition for strength and durability is the well-planned and properly carried out reinforcement of the strip foundation, the drawings and the basic principles of the device of which will be considered in this publication.

In addition to the diagrams, the article will provide several calculators that will help the novice builder in this rather difficult task of creating a strip foundation.

General concepts. Advantages of strip foundation

So, in short, a few general concepts about the device strip foundation. By itself, it is a continuous concrete strip, without gaps for door or gate openings, which becomes the basis for the construction of all external walls and capital internal partitions. The tape itself is buried at a certain calculated distance into the ground and at the same time protrudes from above with its basement. The width of the tape and the depth of its laying, as a rule, is maintained the same throughout the entire length of the foundation. This form contributes to the most uniform distribution of all loads falling on the base of the building.

Strip foundations can also be divided into several varieties. So, they are not only poured from concrete, but also made prefabricated, using, for example, special reinforced concrete foundation blocks, or using rubble filling. However, since our article is devoted to reinforcement, in the future only a monolithic version of the foundation tape will be considered.

The strip foundation can be attributed to the universal type of foundations. This scheme is usually preferred in the following cases:

• When building houses from heavy materials - stone, brick, reinforced concrete, building blocks and the like. In a word, when it is required to evenly distribute a very significant load on the ground.
• When the developer plans to get a full-fledged basement or even a basement at his disposal, only a tape scheme can allow this.
• During the construction of multi-level buildings, with the use of heavy interfloor ceilings.
• When a building plot is characterized by heterogeneity of the upper layers of the soil. The only exceptions are completely unstable soils, when the creation of a strip foundation becomes impossible or unprofitable, and it makes sense to turn to another scheme. A strip foundation is also impossible in regions with permafrost.

A monolithic strip foundation has a considerable number of other advantages, which include durability, estimated for many decades, the relative simplicity and clarity of construction, ample opportunities in terms of laying engineering communications and organizing insulated floors on the first floor. In terms of its strength properties, it is not inferior to monolithic slabs, and even surpasses them, while requiring less material costs.

However, one should not think that the strip foundation is an absolutely invulnerable structure. All of the above advantages will be valid only if the parameters of the foundation being built for the house correspond to the conditions of the construction area, the design load, and have a built-in safety margin. And this, in turn, means that special requirements are always imposed on the design of the foundation (any, by the way). And the reinforcement of the tape in a series of these problems occupies one of the key positions.

The width of the foundation tape and the depth of its laying

These are two key parameters on which the very scheme of reinforcing the future foundation tape will depend.

But the degree of penetration into the ground strip foundations can be divided into two main categories:

• A shallow strip foundation is suitable for the construction of frame structures, small country houses and outbuildings, provided that there is sufficiently stable, dense soil on the site. The sole of the tape is located above the freezing boundary of the soil, that is, it usually does not fall below 500 mm, excluding the basement.
• For buildings constructed from heavy materials, as well as in areas where the condition of the soil is not stable, deep tape is required. Its sole already falls below the freezing level of the soil, at least by 300 ÷ 400 mm, and if there is also a basement (basement) in the construction plans, even lower.

It is clear that the height of the foundation strip as a whole, including the depth of its occurrence, is by no means arbitrary values, but parameters that are obtained as a result of carefully performed calculations. When designing, a whole array of initial data is taken into account: the type of soils on the site, the degree of their stability both in the surface layers, and the change in structure as they deepen; climatic features of the region; presence, location and other features of ground aquifers; seismic characteristics of the area. Plus, the specificity of the building planned for construction is superimposed - the total load, both static, created only by the mass of the structure (naturally, taking into account all its constituent elements), and dynamic, caused by operational loads, and all kinds of external influences, including wind, snow and others.

Based on the foregoing, it would be appropriate to make one important remark. The fundamental position of the author of these lines is that the calculation of the basic parameters of the foundation tape does not tolerate an amateurish approach.

Despite the fact that on the Internet you can find many online applications for carrying out such calculations, it would still be more correct to entrust the issue of designing the foundation to specialists. At the same time, the correctness of the proposed calculation programs is not in the least disputed - many of them fully comply with the current SNiP and are capable of really producing accurate results. The problem lies in a slightly different plane.

The bottom line is that any, even the most advanced calculation program, requires accurate input data. But in this matter, it is impossible to do without special training. Agree that it is correct to assess the geological features of the site for construction, to take into account all the loads that fall on the foundation tape, and - with their expansion along the axes, to provide for all possible dynamic changes - a non-professional simply cannot do it. But each initial parameter matters, and underestimating it may well then "play a cruel joke."

True, if it is planned to build a small country house or an outbuilding, then inviting a specialist designer may seem like an excessive measure. Well, at your own peril and risk, the owner can build a shallow strip foundation, using, for example, the approximate parameters that are shown in the table below. For light buildings, a heavily buried tape is not required (a large depth can even play a negative role, due to the application of tangential forces during frosty swelling of the soil). As a rule, in such cases, they are limited to a maximum depth of the sole of 500 mm.

We emphasize once again that these are only average values ​​that cannot be considered as the ultimate truth. In any case, if an amateur builder uses such sources, he takes a certain risk on his own responsibility.

Now - about the width of the foundation tape.

It also has its own characteristics. Firstly, to ensure the rigidity of the foundation structure, it is customary to adhere to the rule that the total height of the tape should be at least twice its width - but this rule is not difficult to follow. And the second - the width of the tape in the sole area should be such that the distributed load is less than the calculated parameters of soil resistance, of course, also with a certain design margin. In a word, the foundation tape with a full load should stand stably, without sinking into the ground. In order to save materials, often to increase the area of ​​\u200b\u200bsupport, the sole of the strip foundation is made with a broadening.

Probably, it makes no sense to give here formulas and tabular values ​​of soil resistance for independent calculations. The reason is the same: not so much the difficulty in performing calculations, but the problems with the correct determination of the initial parameters. That is, again, it is better to turn to professionals on such issues.

Well, if a light structure or a country house is being built, then you can be guided by the fact that the width of the tape should be at least 100 mm more than the thickness of the walls being built. As a rule, when planning the foundation independently, they take round values ​​that are multiples of 100 mm, usually starting from 300 mm and above.

Foundation tape reinforcement

If a specialist is engaged in the design of a strip foundation, then the finished drawing will, of course, include not only the linear parameters of the concrete belt itself, but also the characteristics of the reinforcement - the diameter of the reinforcing bars, their number and spatial arrangement. But in the case when a decision is made to independently erect a foundation for a building, when planning the structure, it is necessary to take into account certain rules established by the current SNiP.

What fittings are suitable for these purposes?

For proper planning, you need at least a little understanding of the assortment of reinforcement.

There are several criteria for classifying reinforcement. These include:

• Production technology. So, the fittings are wire (cold-rolled) and rod (hot-rolled).
• According to the type of surface, reinforcing bars are distinguished into smooth and having a periodic profile (corrugation). The profile surface of the reinforcement ensures maximum contact with the poured concrete.

• Reinforcement can be designed for conventional or prestressed concrete structures.

To create a reinforcing structure for a strip foundation, as a rule, reinforcement is used that is produced in accordance with GOST 5781. This standard includes hot-rolled products intended for reinforcing conventional and preloaded structures.

In turn, these fittings are distributed into classes, from A-I to A-VI. The difference mainly lies in the grades of steel used for the production and, therefore, in the physical and mechanical properties of the products. If low-carbon steel is used in the fittings of the initial classes, then in the products of high classes the parameters of the metal are close to alloyed steels.

It is not necessary to know all the characteristics of reinforcement classes during self-construction. And the most important indicators that will affect the creation of the reinforcing cage are shown in the table. The first column shows the reinforcement classes according to the two designation standards. So, in brackets there is a designation of classes, the digital designation of which shows the yield strength of the steel used for the production of reinforcement - when purchasing material, such indicators may appear in the price list.

Pay attention to the last column, which indicates the allowable bending angles and curvature diameters. This is important from the point of view that when creating a reinforcing structure, you come to manufacture bent elements - clamps, inserts, paws, etc. In the manufacture of conductors, mandrels or other devices for bending, it is necessary to focus on these values, since a decrease in the bending radius or exceeding the angle can lead to a loss of strength properties by the reinforcement.

Rods of class A-I are produced in a smooth design. All other classes (with some exceptions, which, however, are more dependent on the individual requirements of the customer) are with a periodic profile.

For a strip foundation in private construction, the best choice would be class A-III reinforcement, in extreme cases - A-II, with a diameter of 10 mm and above.

For the structural elements of the armored belt (clamps, jumpers), it is convenient to use a smooth rod of class A-I, with a diameter of 6 or 8 mm. The use of reinforcement of higher classes is unprofitable, due to its high cost with a clear lack of demand in such high physical and technical indicators.

"Classic" scheme of reinforcing the foundation tape. Number of longitudinal rods

To begin with, let's consider a typical reinforcement scheme for straight sections of the foundation tape.

It is based on a rectangle, with mandatory levels of reinforcement at the top and bottom, made of longitudinal reinforcement (pos. 1), which are interconnected by horizontal transverse (pos. 2) and vertical reinforcements, thereby creating a kind of “box-shaped” structure. Such an arrangement of the belts makes it possible to maximally compensate for two main multidirectional forces: from the total load created by the building, and from frost swelling of the soil. In this case, the central part of the tape is loaded the least, and if the foundation has a total height of up to 800 mm, then two belts are most often enough.

For higher belts, the arrangement of longitudinal belts in three or more tiers is used. But, as already mentioned, to calculate such foundations on your own is a rather risky task.

The illustration shows the linking of longitudinal rods into a three-dimensional structure using pieces of reinforcement. This approach is quite acceptable, however, it is not convenient. The work will go much faster and better if you prepare clamps according to the size of the armored belt on the conductor in advance, and then link all the details into a common design.

Pay attention to the illustration, in which the arrows show two dimensions: H - the height of the reinforcement belt and K - its width. It should be correctly understood that this is not the height and width of the tape at all. The metal parts of the foundation must necessarily be protected from oxygen corrosion by a layer of concrete. According to SNiP, the minimum layer is 10 mm, but for a strip foundation, 50 mm to the edge of the concrete structure will be optimal. This must be taken into account when planning, and during installation, simple devices will help to maintain the necessary clearances between the reinforcement and the formwork. So, you can set the desired distance from the bottom of the formwork by placing fragments of bricks or by installing special plastic racks under the lower rods.

And the required clearance from the side walls of the formwork can be observed if you use special fasteners - "stars" that are simply put on the reinforcing bars.

Now - closer to the question of how many rods of longitudinal reinforcement are still needed, and what diameter they should be.

Well, the number of longitudinal rods necessary to ensure the calculated strength of the foundation tape directly depends on its size and on the diameter of the reinforcement used. In accordance with the current requirements of SNiP, the total cross-sectional area of ​​​​the longitudinal reinforcement rods must be at least 0.1% of the cross-sectional area of ​​\u200b\u200bthe tape. Based on this, it is easy to make the necessary calculation. To make it even easier for the reader, the corresponding calculator is placed below.

Calculator for calculating the minimum required number of bars of longitudinal reinforcement of the foundation tape

Specify the requested values ​​and click "Calculate the minimum number of rebars"

Estimated height of the tape (taking into account the depth and base), meters

Estimated tape thickness, meters

Reinforcing bar diameter

After the calculation, it may turn out that even two or three rods are enough for reinforcement. However, with a width of the foundation tape of more than 150 mm and a height of more than 300 mm, it is still recommended to place two belts of longitudinal reinforcement, two rods each, as shown in the diagram. At the same time, the calculator will help determine the minimum diameter value - perhaps by increasing the number of rods to 4 pieces, you can use thinner reinforcement in order to save money. True, we do not forget the recommendations of the table above.

If you get an even value that exceeds 4 rods, then it is recommended to distribute the reinforcement into three belts, placing the middle one in the center between the top and bottom. If an odd number is obtained, five or more pieces, then it makes sense to strengthen the lower tier of reinforcement with an unpaired rod - it is there that the highest bending loads are applied to the foundation tape.

Another rule: the requirements of SNiP established that the distance between adjacent elements of longitudinal reinforcement should not exceed 400 mm.

The binding of longitudinal reinforcement rods into a three-dimensional structure is carried out using prepared clamps. For their manufacture, a special device is usually constructed - it is easy to assemble it on a workbench or on a separate stand.

The installation step of the clamps also obeys certain rules. So, it should not be more than ¾ of the height of the foundation tape, and at the same time - not exceed 500 mm. In areas of reinforcement - at the corners and junctions of walls, clamps are installed even more often - this will be discussed below.

If on a straight section there is a need to connect two reinforcement bars located along the same line, then an overlap of at least 50d is made between them (d is the diameter of the reinforcing bar). When applied to the most commonly used diameters, 10 and 12 mm, this overlap will be from 500 to 600 mm. In addition, it is desirable to install an additional clamp in this area.

The fittings and clamps are connected into a single structure by tying using galvanized steel wire.

Even if there is a welding machine at his personal disposal, and the owner himself considers himself a fairly experienced welder, the reinforcing structure must still be made by wire twisting. A poorly welded joint, and even worse - overheating of the reinforcement will lead to a sharp decrease in the strength characteristics of the structure being created. Not without reason, only highly qualified specialists are allowed to weld reinforcing structures in industrial construction. And besides, it is also necessary to use specialized fittings, in the class designation of which there is an index "C" - welding.

We will not dwell on the issues of practical knitting of the reinforcing cage in this publication - this topic deserves separate consideration.

Reinforcement of complex sections of the frame structure

If everything is quite clear with the installation of the frame on straight sections of the reinforcing belt of the strip foundation, then in difficult areas very often many make mistakes. Evidence of this is the numerous photographs published on the Internet, which clearly show that two frames converging in a corner or adjoining each other are simply connected with wire twists at the points of intersection of the reinforcement.

Incorrectly mounted joints or junctions of reinforcing chords lead to the fact that the uniform distribution along the axes of the load falling on the foundation is disturbed, which in the future may well result in the appearance of cracks or even destruction of the tape in these areas. There are certain schemes for reinforcing such nodes - they will be discussed in the table below.

Basic schemes for reinforcing corners and junction areas

(In the diagrams, the border of the foundation tape is shown in burgundy, dark gray - bars of longitudinal reinforcement, blue - clamps of the frame structure. Additionally, individual specific elements of the reinforcement unit will be highlighted in different colors, which is specified in the text part. All illustrations are given in miniature, which can be enlarged mouse click).

Reinforcement scheme for corners and junctions	Brief description of the scheme
STRENGTHENING IN AREAS OF OBTE-ANGLE CHANGE IN THE DIRECTION OF THE FOUNDATION TAPE
	If it is necessary to perform an obtuse-angle change in the direction of the foundation tape, provided that the angle exceeds 160 degrees, no special reinforcement can be provided. Longitudinal reinforcement is bent at the desired angle. The installation step of the clamps (S) practically does not change. The only feature is that two clamps are placed side by side at the bending point of the reinforcement located on the inner contour of the belt.
	It would seem that the situation is similar, but the angle of change of direction, although obtuse, is less than 160 degrees. The amplification scheme is already different. The reinforcing bar running along the outer contour of the frame simply bends in accordance with the desired direction. The rods converging to the inner contour to the corner are made longer, so that they intersect each other, reach the opposite side of the reinforcement belt, and end on it with paws bent at the desired angle (highlighted in red). The length of this curved part-paw is at least 50d (d is the diameter of the longitudinal reinforcing bar). The paws are tied to an external reinforcement rod, and the installation step of the clamps in this area is halved. At the top of the corner on the outer contour, a vertical piece of reinforcement is additionally installed (shown by an orange arrow).
REINFORCEMENT AT RIGHT ANGLES OF THE REINFORCING FRAME
	Scheme with one large overlap and two "legs". The longitudinal reinforcements converging along the inner contour of the frame intersect each other, reach the opposite walls of the formwork, where they bend with the formation of "legs" (shown in red), located in divergent directions. The minimum length of the "legs" is from 35 to 50d. One reinforcement on the outer contour is cut off at the corner, and the second, perpendicular to it, is bent with the formation of a large overlap (shown in purple), which should be of such a length as to at least completely cover the "foot". The whole structure is linked with clamps, the pitch of which should not exceed half of the calculated one - 1 / 2S. The top of the bending angle is additionally reinforced with vertical reinforcement.
	Scheme similar to the previous one. Longitudinal reinforcements are also wound up and bent with “legs”, and instead of overlapping, an L-shaped insert is installed along the outer reinforcement contour (shown in green). The length of each side of this insert is at least 50d. Linking the knot - using clamps installed with a half-step. The rest is clear from the diagram.
	A scheme that is convenient when the frames on each side are knitted separately, and then placed in the formwork. In this case, the intersection and linkage of frames into a common structure is carried out using U-shaped inserts (shown in dark blue). The length of the "horns" of each of these overlays is not less than 50d. Traditionally, in the reinforcement section, the installation step of the clamps is reduced by half from the calculated one. Pay attention to the additional reinforcement of the intersection of the U-shaped inserts with vertical reinforcement.
REINFORCEMENT IN THE SITES OF THE LATERAL CONNECTION OF THE FOUNDATION TAPE
	Longitudinal reinforcement of the main foundation strip at the junction is not interrupted. The longitudinal reinforcement of the adjoining strip intersect with the inner contour of the reinforcement, reach the outer side of the formwork, and are bent in "legs" (red) that are arranged in converging directions. Linking with clamps with a step reduced by half, and plus, the intersection of the converging "legs" is additionally linked to the external longitudinal reinforcement of the main tape. The length of the "legs" is at least 50d.
	A scheme that is convenient for the separate assembly of adjacent reinforcing cages. The frame of the main tape is not interrupted, and the frame of the adjoining one ends along the line of intersection. Linking into a single structure is carried out using L-inserts (green), which connect the longitudinal reinforcement of the adjacent tape with the outer contours of the main one. The side length of such an insert is at least 50d. All clamp connections are installed and linked with a halved pitch.
	Scheme of reinforcement of the junction area using a U-shaped insert. As in other cases, the frame of the main foundation tape is not interrupted. The longitudinal reinforcement of the adjoining frame is brought to the outer contour and bent with "legs" (red color), which are located in divergent directions. The length of the side of such a foot is from 30 to 50d. The main reinforcement is performed by a U-shaped insert (dark blue) with a length of each of the "horns" of at least 50d. Linking - with a traditionally halved installation step of the clamps. Additional linkage with the installation of vertical reinforcements - in the area where the lower part of the U-shaped insert fits to the outer contour of the reinforcement of the main tape.

Another nuance should be correctly understood. The schemes proposed in the table show the linkage of the upper tier of the reinforcing belt. But exactly the same reinforcement should be provided in the lower belt, especially since the maximum loads usually fall on the lower part of the foundation tape.

Useful applications for calculating the amount of materials needed

Below, the reader will be offered three calculators that will help in calculating the amount of material required to implement the selected strip foundation reinforcement scheme.

Calculator for calculating the number of main reinforcement

To calculate the required amount of the main longitudinal reinforcement of the strip foundation frame, you need to know several initial values:

• First of all, this is the total length of the foundation tape being created. Of course, this should include not only the outer perimeter, but also all internal jumpers, if they are provided for by the project.
• The second parameter is the number of longitudinal reinforcement bars. How to determine this amount was described above in this publication, with the application of the appropriate calculator.
• The third parameter is the number of gain sections, also discussed above. This includes all corners and junctions of foundation strips. Naturally, in these areas, the consumption of reinforcement increases.

The accounting program, in addition, will take into account the need for overlapping reinforcing bars on straight sections of the tape. The overlap length is taken equal to 50d, that is, for the most commonly used reinforcement diameters, it will be from 500 to 600 mm.

The calculator will give the result in a piece quantity of a standard length reinforcing bar (11.7 meters). Sometimes the difficulties of transporting "long lengths" force buyers to purchase rods cut in two (5.85 meters). On the one hand, transportation is simplified, but on the other hand, the number of reinforcement overlaps during the installation of the frame inevitably increases, that is, the total required footage. The calculation program also provides for a second final value, expressed in the number of “halfed” rods. This will allow you to make a comparison and make a subsequent choice in favor of the first or second option.