The universal strip foundation is most often used in private housing construction. It copes well with all loads. Therefore, it can be used both for the house and for service buildings. A key condition for the strength of a structure is a properly manufactured and installed reinforcing frame.
The reinforcement of a strip foundation must be approached from the position of correct selection of the steel reinforcement itself. In terms of its diameter and the number of rods cut to a certain length. Therefore, it is very important to calculate the above indicators at the stage of designing a house. Competently draw up a reinforcement scheme.
Proper reinforcement of a strip foundation means choosing the right reinforcement. This means that we need to understand the range of this building material. The classification of reinforcement includes several types and types that differ from each other in production technology and external structural data.
By type of production
- Hot rolled with marking “A”;
- Cold-deformed with the designation “Вр”;
- Rolled "K".
According to the shape of the drawing 
- With ring profile;
- Crescent-shaped;
- Combined.
So, when they make a frame for a strip foundation, use hot-rolled reinforcement with a crescent or combined profile. Of course, the quality of the foundation for a house will largely depend on the number of rods in the reinforcing lattice and on the diameter of the selected reinforcement. Therefore, it is very important to correctly calculate both indicators.
Calculation of reinforced frame
The rules for reinforcing a strip foundation are based on the assembly diagram of the frame structure. It is divided into three types of reinforcement, laid in different planes.
Working reinforcement
These are reinforcing bars located along the trench. They are installed in several rows in height, the number of which depends on the depth of the foundation itself. The number of rods located in the horizontal plane depends on the width of the foundation trench. For example, if the depth of the foundation is 1 m, then when using reinforcement with a diameter of 8 - 14 mm, they are laid in 2 - 3 rows. As for the width, at this figure of half a meter, two rows of reinforcing bars are installed.
Vertical
These are vertically installed rods, which fasten the working reinforcement bars together, resulting in the main mesh of the reinforced frame.
Transverse
These are segments of reinforcement that fasten together two or more meshes installed in the formwork of the foundation strip. In essence, these are transverse ties that ensure the joint work of the reinforcing grids.
There are certain standards for the reinforcement of monolithic strip foundations, which define standards for the dimensional indicators of reinforcement.
- For transverse reinforcement, rods of at least 6 mm in diameter are used.
- Vertical rods are selected by diameter depending on the depth of the foundation structure. If the depth does not exceed 80 cm, then rods with a diameter of at least 6 mm are used. If the depth exceeds this indicator, then no less than 8 mm.
- As for working reinforcement bars, a special calculation formula is used here:
D=S x 0.001, where S is the cross-sectional area of the foundation, and D is the total diameter of all rods located in the longitudinal direction.
There is one condition. If the length of the working reinforcement does not exceed 3 m, then the minimum diameter for the reinforced frame of a strip foundation will be 10 mm. If the length exceeds 3 m, then the minimum size is 12 mm.
- 4 rods of 8 mm reinforcement is 2.01 cm².
- 6 rods are already 3.02 cm².
- 10 rods of 14 mm rods are 15.39 cm².
- The same amount is for 12 mm - 11.31 cm².
These indicators are in the tables of SNiPs and reinforcement assortments. They are very convenient in terms of choosing the exact quantity and diameter.
When assembling reinforcement into a frame for a strip foundation, it is important not to forget that errors in reinforcement will certainly lead to cracking of the foundation structure. Therefore, when assembling, we must not forget about the little things. For example, when two adjacent lattice frames are connected at the corners of trenches, it is necessary to take into account the reinforcements of their connection.
And these are additional clamps, wire and hooks, with the help of which not only the connection is made, but with their help the structure of the reinforced frame itself is strengthened. But in the corners of the building the foundation undergoes the greatest loads and stresses.
Video
Useful video about reinforcing strip foundations.
Scheme
The reinforcement scheme of a strip foundation is the exact location in space of longitudinal, vertical and transverse rods assembled into one structure. To make it clear, let’s consider the classic scheme as the simplest. Here it is shown in the photo below.
SNiP number 52 - 01 - 2003 clearly stipulates how reinforcement is laid in a strip foundation, with what step in the transverse and longitudinal direction.
Here are a few positions from this document.
- Step of laying rods depends on the diameter of the reinforcement for the strip foundation, the size of the crushed stone granules, the method of laying the concrete solution and its compaction.
- Working reinforcement step– this is a distance equal to two section heights of the reinforcing tape, but not more than 400 mm.
- Transverse reinforcement– this distance between the rods is no more than half the width of the section, but not more than 300 mm.
Pay attention to the photo again. The dimensions of the structure itself are not the dimensions of the foundation strip. The whole point is that the frame must be located inside the body of the foundation, therefore the same SNiP clearly stipulates that the distance from the edges of the planes of the foundation tape to the reinforcement should not be less than 5 cm.
It is this dimensional indicator that is taken as the basis when calculating the cross-sectional dimensions of the frame system. For example, if the width of the foundation is 50 cm, then the length of the transverse elements of the frame will be 40 cm. If the laying depth is 1 m, then the vertical rods are cut to a length of 90 cm. These are the maximum lengths; they may be less.
Using the reinforcement drawings for a strip foundation, you can easily indicate the overall dimensions of the structure. But you need to correctly position the frame inside the trench and From the sides you will be able to see how to place it and at what distance from the formwork surfaces. It's more difficult with the bottom of the trench. Therefore, supports 5-10 cm high are installed at the bottom, on which the reinforced frame is laid.
Reinforcing the corners of a strip foundation is a separate topic, After all, the corners are loaded the most. Therefore, the structure is strengthened in different ways here. For example, clamps made of reinforcement are additionally laid in a horizontal plane, fastened to the frame with wire.
The second option is to release the rods of each structure, located in separate adjacent trenches, and bend them at right angles to insert them into adjacent trenches for fastening to the adjacent reinforcement frame. There are other ways.
Rules
The technology for reinforcing a strip foundation is based on the accurate calculation of all structural elements, taking into account the diameter of the reinforcement and its assembly diagram. We have sorted out the distances and the diagram, now we can proceed directly to the assembly process. The most difficult thing is if the task is to connect the reinforcement with clamps, which are used as transverse fastening of the reinforcing grids. Making clamps is not always easy, especially if they have a complex shape.
Therefore Those who are planning to do the foundation reinforcement with their own hands are advised not to bend the reinforcing bars, but simply cut them to the required length, which corresponds to the distance between the meshes. The reinforcing grids themselves are assembled on a flat area, where they are cut to size and connected to each other with knitting wire. As mentioned above, taking into account the installation step of steel reinforcement.
If the width of the trench allows, then assembly can be carried out directly on site inside the formwork. For this:
- The distance from the surfaces of the formwork structure to the reinforced frame is set.
- At the junctions of the trenches on the formwork, taking into account the distances, self-tapping screws are screwed in or nails are driven in.
- Twine is stretched between them, which will show the location of the working reinforcement.
- Now vertical rods are driven into the ground (sand cushion) along stretched strings, taking into account the installation pitch. In principle, there is no need to drive everything in, the main thing is that you need a quantity that can be used to hold the working reinforcement bars. Therefore, they are driven in in increments equal to three or four calculated steps.
- Now there are horizontal rods at a distance of 5 - 10 cm from the bottom to the vertical rods. It is very important that they are located exactly in the horizontal plane.
- Next, in exactly the same way, but only taking into account the set aside distance of 5 - 10 cm from the surface of the foundation, working reinforcement rods are installed, which are attached with wire to the vertical rods.
- All that remains is to lay transverse sections of reinforcement between the gratings and fasten them with binding wire.
Here is a simple guide (step-by-step instructions) for the strip foundation reinforcement scheme. Despite its apparent simplicity, this is actually labor-intensive work that will take more than one day. It is easier to assemble the gratings on the ground. Then install them in trenches and formwork on supports. Align vertically and secure with cross rods.
True, if the side of the foundation is long, then the lattice will not be short. This means that it will weigh quite a bit, so it will be difficult to lift and lower it into the opening between the formwork elements. Either several assistants or lifting equipment will be required.
Sole reinforcement
To increase the load-bearing capacity of the foundation strip, the design includes a sole in its design. Essentially, this is an extended strip foundation located under the main structure. It allows you to increase the base area, which leads to a decrease in loads on the ground. That is, the foundation becomes more stable.
How to reinforce the base of a strip foundation is a question that worries many novice builders. In principle, everything is the same here. The only thing is to reduce the distance between the frame elements to 20 cm. In this case, the structure is installed in the formwork under the sole, that is:
- The formwork is assembled under the sole.
- A reinforcing frame is installed in it.
- The frame is mounted under the main structure, fastening it with wire to the lower reinforced frame.
- The formwork is assembled under the main tape.
Typically this design is used for a buried foundation. To make it easy to work inside the trench, its width is made one meter larger. This is an increase in the volume of earthworks, but there is no other way out. After all, installing a metal structure to a great depth with the additional installation of wooden formwork requires scope. In this case, the assembly of the reinforced frame is carried out outside the formwork. Inside, only the lower reinforcement is tied to the upper one.
Angles
The correct reinforcement of the corners of a strip foundation must be approached from the position of strengthening the corners. It was already mentioned above that there are several methods (methods) by which two reinforcement structures are connected in adjacent trenches. Let's look at one of the simplest options, as an opportunity to reinforce a strip foundation with your own hands.
Is it necessary to reinforce the strip foundation in the corners in a special way? The answer is only positive. Look at position “a” in the photo above, which shows the simplest diagram of a connection between two adjacent structures. It shows that the ends of the working reinforcement rods bent at 90° extend into the adjacent formwork. There they are connected to the rods of the longitudinal elements.
An overlap is created in these places, which guarantees high joint strength. In this case, the bent reinforcement bars themselves create high connecting strength of two adjacent concrete structures.
Tape reinforcement
The question of the need to reinforce a shallow strip foundation (MSLF) is often asked. To dot all the i's, let's explain some points that are indicated in SNiPs.
- If a one-story building with a height of no more than 10 m is being constructed with a reduced degree of responsibility on any soil. There is no need to reinforce the foundation.
- When constructing buildings higher than 10 m at the normal second level of responsibility. And these are residential and public buildings with several apartments. Reinforcement must be carried out. In this case, the spacing of the reinforcing rows is at least 20 cm.
In design projects for lightweight buildings, the reinforcement method is often specified in the form of laying a single grid similar to a slab foundation. This is completely wrong because in the center of a strip foundation (even a shallow one) the loads are insignificant. They are located along the edges of the tape.
That is why working reinforcement is the main thing in terms of load-bearing capacity. That is why the rods are located from the edges of the concrete structure at a distance of 5 - 10 cm, and not 30 or 40. They have the largest diameter compared to the vertical and transverse elements.
Conclusion on the topic
So, understanding the topic of how to properly reinforce a strip foundation with your own hands, it becomes clear that this is not just reinforcement assembled into a lattice structure. This is a strict assembly scheme of reinforcing bars selected according to diameter and length and laid with a certain step. That is, you cannot make a reinforced frame by eye. Everything in it must be in strict accordance with calculations and standards. In this case, it is very important to carry out the bonding correctly, and not welding.
The question of whether it is necessary to reinforce a strip foundation has not been asked for a long time. Reinforcement must be done taking into account the above-described calculations, nuances and assembly technologies. Don’t forget to choose the right steel reinforcement.
In contact with
The specifics of individual construction are determined by the influence of a huge number of factors, from the availability of roads and electricity to a pond or hill in the neighborhood. All these factors influence the choice of foundation and the method of its installation. What formwork should be used, what concrete mixtures to use, how to reinforce the foundation - these are the first questions at the start of building a reliable and durable house.
Reinforcement is an essential element of a reliable foundation Source newspasky.ru
To avoid problems
When laying the foundation of a private house, it is difficult to foresee what loads it will be subjected to in the future. Perhaps the owner will need to install a massive lathe or arrange a dance hall in the house, a water supply will break, or a powerful structure will be erected in the neighborhood, causing a rise in groundwater or a new underground flow. The loads will change, the foundation, not designed for dramatic changes in loads, will burst and sag, followed by the collapse of the building.
If the developer considers the installation of a strip foundation to be the most appropriate option, then reinforcement is necessary to guarantee its reliability. And you should know at least approximately how the foundation should be reinforced, the calculation of reinforcement, laying and tying should be done, even if other people will build your house.
Source ar.aviarydecor.com
Calculation with reserve
Foundation reinforcement is the installation of a metal frame in its mass, designed to create a single, indestructible structure from concrete.
Making an accurate engineering calculation of the foundation of a small individual building is difficult and expensive; it requires geological surveys, comparisons with promising development projects for the area as a whole, soil and groundwater characteristics, and solving a long list of issues.
Based on this, private developers are guided by two basic rules for constructing foundations:
The base of the foundation should lie below the soil freezing depth according to the maximum indicators of the development region.
Reinforcement of the strip foundation is mandatory and is carried out in accordance with the general recommendations of the standards with a margin of safety.
Basic rules for performing reinforcement Source sevparitet.ru
Arrangement of the foundation frame
The monolithic foundation is reinforced in the form of a single frame throughout its entire height. The distance between individual reinforcing bars should ensure free passage of the concrete mixture between them. In other words, if crushed stone of fraction 20-40 is used in concrete, then the gap between the frame rods should be at least 4 cm.
The use of rubble stone is much cheaper than conventional concrete mixture, but to create a unified structure, it is necessary to bandage the foundation along the entire perimeter. The reinforcement cage is incompatible with large stones; in such cases, the technological solution is to install reinforced belts at the bottom and top of the foundation.
Even the largest fractions of concrete should pass freely through the frame Source earny.ru
On our website you can find contacts of construction companies that offer foundation design and repair services. You can communicate directly with representatives by visiting the “Low-Rise Country” exhibition of houses.
Stages of work on arranging a reinforcement frame
The base for the foundation is made of a layer of sand of at least 10 cm, the sand is covered with a layer of crushed stone of fraction 2-5, then the sand-crushed stone base is compacted, and only then should the laying and tying of the reinforcement frame begin.
Reinforcing rods, cut along the length of the foundation strip on one side, are laid out at a distance of 20-30 cm from each other along the bottom of the foundation. At the corners they are screwed with soft knitting wire to the vertical rods, as well as to each other when overlapping.
To create the vertical corner supports of the frame, the horizontal bottom rods of the frame are bent at an angle of 90 degrees. Extended by overlapping joints and fastening with wire.
To facilitate the work on reinforcing the corners of the foundation, the installation of anchors is allowed; the work is similar to the installation of grillages or armored belts. At all corners of the foundation, 4 metal rods are driven into the ground, covered with bitumen resin on the bottom for waterproofing. They act as anchors for fastening the frame. In cross-section, the driven anchor pins should form a square with sides parallel to the foundation strip.
Anchors driven into the ground on which the frame is attached Source sjthemes.com
Vertical reinforcing rods equal to the height of the foundation are screwed or tacked to the anchors for fixation. All vertical rods are tied or welded together along the perimeter, forming a pillar structure.
In order to avoid contact between the metal and the sand-crushed stone base, brick halves are placed under it along the entire length of the rod at intervals of 1 m.
Rods are cut for transverse laying of reinforcement. Their length should be 10 cm less than the width of the monolithic tape, that is, the crossbars should be completely covered with poured concrete with a distance of 5 cm from the outer wall of the foundation.
The pitch of the foundation reinforcement with transverse rods is 50 cm along the entire length of the longitudinal reinforcement.
All reinforcement connections are twisted with binding wire.
Depending on the length of the foundation side, the distance between the vertical rods ranges from 30 to 80 cm.
Only two longitudinal rows may be enough: top and bottom.
Each horizontal row is parallel to the bottom one and similar to it.
It is quite possible to assemble the frame close to the foundation, and then simply lower it into a trench or formwork.
The frame does not have to be assembled inside a hole prepared for the foundation - installation can be done outside, and then the entire structure can be lowered down Source newspasky.ru
Of course, this method is only possible if there is a flat area for assembly, otherwise it will be difficult to achieve accurate work.
Fastening with binding wire
Two common methods of connecting reinforcement in a frame structure are welding and knitting, and knitting is considered more reliable. When filling a foundation with a concrete mixture, welded joints often cannot withstand the weight of the concrete.
The knitting wire, cut into 40-50 cm lengths, is doubled, inserted from below at the intersection of the rods, and twisted with pliers.
The version with twisting using a hook is simpler and faster: the wire is wound freely with a gap around the junction of the reinforcement, its ends are twisted by hand one or two turns, a hook is inserted into the gap between the reinforcement and the wire, and by turning it the wire is tightened.
Hooks are sold in hardware stores, but bending a cleaned welding electrode is sufficient for this purpose.
For large volumes of fastening reinforcement with wire, there is a special knitting gun. It is very effective in places that are easily accessible, but where access is difficult, and these are usually corner joints, a simple hook is again more useful.
Using a knitting gun significantly speeds up the process of tying foundation reinforcement Source dvamolotka.ru
Plastic clamps are often used instead of wire. This significantly speeds up and facilitates the work process, but at low temperatures such fasteners lose their elasticity and strength.
How fittings work
In construction, reinforcement is usually called rods of various diameters and shapes to counteract compressive and tensile loads, internal and external. The division into types, classes and groups depends on the properties and characteristics specified for the reinforcement.
The division into groups of reinforcement depends on the characteristics:
material of manufacture;
profile shape;
method of use;
installation technique;
appointment.
In the construction of foundations, the spatial arrangement of the reinforcement is important. Longitudinally oriented reinforcement elements work to minimize the formation of cracks by redistributing the load on the surface of longitudinally oriented structures.
Transverse reinforcement connects concrete in the compression zone with longitudinal reinforcement, redistributing and reducing loads.
Why do you need reinforcement: just a concrete beam on top, and reinforced underneath Source rmnt.mirtesen.ru
When studying the markings of reinforcing steel, the designations C and K after the numerical value of the yield strength are of practical importance for a private developer
The C index indicates the possibility of welding the reinforcement; the absence of this index means that welding is undesirable due to the fragility of the joint. The designation K indicates the increased resistance of the reinforcement to corrosion.
Diagram and calculation of metal
The need for metal and estimated costs can be easily calculated if you draw a reinforcement diagram for a strip foundation with all longitudinal, transverse and vertical rods. The reinforcement is sold by weight, so when calculating, you should take into account the diameter of the reinforcement; it is possible to complete the frame with metal of different diameters and types of corrugation.
To reinforce foundations, reinforcement of various brands and diameters is used; the most common are reinforcing bars with a diameter of 10-14 mm, smooth and ribbed. For laying transverse connections, it is permissible to use round smooth reinforcement of a smaller diameter.
The most common types of reinforcement for foundations are made of steel grades M35GS and M25GS, rod lengths up to 12 m, diameter from 10 to 40 mm.
Correct selection of reinforcement cross-section is the key to foundation strength Source armsetka16.ru
Alternative fittings
The difficulty of transporting steel reinforcement due to its length and many problems in working with metal forced developers to pay attention to alternative solutions.
One of them could well be fiberglass reinforcement.
It has many advantages, but to appreciate them, it is worth remembering the original purpose of foundation reinforcement. In essence, the reinforcement cage should protect the concrete foundation from stretching. The modulus of elasticity of metal rods is significantly lower than that of similar plastic rods. This means that the low elasticity threshold of plastic rods will lead to deformation, and therefore destruction of the foundation, much faster than a metal one. And the meaning of replacing metal with a plastic composite disappears.
The second very unpleasant drawback concerns specifically individual developers who do not have special conditions for aligning plastic reinforcement rolled into coils.
The disadvantages of modern plastic reinforcement relate only to the undesirability of using it in monolithic strip foundations. There are many areas of application where this type of reinforcement will perform better than steel reinforcement, but not in foundations.
Conclusion
Reinforcement prevents concrete from collapsing when shear or torsion stresses occur in it, therefore reinforcement is a mandatory stage in the construction of a concrete foundation. The rules for reinforcement are quite simple, but require strict adherence - in this case, your house will receive a reliable foundation.
Foundation reinforcement is a process necessary to strengthen the structure and increase the service life of the building. In other words, this is an assembly of a “skeleton” that plays the role of a protective component that restrains soil pressure on the walls of the base. But in order for this function to be implemented to the maximum extent, it is necessary not only to correctly calculate the reinforcement for a strip foundation, but also to know how to organize the progress of construction work.
The basis of a strip foundation is a concrete solution consisting of cement, sand and water. Unfortunately, the physical characteristics of the building material do not guarantee the absence of deformation of the base of the building. To increase the ability to withstand foundation shifts, temperature changes and other negative factors, the presence of metal in the structure is necessary.
This material is plastic, but provides reliable fixation, so reinforcement is an important stage in the complex of works.
Reinforcement for strip foundation - steel bar with stiffeners
Foundation reinforcement is required in areas where tension zones may occur. It is noted that the greatest tension appears on the surface of the base, which creates the prerequisites for reinforcement close to the upper level. On the other hand, in order to avoid corrosion of the frame, it must be protected from external influences by a layer of concrete.
Important! The optimal distance of reinforcement for the foundation is 5 cm from the surface.
Since the progression of deformation cannot be predicted, stretch zones can appear both in the lower part (when the middle bends down) and in the upper part (when the frame bends upward). Based on this, reinforcement should pass from below and above with reinforcement with a diameter of 10-12 mm, and this reinforcement for a strip foundation should have a ribbed surface.
This ensures perfect contact with the concrete.
Strip foundation stretch zones
The remaining parts of the skeleton (horizontal and vertical transverse rods) may have a smooth surface and a smaller diameter.
When reinforcing a monolithic strip foundation, the width of which usually does not exceed 40 cm, it is allowed to use 4 reinforcement rods (10-16 m), connected into a frame with a diameter of 8 mm.
Important! The distance between the horizontal rods (with a width of 40 cm) is 30 cm.
The strip foundation, although long, has a small width, so longitudinal tensions will appear in it, while there will be no transverse ones at all. It follows from this that transverse vertical and horizontal rods, which will be smooth and thin, are needed only to create a frame, and not to bear loads.
Particular attention must be paid to corner reinforcement
Particular attention must be paid to the reinforcement of corners: there are often cases when deformation occurs not in the middle, but in the corner parts. The corners should be reinforced so that one end of the bent reinforcement element goes into one wall, and the other into the other.
Experts advise connecting rods using wire. After all, not every type of reinforcement is made from steel that can be welded. But even if welding is permissible, problems often arise that can be avoided by using wire, for example, overheating of the steel, leading to a change in properties, thinning of the rod at the welding site, insufficient strength of the weld, etc.
Reinforcement structure construction diagram
Reinforcement begins with the installation of formwork, the inner surface of which is lined with parchment, making it easier to remove the structure in the future. The frame is created according to the following scheme:
1. Reinforcing bars with a length equal to the depth of the foundation are driven into the trench soil. A distance from the formwork of 50 mm and a pitch of 400-600 mm should be maintained.
2. Stands (80-100 mm) are installed at the bottom, on which 2-3 threads of the bottom row of reinforcement need to be laid. Bricks placed on edge will work well as stands.
3. The upper and lower rows of reinforcement are secured together with the transverse jumpers to the vertical pins.
4. At intersections, fastening is carried out using wire tying or welding.
The video will introduce you to a convenient way to knit reinforcement using a template:
Important! The distance to the outer surfaces of the future foundation should be strictly observed. It is better to do this with the help of bricks. This is one of the most important conditions, because metal structures should not be based directly on the bottom. They must be raised above ground level by at least 8 cm.
After installing the reinforcement, all that remains is to make ventilation holes and pour concrete mortar.
You need to know this!
Ventilation holes not only help to increase the depreciation characteristics of the foundation, but also prevent the occurrence of putrefactive processes.
Calculation of material consumption
To calculate a strip foundation, you need to know some parameters in advance. Let's look at an example. Suppose our foundation has a rectangular shape and the following dimensions: width - 3.5 meters, length - 10 meters, casting height - 0.2 meters, belt width - 0.18.
First of all, you need to calculate the total volume of the casting, for which you need to find out the dimensions of the base as if it had the shape of a parallelepiped. To do this, we will perform several simple manipulations: find out the perimeter of the base, and then multiply the perimeter by the width and height of the casting.
P = AB + BC + CD + AD = 3.5 + 10 = 3.5 + 10 = 27
V = 27 x 0.2 x 0.18 = 0.972
But the calculation of a monolithic foundation does not end there. We learned that the base itself, or rather the casting, occupies a volume approximately equal to 0.97 m3. Now you need to find out the volume of the internal part of the foundation, i.e. what is inside our feed.
We get the volume of the “filling”: multiply the width and length of the base by the height of the casting and find out the total volume:
10 x 3.5 x 0.2 = 7 (cubic meters)
Subtract the volume of the casting:
7 – 0.97 = 6.03 m3
Result: casting volume - 0.97 m3, internal filler volume - 6.03 m3.
Now you need to calculate the amount of reinforcement. Let's say the diameter will be 12 mm, the casting will have 2 horizontal threads, i.e. 2 rods, and vertically, for example, the rods will be located every half a meter. The perimeter is known - 27 meters. This means we multiply 27 by 2 (horizontal rods) and get 54 meters.
Vertical rods: 54/2 + 2 = 110 rods (108 0.5 m intervals and two at the edges). We add one more rod per corner and we get 114 rods.
Let's say the height of the rod is 70 cm. It turns out: 114 x 0.7 = 79.8 meters.
The final touch is the formwork. Suppose we build it from boards 2.5 cm thick, 6 meters long and 20 cm wide.
We calculate the area of the side surfaces: multiply the perimeter by the height of the casting, and then by 2 (with a margin, not taking into account the decrease in the internal perimeter versus the external): (27 x 0.2) x 2 = 10.8 m2
Board area: 6 x 0.2 = 1.2 m2; 10.8/1.2 = 9
We need 9 boards 6 meters long. Don't forget to add connection boards (optional).
Result: 1 m3 of concrete will be required; 6.5 m3 of aggregate; 134 meters of reinforcement and 27 linear meters of boards (20 cm wide), screws and bars. The values given have been rounded.
The results of painstaking calculation work
Now you know not only how to properly reinforce a strip foundation, but also how to calculate the necessary components. This means that the foundation you build will be reliable and strong, allowing the construction of monolithic structures of any configuration.
(MZLF) and him.
It would be very interesting to know the opinions of experts on what is true and what is not, possible changes.
Data: First there is 40 cm of fertile layer, then the soil is loam. Groundwater level is low
(because there is a quarry 1 km away - it’s dry there). Installation of foundation insulation and its waterproofing in Fig. 2.
The house is made of porous blocks, one-story, without a basement or basement.
The weight of the house with the foundation is 220 tons. The area of the foundation base is 31.88 m2.
The load of a house with a foundation is 0.69 kg/cm2 on the ground.
The load of the house on the foundation is 0.49 kg/cm2.
Calculation of the approximate load of the house per linear meter of foundation is 2.37 tons/l.m.
Foundation: Concrete M300, Reinforcement in Fig. 1. All connections are made with plastic clamps. The overlap of horizontal working reinforcements is 30 cm, also attached to plastic clamps.
In corner and T-shaped connections, reinforcement of the nodes is additionally used.
Does such a design have a right to life?
There is also a request to evaluate the drainage arrangement.
Please tell me if the following steps for installing drainage and insulating the foundation are correct
1) A pit measuring 16 x 9 meters and 40 cm deep is dug (the fertile layer is removed). The foundation itself measures 15 x 8 meters.
2) Under the foundation strip we dig a trench 40 cm deep and 80 cm wide.
3) Geotextile is laid at the bottom of the trench, so that the edges (side walls) of the trenches are also covered with geotextile (on the inside of the foundation - completely, on the outside - half).
4) The first layer of cushion, coarse sand or SGS (sand and gravel mixture) 20 cm thick is poured onto the geotextile into the trench, then thoroughly compacted with a vibrating plate.
5) The second layer of the cushion, 20 cm thick, is filled with crushed stone/gravel (or ASG), then thoroughly compacted with a vibrating plate.
6) Next comes the formation of the foundation. After the foundation has been poured and gained strength, the formwork will be removed, leaving a layer of roofing felt under the bottom of the foundation (it is necessary so that the cement laitance does not go into the cushion).
7) A layer of foundation waterproofing is applied.
8) Attached to waterproofing Thermal insulation of the foundation made of extruded polystyrene foam ursa xps, thickness 5 cm, for the entire height of the foundation.
9) In the second layer of the cushion, at a distance of 10–15 cm from the foundation, a trench 10–15 cm wide is dug, and a drainage pipe with perforation, wrapped in geotextile below the foundation level, is laid in it.
10) A protective drainage layer (membrane) is attached to the foundation insulation below the zero mark. The lower edge goes under the drainage pipe. Then the pipe is backfilled to the top level of the second layer of fill.
11) from the outside, between the foundation and the edge of the pit, backfilling of ASG with a thickness of 30 cm is carried out, after which it is carefully compacted with a vibrating plate.
12) A sand leveling layer of coarse fraction is poured onto the ASG and compacted.
13) Insulation is laid on the leveled layer of sand made of extruded polystyrene foam ursa xps thickness 5 cm.
14) A coarse sand leveling layer is poured onto the insulation and compacted.
15) A concrete blind area with a reinforced mesh is poured onto the leveled layer of sand.
16) Tiles for drainage are laid on the leveled layer of sand, flush with the winding.
17) The internal space of the foundation is filled with coarse sand with a thickness of 10 cm.
18) Expanded clay 20 cm thick is poured on top of the sand for insulation.
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:
- Sampling of soil from the trench in accordance with the drawings for reinforcing the strip foundation.
- Making a sand cushion with a tamper.
- Installation of a frame made of steel reinforcement.
- When the outside temperature is below five degrees, the concrete should be heated.
- Fastening the formwork.
- 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:
- The rod is bent so that one end goes deep into one wall of the base, the other into the other.
- The minimum allowance for a rod on another wall is 40 reinforcement diameters.
- Simple linked crosshairs are not used. Only with the use of additional vertical and transverse rods.
- If the length of the rod does not allow bending to another wall, then an L-shaped profile is used to connect them.
- 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