In the process of building a foundation, there are several stages, one of which is reinforcement. Proper installation of reinforcement is the key to the foundation’s resistance to mechanical loads. We will learn further about how to make foundation reinforcement with your own hands.
Do-it-yourself reinforcement of a foundation slab - technology and step-by-step instructions
A slab foundation is a type of foundation and is used if the groundwater on the site is too high. The thickness of the installed slab varies in size from 10-30 cm, in relation to the size of the building and the load from it. A slab foundation is the key to protecting the building from distortion, since the load is distributed evenly.
For increase strength characteristics the foundation is reinforced. Since concrete, under the influence of high loads, becomes covered with cracks. Reinforcement prevents the development of these unpleasant phenomena.
With the right approach to slab reinforcement, it is possible to obtain a foundation whose service life exceeds one hundred years. This process must be carried out competently and technologically organized. Correct and competent surface treatment leads to a positive result in the construction of the foundation.
The reinforcement process involves installing a steel grid on the base of the slab, which connects the upper and lower parts of the slab. It is possible to use individual rods, but this method is labor-intensive. The use of ribbed rods improves the strength of the slab, since the ribbed surface has greater adhesion to the base.
The number and size of reinforcement used depends on the total load on the building. Before starting work, you should calculate the amount of wire and reinforcement used in the knitting process.
There are two methods of reinforcing slabs:
- horizontal;
- vertical.
They are used together in the reinforcement process. The number of horizontally or vertically installed rods is determined by the load and weight of the building. If there is no transverse reinforcement on the tapes, then the building will collapse over time. To prevent the concrete base from becoming cracked, it is recommended to use two reinforcement options at once. Before starting reinforcement, do not forget about the construction of communication channels for sewerage and other systems.
Among the advantages of reinforcing the slab under the foundation, we note:
- reinforcement has a positive effect on the strength of the foundation and its resistance to high loads;
- reinforcement allows you to evenly distribute shrinkage from the building;
- lack of reinforcement leads to spreading and deformation of the slab;
- reinforcement increases the resistance of the slab foundation to temperature changes, frost, and temperature fluctuations;
- reinforcement has a positive effect on the soundproofing characteristics of the foundation;
- reinforcement prevents subsidence of the soil under the house.
To perform reinforcement with your own hands, you must first familiarize yourself with the recommendations for its implementation. Initially, the reinforcement is prepared and the required quantity is calculated. pay attention to appearance fittings. It should be free of scratches and corrosion. Please note that reinforcement must be done in two layers. The first is installed 50 cm from the soil, and the second is 50 mm below the top of the formwork.
Knitting of rods is done with a special hook or a special device in the form of a gun. The welding machine allows you to create a reinforced frame for buildings with an increased level of load. The main rule for high-quality installation of reinforcement is to fix the corners at an angle of 90 degrees. We still recommend choosing the ribbed version of the fittings.
In the process of reinforcing the foundation with your own hands, you will need:
- steel reinforcement;
- a hook with which the reinforcement is tied;
- metal wire;
- fasteners.
We suggest that you familiarize yourself with the instructions for performing reinforcement:
1. Cut the wire into specific sizes, in relation to the reinforcement method and the size of the reinforcement.
2. Install the rods on the slab foundation, in the same way it will be located later after knitting.
3. The first rods are fixed with a special thread; they should not touch the ground. The next reinforcement rod is fixed in the same way.
5. To fix two rows, use horizontal jumpers, the interval between which is 100-150 cm.
6. After high-quality reinforcement, the concrete composition is installed.
Please note that the installation of the reinforcement cage is carried out in two rows. Thus, it is possible to avoid deformation and increase the strength of the overall structure. The higher the interval between two rows of reinforcement, the higher the quality of the slab. In some cases, when performing reinforcement, the rods are released from the slab by 30 cm. This is necessary to connect the slab with base part. To ensure that the frame part of the reinforcement is level, use a special square or rectangular shape.
Pay special attention to the process of connecting the reinforcement bars together. If the reinforcement is of poor quality, the slab does not perform its intended functions.
Do-it-yourself foundation reinforcement video:
We suggest that you familiarize yourself with the errors that quite often arise during reinforcement:
- before starting work, it is necessary to create a project according to which calculations are performed to determine the load on the foundation; it is with the help of calculations that the optimal value of the size of the reinforcement is determined;
- during the installation of formwork, no gaps should appear, as concrete will leak out and reduce the strength of the structure;
- Waterproofing must be installed on the kidney, otherwise the quality of the slab will decrease;
- the rods should not be allowed to come into contact with the soil, as they quickly become corroded;
- the interval between the rods should be 20-40 cm;
- the end parts of the rods are equipped with protective elements, and this leads to the metal being coated with corrosion.
High-quality reinforcement of the foundation slab is the key to long-term operation of the building, so due attention should be paid to this process.
Do-it-yourself strip foundation reinforcement step-by-step instructions
The strength of the strip foundation reinforcement is determined by the quality of the metal used. With the help of a strip foundation, it is possible to build a house of any shape, not just rectangular or square, as in the previous version.
Most often, reinforcement is used to reinforce a strip foundation with your own hands. It is installed in a previously equipped trench. To maintain the evenness of the walls, the formwork is first installed. Frame reinforcement is installed after the formwork is installed, then concrete is poured, waterproofing work, etc.
The main part of the foundation is a concrete-based solution. However, it does not guarantee the prevention of deformation and shrinkage of the building. In order to increase the ability to withstand deformation of the foundation, it is reinforced. This material is flexible and allows it to take on the total load of the building.
Reinforcement is necessary in areas that are most susceptible to stretching. First of all, reinforcement is installed at the corners and at the top of the formwork. In order to prevent corrosion of metal elements, they are protected from moisture with concrete mortar and additional waterproofing. The reinforcement should be located 50 mm both from the ground and from the top of the fill.
The upper and lower sections of the reinforcement are equipped with ribbed rods. They are characterized by higher adhesion to the concrete base. Areas of horizontal and vertical value can be created from a smooth surface. If the width of the foundation exceeds 400 mm, then four reinforcement rods are used to perform reinforcement. Please note that the optimal spacing between horizontal type rods is 300 mm.
Foundation belt type is prone to stretching across its width, therefore the presence of longitudinal stretching on its surface is eliminated precisely with the help of reinforcing ties. The rods installed in the transverse direction should be made of smooth steel, since they only create a frame.
Pay attention to the reinforcement of the corner elements. Proper do-it-yourself reinforcement of a strip foundation must be done in compliance with right corner connections. One part of the reinforcement is installed in one part of the wall, and the second - in the second. Wire is used to connect the rods. Since some types of reinforcement cannot be welded, and even under the influence of concrete mortar, the welds quickly collapse.
We invite you to familiarize yourself with the do-it-yourself strip foundation reinforcement diagram:
1. Install rods in the soil, the length of which is the same as the depth of the trench. The interval between the formwork and the end of the bar is 5 cm, the reinforcement interval is at least 40 cm.
2. The first rows of reinforcement are laid on special supports located at the bottom of the trench. The role of stands is played by bricks laid on edge.
3. Two rows of reinforcement are fixed in the vertical direction using jumpers. At the places where they intersect, knitting or joining is performed using a welding machine.
Please note that the interval between the outer surfaces of the base and the reinforcement must be strictly observed. For these purposes, use a brick. Steel structure made of reinforcement is not installed directly on the bottom, as there is a risk of corrosion and premature damage to the foundation.
Don't forget to install ventilation openings, which increase shock absorption characteristics and also protect the concrete from mold and excessive exposure to moisture.
Do-it-yourself foundation reinforcement - step-by-step instructions
The process of selecting fittings should be given Special attention. If the material is marked “c”, then it can be welded. If marked “k”, the reinforcement is not susceptible to corrosion. If there is no marking, foundation reinforcement does not need to be used.
In order to weld the frame part of the reinforcement, you must have some experience working with a welding machine. If the duration of the reinforcement exceeds twelve reinforcing bars, then welding is not performed.
To prevent damage to the reinforcement under the influence of moisture, temperature changes or corrosion, there is a protective layer located underneath it. The reinforcement is installed in the foundation so as not to touch the soil.
An insufficient amount of reinforcement installed in the foundation leads to its cracking and rapid destruction.
There are several types of fittings. The first option is reinforcement made of steel. It comes in two types - smooth and grooved. The first is used for installation and does not take the load, and the second - mounting - provide good adhesion to the concrete mortar and prevent stretching of the foundation.
Before starting reinforcement, check the reinforcement for dirt or corrosion. Initially, after constructing a pit or trench, the surface is covered with sand and gravel. This pillow is a shock-absorbing layer that transfers the weight of the entire building to the ground.
Next, the formwork is installed and only after that the reinforcement is installed. In the process of reinforcing corners, special technologies are used to prevent their destruction. Reinforcement is performed in two ways - p- and g-shaped. For these purposes, clamp elements are used. At corners, installation of clamps is performed several times more often than at conventional connections. It is with the help of these methods of organizing reinforcement that it is possible to achieve the most uniform load distribution.
Do-it-yourself strip foundation reinforcement video:
Even if we roughly calculate the costs of pouring a strip foundation for a private house of any size, it becomes clear that up to 30% of the total construction estimate is spent on the construction of the foundation. But this is the case if the developer buys absolutely everything - from concrete and its delivery and pouring to the labor of workers on the site. This also includes the cost of steel or fiberglass reinforcement and reinforcement frame knitting. But a correctly drawn up reinforcement scheme for a strip foundation or pile reinforcement screw design plus independently completed work (meaning all construction works which can be done on your own) allow you to save your budget by 100-140%!
Reinforcement Basics
Reliable means error-free amplification process concrete structure in accordance with the standards of SNiP 52-01-2003, SNiP II-21-75 and SN 511-78 and other regulatory documents. What are the most frequently repeated errors that affect the reliability, strength and service life of the strip base:
- It is recommended to make the reinforcing frame for the concrete strip of the foundation of a low-rise building from corrugated metal rods Ø 10-24 mm or from fiberglass rods;
- It is strictly prohibited to connect reinforcement intersections by welding; rods can only be connected with soft knitting wire Ø 3-5 mm. Electric arc welding is ultra-high temperatures, when exposed to which the metal overheats and loses its strength properties by 150-200%, especially in areas of connections of perpendicular intersections;
- If there is homogeneous soil on the foundation laying area, it is allowed to use thinner rods of metal or fiberglass reinforcement - Ø up to 14 mm. For heterogeneous soil layers, reinforcing rods must be at least 16 mm in diameter;
- Only corrugated rods are used - smooth rods adhere worse to concrete, and all mathematical calculations related to strength and loads on the foundation are designed specifically for the use of corrugated rods. Smooth rods are allowed to be used in a reinforced frame only to form transverse fastenings, since in these areas the load on the concrete and reinforced frame is small;
- The longitudinal reinforcement bars in the body of the concrete strip must be located at a distance of ≥ 5 cm from the side, top and bottom walls of the formwork. If the reinforcement is exposed, then it will quickly be eaten away by corrosion, while the concrete will deteriorate in parallel with the corrosion of the metal - crumble, crack, swell;
- A distance of 30-45 cm is maintained between transverse reinforcement;
- Strengthening the corners of a strip-type foundation is carried out according to a different pattern from the standard knitting. This issue will be discussed separately below;
- Also, the reinforcement of the strip foundation involves laying longitudinal reinforcement every 40 cm along the height of the strip. That is, if the height of the foundation is 160 cm, then you need to lay four longitudinal rows of rods.
Self-assembly of formwork
Properly installed will not only save the construction budget by reducing the consumption of concrete mortar, but will also make the work of reinforcing the base much easier and faster.
- The material for assembling formwork decks (panels) can be very different: if the height of the base is no more than 1.5 meters, then use thick plywood, slabs (unedged boards), OSB sheets, fiberboard or chipboard, slate, sheet metal, etc. . The main requirement for formwork is that it withstand the pressure of the mortar and soil. For foundations with a height of more than one and a half meters, it is recommended to do so only because of the high pressure on its walls;
- Preparatory work for the installation of formwork begins with compaction of the base of the trench. To do this, a sand cushion is made with a layer of 15 cm, moistened and compacted, and a 5 cm layer of concrete mortar is poured on top of the sand to level the base. If they pass through the body of the foundation engineering Communication(plumbing, sewerage, heating or communications), then holes for them are pre-equipped in the tape. To do this, embedded pipes are attached to the formwork in the right places through which the pipelines will pass;
- According to the project plan, the site is marked with pegs with a cord stretched between them along the outer width of the foundation. To ensure that the lower part of the formwork panels collapses, the panels are propped apart with slats or bars at 70% of the height of the base. The length of the spacer should be approximately twice the height of the trench;
- The spacers are attached to the panels with self-tapping screws or nails. If the base height is ≥ 1.5 meters, the formwork panels should be tied together with soft steel wire in 1 meter increments in a checkerboard pattern;
- The gaps in the formwork should not exceed 2-3 cm so that the solution does not seep through them into the ground, reducing the strength of the concrete strip.
It is recommended to lubricate the inside surfaces of the formwork panels with machine oil or petroleum distillation products so that when dismantling the formwork it is easier to tear off the concrete. This is done if the formwork will be used as a reusable structure.
Rebar weight calculator GOST 5781-82
Installation of reinforcement cage
After preparing the trench and installing the formwork, reinforcement of the shallow strip foundation begins. Reinforcing the foundation with fiberglass or iron reinforcement is technologically no different, so let’s consider a more familiar option - knitting a frame from steel rods. For work you will need the following materials:
- Corrugated reinforcing bars Ø 14-18 mm (choice of diameter - according to calculations in the project);
- Vertical and transverse smooth reinforcement Ø 10-12 mm;
- Soft knitting wire Ø 3-5 mm;
- Pliers, pliers, pliers, a narrow pry bar or other metal lever Ø 20-25 mm, or a special crochet hook that you can purchase or make yourself.
Important: the fastening of steel or fiberglass reinforcement is carried out using annealed steel wire, since it stretches well and has a good strength margin.
The first step to creating a reinforced frame is to carry out calculations to determine the diameter of the rods, their length and weight. Calculating the correct reinforcement of a strip foundation is quite simple: transverse rods are laid in increments of 30 cm, longitudinal rods in increments of 40 cm, vertical rods in increments of 50 cm. The total number of connections is calculated as follows: the size of the long side of the foundation must be divided by the number of transverse rods and the number vertical rows of longitudinal reinforcement bars.
Let's say a house is being built 10 x 10 meters (base perimeter) with a foundation wall height of 120 centimeters:
- The length of one foundation wall is 1000 cm. The step of laying transverse reinforcement bars is 30 cm, therefore 1000 / 33 = 33 (transverse reinforcement in one row);
- 33 x 3 = 99 (cross bars for one side);
- 99 x 4 = 396 (total number of reinforcing bars on all four sides).
The number of fiberglass reinforcement rods is calculated in the same way.
Further actions: the total number of reinforcement (396 rods) is multiplied by the width of the tape (let's say the tape is 0.6 meters wide): 396 pcs. x 70 cm = 237.6 meters - this is the total length of the reinforcement used in the frame. The footage of longitudinal rods is calculated in the same way:
- 1000 cm x 2 = 2000 cm (one row);
- 2000 cm x 3 = 6000 cm (one side);
- 6000 cm x 4 = 24000 cm (240 meters).
Calculation of vertical rods (knitting through a jumper, i.e., after 60 cm):
- 2 x 17 = 34 units per side;
- 34 x 4 = 136 units for the entire foundation;
- 136 x 1.20 m = 163.2 meters.
In order not to purchase additional reinforcement bars (in case of erroneous calculations), add 5-8% to the total result.
You can knit a frame both on the ground and in a trench, but if the trench is narrow, this will be inconvenient. On the other hand, you won’t be able to lower the huge frame alone - you need help.
More information about reinforcing a strip-type base with your own hands:
- The beginning of the knitting is the lower transverse rods: they must be laid at a distance of 30 cm from each other, two long rods should be placed on top, and tied with wire at the intersections;
- Vertical rods are installed through one transverse rod and tied together;
- In this way, two or three more rows (as needed) are knitted at a distance of 40 cm in the upward direction;
- Upon completion of assembling the entire frame, there should be four nodes.
Now you need to learn how to correctly tie them together, as well as correctly tie the rods at the corners of the foundation.
How to reinforce corners
The corners of the foundation are constantly subjected to multidirectional compressive forces, so reinforcement at the corners must be carried out equally and without errors, so that each corner evenly absorbs the same loads, and does not create a separate local area with different load-bearing values. There are several methods for strengthening corner foundation structures:
- Using welded metal coarse mesh. Such a ready-made rigid structure has cells ≤ 200 x 200 mm, and the thickness of the reinforcement bars in the mesh can vary from 8 to 24 mm - this depends on the mass of the building and the length of the foundation. After 05-0.6 meters, horizontally laid rows of reinforcing mesh are connected to vertically located reinforcing bars, as when knitting a rod frame, with an overlap of about 0.8 meters at the corners of the frame.
- Reinforcement with individual rods:
- Using L-shaped bent rods with an overlap of ≥ 60 cm;
- U-shaped rods are usually used to reinforce right angles and foundation junctions;
- Reinforcement of connections with L-shaped brackets.
Correct formation of angles is based on following several recommendations:
- The length of the overlaps is calculated as 50 diameters of the reinforcement bars;
- When knitting corners more than 160 cm wide, the rods must be solid and bend along the corner;
- The distance between the transverse rods should not be less than 0.75 of the height of the tape, but not more than 50 cm;
- The reinforcement is attached to concrete with special claws, hooks, loops or straight ends. Welding and overlay cementation cannot be used.
Reinforcing the foundation of any structure with your own hands poses a certain problem for a novice craftsman, but if you follow the above recommendations, common mistakes can be avoided, and the foundation will be strong and durable.
Strip foundation reinforcement scheme updated: February 27, 2018 by: zoomfund
For correct reinforcement For the foundation of a private house, it is necessary to calculate the reinforcement, its proper installation and tying. An incorrect calculation will lead to damage to the foundation or unnecessary costs. Let's discuss foundation reinforcement various designs and the principle of calculating steel reinforcement, accompanied by diagrams and summary tables.
Reinforcement of the foundation requires elaboration of the structure of the frame made of reinforcement, selection and calculation of the cross-section, length and weight of rolled profiles. Insufficient reinforcement leads to a decrease in strength and a possible violation of the integrity of the building, and its excess leads to unreasonably inflated costs for this stage.
What you need to know about fittings
When strengthening a concrete base, two types of construction reinforcement are used:
- class A-I- smooth;
- class A-III - ribbed.
Smooth reinforcement is used in unloaded areas. It only forms the frame. Ribbed reinforcement, due to its developed surface, provides better adhesion to concrete. Such rods are used to compensate for the load. Therefore, the diameter of such reinforcement is, as a rule, larger than that of smooth reinforcement within the same foundation.
The diameter of the rod depends on the type of soil and the weight of the structure.
Table No. 1. Minimum standard diameters of reinforcement
| Location and operating conditions | Minimum size | Regulatory document | |
| Longitudinal reinforcement, no more than 3 m long | Ø 10 mm | ||
| Longitudinal reinforcement, length more than 3 m | Ø 12 mm | Appendix No. 1 to the design manual “Reinforcement of elements of monolithic reinforced concrete buildings”, M. 2007 | |
| Structural reinforcement in beams and slabs over 700 mm high | Sectional area not less than 0.1% of the cross-sectional area of concrete | ||
| Transverse reinforcement (clamps) in knitted frames of eccentrically compressed elements | Not less than 0.25 of the largest diameter of the longitudinal reinforcement and not less than 6 mm | ||
| Transverse reinforcement (clamps) in knitted frames of bending elements | Ø 6 mm | “Concrete and reinforced concrete structures without prestressing reinforcement” SP 52-101-2003 | |
| Transverse reinforcement (clamps) in knitted frames of bending elements at height | less than 0.8 m | Ø 6 mm | "Guide to the design of concrete and reinforced concrete structures made of heavy concrete (without prestressing)", M., Stroyizdat, 1978 |
| more than 0.8 m | Ø 8 mm | ||
If you plan to build a wooden one-story building on dense soil, you can take the tabulated values for the diameters of the reinforcement. If the house is massive and the soil is heaving, the diameters of the longitudinal reinforcement are taken in the range of 12-16 mm, in exceptional cases - up to 20 mm.
In your calculations, you will need information about reinforcement from GOST-2590-2006.
Table No. 2
| Rolled diameter, mm | Cross-sectional area, cm 2 | Specific theoretical mass, kg/m | Specific length, m/t |
| 6 | 0,283 | 0,222 | 4504,50 |
| 8 | 0,503 | 0,395 | 2531,65 |
| 10 | 0,785 | 0,617 | 1620,75 |
| 12 | 1,131 | 0,888 | 1126,13 |
| 14 | 1,540 | 1,210 | 826,45 |
| 16 | 2,010 | 1,580 | 632,91 |
| 18 | 2,540 | 2,000 | 500,00 |
| 20 | 3,140 | 2,470 | 404,86 |
| 22 | 3,800 | 2,980 | 335,57 |
Consumption of reinforcement for various types of foundation
Foundations of different designs differ in the area over which the load from the structure is distributed. For each type, the calculation of the amount of reinforcement is carried out according to its own requirements. For a correct comparison, we will calculate all foundations for the following house sizes:
- width - 6 m;
- length - 8 m;
- length of load-bearing walls - 14 m.
Calculation of reinforcement for a slab foundation
This is the most material-intensive type of foundation. There are two levels of reinforcing bars in the concrete, located 50 mm below the top and above the bottom border of the slab. The laying step depends on the perceived loads. For houses made of stone/brick, the frame cell is usually 200x200 mm. At the intersection points of the reinforcement, the upper and lower levels of the frame are connected by vertically located rods.
Reinforcement frame of a slab foundation
Let's calculate the reinforcement for our reference house (see above).
1. Horizontal reinforcement, Ø 14 mm, corrugated.
- 8000 mm / 200 mm + 1 = 41 pcs. 6 m long.
- 6000 mm / 200 mm + 1 = 31 pcs. 8 m long.
- Total: (41 pcs x 6 m + 31 pcs x 8 m) x 2 = 988 m - for both levels.
- Weight 1 linear m rod Ø 14 mm - 1.21 kg.
- Total weight - 1195.5 kg.
2. Vertical reinforcement, Ø 8 mm, smooth. For a slab thickness of 200 mm, the rod length will be 100 mm.
- Number of intersections of horizontal reinforcement: 31 x 41 = 1271 pcs.
- Total length: 0.1 m x 1271 pcs. = 127.1 m.
- Weight: 127.1 m x 0.395 kg/m = 50.2 kg.
3. Heat-treated wire Ø 1.2-1.4 mm is usually used as a knitting wire. Since the place of one connection, as a rule, is tied twice - first when laying horizontal rods, then vertical ones, the total amount of wire doubles. One connection requires approximately 0.3 m of thin wire.
- 1271 pcs. x 2 x 0.3 m = 762.6 m.
- The specific gravity of wire Ø 1.4 mm is 12.078 g/m.
- Wire weight: (762.6 m x 12.078 g/m) / 1000 = 9.21 kg.
Since thin wire can break/get lost, you need to purchase it with a reserve.
The total amount of materials for reinforcing the slab frame is given in Table No. 3.
Table No. 3
Calculation of strip foundation reinforcement
Strip foundations are reinforced concrete beams located under all load-bearing walls. It contains straight sections, corners and tees. The calculation is performed for straight sections with a small margin for strengthening corners. We assume the width of the tape is 400 mm, the depth is 700 mm.
Schematic representation of a straight section of a strip foundation
The junction of the load-bearing internal and external walls
External or internal corner of external walls
The reinforcement of strip foundations is also two-level. For longitudinal sections, a class A-III rod is used, and for vertical and transverse sections (clamps), a class A-I rod is used. The cross-section of the reinforcement is assumed to be slightly lower for strip foundations than for slab foundations, under the same construction conditions.
Let us calculate the reinforcement for the reference building chosen as an example (see above).
1. Horizontal longitudinal reinforcement, Ø 12 mm, corrugated. For a tape width of 400 mm, it is enough to lay two rods in each of two levels. For a wider tape, 3 rods should be laid.
- Length of all tapes: (8 m + 6 m) x 2 + 14 m = 42 m.
- Total length of reinforcement: 42 m x 4 = 168 m.
- Weight of reinforcement: 168 m x 0.888 kg = 149.2 kg.
- Taking into account the reinforcement of the corners, the mass of the rods will be 160 kg.
2. Vertical reinforcement Ø 8 mm, smooth. For a tape depth of 700 mm, the rod length will be 600 mm. The distance between the vertical rods along the length of the tape is taken to be 500 mm.
- Total length of rods: 85 pcs. x 0.6 m = 51 m.
- Weight of rods: 51 m x 0.395 kg/m = 20.1 kg.
3. Horizontal transverse (clamp) reinforcement Ø 6 mm, smooth. For a tape width of 400 mm, the rod length will be 300 mm. The distance between the transverse rods along the length of the tape is taken to be 500 mm.
- Number of rods: 42 m / 0.5 + 1 = 85 pcs.
- Total length of rods: 85 pcs. x 0.3 m = 25.5 m.
- Weight of rods: 25.5 m x 0.222 kg/m = 5.7 kg.
4. Knitting wire. Calculation when tying each connection with one wire Ø 1.4 mm:
- Number of nodes: 85 x 4 = 340 pcs.
- Total length: 340 pcs. x 0.3 m = 102 m.
- Total weight: (102 m x 12.078 g/m) / 1000 = 1.23 kg.
- When tying knots twice, the weight of the wire will be 2.5 kg.
The total amount of materials for reinforcing the strip frame is given in Table No. 4.
Table No. 4
Consumption of metal elements for a columnar foundation
Such a foundation consists of supports, the lower part of which is below the freezing zone, and a strip foundation resting on them. For a freezing depth of 1.5 m, the height of the pillars is 1300 mm (see figure), i.e. their base is 1700 mm below the soil level.
Location of reinforcement in a columnar foundation, side view: 1 - sand cushion; 2 — fittings Ø 12 mm; 3 - pile reinforcement
The pillars are installed in the corners of the building and along the strip every 2-2.5 m.
Let's calculate the number of rods for the configuration of the house taken as an example (see above). To do this, you need to calculate the amount of reinforcement for the pillars and sum it with the calculation result for the strip foundation.
In the pillars, only vertical rods are loaded; horizontal rods are used to form the frame. A column with a diameter of 200 mm is reinforced with four vertical reinforcements. Number of pillars: 42 m / 2 m = 21 pcs.
1. Vertical reinforcement Ø 12 mm, corrugated.
- Total length of fittings: 21 pcs. x 4 pcs. x 1.3 m = 109.28 m.
- Weight of reinforcement: 109.29 m x 0.888 kg = 97.0 kg.
2. Horizontal reinforcement Ø 6 mm, smooth. For dressing, you need to place horizontal clamps at a distance of no more than 0.5 m. For a depth of 1.3 m, three levels of dressing are sufficient. The vertical sections are located at a distance of 100 mm from each other. The length of each horizontal segment is 130 mm.
- Total length of horizontal rods: 21 pcs. x 3 pcs. x 4 pcs. x 0.13 m = 32.76 m.
- Weight of rods: 32.76 m x 0.222 kg/m = 7.3 kg.
3. Knitting wire. Each column has three levels of horizontal rods that tie four vertical ones.
- Length of tie wire per post: 3 pcs. x 4 pcs. x 0.3 m = 3.6 m.
- Wire length for all posts: 3.6 m x 21 pcs. = 75.6 m.
- Total weight: (75.6 m x 12.078 g/m) / 1000 = 0.9 kg.
The total amount of materials for reinforcing a columnar foundation, taking into account the strip frame, is given in Table No. 5.
Table No. 5
Methods and techniques for connecting reinforcement
Welding and wire knitting are used to connect intersecting rods. For foundations, welding is not The best way installation, as it weakens the structure due to a violation of structural integrity and the risk of corrosion. Therefore, as a rule, the reinforced frame is “knitted”.
This can be done manually using pliers or hooks, or with a special gun. Using pliers, unannealed wire of large diameter is knitted.
Techniques for manually knitting reinforcement using pliers: 1 - knitting with wire in bundles without pulling; 2 - knitting corner knots; 3 - double-row knot; 4 - cross knot; 5 - dead node; 6 - fastening of rods with a connecting element; 7 — rods; 8 — connecting element; 9 — front view; 10 - rear view
For thin annealed wire, it is more convenient to use hooks: simple or screw.
Video: Visual lesson on crocheting reinforcement with a homemade hook
Knitting gun
For large volumes of work, a knitting gun is used. The knitting speed is much higher than traditional methods, but there is a dependence on the power source. In addition, the gun cannot be used everywhere for foundations - some areas are difficult to access.
The foundation is the most critical structure of a building. Once a pit is backfilled, access is limited and correcting any deficiencies becomes a difficult task. It is important to ensure sufficient structural strength at the design stage.
Concrete works well in compression, but does not cope well with bending. The soil is considered an elastic base, which does not prevent slight deflections of the foundation strip. To increase the strength of the structure when exposed to lateral loads, longitudinal steel rods are laid.
All reinforcement in the structure is divided into two types: working and structural. In a strip foundation, longitudinal rods become the working reinforcement. They are selected by calculation. Structural reinforcement is assigned based on the minimum requirements of regulatory documents; calculations are not carried out. They are installed to allow individual longitudinal bars to work together.
Reinforcement classes and steel grades
The fittings differ not only in diameter. It is very important to choose the right product class. Rod steel is marked A, and wire steel Br. For the foundation, metal of class A400 yield strength is used (All is an outdated marking). The rods are easily distinguished visually:
- A240 (Al) - smooth surface;
- A300 (All) - periodic profile with a ring pattern;
- The A400 (Alll) required for the foundation is a periodic crescent-shaped profile, or as it is also called a “herringbone”.
It is allowed to use reinforcement of higher classes, but in most cases this is not economically profitable. Downgrading of fittings is not allowed.
When making rods, they are guided by. According to this document, class A400 fittings are made of steel grades 5GS, 25G2S, 32G2Rps. The consumer himself chooses which raw materials to use. If there is no steel grade in the order, GOST allows the manufacturer to assign it independently.
Besides everything in regulatory document the rules for acceptance of fittings, test methods, transportation and storage conditions are indicated.
Minimum diameters of reinforcement
When calculating, the total area of all working reinforcement is calculated, and the number and cross-section of individual rods is already selected according to the assortment.
For convenience, diameter restrictions are summarized in one table.
Requirements for the selection of working fittings are given in. This 2012 document is an updated version of the SNiP of the same name, released in 2003. The basic information in the documents is identical, only minor changes have been made. More detailed instructions are presented in the Manual on the design of concrete and reinforced concrete structures without prestressing reinforcement.
Diameters greater than 40 mm cannot be used for concrete structures.
Calculation of working reinforcement
When constructing serious structures, detailed calculations of the strip foundation are required, which will accurately determine which reinforcement to use for a given structure. All calculations in construction are carried out according to limit states, that is, the minimum conditions under which the element will perform its function are determined.
- The first group of limit states is strength calculation. Reliability and safe operation of the structure are ensured.
- The second group of limit states is rigidity calculation. Prevents excessive opening of cracks, distortions, and large deflections.
Calculations using these formulas are labor-intensive and require technical education. To simplify the design of small private buildings, strip foundation reinforcement is taken based on minimum values.
An example of calculating rods for a strip foundation
Initial data:
- tape height - 100 cm;
- tape width - 40 cm.
It is required to construct a frame for an individual residential building. Longitudinal, transverse and vertical reinforcement is used. The vertical one is taken with a cross-section of 8 mm and is installed in increments of 25 cm. The transverse horizontal one is mounted with the same increment, but with a diameter of 6mm.
In order to determine what working fittings are needed, perform a simple calculation
- Cross-sectional area of the foundation = width * height = 100 cm * 40 cm = 4000 cm².
- Required cross-sectional area of reinforcement bars = 0.1% * 4000 cm² = 4 cm².
| Diameter of fittings, mm | Total calculated cross-sectional area of reinforcing bars, cm 2 | Weight of 1 meter of reinforcement, kg | ||||
| 2 rods | 4 rods | 6 rods | 8 rods | 10 rods | ||
| 8 | used only for foundation heights of 15 cm or less, which is not suitable for strip structures | 2,01 | 3,02 | 4,02 | 5,03 | 0,395 |
| 10 | 3,14 | 4,71 | 6,28 | 7,85 | 0,617 | |
| 12 | 4,52 | 6,79 | 9,05 | 11,31 | 0,888 | |
| 14 | 6,16 | 9,23 | 12,37 | 15,39 | 1,21 | |
| 16 | 8,04 | 12,06 | 16,08 | 20,11 | 1,58 | |
| 18 | 10,18 | 15,27 | 20,36 | 25,45 | 2,0 | |
| 20 | 12,56 | 18,85 | 25,13 | 31,42 | 2,47 | |
For this strip foundation, the minimum diameter is 12 mm according to the document “Reinforcement of elements of monolithic reinforced concrete buildings. Design Manual”, we accept it. According to the assortment, 4 rods are required: 2 are located at the bottom and 2 at the top.
If rods of different diameters are used (those that are available), larger rods are placed at the bottom.
Calculation of the amount of reinforcement for the foundation
Initial data:
- materials are indicated in the previous paragraph;
- the length of the strip foundation walls is 40 m.
- Length: perimeter of the building * number of rods in the section + allowance for overlap when welding rods = 40 * 6 + 5 = 245 m.
- Anchoring of corners: number of rods in the section * number of corners * minimum anchoring length (50 reinforcement diameters) = 6 * 4 * (50 * 12) = 14.4 m.
- Weight: length*weight of one meter = (245+14.4)*0.617 = 230.3 kg of rods with a diameter of 12 mm.
Structural horizontal reinforcement
The length of the rods is taken depending on the width of the tape wall minus the protective layer of concrete - 2-3 cm on each side. We accept longitudinal rods 34 cm.
- Total length: quantity*length of one rod = 160*0.34 = 54.4 m.
- Weight: 54.4*0.222 (not indicated in the table above, but available in the full range) = 12.1 kg of rods with a diameter of 6 mm.
Structural vertical reinforcement
Everything is as in the previous paragraph, the rods are installed with a length equal to:
The height of the strip foundation minus 3 cm*2 = 100 - 3*2 = 94 cm.
- Number of rods: perimeter of the building/step of clamps (25 cm is assumed in the previous paragraph) = 40/0.25 = 160 pcs.
- Total length: quantity*length of one rod = 160*0.94 = 150.4 m.
- Weight: 150.4*0.395 = 59.41 kg of rods with a diameter of 8 mm.
For convenience, the obtained figures can be summarized in a table.
Calculating the diameter of the reinforcement takes no more than 10 minutes, but will allow you to avoid waste of material or costs for repairing strip foundations. The table obtained in the last paragraph is convenient to use when purchasing material.
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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.