Calculation of the foundation is a critical stage in preparation for construction. You need to do it in order to understand what section sizes are needed, how much reinforcement is needed and what diameter. Before correctly calculating the supporting part of the building, you will need to collect initial data. The literacy of calculations will depend on their accuracy.
What should be done
Most often, in private construction, strip foundations are used. This type allows you to make a basement in your house, but in some cases it may not be economically viable. To make an estimate for the work (or roughly estimate how much investment will be required), you need to calculate the fittings for strip foundation, also calculate the volume of concrete and its geometric dimensions.
Most often in private construction they lay a strip foundation
The calculation method involves calculating three quantities. The calculation of the strip foundation should result in the following information about the structure:
- depth of the sole;
- base width;
- width over entire height.
Calculation of the foundation for a house made of brick or other materials must begin with determining the depth of the foundation. It depends on the heaving of the soil, the level groundwater and climate. If this characteristic is incorrectly calculated, the building may collapse under the influence of frost heaving forces. The tape will be simultaneously exposed to moisture and cold, which will lead to uneven deformations and cracks.
The width of the base must be sufficient to evenly transfer the mass of the building to the ground. The weaker the soil, the wider the base will be needed. Due to the large area, it is possible to distribute the load from the strip foundation for the house onto the base so that each section of it bears no more than the permissible value.
The foundation must be laid below the soil freezing level The width of the tape over the entire height is usually taken structurally. It should be slightly larger than the outer walls. In this case, the method of manufacturing the tape is taken into account. For monolithic foundation a section width of 200-300 mm may be sufficient, while a prefabricated one is recommended to be made at least 400-600 mm. This indicator also depends on the depth of placement. The larger it is, the stronger the overturning effects will be (more powerful basement walls will be required).
Preparatory work
Before calculating the foundation for a house, the designer needs to find out the geological data of the site. For large buildings, special geological surveys are carried out. In private construction, it is permissible to conduct research yourself. In this case, all characteristics are assigned based on visual inspection.
- excerpts of pits, which are deep holes with plan dimensions of 1x2 m (on average);
- drilling wells with a hand drill.
In the first case, the type of soil is looked at by the walls of the pit. In the second, they check the soil on the drill blades.
To study the soil, the walls of the pit are inspected Research is carried out to a depth that is 50 cm greater than the intended laying of the tape (which was determined only by the freezing mark). When carrying out work, you need to find out the following characteristics:
- type of soil at the base level;
- location of groundwater level (GWL);
- the presence of weak soil in the lens area.
To accurately understand the GWL, it will be necessary to conduct research at several locations. At least one of these points must be located at the bottom of the site. Working in a drought does not give an accurate result, since moisture can go deep into the ground.
It is best to find out the ground level in the spring. In this case, the strip foundation will not be afraid even of floods.
Soft ground lenses can be difficult to find. To do this, you need to make pits or wells very often. In most situations this is not necessary. If such a nuisance is discovered during construction, it is covered with crushed stone, gravel or a sand-gravel mixture.
If the groundwater level on the site is deep, then you can use a deep tape (more than 1.5 m). In this case, the water should be located 50 cm below the base of the building. When the groundwater level is located at a distance of less than 1.5 m from the surface, it is reasonable to choose a shallow structure. But this type has limitations. If the moisture is higher, it is worth considering another foundation option: slab or piles.
The choice of foundation depth depends on the groundwater level To calculate the foundation base, you will need to know the strength of the soil. Characteristic signs each type of soil can be found in GOST 25100-2011. Particular attention should be paid to the appendices to this document. The load-bearing capacity of each type is taken from the table below.
| Base type | Maximum load bearing capacity in kg/cm2 |
|---|---|
| Pebbles mixed with clay | 4,50 |
| Gravel | 4,00 |
| Coarse sand | 6,00 |
| Medium sand | 5,00 |
| Fine sand | 4,00 |
| Sand of silt fraction | 2,00 |
| Loam or sandy loam | 3,50 |
| Clayey | 6,00 |
| subsidence | 1,50 |
| Bulk with compaction | 1,50 |
| Bulk without compaction | 1,50 |
Types that have a strength of 2 or less kg/cm2 are not recommended for use as a base. Before construction, you will need to replace them with medium or coarse sand.
Determination of depth
- UGV (sole should be at least 50 cm higher);
- basement floor level (the sole is located at least 20-30 cm lower);
- frost mark (the sole should be at least 30 cm lower).
The freezing depth is calculated using formulas from regulatory documents. To simplify the task, you may need ready-made tables. They give values for large settlements.
To determine the freezing depth, the easiest way is to use a ready-made table Calculation of loads
Before calculating the foundation for the house, you will need to calculate the load. It is more convenient to collect foundation loads in tabular form. All loads are divided into two types: permanent and temporary. The latter are temporary, conditionally, since they include furniture, equipment, etc. The permanent ones consist of the mass of the building structures.
The calculation of the load on the foundation can be done completely independently, taking into account the exact characteristics of the materials used. But it will be enough to use the table below. It shows average values, but the load on the foundation will change uncritically.
| Design | Load value, kg/m2 | Reliability factor |
|---|---|---|
| Brick wall 510 mm | 920 | 1,3 |
| Brick wall 640 mm | 1150 | |
| Timber wall 150 mm | 120 | 1,1 |
| Timber wall 200 mm | 160 | |
| Wall on a wooden frame with 150 mm insulation | 30-50 | |
| Partitions made of plasterboard 80 mm | 30 | |
| Flooring made of PC slabs with cement screed | 625 | 1,2 |
| Wooden ceiling with insulation | 150 | 1,1 |
| Reinforced concrete foundation in kg/m3 (!) | 2500 | 1.2 - for prefabricated 1.3 - for monolithic |
| Roof depending on the type of covering | ||
| Metal | 60 | 1,05 |
| Ceramics | 120 | 1,2 |
| Bituminous materials | 70 | 1,1 |
| Live loads | ||
| From people and furniture | 150 | 1,2 |
| Snow cover | According to SP "Loads and impacts" table. 10.1 taking into account the location of the construction site | 1,4 |
In order to correctly calculate the cross-section, the load on the foundation of each type is multiplied by the safety factor.
Calculation of the sole based on load-bearing capacity
The strip foundation, the calculation of which must be performed, requires the use of only one formula. To select the dimensions of the strip foundation, consider this:
B = P/(L*R),
Here the letter B means the width of the foundations that needs to be found. P is the mass of the entire building, taking into account the underground part, which can be found by calculating the collection of loads. R is the strength of the foundation from the first table of the article. L is the total perimeter of the strip structure. To correctly calculate the foundation, you need to include both the external and internal walls of the basement in the perimeter.
Calculation example
The calculations include the following steps:
- selection of geometric parameters;
- calculation of concrete for the foundation;
- and calculation of strip foundation reinforcement.
Geometry calculation example
To calculate the foundation, let’s take a two-story brick house with an external wall of 510 mm, the total height of the external wall is 4.5 m. There are no internal walls. It is located in Moscow, the soil on the site is medium-grained sand (R = 5 kg/cm2). Floors (2 pcs., above the basement and above the first floor) made of PC slabs, plasterboard partitions with a height of 2.7 m and a total length of 20 m. Floor height - 3 m, dimensions in plan - 6x6 m. The water in the area is low, so a decision was made to build a buried foundation 2 m high. The roof is hipped and covered with metal. The slope of the slope is 30°.
The calculation example begins by collecting the loads in tabular form.
| Load type | Computations |
|---|---|
| The foundation is monolithic (preliminarily 0.6 m wide along the perimeter of the building, equal to 36 m) | 36m*0.6m*2m*2500kg/m3*1.3 = 140400 kg |
| Brick wall | 6m*4.5m*4pcs.*920 kg/m2*1.3 = 129168 kg |
| Plasterboard partitions | 20m*2.7m*30kg/m2*1.1 = 1782 kg |
| Floors | 2pcs*6m*6m*625 kg/m2*1.2 = 54000 kg |
| Roof | 6m*6m*60kg/m2*1.05 = 2268 kg 2268 kg/cos30° = 2607 kg |
| Useful | 2 floors*36m2*150kg/m2*1.2 = 12960 kg |
| Snegovoe | 36m2*180kg/m2*1.4 = 9072 kg |
| Sum | 349,989 kg |
B = P/(L*R) = 349989kg/ (36000cm*5kg/cm2) = 1.94m. The design is calculated.
We round the calculated width to 2 m. For the width over the entire height, this is a lot; 50 cm under the walls of 51 cm will be enough. An overhang of 1 cm is allowed (the maximum is 4 cm in one direction). The width of the sole is greater than that used in the calculation, but the entire height is smaller than the original size. For this reason, there is no need to redo the calculations with the new mass of the underground structure.
Concrete counting
Before purchasing a mixture, its required cubic capacity must be calculated. To do this, you just need to find the volume of the tape. It is recommended to add a margin of 5-7% to the amount of concrete for a strip foundation.
Reinforcement
Reinforcement for a strip foundation is needed to compensate for bending effects. What kind of reinforcement should be used for reinforcement? It all depends on the height of the underground part and its length. To understand what kind of reinforcement is needed as a working one, do simple calculations. The amount of reinforcement is calculated so that its total cross-section is 0.1% of the cross-section of the concrete structure. There are minimum design requirements:
- What kind of reinforcement is needed for a structure with a side length of less than 3 m? The answer is a cross section of 10 mm.
- With a side length of more than 3 m, 12 mm reinforcement for the foundation will be required.
Foundation reinforcement compensates for bending effects The calculation is carried out approximately. Only a professional can calculate the reinforcement more accurately. The pitch of the working rods is selected so that they are distributed evenly. It is advisable to use the same step, placing elements at the bottom of the tape, at the top and in the middle.
Next you need to calculate the quantity for the clamps. They connect the working parts of the frame to each other. The layout of reinforcement in a strip foundation requires the presence of vertical and horizontal clamps. They are made from rods with a diameter of 8 mm. The step is set within 20-30 cm. In the corners the step is halved.
Calculating the amount of reinforcement for a strip foundation helps save time and money. Knowing the exact amount of reinforcement for each diameter and its pitch, you can easily reinforce the tape and purchase materials.
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.
To increase the strength characteristics of the foundation, it 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. There should be no scratches or corrosion on it. 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 increased level loads. 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 removed from the slab by 30 cm. This is necessary to connect the slab to the 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 is not a guarantee of preventing 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.
A strip-type foundation is prone to stretching across its width, so the presence of longitudinal stretching on its surface is eliminated precisely with the help of reinforcement ties. 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 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. A 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:
Reinforcement of a strip foundation significantly increases its strength characteristics and allows you to create stable structures while reducing weight.
Calculations of reinforcement and reinforcement schemes are carried out in accordance with the provisions of the current SNiP 52-01-2003. The document has detailed requirements for calculations, provides footnotes to regulatory documents and codes of practice.
SP 63.13330.2012 Concrete and reinforced concrete structures. Basic provisions. Updated version of SNiP 52-01-2003. File for download
The strip foundation must meet the requirements for durability, reliability, resistance to various climatic factors and mechanical loads.
The main characteristics of the strength of concrete structures are the resistance to axial compression (Rb,n), tensile strength (Rbt,n) and transverse fracture. Depending on the normative standard indicators of concrete, its specific brand and class are selected. Taking into account the responsibility of the design, reliability correction factors can be used, which range from 1.0 to 1.5.
Requirements for fittings
During the reinforcement of strip foundations, the type and controlled values of the quality of the reinforcement are established. The standards allow for the use of hot-rolled construction reinforcement of periodic profile, heat-treated reinforcement or mechanically strengthened reinforcement.
The class of reinforcement is selected taking into account the guaranteed value of the yield strength at maximum loads. In addition to tensile characteristics, ductility, corrosion resistance, weldability, resistance to negative temperatures, relaxation resistance and permissible elongation before the onset of destructive processes are standardized.
Table of reinforcement classes and steel grades
| Profile type | Class | Diameter, mm | steel grade |
|---|---|---|---|
| Smooth profile | A1 (A240) | 6-40 | St3kp, St3ps, St3sp |
| Periodic profile | A2 (A300) | 10-40, 40-80 | St5sp, St5ps, 18G2S |
| Periodic profile | A3 (A400) | 6-40, 6-22 | 35GS, 35G2S, 32G2Rps |
| Periodic profile | A4 (A600) | 10-18 (6-8), 10-32 (36-40) | 80С, 20ХГ2Ц |
| Periodic profile | A5 (A800) | 10-32 (6-8), (36-40) | 23Х2Г2Т |
| Periodic profile | A6 (A1000) | 10-22 | 22Х2Г2АУ, 22Х2Г2Р |
The calculation of the strip foundation is carried out in accordance with the recommendations of GOST 27751, the indicators of limiting loaded states are calculated by group.
The first group includes conditions that lead to complete unsuitability of the foundation, the second group includes conditions that lead to partial loss of stability, complicating the normal and safe operation of buildings. According to the maximum permissible states of the second group, the following are produced:
- calculations for the appearance of primary cracks on the surface of a strip foundation;
- calculations based on the time period of increase in cracks formed in concrete structures;
- calculations of linear deformations of strip foundations.
The main indicators for resistance to deformation and strength of building reinforcement include maximum tensile or compressive strength, determined in laboratory conditions on special test benches. Technology and test methods are prescribed in state standards. In some cases, the manufacturer may use regulatory and technical documentation developed by the enterprise. At the same time, regulatory and technical documentation must be approved by regulatory authorities.
For concrete structures, these values may be limited by the maximum rates of change in concrete linearity. Actual diagrams of the state of reinforcement under short-term one-sided exposure to design standard loads are taken as generalized indicators. The nature of the state diagrams of building reinforcement is established taking into account its specific type and brands. During the engineering calculation of a reinforced foundation, the state diagram is determined after replacing the standard indicators with actual ones.
Reinforcement requirements
Reinforcement cage - photo
- Size Requirements reinforced concrete structure. Geometric dimensions foundation should not interfere with the correct spatial placement of reinforcement.
- The protective layer must provide joint resistance to the loads of reinforcement and concrete, protect against the influence of the external environment and ensure the stability of the structure.
- The minimum distance between individual reinforcement bars must guarantee working together it with concrete, allow for correct joining and ensure correct technological pouring of concrete.
For reinforcement, only high-quality reinforcement can be used; mesh knitting is carried out taking into account the calculated design parameters. Deviations from the values cannot exceed the tolerance fields regulated by SNiP 3.03.01. Special construction measures must ensure reliable fixation reinforcing mesh according to existing rules.
SNiP 3.03.01-87. Load-bearing and enclosing structures. Building codes and rules. File for download
When bending reinforcement, you need to use special devices; the minimum bending radius depends on the diameter and specific physical characteristics of the building reinforcement.
Prices for reinforcing mesh
reinforcement mesh
Video – Manual machine for bending reinforcement, video instructions
Video - How to bend reinforcement. Working on a homemade machine
The reinforcement is inserted into the formwork; the manufacture of the formwork should be carried out taking into account the requirements of GOST 25781 and GOST 23478.
STEEL MOLDS FOR THE PRODUCTION OF REINFORCED CONCRETE PRODUCTS. Specifications. File for download
Formwork for the construction of monolithic concrete and reinforced concrete structures. Classification and general technical requirements
Calculation of the quantity and diameter of reinforcement
For strip foundations of baths, construction reinforcement with a periodic profile Ø 6÷12 mm is used.
Current government regulations regulate the minimum number of rods in concrete to give it maximum strength characteristics. The minimum total cross-section of longitudinal reinforcement bars cannot be ≤ 0.1% of the cross-sectional area of the foundation strip. For example, if the strip foundation has a cross-section of 12000×500 mm (sectional area is 600000 mm2), then the total area of all longitudinal rods must be at least 600000×0.01% = 600 mm2. In practice, developers rarely maintain this indicator; the weight of the bathhouse, the nature of the soil and the specific brand of concrete are also taken into account. This calculated value can be considered approximate; deviations from the recommended values should not exceed ≈20% downwards.
To calculate the amount of reinforcement, you need to know the cross-sectional area of the foundation strip and the cross-sectional area of the reinforcing bar. To make the calculations easier, we present to your attention a ready-made table.
| Number of rods | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Diameter, mm | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| 6 | 28,3 | 57 | 85 | 113 | 141 | 170 | 198 | 226 | 254 |
| 8 | 50,3 | 101 | 151 | 201 | 251 | 302 | 352 | 402 | 453 |
| 10 | 76,5 | 157 | 236 | 314 | 393 | 471 | 550 | 628 | 707 |
| 12 | 113 | 226 | 339 | 452 | 565 | 679 | 792 | 905 | 1018 |
| 14 | 154 | 308 | 462 | 616 | 769 | 923 | 1077 | 11231 | 1385 |
| 16 | 201 | 402 | 603 | 804 | 1005 | 1206 | 1407 | 1608 | 1810 |
| 18 | 254,5 | 509 | 763 | 1018 | 1272 | 1527 | 1781 | 2036 | 2290 |
| 20 | 314,2 | 628 | 942 | 1256 | 1571 | 1885 | 2199 | 2513 | 2828 |
Now calculations are greatly simplified. For example, to reinforce a strip foundation you use eight rows of reinforcement with a diameter of 10 mm. According to the table, the total area of the rods is 628 mm. Such a frame can work with a concrete strip 120 cm deep and 50 cm wide. A few extra square millimeters can be ignored; they will be additional insurance in case of violation of the knitting technology or production of low-quality concrete.
In addition to these indicators, you need to decide on the diameters of the rods for the foundations. These indicators depend on many components; for simplified calculations, you can use the proposed table.
Using this table, you can easily select the recommended reinforcement diameter for a strip foundation.
Rules for reinforcing strip foundations
There are several patterns for tying reinforcement; each developer can use the one that is most convenient for himself. The choice of scheme must be made taking into account the size of the foundation and its load-bearing characteristics.
The reinforcement can be knitted separately, and then the finished structural elements are lowered into the foundation trench and connected to each other, or they can be knitted directly in the trench. Both methods are almost equivalent, but there is a slight difference. On the ground, all the main straight elements can be done independently; when working in a trench, an assistant is required. To knit, you need to make a special hook; the connection is made with soft wire with a diameter of ≈0.5 mm.
In some articles you can find advice to use a hand-held electric drill while knitting - do not pay attention to them. This can be written by those who have no idea about work.
Firstly, a drill will tire your hand much more and faster than a light hook. Secondly, cables will always get tangled underfoot, cling to the ends of fittings, etc. Thirdly, not all construction sites have Electric Energy. And, fourthly, your wire knots will always be either loose or torn.
For tying reinforcement, thin soft wire is used, but it has low strength. Stretch the wire well; strong tying should occur within two to three turns of the hook. Otherwise, labor productivity decreases significantly and fatigue increases. There are also options for welding reinforcement, we will talk about them in the next section of the article.
Prices for knitting wire
knitting wire
How to knit reinforcement mesh yourself
We have already said above that in this way you can knit reinforcement on the ground. Only straight sections of the mesh are made, the corners are tied after they are lowered into the trench.
Step 1. Prepare pieces of reinforcement. The standard length of the rods is six meters; if possible, there is no need to touch them. If you are afraid that such dina will be difficult to work with, cut them in half.
We advise you to start knitting reinforcement for the shortest section of the strip foundation; this will give you the opportunity to gain a little experience and be more confident in handling long rods. It is not recommended to cut them; this increases metal consumption and reduces the strength of the foundation. Let's consider the dimensions of the blanks using the example of a strip foundation 120 cm high and 40 cm wide.
The reinforcement must be filled with concrete on all sides with a thickness of at least 5 centimeters. These are the initial conditions. Taking into account such indicators, the net dimensions of the reinforcement frame should be no more than 110 cm in height (minus 5 cm on each side) and 30 cm in width (minus 5 cm on each side). To knit, you need to add two centimeters on each side for the overlap. This means that the blanks for horizontal jumpers should have a length of 34 cm, the blanks for vertical jumpers should have a length of 144 cm. But you shouldn’t make the frame so high, it’s enough to have a height of 80 cm.
Step 2. Choose a flat area, lay two long rods, and trim their ends.
Step 3. At a distance of ≈ 20 cm from the ends, tie horizontal spacers on both extreme sides. For knitting you need a wire approximately 20 centimeters long. Fold it in half, slide it under the tying point and tighten the wire with the usual twist of a crochet hook. Do not overdo it with force, the wire may not withstand it. The amount of twisting force is determined experimentally.
Step 3. At a distance of approximately 50 centimeters, tie all the remaining horizontal struts one by one. Everything is ready - set the structure aside in a free space and make another frame element in the same way. You have the top and bottom parts, now you need to fasten them together.
Step 4. Next, you should adapt stops for two parts of the mesh; you can rest them on any object. The main thing is that the connected elements occupy a stable lateral position; the distance between them should be equal to the height of the knitted reinforcement.
Step 5. Attach two vertical spacers at the ends; you already know the dimensions. When the frame began to more or less resemble ready product– tie all other pieces. Take your time and check all sizes. Even though your pieces are the same length, checking the dimensions won't hurt.
Step 6. Using the same algorithm, you need to connect all the straight sections of the frame on the ground.
Step 7 Place pads at least five centimeters high at the bottom of the foundation trench; the lower mesh bars will lie on them. Place side supports and set the net in the correct position.
Reinforcement (frame installed in formwork)
Step 8 Take measurements of unknitted corners and joints, prepare pieces of reinforcement to connect the frame into a single structure. Keep in mind that the overlap of the ends of the reinforcement must be at least fifty bar diameters.
Step 9 Tie the bottom turn, then the vertical posts and the top one to them. Check the reinforcement distance to all formwork surfaces.
The reinforcement is ready, you can start pouring the foundation with concrete.
Knitting reinforcement using a special device
To make the device, you will need several boards approximately 20 mm thick; the quality of the lumber can be arbitrary. Making a template is not difficult, and it will simplify the work significantly.
Step 1. Cut four boards along the length of the reinforcement, connect them two at a time at the spacing of the vertical posts. You should end up with two identical templates. Carefully ensure that the markings of the distance between the slats are the same, otherwise there will be no vertical position of the connecting elements.
Step 2. Make two vertical supports; the height of the supports should correspond to the height of the reinforcing mesh. The supports must have side corner stops to prevent them from tipping over. All knitting work must be carried out on a level area. Check the stability of the assembled device and eliminate the possibility of it tipping over during work.
Step 3. Place the legs of the stops on two knocked down boards, place the two upper boards on the top shelf of the stops. Fix their position in any way.
You have now created a model of the reinforcement mesh; now the work can be done quickly and without outside help. Install the prepared vertical reinforcement struts at the marked places; first, use nails to temporarily fix their position. Place a reinforcement bar on each horizontal metal jumper. This operation should be repeated on all sides of the frame. Check their position again. That's right - take the wire and hook and start knitting. It is advisable to make the device if you have many identical sections of mesh made of reinforcement.
Video - How to knit reinforcement using a device
How to knit reinforced mesh in a trench
Working in a trench is much more difficult due to cramped conditions. You need to think carefully about the knitting pattern of individual elements so that you don’t have to crawl between the reinforcement bars later. In addition, you won’t be able to knit the mesh yourself; you need to work with an assistant.
Step 1. Place stones or bricks at least five centimeters high at the bottom of the trench; they will lift the metal from the ground and allow the concrete to cover the reinforcement on all sides. The distance between the stones should be equal to the width of the mesh.
In the photo - a retainer for the reinforced frame
Step 2. Longitudinal rods must be placed on the stones. Horizontal and vertical rods should already be cut to size, as we have already told you how to measure them.
Step 3. Start forming the skeleton of the frame on one side of the foundation. If you first tie horizontal struts to the lying rods, the work will be easier. An assistant must hold the ends of the rods until they are locked in the desired position.
Step 4. Continue knitting the reinforcement one by one, the distance between the spacers should be approximately fifty centimeters.
Step 5. Using the same algorithm, tie the reinforcement on all straight sections of the foundation tape.
Step 6. Check the dimensions and spatial position of the frame; if necessary, you need to correct the position and prevent metal parts from touching the formwork.
Step 7 Now it's time to work on the corners of the foundation. The picture shows a rather complex version of knitting in the corners, you can come up with an easier one for yourself. The main thing is to maintain the length of the overlaps. And one more note. In corners, the foundation works not only for bending, but also for vertical discontinuity. These forces hold the vertical bars of construction reinforcement; do not forget to install them. To guarantee, reinforcement with a larger diameter can be used for these purposes.
You need to know that any welding worsens physical characteristics strength of the reinforcement, this method should be used only in extreme cases.
If you still have to use welding, then do everything possible to put a minimum number of seams in one place, shift the fixation step of the horizontal and vertical stops by a few centimeters. During welding, accurately maintain the optimal current strength and electrode diameter. The metal in the places where the seam is applied should not overheat.
Welding reinforcement – photo
And the most important thing is that only special fittings are suitable for welding; brands of such fittings are designated by the letter “C”. By the way, this fittings are significantly more expensive than ordinary ones.
There are several ways in which you can speed up and facilitate the knitting process and at the same time improve the quality of the design and reduce material consumption.
For spacers, bend the reinforcement into a “P” shape. To do this, you can make a basic machine in a couple of hours, and it will be useful not only for bending rods. First you need to bend one sample, check its dimensions and only then, using the sample as a template, prepare all the connections. Such spacers are much easier to knit; they immediately hold right size designs. Another plus is that the consumption of expensive material is reduced. At first glance, the savings seem insignificant, a maximum of ten centimeters per connection. But if you multiply ten centimeters by the number of pieces and the price of the fittings, you get a very “pleasant” amount.
For spacers, you can use reinforcement of a smaller diameter and not necessarily expensive construction reinforcement of a periodic profile. Even metal rods or wire rod of the appropriate diameter will do.
If you do not have any experience in performing such work, then it is better not to do it yourself. Having an assistant makes the process much easier and safer.
The price of a reinforced foundation is much more expensive than an ordinary one; use this method of strengthening architectural structures in extreme cases. There are many cheaper ways to increase the load-bearing characteristics of a strip foundation. True, they cannot always be used; it all depends on the specifics of the bathhouse design, the characteristics of the soil and landscape.
A few words can be said about preloaded reinforcement. This complex method, which allows you to significantly improve all the indicators of a strip foundation without increasing the amount of reinforcement. The essence of the method is to preload the rods with forces opposite to those that will act on the structure during operation of the foundation. For example, if the rod will work in tension, then it is pre-compressed, etc.
Video - Reinforcement of shallow monolithic strip foundations
Video - Do-it-yourself foundation reinforcement
The foundation is the most vulnerable part of the structure. Due to the fact that the upper part of the building is subject to compression loads and the lower part is subject to tensile loads, proper foundation laying plays an important role. For execution correct reinforcement strip foundation with your own hands, you need to perform the calculation according to the diagram.
Such a base is, in fact, a reinforced concrete strip running along the outer part of the building and under the load-bearing walls inside.
In compression, concrete structures can withstand 50 times more than in tension.. Both the upper and lower parts of the structure experience overloads, so it is necessary to reinforce both parts. There is almost no load on the middle part. Metal fittings helps solve these problems.
To ensure the strength, reliability, durability of the building, any foundation must be reinforced. After all, the foundation is subject to various loads. This includes the weight of the entire house and various movements of the soil. The reinforcement scheme for a strip foundation resembles the skeleton of a structure, which is assembled from steel rods. In order to choose the necessary scheme for it, you need to understand what it is.
Reinforcement of a strip foundation can be easily done with your own hands, without the involvement of specialists. It is important, first of all, to choose the right required diameter fittings
Reinforcing material
The choice of material is a fairly important step. To reinforce a strip foundation with your own hands, use steel rods of different sections or fiberglass reinforcement. But most often metal is used.
The main horizontal reinforcement has a cross-section of rods from 12 to 24 mm. The rods that will be positioned vertically are auxiliary. That's why usually the cross-section of vertical rods is from 4 to 12 mm. Such a large difference is due to the variation in loads on the foundation and is directly dependent on the type of soil and the weight of the structure.
Auxiliary vertical rods are installed if the height of the foundation exceeds 15 cm. In this case, reinforcement with a cross section of 6-8 mm of class A1 is used. The frame is assembled from rods and clamps, cleaning them from rust. If necessary, the rods are straightened and cut. Knitting wire and a hook are used to connect the rods. Welding work can be performed if the rods are marked “C”.
The choice of diameter is influenced by the number of horizontal levels and the reinforcement scheme of the strip foundation.
Calculation of strip foundation reinforcement
The number of reinforcement elements must be calculated based on the size of the base. For foundations whose width is 40 cm, 4 longitudinal rods are sufficient - two at the top and two at the bottom. To install a row of frames in a strip base measuring 6x6 m, you will need, on average, 24 m of reinforcement. If you lay 4 rods at a time, you will need 96 m of longitudinal rods.
For transverse and vertical reinforcement of a foundation, the width of which is 0.3 m and the height of 1.9 m for each fastening at a distance of 5 cm from the surface, according to the concrete calculator, it is necessary (30-5-5)x2+(190-5-5)x2= 400 cm or 4 m of smooth shaped reinforcement elements.
If the mounting step of the clamps is 0.5 m, the number of connections will be: 24/0.5+1=49 pcs. This means, based on the calculations, you will need 4x49 = 196 m of transverse and vertical rods.
The total cross-sectional area of the reinforcement and its weight, based on the diameter of the rods, can be calculated from the table:
Diameter of fittings, mm |
Calculated area of the transverse rod, mm 2, with the number of rods | Theoretical weight of 1 m length of reinforcement, kg | ||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | ||
| 6 | 28,3 | 57 | 85 | 113 | 141 | 170 | 198 | 226 | 254 | 0,222 |
| 8 | 50,3 | 101 | 151 | 201 | 251 | 302 | 352 | 402 | 453 | 0,395 |
| 10 | 78,5 | 157 | 236 | 314 | 393 | 471 | 550 | 628 | 707 | 0,617 |
| 12 | 113,1 | 226 | 339 | 452 | 565 | 679 | 792 | 905 | 1018 | 0,888 |
| 14 | 153,9 | 308 | 462 | 616 | 769 | 923 | 1077 | 1231 | 1385 | 1,208 |
The minimum area of foundation reinforcement is regulated regulatory documents, and the strength of the foundation depends on this
Which scheme is better to choose?
There are two main reinforcement schemes that are most often used to strengthen the foundation for low-rise buildings:
- four rods;
- six rods.
In accordance with SNiP 52-101-2003, adjacent reinforcement bars should be located at a distance of 40 cm (400 mm) in one row. The extreme longitudinal reinforcement should be at a distance of 5-7 cm (50-70 mm) from the side walls of the base. That's why, if the width of the base is more than 50 cm, then it is better to use a reinforcement scheme with six rods.
Depending on this, the diameter of the steel rods is selected.
Usually for strip base the rods are laid “in a cage”. In this case, all rods are attached at an angle of 90°. For longitudinal arrangement, reinforcing materials of class A3, having a round shape, are used.
How to reinforce corners
The corners bear a lot of load. Therefore, when reinforcing, care must be taken to strengthen them.
AtThe following rules must be taken into account:
- the rod must be bent so that one side of it is buried in one wall of the foundation, and the other in the other wall;
- if the rod is not long enough to make a bend, then L-shaped profiles can be used to fasten the rods at the corner.
Most often, class A3 fittings are used for this.
How to do reinforcement yourself
To do this, take a square or rectangle as a basis.
Before installing the frame, a sand cushion 1 m deep must be laid on the bottom of the trench.
The frame is installed as follows:
- bricks are laid at the bottom of the trench, the height of which is 5 cm (in order to create a gap between the lower part of the base and the frame);
- to install rack rods, it is necessary to make a sample in advance, according to which the rods will be cut;
- longitudinally shaped rods are laid on the bricks;
- Horizontal jumpers with a length slightly less than the thickness of the base (approximately 5 cm on each side) are tied to the longitudinal rods in increments of 50 cm using knitting wire;
- rods are attached vertically to the corners of the formed cells, 10 cm long less than the height of the base;
- the upper longitudinal rods are mounted to the vertical reinforcement;
- The upper transverse rods are tied to the resulting corners.
When reinforcing a strip foundation, it is necessary to adhere to the requirements of SNiP 52-01-2003
Basic provisions of SNiP 52-01-2003
The main provisions of SNiP 52-01-2003 concern the distance between the horizontal ribs of the steel frame and the diameter of the reinforcement. So, between the longitudinal rods should not be less than 25 cm and more than 40 cm.
The cross section of the rods is selected according to the number longitudinal rods. For a strip foundation, it must be at least 0.1% of the working sectional area of the base. For example, if the height of the foundation is 1 m and the width is 0.5 m, the cross-sectional area should be approximately 500 mm2.
You can see the minimum diameter of the reinforcement more clearly in the table of examples:
| Terms of use of fittings | Minimum diameter of reinforcement | Regulatory document |
| Longitudinal working reinforcement along a side 3 meters or less | 10 mm | |
| Longitudinal working reinforcement along a side of more than 3 meters | 12 mm | Reinforcement of elements of monolithic reinforced concrete buildings |
| Structural reinforcement | The cross-section is equal to 0.1% of the cross-sectional area along the height of the distance between the layers of reinforcement and half the width of the tape | |
| Transverse reinforcement (clamps) of compressed elements | Not less than ¼ of the largest diameter of the longitudinal reinforcement and not less than 6 mm | |
| Transverse reinforcement (clamps) of knitted bending frames | not less than 6 mm | SP 52-101-2003 Concrete and reinforced concrete structures without prestressing reinforcement. |
| Transverse reinforcement (clamps) of knitted frames with a section height of 80 cm or less | 6 mm | Guidelines for the design of concrete and reinforced concrete structures made of heavy concrete |
| Clamps for knitted frames with a section height of more than 80 cm | 8 mm | Guidelines for the design of concrete and reinforced concrete structures made of heavy concrete |
Reinforcing a strip foundation is easy to do with your own hands; all you need to do is follow the technology and perform the calculations correctly. If it is difficult to do this on your own, it is better to seek the help of professionals. After all, a reliable and solid foundation is the price and guarantee of the stability of the entire building.
More information about reinforcing a strip foundation with your own hands can be seen in the video:
Often in the process of preparing for construction, the question arises, what thickness of reinforcement is optimal? On the one side, correct calculation foundation reinforcement affects its strength, and therefore the reliability and durability of the entire structure. This is especially important considering the funds spent on construction. On the other hand, there is a natural desire not to overpay.
Professional builders, when calculating the parameters of foundation reinforcement, use the provisions of SNiP 52-01-2003 “Concrete and reinforced concrete structures”. In private construction, for calculations, it is more than enough to follow one single rule: in the cross-sectional area of a reinforced concrete structure, the proportion total area of all reinforcing rods should not be less than one thousandth (or 0.1%).
Although the wording may seem a little confusing, the rule is actually not difficult to use. For clarity, we will make, as examples, several practical calculations of the thickness and amount of reinforcement for strip, slab and pile foundations. In the calculations we will need some initial data, we will take them from the table below.
Table of cross-sectional area of reinforcement for reinforcing reinforced concrete structures
(GOST 5781-82)
| Rod diameter, mm. | Cross area rod cross-section, cm2 | Cross area rod cross-section, m2 |
| 6 | 0,283 | 0,0000283 |
| 8 | 0,503 | 0,0000503 |
| 10 | 0,785 | 0,0000785 |
| 12 | 1,131 | 0,0001131 |
| 14 | 1,540 | 0,000154 |
| 16 | 2,010 | 0,000201 |
| 18 | 2,540 | 0,000254 |
| 20 | 3,140 | 0,000314 |
| 22 | 3,800 | 0,000038 |
| 25 | 4,910 | 0,000491 |
| 28 | 6,160 | 0,000616 |
| 32 | 8,010 | 0,000801 |
| 36 | 10,180 | 0,001018 |
| 40 | 12,570 | 0,001257 |
| 45 | 15,000 | 0,0015 |
| 50 | 19,360 | 0,001936 |
| 55 | 23,760 | 0,002376 |
| 60 | 28,270 | 0,002827 |
| 70 | 38,480 | 0,003848 |
| 80 | 50,270 | 0,005027 |
Depending on the mechanical properties reinforcing steel is divided into classes A-I (A240), A-II (A300), A-III (A400), A-IV (A600), A-V (A800), A-VI (A1000).
Reinforcing steel is manufactured in bars or coils. Reinforcing steel class A-I(A240) are made smooth, classes A-II (A300), A-III (A400), A-IV (A600), A-V (A800) and A-VI (A1000) - periodic profile.
An example of calculating the reinforcement of a strip foundation
A strip foundation with the following section is designed:
- height 1.8 m;
- tape width 0.4 m.
Let's calculate the cross-sectional area of the foundation: 1.8 x 0.4 = 0.72 sq.m.
Minimum total cross-section of reinforcement: 0.72 / 1000 = 0.00072 sq. m.
Dividing the obtained value by the cross-sectional area of reinforcement of various diameters (from the table above), we obtain the minimum required number of veins. So for reinforcement with a diameter of 6 mm we have:
0.00072 / 0.0000285 = 25.30580079 pcs.
Rounding the resulting value up (for the safety margin), we get: in order to reinforce a foundation with given dimensions with “six” reinforcement, you will need to install 26 longitudinal rods. Of course - not the best engineering solution.
Continuing the calculation for other reinforcement diameters, we obtain the following options:
- for rods with a diameter of 6 mm - 26 pcs., by analogy below (mm and pcs are omitted):
- 8 — 15;
- 10 — 10;
- 12 — 7 ;
- 14 — 5 ;
- 16 — 4 ;
- 18 — 4 ;
- 20 — 3 ;
- 22 — 3 ;
- 25 — 2 ;
- 28 — 2 ;
- 32 — 2 ;
- 36 — 1 ;
- 40 — 1 .
It is easy to see that “our” options are reinforcement bars with a diameter of 16 or 18 mm. 4 of them are required for the foundation - two each for the lower and upper tiers.
An example of calculating the reinforcement of a slab foundation
A slab foundation is being designed for a building 8 by 5 meters. The thickness of the slab is 35 cm. The owner has at his disposal fittings with a diameter of 10 mm. It is necessary to determine the parameters of the reinforcement structure.
Cross section. Let's determine its area: 8.0 x 0.35 = 2.8 square meters.
Number of veins: 0.0028 / 0.000079 = 35.5 = 36 pieces
(18 in the top layer and 18 in the bottom).
In total, in the transverse direction, the upper and lower layers each contain 18 reinforcement bars.
Longitudinal section. Let's determine its area: 8.0 x 0.35 = 1.75 square meters.
Minimum total cross-section of reinforcement: 1.75 / 1000 = 0.00175 sq.m.
Number of veins: 0.00175 / 0.000079 = 22.2 = 23 pieces, accept 24 pieces. (12 in the top layer and 12 in the bottom).
In total, in the transverse direction, the upper and lower layers each contain 12 reinforcement bars.
An example of calculating the reinforcement of a pile foundation
Let us determine the most optimal and cost-effective method of reinforcing cast-in-place piles of circular cross-section with a diameter of 20 cm (0.2 m).
Let's determine the cross-sectional area of the pile:
S = PR2 = 3.14 x (0.2 / 2)2 = 0.0314 m kV.
Minimum total reinforcement cross-section:
0.0314 / 1000 = 0.0000314 sq.m.
By dividing the obtained value by the tabulated areas of cuts of reinforcement of various diameters, we obtain:
- for rods with a diameter of 6 mm - 2 pcs;
- 8 mm - 1 piece;
- 10 mm - 1 piece;
- 12 mm - 1 pc.
The calculation results show that two reinforcement bars with a diameter of 6 mm are quite sufficient. However, reinforcement reinforced concrete products less than 3 veins are not recommended, as this sharply reduces their strength. In our case, the cheapest solution, but at the same time absolutely meeting the strength requirements, would be 3 rods with a diameter of 6 mm.
An example of calculating the scheme and costs for foundation reinforcement
1. Calculation of longitudinal reinforcement (cross section 7.0 x 0.40).
Sectional area: 7 x 0.4 = 2.8 sq.m.
Minimum total cross-section of reinforcement: 2.8 / 1000 = 0.0028 sq.m.
Let's make a calculation for one of the reinforcement diameters, 8 mm;
Number of veins:
0.0028 / 0.0000503 = 55.6 = 56 pieces, or 28 at the bottom and top.
Let's calculate the reinforcement mesh cell in this case:
From the width of the slab we subtract the value of the minimum distance from the reinforcement to the outer wall (50 mm = 0.05 m), multiplied by two (left and right). On the remaining length we will evenly place the calculated number of rods, namely, divide it by the calculated number of veins minus one. The resulting value is the cell width:
A= (7.0 m – 2 x 0.05 m) / (28 – 1) = 0.26 m = 26 cm.
For longitudinal reinforcement, we will need 56 rods 9 m long, so the total length of the reinforcement with a diameter of 8 mm will be:
56 x 9 = 504 meters
According to the reference table, one linear meter of figure eight reinforcement weighs 0.395 kg, which means the total weight will be:
504 x 0.395 = 199 kg.
We carry out similar calculations for other types of reinforcement and get:
- for 6 mm - 99 pcs, cell 14 cm, total weight: 208 kg;
- 8 mm - 56 pcs, cell 26 cm, total weight: 199 kg;
- 10 mm - 36 pcs, cell 41 cm, total weight: 200 kg;
- 12 mm - 25 pcs, cell 58 cm, total weight: 209 kg;
- 14 mm - 19 pcs, cell 77 cm, total weight: 202 kg;
- 16 mm - 15 pcs, cell 99 cm, total weight: 229 kg;
- 18 mm - 12 pcs, cell 138 cm, total weight: 216 kg;
- 20 mm - 10 pcs, cell 173 cm, total weight: 223 kg.
2. Calculation of transverse reinforcement (longitudinal section 9.0 x 0.40).
Sectional area: 9 x 0.4 = 3.6 sq.m.
Minimum total cross-section of reinforcement: 3.6 / 1000 = 0.0036 sq.m.
We calculate the values we are interested in for several reinforcement diameters:
- for 6 mm - 127 pcs, cell 14 cm, total weight: 207 kg;
- 8 mm - 72 pcs, cell 25 cm, total weight: 199 kg;
- 10 mm - 46 pcs, cell 40 cm, total weight: 199 kg;
- 12 mm - 33 pcs, cell 56 cm, total weight: 213 kg;
- 14 mm - 24 pcs, cell 81 cm, total weight: 188 kg;
- 16 mm - 19 pcs, cell 99 cm, total weight: 222 kg;
- 18 mm - 15 pcs, cell 127 cm, total weight: 224 kg;
- 20 mm - 12 pcs, cell 178 cm, total weight: 208 kg.
Let's consider the obtained values. When making a slab foundation, it is recommended to take the cell size as 40...70 mm. Two diameters fall into this range: 10 and 12 mm.
longitudinal:
- for 10 mm - 36 pcs, cell 41 cm, total weight: 200 kg
- for 12 mm - 25 pcs, cell 58 cm, total weight: 209 kg
transverse:
- for 10 mm - 46 pcs, cell 40 cm, total weight: 199 kg;
- for 12 mm - 33 pcs, cell 56 cm, total weight: 213 kg.
Total weight for 10 mm diameter: 200+199 = 399 kg; total weight for diameter 12 mm: 209+213 = 422 kg.
Since the cost of fittings is mostly determined by weight, in our case the best option there will be a rod with a diameter of 10 mm. Geometric parameters cells 41 x 40 cm.