The developer is always concerned about how wide the foundation of a strip structure should be. The greater the width of the foundation, the more labor and materials must be invested in its construction. Any excess in the consumption of building materials increases the cost of building a facility. To prevent this from happening, you need to accurately calculate the width and height strip foundation. Calculation of the foundation of the building determines the depth of the building, the height of the walls and the width of the foundation. It is also necessary to determine the amount of reinforcement and its diameter.
Why choose strip foundation
Compared to other foundation designs, strip support allows the load from the building to the ground to be transferred most evenly, therefore, if the results of a study of the strength of the soil foundation allow it, a strip foundation is chosen.
You need to make a strip foundation along the entire perimeter of the house and under the internal load-bearing walls. If heavy equipment is installed inside the house technological equipment(boiler), then a foundation strip is also placed under it.
Types of strip foundation
Among foundations of different designs, the developer often chooses a strip foundation for his home. Tape base buildings are mainly of two types:
- strip foundation made of precast reinforced concrete;
- monolithic reinforced concrete strip.
Precast concrete
When installing reinforced concrete blocks in the design position, there is no need to arrange formwork. The block manufacturing technology includes vibration and steaming of concrete, which guarantees their strength.
When constructing a strip foundation from precast reinforced concrete on soft soils, the blocks are supported on concrete pads (wide slabs). Pillows increase the support area of the base of the house, thereby reducing pressure on the soil.
Monolithic reinforced concrete foundation blocks have letter marking- FBS. The main dimensions of the FBS are shown in the table:
In addition, the industry produces FBP blocks. The blocks are a lightweight version of FBS of similar height and width with square voids. The length of the FBP is 238 cm. The blocks are used to support internal load-bearing fences and basement walls.
Disadvantages and advantages of a block foundation
Precast concrete foundation calculations cannot be economically accurate. The reason for this is the standardization of the sizes of reinforced concrete blocks. For example, if the calculation determined the thickness of the strip foundation to be 550 mm and the height of the wall to be 500 mm, then the size of the blocks used will be 600 mm and 580 mm, respectively.
Along with this, the block base has a number of advantages over monolithic tape:
- significant reduction in the volume of wet processes;
- no costs for formwork work, reinforcement, preparation and pouring of concrete solution;
- all-season installation work;
- the construction of the foundation of the house is carried out in short time and does not depend on the concrete hardening time.
Monolithic reinforced concrete strip
The calculation of a monolithic tape should guarantee the construction of a durable and reliable foundation building.
If the depth of the tape depends on the level groundwater, bearing capacity of the soil foundation, soil freezing thickness, then the width of the strip foundation is determined based on the total load from the structure and the thickness of the external walls.
The strip foundation must be made of such a width that the total area of the base of the building corresponds to the resistance of the soil foundation.
Calculation of the area of the base of a strip foundation
The calculation of the base area of the building must be such that, under the action of the total load, the house does not push through the ground and is not pushed upward by frozen, swollen soil. In the regulatory documentation you can find a formula for calculating the base area of a house.
S>kF/k(c)R, where
S – area of the foundation base;
k – reliability coefficient equal to 1.2, that is, an area reserve of 20% is provided;
k(c) – soil composition coefficient (plastic clay – 1, sand – 1.4, etc.);
R – calculated soil resistance (taken from the SNiP table).
All elements of the formula are for reference only, except for the total load F. The total load is calculated using reference tables of regulatory documentation. For this purpose, indicators of the average specific gravity of roof, wall and ceiling structures are used.
Data such as snow load are also taken into account. In central Russia this is 100 kg/m2, in the north of the country – 190 kg/m2, in the south – 50 kg/m2.
The total amount takes into account the weight of the foundation itself and the payload (technical equipment, filling the premises with furniture, etc.).
Video " Self-calculation reference area foundation":
An example of independent calculation of the width of a strip foundation
Initial data:
- size of the house in plan – 10 m x 10 m. Building area – 100 m 2;
- inside the house there is a load-bearing wall in the middle;
- brick walls, 1 brick thick - 250 mm and height 2.7 m. Specific gravity brickwork– 1600 kg/m 3 ;
- slate roofing – 40 kg/m2;
- flooring made of reinforced concrete slabs - 500 kg/m2;
- soil freezing depth – 700 mm;
- groundwater level – 2.2 m;
- soil base – dry loam of medium density with a design resistance of 2 kg/cm2;
All values of standard loads are taken based on reference data. The amount of snow load is determined from the corresponding section of SNiP for the southern regions of Russia.
Determination of the total load from the house on a strip monolithic foundation
Based on the available initial data, the total load on the foundation is calculated. The dimensions of the monolithic tape are also determined. It is necessary for developers to make calculations in the following order:
Roof
The roof is made of slate and has a gable roof. Taking into account the slope of the roof and its overhangs, a coefficient of 1.1 is used. The load from the roof will be: 100 m 2 x 1.1 x 40 kg/m 2 = 4000 kg.
Brick walls
To determine the load from the walls, knowing their thickness, you need to calculate their length. The length of the walls along the perimeter will be: (10 x 4) – (0.25 x 4) = 39 m. The deduction of the double thickness of the brickwork is made because the axes of the house plan are drawn in the middle of the thickness of the walls. The length of the internal load-bearing wall will be 10 - 0.25 = 9.75 m. The total length of the load-bearing walls will be equal to 48.75 running meters.
The volume of brickwork will be: 48.75 x 0.25 x 2.7 = 32.9 m3. The total load from the brick walls is: 32.9 x 1600 = 52,670 kg.
Flooring made of reinforced concrete slabs
The one-story house has ceilings on two levels. This is the ceiling of the basement and the ceiling in the house. The floor area is: 100 x 2 = 200 m 2. Accordingly, the load from the floor slabs will be equal to: 200 m 2 x 500 kg/m 2 = 100,000 kg.
To calculate the snow load, take the total roof area of the house - 100 x 1.1 = 110 m2. The snow load will be: 110 m 2 x 50 kg/m 2 = 5,500 kg.
The rate of this load is calculated based on the average weight of technical equipment, internal communications, room decoration, furniture and other things. The specific weight of the payload ranges from 18 to 22 kg/m2.
The payload is calculated on the basis of an average of 20 kg/m2. The weight will be: 100 m 2 x 20 kg/m 2 = 2000 kg.
In total, the total load on the foundation will be equal to: 4,000 + 52,670 + 100,000 +2,000 = 159,000 kg.
Calculation of the width of a monolithic tape
According to the above formula, the minimum area of the foundation base is determined:
(1.2 x 159,000 kg): 2 kg/cm 2 = 95,400 cm 2. That is, the minimum allowable area of the base of the house will be 10 m2.
The total supporting area of brick walls is determined by the product of the plan length of the load-bearing walls and their thickness: 48.75 m x 0.25 m = 12.18 m 2.
According to generally accepted practice, the minimum width of the strip foundation is 100 mm greater than the thickness of the walls.
The result shows that the calculated support area is less than the minimum support area of the walls. Therefore, the width of the strip foundation should be equal to 250 mm + 100 mm = 350 mm.
Requirement for materials for the construction of a monolithic tape
Taking into account the thickness of soil freezing (0.7 m) and the depth of the groundwater level (2.2 m), the monolithic tape is made shallowly buried - 1 m.
To fill the formwork, concrete M 300 is used. The volume of need for concrete solution is equal to: 0.35 m x 1 m x 48.75 m = 17 m 3. . Taking into account unforeseen losses, the need for concrete will be 17.3 m 3.
The reinforcement frame consists of 4 longitudinal reinforcing bars of a periodic profile with a diameter of 12 mm. Since the transverse rods of the frame are made from the same rods, the total need for reinforcement will be: 50 m x 4 = 200 m.
From all of the above, we can conclude that it is quite possible for people who are more or less knowledgeable in the construction business to calculate the width, height and length of the strip foundation for their home.
Calculation of the foundation of a building includes the determination of such important parameters as depth, area of support on the ground, dimensions of the base. It must take into account all the determining factors - geophysical characteristics of the soil, climatic features, magnitude and direction of loads, including the weight of all elements of the structure and the foundation itself.
The necessary initial data should be taken from organizations specializing in geological surveys, as well as from trusted sources.
Before starting construction, it is necessary to determine the need for concrete, reinforcing elements and other materials. The construction of the foundation cannot be stopped in the middle, and therefore calculations should help correctly purchase the right quantity of them.
Please note that the calculations are slightly different for different types foundations. There are different methods for and variants of bases. In the absence of reliable data on the condition of the soil at the site where the house was built, geological research will have to be carried out with the involvement of specialists.
Taking into account soil conditions
The bearing capacity of the soil is considered the most important characteristic that determines the type and size of the foundation. First of all, it depends on its density and structure. It can be assessed by its resistance to loads - Ro, indicating what load per unit area is permissible without subsidence (at the surface level). Ro is expressed in kg/cm² and is considered tabular, i.e. reference size.
The amount of resistance depends on the porosity (density) of the soil and its moisture content. The table below shows the values of this indicator for the most typical soils.
Load resistance values for some soil types:
| Nature of the soil | Coefficient porosity |
Ro, kg/cm² |
|
| Dry | Wet | ||
| Sandy loam | 0,5 0,7 |
3,1 2,6 |
3,1 2,0 |
| Loams | 0,5 0,7 1,0 |
3,0 2,6 2,0 |
2,4 1,8 1,1 |
| Clays | 0,5 0,6 0,8 1,0 |
6,0 5,0 3,1 2,6 |
4,2 3,0 2,0 1,2 |
Gravel and crushed stone soils have a fairly high resistance - 4-5 and 4.4-6 kg/cm², respectively, depending on the clay or sand filling. Coarse-grained sandstone has Rо 3.6-4.4 kg/cm², medium-grained sandstone - 2.6-3.4 kg/cm², fine-grained sandstone - 2-3 kg/cm², depending on moisture content.
As the depth of the formation increases, the density of the soil changes, and hence the resistance to loads. Its value at different depths (h) can be determined by the formula R=0.005R0(100+h/3).
When determining the depth of the foundation important role The following soil condition parameters play a role:
- Groundwater level. The foundation should not reach the water layer. This parameter often becomes decisive for choosing the type of base. In particular, with a high location of water it is necessary to build a slab foundation.
- Depth of winter soil freezing. The base of the foundation should be located 30-50 cm below the freezing level. The fact is that when the soil freezes, it swells greatly, which creates a buoyant load on the base.
- Level of occurrence of highly heaving layers. The foundation sole cannot rest against such soil, which means it must be passed through.
The depth of the foundation of a private house is usually not calculated, because requires the use of complex techniques. Its choice is made based on the specified practical recommendations.
Calculation of reference area
When choosing a foundation, it is important to correctly determine the minimum permissible area of its support on the ground. It can be calculated using the formula S= γn F / (γc Ro), Where:
- γc – operating conditions coefficient;
- γn – safety factor taken equal to 1.2;
The coefficient of operating conditions (working conditions) depends on the nature of the soil and structure. So, on clay soils for brick structures it is taken equal to 1.0, and for wooden ones - 1.1.
In the case of sandy soil: γc is 1.2 for large and long buildings, rigid small houses; 1.3 – for any small buildings; 1.4 – for large, non-rigid houses.
Collection of ground loads (F)
Weight of the structure
The calculation is based on the load arising from the weight of all elements of the structure, including the foundation itself. Of course, it is quite difficult to accurately calculate the mass of all structural parts, and therefore average values of the specific gravity per unit surface area are taken.
Wall structures:
- frame houses with insulation with a wall thickness of 15 cm - 32-55 kg/m²;
- log and block house - 72-95 kg/m²;
- brickwork 15 cm thick – 210-260 kg/m²;
- walls made of reinforced concrete panels 15 cm thick - 305-360 kg/m².
Floors:
- attic, wooden floor, porous insulation - 75-100 kg/m²;
- the same, but with dense insulation - 140-190 kg/sq.m;
- floor covering (basement), wooden beams – 110-280 kg/m²;
- covering with concrete slabs – 500 kg/m².
- metal roofing made of sheets – 22-30 kg/sq.m;
- roofing felt, roofing felt – 30-52 kg/sq.m;
- slate – 40-54 kg/sq.m;
- ceramic tiles – 60-75 kg/sq.m.
Calculating the weight of a structure taking into account the given specific gravities comes down to determining the area of the corresponding element and multiplying it by this indicator. In particular, to obtain the area of the walls, you need to know the perimeter of the house and the height of the walls. When calculating the roof, it is necessary to take into account the angle of the slope.
The support area of the structure is determined at the level of the base, which means that the weight of the foundation must also be taken into account in the total load on the ground. The calculation method depends on its type:
- Strip foundation. First of all, the depth (Df) is determined, which should be below the freezing level. For example, at a level of 1.3 m, the normal depth is 1.7 m. Then, the perimeter of the tape (P) is determined as 2(a + b), where a and b are the length and width of the house, respectively. The width of the tape (bl) is selected taking into account the thickness of the wall. On average, it is 0.5 m. Accordingly, the volume of the strip foundation V=P x bl x Nf. Multiplying it by the density of reinforced concrete (on average 2400 kg/m³), we obtain the estimated weight of the strip foundation.
- Columnar foundation. The calculation is carried out for each support. The weight of one column will be determined as the product of the density of concrete and the volume of pouring ( V=SxНф, where S is the area of the column). In addition, the weight must be taken into account, which is calculated similarly to a strip foundation.
- To determine weight monolithic concrete slab its volume is calculated ( V=SxНф, where S is the area of the slab). The depth is usually about 40-50 cm.
In winter, the load on the ground can increase significantly due to the accumulation of snow on the roof. It is generally accepted that when the roof slopes at an angle of more than 60 degrees, snow does not accumulate, and snow load can be ignored.
If the roof angle is smaller, it must be taken into account. Long-term observations give the following parameters for this load:
- northern regions - 180-195 kg/m²;
- middle zone of the Russian Federation - 95-105 kg/m²;
- southern regions – up to 55 kg/m².
After determining all the specified weight parameters, you can begin to calculate the minimum sole area according to the above formula. The complete one will be determined as sum of the weight of walls, ceilings, roof, foundation and snow load.
When calculating columnar and pile foundation the total load is divided by the number of supports, because the grillage distributes it evenly onto the supports.
Calculation of concrete requirements
Concrete pouring work should not be stopped until it is completely completed. To do this, it is important to correctly assess the need for it. The required quantity is calculated taking into account the type of foundation:
- Tape option. The calculation procedure can be seen using an example. The foundation is made for a house measuring 6x8 m. The freezing depth of the soil is 1 m, and therefore we choose a depth of 1.4 m. The width of the tape (specified by calculating the minimum support area) is 0.5 m. The volume of the foundation will be V=PxblхНф, i.e. (2x6x8)x1.4x0.5=67.2 m³. It is recommended to take a margin of about 8-10 percent. Finally, for this foundation you will need 74 m³ concrete.
- Columnar type. If the support has a rectangular cross-section, then its area will be determined as the product of two sides. When erecting a round pillar, the well-known formula for calculating the circumference is used S=3.14R2, where R is the radius of the column.
- Slab foundation. The volume is determined by the formula for a regular parallelepiped, i.e. V=axbxHф, where a and b are the dimensions of the sides of the slab (m). For example, for a house 6x8 m with a depth of 0.4 m, the volume will be 19.2 m³.
It is somewhat more difficult to take into account the additional need for concrete when forming stiffeners on slab base. They are usually made in increments of 2 m, and they must be located along the edges.
For the selected example, the number of ribs in length is 4, and in width 3. The total length of these elements will be (8x4) + (6x3) = 50 m. The most characteristic width and height of the ribs is 0.1 m. Therefore, the total additional volume of concrete will be 50x0.1x0.1=0.5 m³.
Calculation of reinforcement requirements
Before starting work, it is important to correctly assess and materials need to provide foundation reinforcement. The calculation is carried out as follows.
Strip foundation
For it, 2 horizontal rows of steel reinforcement of a periodic profile with a diameter of 10-14 mm are usually used.
For vertical and transverse linking, you can use smooth rods with a diameter of 8-10 mm.
The connection between the rods is ensured by steel binding wire.
An example of calculation for a house 6x8 m. The total length of the foundation is 28 m. For longitudinal reinforcement, reinforcement with a diameter of 12 mm is used, and it is laid in 2 pieces in each row (in cross-section - 4 pieces). The standard length of the rods is 6 m.
When connecting, an overlap of 0.2 m is used, and at least 5 joints are required per 28 m. For horizontal reinforcement, 28x4 = 112 m are needed. Additionally, for overlaps - 5x4x0.2 = 4 m. The overall result is 116 m.
For vertical linking, rods with a diameter of 8 mm are needed. With a foundation height of 1.4 m, the length of each rod will be 1.2 m. They are installed in increments of 0.6 m, i.e. the number of rods for the entire length is 2x28/0.6 = 94 pieces.
The total length will be 94x1.2=113 m. In the transverse direction, the ligament is provided at the same points. With a tape width of 0.4 m, the length of each rod is 0.3 m. The need is determined as 94x0.3 = 29 m. The total need for reinforcement with a diameter of 8 mm will be 142 m.
The need for binding wire is determined by the number of knots. There are 4 of them in one section, and the total number is 4x28/0.6 = 188. One bundle will require about 0.3 m of wire. The total requirement is 0.3x188=57 m.
Online calculation of dimensions, reinforcement and concrete needs
Columnar
The reinforcement is installed in a vertical position (rods with a diameter of 10-12 mm), tied in cross section with rods with a diameter of 6-8 mm. 4 main rods are required per post, and the tying is done in 3 places.
In the example under consideration (depth 1.4 m), one column requires 4x1.4 = 5.6 m of periodic profile reinforcement with a diameter of 10 mm. For transverse tying, rods 0.3 m long are used.
Their total need is 3x4x0.4 = 4.8 m. Knitting wire needs 3x4x0.3 m = 3.6 m.
Online calculation of dimensions, reinforcement and concrete needs
Slab
Typically, reinforcement is made from steel rods with a diameter of 6-8 mm, laid in a grid in one row. The laying step is 0.3 m. For a house 6x8 m, you will need 6/0.3 = 20 rods in width, and 8/0.3 = 27 in length.
The total length will be (27x6)+(20x8) =382 m. The number of intersections of the rods is 27x20=540, i.e. knitting wire you need 540x0.3=162 m.
Online size calculator, as well as reinforcement and concrete needs
Proper procurement of materials allows you to avoid problems during construction. When purchasing them, you should take into account the availability of construction skills. Lack of experience can lead to unplanned waste.
The construction of any type of foundation requires calculations. Without taking into account the actual loads and soil conditions, it is impossible to ensure its reliable design.
The discrepancy between its dimensions and loads can lead to subsidence of the structure, or even to its destruction. Only specialists can make an accurate calculation, but any person can carry out the necessary estimation calculations.
A monolithic strip foundation is a reinforced concrete looped strip that is poured along the entire perimeter of a residential building. This design allows the weight of the house to be evenly distributed over the entire foundation, preventing its local destruction under the influence of heaving forces. The corners of the base receive more loads than other areas, so the corners are additionally reinforced with pillars and reinforcement (pile-strip construction). This type is the most popular in individual construction, as it is much stronger, due to the fact that the consumption of reinforcement per 1 m3 of concrete is much greater than that of other structures. Also, the strength of the base increases due to the monolith of the tape and the depth of its placement.
The concrete strip is made prefabricated and monolithic, shallow and deep buried. The type of foundation for the house is selected based on the properties of the soil, design load on a pile-tape base, the weight of the building and other individual characteristics of the construction site. An exact or approximate calculation of a strip foundation can be done manually, using an online calculator or in a special computer program. When using the calculator, the user will receive the following data:
- Tape length monolithic foundation and its perimeter;
- Dimensions of the tape base and supporting area for calculating waterproofing materials;
- The area of the external walls of the monolith to calculate the amount of insulation materials;
- The volume and weight of the solution, based on the average density. A 10% margin should be added to the calculated value;
- The total load on the soil and the load distributed over the entire surface of the concrete;
- D min of reinforcement according to SP 52-101-2003 – the ratio of the number of reinforcing bars and the cross-section of the base is taken into account;
- The number of rows of reinforcement per 1 m3 of foundation concrete in all rows of the frame, as well as how many rows of reinforcement are needed in a single belt;
- D min of the transverse and vertical rod in the armored belt according to standards and rules;
- The distance between the transverse reinforcement and the distance between the attachment points with clamps (knitting wire);
- The distance for the rods to overlap each other;
- Length of reinforcement rods for reinforcing strip foundations with and without overlap;
- Total mass of reinforcement and reinforcement frame weight;
- The thickness of wooden formwork and the number of boards according to GOST R 52086-2003;
- The quantity of all building materials for the installation of dimensional formwork.
A monolithic concrete strip is a continuous pouring of a strip foundation with a reinforced frame; a prefabricated foundation is a foundation made of solid foundation blocks (FBS) or brick, natural stone and other piece building materials. The depth of the foundation divides structures into deep and shallow foundations.
Advantages of a deep-seated monolithic strip foundation without permanent formwork:
- Very strong base that can withstand the weight of multi-story buildings;
- Durable and reliable structure;
- Foundation designed for independent or professional construction;
- You can make a basement in your house.
Flaws:
- High labor costs, high consumption of building materials for pouring and reinforcing the strip foundation;
- Construction without special equipment is difficult or impossible;
- The influence of the proximity of groundwater - in some cases, drainage of the area or area around the house is required.
How to calculate the foundation
Calculation of parameters for a strip foundation takes into account the mass of the building and the weight of concrete with reinforcement, as well as the load-bearing characteristics of the soil. The weight of the building must be less than the weight of the base. The calculation is carried out in the following sequence:
- Study of site characteristics. The depth of the tape should be 0.3-0.5 m below the soil freezing value in the region;
- The theoretical width of the tape is assumed to be 0.2 m - with further calculations this value will increase;
- The weight of the building is calculated - approximate data for individual building structures are shown in the table:
| Construction elements | Specific gravity, kg/m2 |
| Wall | |
| Half-brick wall (0.12 m) | 200-250 |
| Foam or aerated concrete wall, D600 blocks, wall thickness – 0.3 m | 180 |
| Log wall Ø 0.24 m | 135 |
| Wall made of timber with a cross section of 0.15 m | 120 |
| Frame-panel wall with a cross-section of 0.15 m with a layer of insulation | 50 |
| Interfloor and ceiling slabs | |
| Basement or interfloor flooring made of wood (layer of insulation with a density of ≤ 200 kg/m 3) | 100 |
| Wood flooring of the attic (layer of insulation with a density of ≤ 200 kg/m 3) | 150 |
| Slab with voids | 350 |
| Monolithic reinforced concrete slab | 500 |
| Load on the basement and floors between floors | 105 |
| Roof, rafter system and sheathing | |
| Sheet metal roofing, corrugated sheet or metal tiles | 30 |
| Ruberoid in two layers | 40 |
| Slate | 50 |
| Ceramic or clay tiles | 80 |
| Snow load for continental climate zone | 100 |
| Snow load for southern regions | 50 |
| Snow load for the north of the Russian Federation | 190 |
If the roof has a slope of more than 60 0, then the load from the snow layer is not taken into account when the calculation is carried out.
- The mass of concrete for the strip foundation is calculated. The total volume of the base (length, height and width are multiplied) must be multiplied by the specific gravity of reinforced concrete (2500 kg/m³) - this will be the total weight of the concrete strip. The total load from the house on the soil (P, kg) is the sum of the weight of the base and the house.
- The figures for the bottom width of the sole B (cm) are calculated:
B = 1.3 × R / (L × R o);
- 1.3 – load reserve;
- P – the entire mass of the building with the foundation, kg;
- L – length, cm;
- R o – soil resistance, kg/cm². The approximate value is shown in the table:
- Initial width of the base: 0.2 m - if the calculation gave a smaller result, then the final value is taken to be exactly 0.2 m. If the calculated width is more than 20 centimeters by 0.05 m, then the calculation of the shallow strip foundation is repeated with a new initial value width until the results show an increase in base width of less than 5 cm.
Amateur calculation of a shallow strip foundation
Here is an example of manually calculating a shallow strip foundation:
- The hydrogeological parameters of the soil at the construction site, and the characteristics of the occurrence of groundwater, as well as the properties of heaving and buoyancy of the soil are studied;
- A structure with a shallow burial is placed on sandy or homogeneous soil;
- The reinforcement parameters of the strip foundation and the dimensions of the foundation itself are calculated;
- The mass of the entire structure and individual elements is calculated;
- Dimensions and design calculation results are adjusted.
An amateurish, but fairly accurate manual - calculating the foundation - requires determining specific values:
- Parameter b is the width of the side wall of the tape, h is the height of the fill, p is the perimeter of the house;
- Formula to calculate the volume and amount of concrete: H > / Z + 10 cm, where H is the height of the foundation, Z is the depth;
- The result is compared with the length, width and height of the reinforcement for the foundation: the depth of the base must be greater than or equal to the height of the reinforced belt;
- The ebb volume is calculated by multiplying the values of b, p and h;
- Now you need to calculate the area of the formwork. the area of the side wall of the tape must be multiplied by the perimeter of the foundation, previously multiplied by the height of the trench. The area of one board for formwork is also determined;
- The number of boards is calculated as follows: you need to divide by the sum of the lateral areas of the concrete base by the area of the entire formwork.
Calculation of reinforcing bars
- Perimeter: (6 + 7) x 2 = 26 m;
- Length of the entire structure: 26 + 6 = 31 m, where 6 is the length of the internal transverse tape;
- Length of all reinforcing bars: 31 x 4 = 124 m.
- If you allow only one connection of reinforcement per rod, you will need 4 rods, which must be multiplied by the number of walls (5 walls with an internal wall): 20 joints are obtained. This means that you need to add another 20 m to the result;
- The total length of the reinforcing bars is 124 + 20 = 144 m.
- The distance between the rods is 0.5 m;
- Number of armor rings in the belt: 31 / 0.5 = 62;
- The perimeter of the reinforced ring: for a reinforcing lattice with a height of 0.5 m and a distance between the rods of 0.25 m, the calculation is as follows: (0.5 m + 0.25 m) x 2 = 1.5 m;
- To calculate the required length of all reinforcing rods with a margin for overlap, the calculated length of the rods is multiplied by 1.5: 62 x 1.5 = 93 m;
To make it work correct calculation The strip foundation must always be made with a supply of all materials. Another simplified calculation option:
N r x L x S = 1.3 x M z + M m + N s + N v ;
- N r – soil resistance;
- L – foundation length;
- S – width;
- M z – weight of the house;
- M m – furniture weight;
- Using the above formulas, the width of the base S is also calculated.
The estimated depth of soil freezing is determined by the formula: d = k n d fn;
- k n – coefficient of thermal state of the house;
- d fn – soil freezing depth.
Calculation of strip foundation updated: December 25, 2016 by: Artyom
A project is needed when building any house. It does not have to be professional, that is, carried out by a specialist from a construction or design organization. These calculations can be performed independently, at least in order to accurately represent the amount of concrete in cubic meters required to pour the foundation. After all, this is the most important calculation, the correctness of which will allow you to avoid, for example, overuse of building materials, and therefore save money.
The initial data that will be required to determine the amount of concrete required to pour the foundation will be as follows:
- type of foundation, determined depending on characteristics such as the load on it (depends on the material of the walls: and have different weights) and load bearing capacity soil;
- foundation configuration, i.e. its dimensions and geometry.
Concrete calculation for strip foundation
A strip foundation is an inextricable rigid structure laid under each load-bearing wall of a building and forming a closed loop. The method for calculating this type of foundation is associated with these features.
Basic formulas for calculating the volume of concrete for a foundation
To calculate the amount of concrete you will need the following data:
- Width and height of the foundation strip,
- Total length of the tape.
The width of the foundation strip is determined based on the support area of the foundation. Typically this value is 20-40 cm. The height of the tape is determined by the height of the above-ground part of the foundation, which is usually no more than 50 cm, as well as its depth, which can reach several meters.
This value is determined based on several factors, for example, how deep the groundwater runs under the building under construction, as well as the depth of soil freezing. For example, in sandy soil and in water-saturated soils, the most justified depth is 2.5 m. For small country houses in normal conditions middle zone One and a half meters is enough. Accordingly, to determine the height of the strip of such a foundation, it will be necessary to add 40 cm of the above-ground part to the 1500 cm depth of the foundation.
The total length of the tape will be entirely determined by the configuration of the foundation. In most cases, calculating the total length is not difficult - you need to add the internal load-bearing walls to the total length of the external walls. And we get the volume of concrete by simply multiplying the length of the foundation by its height and width:
Vb = lhs, where l, h and s are the length, height and width of the foundation, respectively.
It should be borne in mind that the amount of concrete calculated using this formula does not take into account the inevitable losses during transportation, pouring, compaction of the mixture, its leakage through gaps, as well as absorption into the wooden elements of the formwork. On the other hand, the design also contains metal fittings, which, by reducing the useful volume, somewhat compensates for losses.
However, in practice the latter are still much more significant, so the result obtained from the formula presented above needs to be corrected:
- round up to the nearest whole number,
- increase the value by another 1.5-2%.
That is, the final formula for calculating the amount of concrete for a strip foundation will take the following form: V = Vb + 0.02Vb
Amount of concrete for slab foundation
A slab foundation is an ordinary monolithic reinforced concrete slab at the base of a building. Accordingly, to calculate the volume of concrete required to pour a given type of foundation, you simply need to multiply its length, width and height. The minimum height for this type of foundation is 10 cm. In accordance with this, we can give approximate data on the consumption of concrete for a building with sides, for example, 8 x 8 m:
- 10-centimeter slab - 3.6 m 3;
- 20-centimeter slab - 7.2 m3;
- 30-centimeter slab - 10.8 m3;
However, this type of construction also has some of its own characteristics, which directly affect the consumption of concrete. So that the slab is stiffer and more resistant to deformation, stiffening ribs are made along its edges, as well as in the longitudinal and transverse directions in increments of approximately 3 meters, dividing the foundation into squares.
They are usually performed on the lower surface due, firstly, to a simpler pouring technology, and secondly, this way the upper part of the slab remains smooth. Accordingly, these stiffeners will also require concrete in an amount that can be calculated knowing their cross-sectional area and total length.
The ribs can be either rectangular or trapezoidal. The height of these structural elements of a slab foundation is usually taken equal to the thickness of the latter, and the width is approximately 80% of the height. Thus, the formula for calculating the amount of concrete for a slab foundation with rectangular stiffeners is quite simple:
Vb = lhs + lр*sр*h, where the following values:
- l, h and s are the length, height and width of the slab, respectively;
- lр, sp – the total length of the stiffening ribs and their width, respectively.
If the latter are planned to be made with a cross section in the form of a trapezoid rather than a rectangle, then calculating the volume of concrete mixture required to fill these ribs will be reduced to multiplying the area cross section of this trapezoid by the total length of the ribs.
Trapezoidal ribs have their own peculiarity - usually the ratio of the lengths of their bases is 1.5, that is, the larger base of the rib will be approximately one and a half times longer than its height, and the smaller one will be equal to the height or even be slightly shorter - up to 80% of its value.
Let us recall the formula for calculating the area of a trapezoid:
S = h(a+b)/2, where a and b are the bases, h is the height of the trapezoid.
Thus, the formula for calculating the volume of a slab foundation with trapezoidal stiffeners will look like:
Vb = lhs + lр*h(0.8h+1.5h)/2
Methodology for calculating the volume of concrete for arranging a columnar foundation
Even from the name it is clear that a columnar foundation is a set of concrete piles dug into the ground. They are, as a rule, located at the intersections of the walls of the house, but if necessary, they are also dug into the spans. The head is the upper part of the pile, usually located at a height of 40-50 cm, but the full height is also determined by its lower part - the base.
One of the advantages columnar foundation– economical, that is, the consumption of concrete for pouring it is minimal. Calculating the amount of concrete should also not cause much difficulty. For round columns, when making calculations, you need to know the following initial data:
- number of piles,
- cross section radius,
- height.
It is not difficult to guess that the volume of one such column will be equal to the height multiplied by the cross-sectional area of the pile. The latter is equal to the square of the radius multiplied by 3.14. Accordingly, the volume of concrete will be calculated using the formula:
V = 3.14R 2 nh, where R, n and h are the radius, number of piles and their height, respectively.
If square columns are used, then the calculation becomes even simpler:
V = a*h*n, where a is the length of the side of the pile.
Note: accurate concrete calculations are carried out for dry sand and crushed stone; if they are moistened, the volume of water will be different. Here you need to experiment with the volume of water.
Foundation base width A- depends on the weight of the building, the strength characteristics of the soil under the building, etc. It is recommended to accept based on the calculation results.
The width of the roof must be increased.
H- height of the foundation. Depends on the degree of soil subsidence (the more subsidence the soil, the higher)
HC- the height of the foundation (basement) above ground level. The required formwork area depends on it. The excess level should not be less than 200 mm.
The depth of the foundation into soil subject to frost heaving (loams, clays) should be no less than the depth of soil freezing in the given region. The depth should be no less than the thickness of the plant soil layer (30-50 cm)
In underground soils, the walls of the trench are unstable and will crumble.
Horizontal rows of reinforcement are made from “working” reinforcement with a diameter of more than 10 mm, and vertical rows are made from “structural” reinforcement with a diameter of 8-10 mm of smooth or periodic section.
The pitch of vertical reinforcement is taken from the conditions of non-sagging of the working reinforcement of the upper row.
It is prohibited to insert vertical reinforcement into the ground or install it on pieces of crushed stone and other improvised objects. The reinforcement frame must either be suspended or installed on specially made concrete support cubes.
The distance between the ends of the reinforcement must be at least 15 mm.
Since a strip foundation for a house is a closed loop of reinforced concrete beams erected under all the load-bearing walls of the house, choose one of the eight proposed standard foundation options based on how many load-bearing walls are planned in the house.
Option No. 1 is relevant if construction is planned without internal supporting walls, No. 2 if an internal supporting wall is needed, options No. 3-8 if necessary more load-bearing walls in the house.
Fill in the dimensions in millimeters:
X– The width of the foundation depends on your wishes and the possibility of construction on the site. Parameter value X take more than the width of the walls (i.e. the distance between the outer planes of the walls) by approximately 100 mm on each side to allow finishing. When you select the option X SP 50-101-2004 “Design and installation of foundations and foundations of buildings and structures” should be taken into account.
A shallow strip foundation is suitable for all types of soil except subsidence, peat bogs and water-saturated soils. And it is often optimal for frame, timber, and brick houses.
Y– the length of the strip foundation is determined by the length of the house.
H– The height of the foundation depends on the depth of the foundation (shallow from 0.3-1 m, buried up to 2-3 m) and the elevation above ground level. The foundation must be made below the freezing line and above the groundwater level. If it is not planned to equip auxiliary premises in the basement, then a height of about 150-300 mm above ground level is sufficient, and if the base is to be used, more. The height of the strip foundation H is taken from 0.3 m for light houses and reaches about 4 m for heavy stone ones. The key to a reliable foundation - individual project, taking into account the characteristics of the soil on the site; height of groundwater; the depth of soil freezing in your region; the weight of the house (i.e. the load on the foundation from the weight of the walls, ceilings and roof).
A– thickness of the foundation strip, i.e. the distance between the outer and inner planes of the foundation depends on the thickness of the walls being built (accepted to be 100-150 mm more). Approximate values the thickness of the strip foundation for outbuildings (barn, bathhouse, garage) is in the range of 250-400 mm; for a 1-story light (for example, frame) house 300-650 mm; 2-storey brick house built on a foundation 650-750 mm thick.
WITH– the center-to-center distance between the foundation lintels (relevant for options No. 2-No. 8) depends on the features of your project.
Reinforcement parameters:
G– Number of horizontal reinforcing rows, for strip foundation G=2. It may be more depending on the magnitude of the existing loads. It is recommended that you familiarize yourself with SP 63.13330.2012. The capabilities of the online calculator allow you to calculate up to 10 rows of reinforcement.
V– The number of vertical rods connecting the reinforcing belts to each other can be from 1 to 5.
Z– The number of connecting rods is taken from 1 to 5.
S– Step length is the distance between adjacent vertical reinforcing straps. Optimal value S 300-500 mm.
Weight of 1 m reinforcement depends on its diameter. Approximate weight of one meter different diameters iron reinforcement is given in the table.
| Diameter fittings, mm |
Weight of 1 linear meter of reinforcement, kg |
| 6 | 0,222 |
| 8 | 0,395 |
| 10 | 0,617 |
| 12 | 0,888 |
| 14 | 1,21 |
| 16 | 1,58 |
| 18 | 2 |
| 20 | 2,47 |
| 22 | 2,98 |
| 25 | 3,85 |
| 28 | 4,83 |
| 32 | 6,31 |
Formwork parameters:
Board thickness for assembling formwork, it is taken from 25 mm to 50 mm on the basis that the thicker the better (but also more expensive).
Board length. This parameter is usually selected around 4000-6000 mm, depending on the availability of lumber in the warehouse and the price of the formwork board.
The board is wide. To make formwork, use an edged board (possible on one side) with a width of 100-200 mm.
Installation of formwork requires care and a responsible attitude of performers in order to ensure the correct geometry of the future foundation.
It is important to strengthen the assembled formwork with wire so that it does not fall apart due to the weight of the concrete, cover the inside with plastic film, this will prevent concrete leakage and make it possible to reuse the boards for construction purposes.
Concrete composition parameters:
Bag weight, kg– here enter how much 1 bag of cement weighs in kilograms.
Concrete proportions by weight. The approximate ratio of components for a concrete mixture is 2-3 parts sand for 1 part cement, 4-5 parts crushed stone, 1/2 part water (the mixture should be plastic and not too liquid). However, depending on the required grade of concrete, the grade of cement used, the characteristics of sand, crushed stone, the use of plasticizers or additives, the proportions may vary. Model standards cement consumption for the preparation of prefabricated and monolithic concrete, reinforced concrete products and structures are regulated by SNiP 5.01.23-83.
Enter prices for Construction Materials : cement (per bag), sand (per 1 ton), board (per 1 cubic meter) and fittings (per 1 ton).
This construction calculator will:
- calculation of the base area of the strip foundation and the required volume of concrete for pouring it;
- calculation of the formwork area (i.e. the area of the side surfaces) and the required amount of lumber for the formwork of a strip foundation and their price (if the height of the slab is not a multiple of the height of the board, then the number of boards is calculated taking into account covering the entire height of the slab);
- calculation of the number of bags of cement, tons of sand and crushed stone for a strip foundation and the cost of these components of concrete for pouring;
- calculation of the required reinforcement of a strip foundation, namely the number of horizontal, vertical and connecting rows of reinforcement, its length, weight and cost of reinforcement.
The calculator will also calculate the final price of constructing a strip foundation, which will give an idea of the level of material investment in the foundation of your home and will allow you to accept deliberate decision about the feasibility of this type of foundation. You can also calculate other foundation options using our calculators and choose the optimal solution.