The foundation of any major construction work is laying the foundation. How reliably this is done depends on what kind of operation life is expected for the erected building. For this reason, laying the foundation in construction is considered one of the most important stages.
In order for the base to easily withstand all the expected loads, it is important not only to monitor the technology of its installation, but also to pre-calculate all the possible effects on it. Only a specialist with extensive experience in this field can carry out the correct calculations, taking into account all factors that can have even the slightest effect on the foundation. But any person will be able to make a general preliminary calculation of the load on the foundation, thereby understanding how durable it is and eliminating unnecessary costs.
Required Information
The first question is what you need to know in order to correctly calculate the load on the foundation. This is the following:
- general layout of the building, height, that is, the number of floors, the material from which the roof will be made;
- soil type, groundwater depth;
- material used in the manufacture of individual elements of the building;
- construction region;
- the depth of the foundation;
- soil freezing depth;
- the thickness of the soil layer that is subjected to deformable loads.
This information is needed in order to take into account small indicators for accuracy in the calculations.
Why do we need calculations
What gives the future developer the calculation of the load on the foundation?
- The correct values โโwill allow you to find the most suitable and reliable place where you can erect the structure.
- If you calculate everything correctly, then you can easily prevent the possible deformation of the walls or the foundation itself, and beyond it the structure.
- The calculation will help prevent subsidence of the soil (the rapid destruction of the entire building).
- It will be possible to understand how much it is necessary to purchase materials in order to carry out construction work. This will greatly reduce overall costs.
If the calculations are done incorrectly or not done at all, then deformations of the building and foundation are possible, such as skew, bend, subsidence, bend, roll, shift or horizontal displacement.
The main types of load
Before starting the load calculation, it is important to find out that there are three main categories that can make up this load:
- Statistical value. This category includes the weight of the structure itself and each individual element of the house.
- The second type is impacts caused by weather conditions. Wind, rain and other precipitation should also be included in the calculation.
- Items that will already be inside the house also exert a certain pressure, so the calculation of the load on the foundation must necessarily include these indicators.
The type of foundation depends on the type of soil on which it is being built. Therefore, it is important to calculate the load on the ground. The foundation also exerts pressure and is characterized by indicators such as the total area of โโthe support and its depth.
Calculation formula for soil load
To determine the required value, the following basic formula is used:
= + + + ,
where N is the initial value, that is, the total load on the soil, Nf is the value denoting the load from the foundation, Nd is the load of the house, that is, the load from the structure, Ns is the seasonal load from the snow, Nv is the load from the wind.
Nd for all types of foundation is calculated equally. Nf is calculated differently depending on the type of foundation.
Tape and monolithic base load
The indicator of the base load on the soil will help determine the optimal size of the foundation area and evaluate the load allowed for it. For this calculation, the strip foundation is structurally suitable. The calculation of the load is carried out according to the following formula:
Nflm = V ร Q,
where V is the total volume of the foundation, which was obtained by multiplying the height, length and width of the base (tape or monolithic); Q is the specific gravity (density) of the material that was used in the construction of the base. You donโt have to calculate this value, in the tables of the directories you can find all the necessary indicators.
Next, the indicator Nf is divided by the area of โโthe base (S) and the value of the specific load (Well) is obtained, which should be less than the reference value of the soil resistance (Cg):
Well = Nflm / S โค Cg.
In order to avoid the influence of calculation errors, this deviation should exceed 25%. If the obtained value exceeds the reference value, it is better to increase the width of the base, otherwise it will begin to crack and sag.
The calculation of the load on the foundation slab in the case of the construction of a monolithic base is carried out similarly. It is only necessary to take into account the deformation loads, the stress of the base and the banks. For this, the foundation is laid with an increased margin from the calculated values.
Column Base Load
The calculation will help calculate the correct number of piles or soles of the foundation for safe construction.
The specific gravity is that value that shows what maximum design pressure the soil can withstand so that there is no subsidence and displacement. The specific value depends on what kind of soil we are talking about and in what climate zone the construction of the house is planned. However, in calculations often take the average figure - 2 kg / cm2.
The total load that the sole of the columnar base gives to the soil consists of the distributed mass of the structure and the weight of the column itself. Therefore, the calculation of the load on the columnar foundation will look like this:
- Vc = Sc x Hc;
- Pc = Vc xq;
- Pfc = Pc x N;
- Sfc = Sc x N;
where Sc is the pillar reference area, Hc is the height, Vc is the column volume, Pc is the column weight, q is the column material density, N is the total number of columns, Pfc is the total foundation weight, Sfc is the total area of โโthe support.
Pile base load
Using this formula in order to calculate the loads on the pile foundation is also possible, but it will have to be slightly modified. Namely, when the result according to the previous formula is already obtained, it will need to be multiplied by the total number of piles, then add the weight of the belt (if this belt was used during construction). In order to obtain the desired value, it is necessary to multiply the obtained value by the density (specific gravity) of those materials that were used in the production of piles.
When the number of screw supports (N) and the weight of the structure (P) are known, the bearing property of one support is equal to the ratio P / N. It is necessary to choose ready-made, most suitable piles with a certain bearing capacity and the length that suits local geological features.
The load of the house on the foundation
To make a general calculation of the load of the house on the foundation, the mass indicators of the individual parts of the house should be summarized:
- Ceilings and all walls.
- Doors and windows.
- Rafter and roof systems.
- Heating and ventilation pipes, plumbing.
- All decorative finishes, steam and waterproofing.
- Various appliances, furniture and stairs.
- All kinds of fasteners.
- People who live in a building at the same time.
To do this, you need some indicators from the tables (specific gravity depending on the material from which each part is made), previously calculated by specialists. Now you can just take advantage of this. For example:
- For buildings using a framework whose thickness is not more than 150 mm, the load indicator is 50 kg / m2.
- If we are talking about walls made of aerated concrete, the thickness of which is up to 50 cm, then - 600 kg / m2.
- Reinforced concrete walls up to 15 cm thick exert a load of 350 kg / m2.
- Ceilings based on reinforced concrete structures were pressed with a force of 500 kg / m2.
- Overlapping with insulation and wooden beams - up to 300 kg / m2.
- Roofing - on average up to 50 kg / m2.
- If a value is needed that shows the temporary load of snow, then usually take an average of 190 kg / m2 for the northern regions, 50 kg / m2 for the southern, 100 kg / m2 for the middle strip, or find it by multiplying the roof projection area on the specific reference load of the snow cover.
- If you need to calculate the wind load, then the following formula will come in handy:
HB = P ร (40 + 15 ร N),
where P is the total area of โโthe building, and H is the total height of the house.
Calculation Example
Using the above calculations will correctly determine the necessary dimensions of the foundation and protect yourself for many years with a reliable structure. And to make it easier to understand how to use quantities, you should see an example of calculating the loads on the foundation.
As an example, take a one-story aerated concrete house located in a zone protected from snow and wind. Gable roof with a slope of 45%. The foundation is a monolithic tape 6x3x0.5 m. Walls: height 3 m and thickness 40 cm. Soil - clay.
- The roof load is calculated according to the load of 1 m2 of the projection, in this example - 1.5 m. The specific gravity from point 6 is 50 kg / m2 / NK = 50 * 1.5 = 75 kg.
- The wall load is determined by multiplying the height and thickness by the specific reference load from point 2: Hs = 600 * 3 * 0.4 = 720 kg.
- The load of the floors is found by multiplying the cargo area by the value from point 4: = (6 * 3/6 * 2) * 500 = 750 kg. Cargo area is determined by the ratio of the area of โโthe foundation to the length of those sides on which the lags of the floor are pressing.
- The load from the tape base (Q for concrete and crushed stone - 230 kg / m2): 6 * 3 * 0.4 * 230 = 1656 kg.
- The load on one meter of the base: But = 75 + 720 + 750 + 1656 = 3201 kg.
- Reference value of the load for clay: Cr = 1.5 kg / cm2. In the example, the ratio of the load to the base area is: Well = 3201/1800 = 1.8 kg / cm2, where 6x3 = 18 m2 = 1800 cm2.
It can be seen from the example that for such initial data the size of the selected foundation is insufficient, since the calculated value is greater than the allowable reference and does not guarantee the reliability of the building. The desired value is determined by phased selection.
When planning construction, calculations and their analysis must be carried out, otherwise the consequences of applying the wrong values โโcan be dire.