Calculation of the load on the foundation. Example of calculation of loads on the foundation

The foundation of any major construction work is laying the foundation. On how reliably it will be done, it depends on what the erected building is expected to have an operational life. It is for this reason that the laying of the foundation in construction is considered one of the most important stages.

To ensure that the base can easily withstand all the expected loads, it is important not only to monitor the technology of its laying, but also to calculate all possible impacts on it. Carry out the correct calculations taking into account all the factors that may have even the slightest influence on the foundation, can only be a specialist with extensive experience in this field behind him. But any person will be able to make a general preliminary calculation of the load on the foundation, thereby understanding how strong it will be, and to exclude 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;
• Type of soil, depth of groundwater;
• Material used in the manufacture of individual building elements;
• Region of construction;
• Depth of foundation penetration;
• Depth of soil freezing;
• The thickness of that layer of soil that undergoes deformable loads.

This information is needed in order to take into account the small indicators for accuracy in calculations.

Why we need calculations

What gives the future developer a calculation of the load on the foundation?

• The right values will allow you to find the most suitable and reliable place where you can build a structure.
• If you calculate everything correctly, then you can easily prevent possible deformation of the walls or the foundation itself, and behind it the structures.
• The calculation will help to prevent the subsidence of the soil (the rapid destruction of the entire structure).
• It will be possible to understand how much it is necessary to purchase materials in order to produce construction work. This will greatly reduce overall costs.

If the calculations are done incorrectly or not at all, then such deformations of the building and foundation as a skew, bending, subsidence, buckling, roll, shear or horizontal displacement are possible.

Main types of load

Before you start calculating the loads, it is important to know that there are three main categories that can make up this load:

1. Statistical value. This category includes the weight of the structure itself and each individual element of the house.
2. The second type is impacts caused by weather conditions. Wind, rain and other rainfall should also participate in the calculation.
3. Items that will be already 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 erected. Therefore, it is important to calculate the load on the ground. The foundation also exerts pressure and is characterized by such indicators as the total area of the support and the depth of its bedding.

Calculation formula for soil load

To determine the required value, the following basic formula is used:

Н = Нф + Нд + Нс + Нв,

Where Н is the initial value, that is, the total load on the soil, Нф is the value denoting the load from the foundation, Нд is the load at home, that is, the load from the structure, Нс is the seasonal load from the snow, Нв is the load from the wind.

Nd for all types of basement is calculated equally. HF is calculated differently depending on the type of foundation.

Load of belt and monolithic base

The indicator of the foundation load on the soil will help determine the optimal size of the foundation area and estimate the load allowed for it. For this calculation, the ribbon foundation is structurally suitable. Calculation of the load is carried out according to the following formula:

Nflm = V × Q,

Where V is the total volume of the basement, 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 substrate. This value will not have to be calculated, all the necessary indicators can be found in the tables of reference books.

Further, the index Hf is divided by the area of the base (S) and a specific load (Nu) is obtained, which should be less than the reference-permissible value of the soil resistance (Cr):

Well = Nflm / S ≤ Cr.

To avoid the influence of errors in calculations, this deviation should exceed 25%. If the obtained value exceeds reference, the width of the base is better to increase, otherwise it will begin to crack and sag.

Calculation of the load on the foundation plate in the case of erection of a monolithic base is made similarly. It is only necessary to take into account deformation loads, base stress and roll. For this, the foundation is laid with an increased margin from the calculated values.

Pallet base load

The calculation will help to calculate the correct number of piles or base solids for safe construction.

The specific gravity is the value that indicates which maximum design pressure can withstand the ground so that there is no subsidence and displacements. The specific value depends on what soil is at stake and in what climatic zone the construction of the house is planned. However, in calculations, an average of 2 kg / cm2 is often taken.

The total load that the sole of the columnar base gives to the ground 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 × N;
• Sfc = Sc x N;

Where Sc is the reference area of the column, Hc is the height, Vc is the volume of the column, Pc is the weight of the column, q is the density of the column material, N is the total number of posts, Pfc is the total weight of the foundation, Sfc is the total area of the support.

Pile foundation load

The use of this formula in order to calculate the load on the pile foundation is also possible, but it will have to be slightly modified. Namely, when the result of the previous formula is already obtained, it will have to be multiplied by the total number of piles, then add the weight of the belt (in case this belt was used in construction). In order to obtain the required 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 of P / N. Choose the ready, most suitable piles, with a certain bearing capacity and the length that is suitable for local geological features.

Load of the house on the foundation

To make the general calculation of the load of the house on the foundation, it is necessary to summarize the weight indices of the individual parts of the house:

• Overlapping and all walls.
• Doors and windows.
• Systems of rafters and roofing.
• Heating and ventilation pipes, plumbing.
• All decorative finishes, steam and waterproofing.
• Various appliances, furniture and stairs.
• All kinds of fasteners.
• People who live in the same building.

To do this, you need some indicators from the tables (specific weight, depending on the material from which each part is made), previously calculated by specialists. Now you can just use it. For example:

1. For buildings using a frame, the thickness of which is not more than 150 mm, the load index is 50 kg / m2.
2. If we are talking about walls made of aerated concrete, the thickness of which is up to 50 cm, then - 600 kg / m2.
3. The walls of reinforced concrete up to 15 cm thick exert a load of 350 kg / m2.
4. Overlapping, in the basis of which the structures based on reinforced concrete were used, are pressed with a force of 500 kg / m2.
5. Overlapping with insulation and beams made of wood - up to 300 kg / m2.
6. Roofing - an average of 50 kg / m2.
7. If a value is needed that shows the time load from the snow, then an average of 190 kg / m2 is assumed for the northern regions, 50 kg / m2 for the southern, 100 kg / m2 for the middle band, or it is found by multiplying the area of the roof projection On the specific reference load of the snow cover.
8. If it is necessary to calculate the wind load, then the following formula is useful:

Нв = П × (40 + 15 × Н),

Where P is the total area of the building, and H is the total height of the house.

Example calculation

Using the above calculations will correctly determine the necessary dimensions of the foundation and secure yourself for many years with a reliable structure. And to make it easier to understand how to use the values, you should see an example of calculating the loads on the foundation.

As data for an example, let's take a one-story house made of aerated concrete, 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. The walls are 3 m high and 40 cm thick. The soil is clay.

1. Roof load is calculated from the load of 1 m2 projection, in this example - 1.5 m. The specific gravity from point 6 is 50 kg / m2 / Hq = 50 * 1.5 = 75 kg.
2. The wall load is determined by multiplying the height and thickness by the specific reference load from point 2: Hc = 600 * 3 * 0.4 = 720 kg.
3. The load of the overlap is the multiplication of the cargo area by the value from point 4: Нп = (6 * 3/6 * 2) * 500 = 750 kg. The cargo area is determined by the ratio of the area of the foundation to the length of those sides of it, on which the lag overlapping presses.
4. Load from the tape base (Q for concrete and crushed stone - 230 kg / m2): 6 * 3 * 0.4 * 230 = 1656 kg.
5. The load per one meter of the base: But = 75 + 720 + 750 + 1656 = 3201 kg.
6. 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: Hy = 3201/1800 = 1.8 kg / cm2, where 6x3 = 18 m2 = 1800 cm2.

From the example it is evident 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 construction. The desired value is determined by a step-by-step selection.

When planning the construction of calculations and their analysis must be carried out necessarily, otherwise the consequences of using incorrect values can be deplorable.