The basis of any major construction work is laying the foundation. It depends on how reliably this will be done, what is the expected service life of the erected building. It is for this reason that laying the foundation in construction is considered one of the most important stages.
In order for the foundation to easily withstand all the expected loads, it is important not only to follow the technology of its laying, but also to pre-calculate all possible impacts on it. Only a specialist who has extensive experience in this field can carry out the correct calculations, taking into account all the factors that can have even the slightest impact on the foundation. But anyone can make a general preliminary calculation of the load on the foundation, thereby understanding how strong it will be and eliminating unnecessary costs.
Required information
The first question is what you need to know in order to correctly calculate the loadto 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 building elements;
- construction region;
- value of foundation penetration;
- depth of soil freezing;
- 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 calculations.
Why calculations are needed
What does the calculation of the load on the foundation give the future developer?
- The correct 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 the possible deformation of the walls or the foundation itself, and behind it the structure.
- Calculation will help prevent subsidence of the soil (soon destruction of the entire building).
- It will be possible to understand how much materials need to be purchased in order to carry out construction work. This will greatly reduce the overall cost.
If the calculations are done incorrectly or not done at all, then such deformations of the building and foundation as skew, bending, subsidence, bending, roll, shift or horizontal displacement are possible.
Main types of load
Before you start calculating loads, it is important to know that there are three maincategories 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 weather-induced impacts. Wind, rain and other precipitation should also be included in the calculation.
- Objects 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 built. Therefore, the calculation of the load on the ground is also important. The foundation also exerts pressure and is characterized by such indicators as the total area of \u200b\u200bthe support and its depth.
Calculation formula for soil load
To determine the required value, the following basic formula is used:
N=Nf + Nd + Ns + Nv, where H is the initial value, that is, the total load on the soil, Nf is the value indicating the load from the foundation, Nd is the load of the house, that is, the load from the building, Hs is the seasonal load from snow, Hv is the load from wind.
Nd for all types of foundation is calculated the same way. Nf is calculated differently depending on the type of foundation.
Load of strip and monolithic base
The indicator of the load of the base on the soil will help determine the optimal size of the foundation area and evaluate the load allowed for it. For this calculation, a strip foundation is structurally suitable. Load calculation is carried out according to the following formula:
Nflm=V × 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. This value does not have to be calculated, in the reference tables you can find all the necessary indicators.
Next, the Nf indicator is divided by the base area (S) and the value of the specific load (Nu) is obtained, which should be less than the reference permissible value of soil resistance (Сg):
Well=Nflm/ S ≦ Сг.
To avoid the influence of calculation errors, this deviation should exceed 25%. If the value obtained 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 erection of a monolithic base is carried out similarly. It is only necessary to take into account deformation loads, warp stress and rolls. To do this, the foundation is laid with an increased margin of the calculated values.
Load of column base
The calculation will help to calculate the correct number of piles or foundation soles for safe construction.
Specific gravity is the 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 climatic zone the house is planned to be built. However, when calculatingtake the average - 2 kg / cm2.
The total load that the sole of the column 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 x q;
- Pfc=Pc x N;
- Sfc=Sc x N;
where Sc is the bearing 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 columns, Pfc is the total weight of the foundation, Sfc is the total area of the support.
Load of pile foundation
Using this formula to calculate loads on a pile foundation is also possible, but it will have to be slightly modified. Namely, when the result is already obtained according to the previous formula, it will need to be multiplied by the total number of piles, then add the weight of the belt (in the event that this belt was used during construction). In order to get the desired value, you need 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 building (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.
Load at home onfoundation
To make a general calculation of the load of the house on the foundation, you should sum up the mass indicators of the individual parts of the house:
- Slabs and all walls.
- Doors and windows.
- Rafter and roof systems.
- Heating and ventilation pipes, plumbing.
- All decorative finishes, vapor and waterproofing.
- Various appliances, furniture and stairs.
- All kinds of fasteners.
- People who live in the building at the same time.
To do this, you will need some indicators from the tables (specific gravity depending on the material from which each part is made), previously calculated by specialists. Now this is easy to use. For example:
- For buildings using a frame that is not more than 150 mm thick, the load factor 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.
- Slabs based on reinforced concrete structures are crushed with a force of 500 kg/m2.
- Floorings with insulation and wooden beams - up to 300 kg/m2.
- Roof - up to 50 kg/m2 on average.
- If a value is needed that shows the temporary load from snow, then they usually take an average value of 190 kg / m2 - for the northern regions, 50 kg / m2 - for the south, 100 kg / m2 - for the middle lane, or its are found by multiplying the roof projection area by the specific reference loadsnow cover.
- If you need to calculate the wind load, then the following formula will come in handy:
Hv=P × (40 + 15 × N), where P is the total area of the building and H is the total height of the house.
Calculation example
Using the above calculations will allow you to correctly determine the required 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 look at the example of calculating the loads on the foundation.
As an example, let's take a one-story house made of aerated concrete, located in an area protected from snow and wind. Gable roof with a slope of 45%. Foundation - monolithic tape 6x3x0.5 m. Walls: height 3 m and thickness 40 cm. Soil - clay.
- The load of the roof is calculated by the load of 1 m2 of the projection, in this example - 1.5 m.
- The wall load is determined by multiplying the height and thickness by the specific reference load from point 2: Hc=60030, 4=720 kg.
- The floor load is found by multiplying the cargo area by the value from point 4: Нп=(63 / 62)500=750 kg. The load area is determined by the ratio of the area of the foundation to the length of those sides, which are pressed by the floor logs.
- Load from strip base (Q for concrete and crushed stone - 230 kg/m2): 630, 4230=1656 kg.
- Load per meter of base: But=75+720+750+1656=3201 kg.
- Reference load valuefor clay: Cr=1.5 kg/cm2. In the example, the ratio of load to base area is: Well=3201/1800=1.8 kg/cm2, where 6x3=18 m2=1800 cm2.
The example shows that for such initial data the size of the selected foundation is insufficient, since the calculated value is greater than the allowable reference value and does not guarantee the reliability of the building. The required value is determined by a step-by-step selection.
When planning construction, calculations and their analysis must be carried out, otherwise the consequences of using incorrect values \u200b\u200bcan be disastrous.
