Single nail What are they usually built for and what are their effects? How to build a single foundation in the most scientific and effective way? Let’s answer the above knowledge with CityA Homes in this article!
What is a single nail?
This type of foundation can withstand a large column or a beam of columns standing close together. They are load-bearing and are used for reinforcement or construction in structures with relatively light loads, not too heavy such as residential houses, warehouses or 1- to 4-storey houses, etc. Single nail There are 3 popular types today: Hard nails, soft nails or and individual nails. Not only that, this type of foundation also has many different shapes such as square, round or rectangular, depending on the type of project.
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Note that the ground when building a single foundation needs to be stable and has a relative stiffness.
What are cup nails?
In fact, cup nails are also single nail. In residential construction, the bearing capacity of cup or single foundation will depend on the structural components and concrete grade. They are applied to buildings with light loads such as: 2-storey houses, warehouses or factories. The works must have the ground ground in the area must have a certain hardness and high stability.
Single foundation structure
Single nail is made from steel and concrete, will normally consist of a single thick and cylindrical reinforced concrete, which is responsible for absorbing the load from the structure and transmitting that load to the building foundation. For soft ground, especially where there is a lot of mud, the bottom of the foundation is usually placed on a layer of soil mixed with rock and has a depth of at least 1m to ensure. In detail, the structure of a single foundation includes the following 4 basic parts:
The foundation, also known as the foundation plate, has a rectangular bottom structure, beveled with a moderate slope, so during the construction process, it is necessary to calculate accurately to determine the reasonable size. When designing the foundation, the architects will balance it to best suit the overall construction.
Also known as momentum: The foundation brace structure has the effect of supporting the upper partition wall and reducing the settlement and deviation between the foundations in the building. When combining the foundation beam with the foundation brace, it must be calculated carefully, considering it as a beam in the frame structure to reduce the foundation eccentricity.
Depending on the building structure, design, and the influence of external conditions, the foundation neck size may be equal to the ground floor column, but normally to increase the protective layer of concrete reinforcement in the foundation neck will be enlarged further. 2.5cm each side.
Concrete lining: Usually 100 thick, 4×6 stone concrete or broken brick concrete, cement mortar grade 50÷100, has the effect of cleaning, flattening the foundation pit, preventing cement water loss, in addition it also makes formwork for pouring concrete foundation.
Advantages of single nail
- The biggest advantage of single footing is cost savings by simple foundation structure.
- The construction time is fast and the process is simple and easy to implement.
- Suitable for small-scale low-rise buildings
Single nail classification
Based on load
In this way one divides the texture single nail into categories:
- The foundation is centered under the load.
- Foundations are subjected to eccentric loads.
- Foundations of tall buildings
- Large horizontal bearing foundation
- Foundations withstand vertical loads.
Based on hardness
- Absolutely Hard Nail: This is a nail with great stiffness and very low deformation. Belongs to brick, stone and concrete foundation.
- Soft nails: They have the same deformability as the base soil, the long/short side ratio is greater than 8, and they belong to the soft foundation type.
- Finite hard foundation: This is a reinforced concrete foundation with a long side/short side ratio ≤ 8.
Based on the manufacturing method
- Solid foundations: They are made from different materials and are fabricated at the construction site.
- Prefabricated foundations: They are made up of many blocks assembled and are prefabricated when constructing the foundation of the building.
Formula for calculating standard single foundation
Principles of determining the correct footing bottom size:
In order to ensure the right economic and technical, the foundation form of the foundation must not be too large, must ensure its elasticity and know how to take advantage of the ability to work as much as possible in the process of linear deformation.
CT: Ptb Rtc
Eccentric load, that is: Pmax 1.2 Rtc
Ptb, Pmax: Is the medium and large foundation pressure
Rtc: Standard strength of the ground
CT: Rtc = m ( A1/4 . y. b + B. q + Dc)
A1/4, B, D: This is a coefficient that depends on the internal friction angle of the soil
b: width of foundation
c: adhesive force of the ground
q: footing side load
m: coefficients, working conditions of the background
Dimensions of foundation load bearing center: Ptb = ( Ntc + G)/ ( Ib )
Ptb = ( Ntc / a.b2 ) + Ytb. Hmm
A = I / b
Yyb: Specific gravity or average weight of soil
Hm: Depth to lay the foundation
G: Weight of foundation, soil above
From Ptb = Rtc we have:
(Ntc / α.b²) + γtb.Hm = m(A1/4.γ.b+B.q+Dc)
γtb.Hm = m(A1/4.γ.b+B.q+Dc)
Width is determined as follows: b³ + k1b² – k2 = 0
The coefficients M1, M2, M3 depend on the friction angle ϕtc.
Single nail design
Standard for single foundation design in construction works
Based on the geological survey data, topography and the scale of the work to be able to choose the appropriate construction and construction plan. There must be backup plans if the actual geological conditions of the construction site are not consistent with the calculations in the design. single nail.
Check to ensure that all materials, machinery and supporting equipment, structural parts used in the construction of cup foundations (single) must meet the requirements of the design. When building a single foundation, technical inspection by the agency is required.
Eccentric single foundation design
The cause of the eccentricity is the imbalance of the calyx block. Engineers can create this balance in the following ways:
The ground reaction has a triangular or trapezoidal shape. Then the center of this jet system will shift relative to the center of the platform. Foundation balance will be established when the center of gravity of this reaction system coincides with the set point of the force system transmitted down from the column. This method is often less effective or unusable in the case of large eccentric moments. At that time, the reaction is usually triangular, in order to balance as above, the maximum width of the mobilized foundation calyx is only 3/2 the width of the column. If the longitudinal force is large, it cannot be designed to satisfy the ground pressure condition.
Human toenails or propeller toenails can be used to reduce eccentricity. In addition, there are many opinions that it is necessary to add an anti-roll column, but the calculation is that the propeller type is correct.
Calculation of single foundation design
When the background strain is not too large, we apply the elastic theory to calculate the deformation characteristics. Take advantage of the background workability in the linear deformation phase. The formula for calculating single foundation according to the technical process is as follows:
When the load is right with the center of gravity: P ≤ R
When the load is deviated from the center: P ≤ 1.2 R (P , P : average & maximum foundation bottom pressure; R : standard strength of foundation soil)
- b : Width of foundation base
- q : Lateral load of the footing
- c : Unit adhesive force of the ground layer
- A , B , D : The coefficients depend on the internal friction angle of the soil.
- m : Working condition coefficient of single foundation
Construction process of single foundation
Step 1: Prepare construction site and complete equipment
After the survey and surveying stages have been completed, the construction selection plan single nail will be given so that the work is prepared. At this stage, the homeowner needs to prepare a neat ground, labor and calculate enough construction materials and materials.
Step 2: Dig a single foundation pit
Determine the exact location of the foundation pits and use the equipment to start digging. The size of the foundation pit needs to be ensured to be of sufficient width, length and depth according to the drawings single nail
The excavation stage is extremely important, because if the hole is dug with a non-standard size, it will lead to difficulties for the later construction process, plus it distorts the structure, causing unsafety, leading to danger. dangerous for the project.
Step 3: Flatten the foundation pit
Use specialized leveling equipment to level the surface of the hole just dug. Should spread a thin layer of crushed stone on the surface to create better flatness.
Step 4: Pour concrete lining
The concrete lining will be poured on top of a thin layer of rock to spread on the surface with a thickness of about 100mm. This step is to limit water loss for the mortar, concrete and to fix and smooth the bottom of the foundation.
Step 5: Arrange single foundation steel
Depends on the shape of single nail but the layout of the bearing steel bars will also be different. The steel used will usually have sizes Φ12 – Φ16, the distance between the steel bars is 10-15 cm.
Single foundation reinforcement needs to be placed about 5cm from the concrete lining, because this avoids the steel from corroding, and increases the connection between the foundation and the foundation lining.
Step 6: Pour concrete foundation
This last step is to ensure the structure is safe, then proceed to mix concrete with the standard ratio.
The process of pouring concrete must ensure that the principle is to pour from far to near. When the foundation pit is flooded or stagnation of water, it is necessary to have workers suck all the water out so as not to affect the quality of the concrete.
Rules for determining the size of the bottom of the foundation
In order to maintain the correct technique and protect the foundation, the foundation shape of the foundation must not be too large compared to the allowable norm, be resilient and take advantage of the maximum working capacity of the foundation during linear deformation. count.
Eccentric load: Pmax 1.2 Rtc
- Ptb , Pmax : Medium and large foundation pressure
- Rtc: Is the standard strength of the ground
|Rtc = m ( A1/4 . y. b + B. q + Dc)|
- A1/4 , B , D : coefficient depending on the internal friction angle of the soil
- b: width of foundation
- c: adhesive force of the ground
- q: footing side load
- m: coefficients, working conditions of the background
The formula for calculating the size of the foundation bearing the correct center:
Ptb = ( Ntc + G) / ( Ib )
Ptb = ( Ntc / a.b2 ) + Ytb. Hmm
A = I / b
- Yyb: Specific gravity, average weight of soil, foundation
- Hm: Depth to lay the foundation
- G: Weight of foundation, soil above
- From Ptb = Rtc we have:
- (Ntc / α.b²) + γtb.Hm = m(A1/4.γ.b+B.q+Dc)
- γtb.Hm = m(A1/4.γ.b+B.q+Dc)
The width is defined as follows:
The coefficients M1, M2, M3 depend on the friction angle ϕtc.
Note when designing eccentric single foundation
Single nail Eccentric is a structure whose foundation center does not coincide with the center of the foundation calyx. This method of foundation construction is often applied when constructing foundations in modern townhouses, townhouses, or buildings where the foundation ground is not favorable. To create balance in the structure, engineers need to do the following:
- Use this type of propeller to reduce eccentricity.
- The reactive part of the ground will form a triangle or a trapezoid.
- The center of the jet system will shift relative to the center of the radio. Foundation balance will be re-established.
- This method is less effective in the case of large eccentric moments.
Current popular single nail design drawings
Single foundation design drawing of 2-storey townhouse
Single nail design drawing
Structural drawing of single foundation
Here is some useful information about single nail that we want to send to you, hopefully through here, you will have useful information about this type of nail!
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