A pile foundation is a universal foundation for the construction of brick (read about it separately), wood, aerated concrete (read about it separately) and foam concrete low-rise buildings in any ground conditions. Such bases are also used for other structures (for example, fences). Durability and reliability pile foundation The grillage directly depends, the reinforcement technology of which we will talk about in this article.
You will learn why a pile-grillage foundation is needed, what materials are used for this and how the process itself is performed. Diagrams and drawings will be provided that explain all the nuances of reinforcement of a monolithic grillage.
1 What functions does the grillage perform and why is it reinforced?
The grillage is a strip structure (we read separately about how a regular grillage is reinforced), connecting free-standing piles to each other. By tying the supports, they receive additional spatial rigidity and resistance to overturning loads. The grillage also acts as a supporting surface on which the walls of the building are erected.
1.1 What and how to reinforce?
Reinforcement of the strip grillage is carried out using a spatial reinforcement frame, consisting of two longitudinal reinforcement belts (upper and lower), connected to each other by horizontal and vertical jumpers.
Longitudinal belts are made from reinforcement bars of class A3 (hot-rolled corrugated profile), the diameter of which is 13-16 mm. It can be used, as confirmed by reviews of the successful operation of such pile-grillage foundations on specialized forums.
Connecting vertical and horizontal jumpers can be made in two versions - in the form of separate rods of reinforcement welded to the longitudinal chords (the diagram shows the configuration). In this case, it is necessary to use rods of the same standard size as when arranging the longitudinal belt.
The frame can also be connected by jumpers made of rectangular reinforcement bent into clamps (diagram below). With this approach, smooth rods of class A2 (diameter 8-10 mm) are used. Bent clamps are labor-intensive to install, but due to the smaller number of welds, they are more reliable and durable. Fiberglass reinforcement that cannot be bent is not used to create clamps.
According to the provisions SNiP No. 2.03.01 “Manual for the design and arrangement of pile-grillage foundations”, when installing the reinforced frame, it is necessary to observe the following step between the constituent elements:
- the number of rods in the longitudinal belts is at least 4, the distance between them is up to 10 cm;
- the pitch between the transverse jumpers of the longitudinal belt is 20-30 cm;
- the step between the vertical connecting jumpers is up to 40 cm;
- protective layer of concrete - at least 5 cm.
The protective layer is the distance between the outer contours of the reinforced frame and the walls of the concrete body of the monolithic grillage. If the protective layer does not have the required thickness, two problems will arise - the frame will not be able to correctly redistribute the loads acting on the grillage and the reinforcement will be excessively susceptible to corrosion under the influence of moisture penetrating into the micropores of the concrete.
To create a protective layer along the bottom edge of the grillage, special plastic mushroom stands are used, which lift the reinforcement above the formwork. The use of pieces of brick for these purposes is not permitted.
1.2 How to calculate the amount of reinforcement?
As an example, we give for a monolithic grillage with a perimeter of 8 * 6 m. We use the conventional dimensions of the strapping 40 * 40 cm. The reinforcement frame for such a strapping will consist of two longitudinal belts of 3 A3 rods with a diameter of 14 mm in each (the pitch between the rods is 10 cm, 5 cm on each side eats up the protective layer of concrete). The belts are connected by jumpers made of A1 reinforcement with a diameter of 11 mm, located in increments of 20 cm.
The calculation is performed using the following algorithm:
- We define total length rods in the upper longitudinal belt. To do this: a) determine the perimeter of the grillage: 8+8+6+6 = 30 m; b) we calculate the length of 3 rods: 3*30 = 90 m; c) calculate the length of reinforcement A3 for both belts: 90*2 = 180 m.
- To connect the rods of the longitudinal belt, we will need jumpers 30 cm long, which will be located in increments of 20 cm. We calculate their number for both contours of the grillage: 2*(30/0.2) = 300 pcs, after which we calculate the total length of the transverse jumpers: 300* 0.3 = 100 m.
- It remains to calculate the length of the vertical jumpers connecting the upper and lower contours of the frame to each other. But since in the example a rectangular grillage is calculated, their number and length will be identical to the transverse lintels. If a grillage of rectangular configuration is used, the calculation is performed according to the formula specified in point No. 2.
As a result, the calculation showed us that the grillage reinforcement requires 180 m of A3 class reinforcement and 200 m (100+100) A2 rods with a diameter of 11 mm. Calculations may also be required if you do not plan to use welding. It is carried out taking into account the fact that about 40 cm of material is required for one connection: we determine the number of connections: 4*(30/0.2) = 600 pcs; and calculate the material consumption - 600 * 0.4 = 240 m.
1.3 Features of grillage reinforcement (video)
2 Technology of reinforcement of a monolithic grillage
The amplification of the grillage begins after all the previous stages of arranging the pile foundation have been completed - installation of piles, their trimming and arrangement of formwork. You must have a ready-made formwork, inside which the reinforced frames of the piles protrude to a height equal to the cross-section of the framing.
When assembling the frame, the reinforcement can be tied together using wire or the rods can be connected by welding. There is no significant difference in the joining method - it is often argued that a welded frame, due to the lack of elasticity, resists deformation worse than a viscous structure, however, in industrial multi-storey construction the frames of pile-grillage foundations are always welded, so these fears are unfounded. In addition, welding is a more practical and quicker method to implement.
Grillage reinforcement - step-by-step instructions:
Assembling the reinforced frame on straight sections of the grillage is quite simple to perform. Difficulties arise when reinforcing the corners, which must be further strengthened, since this part of the frame experiences maximum loads.
Corners and joints interior walls strapping to external cannot be reinforced with overlapping reinforcement. In these areas it is necessary to lay solid rods curved in an L or U-shaped configuration. A diagram of the correct reinforcement of the corners of a pile grillage is shown in the image.
Laying the foundations for any building is a very responsible and important stage from which the main construction work begins. It is recommended that foundations be manufactured in strict accordance with the design documentation.
For monolithic structures, a fairly important part of the work is the grillage reinforcement. The strength of the entire structure largely depends on the quality of the associated reinforcement. You can carry out reinforcement yourself, having previously familiarized yourself with the technology of this type of work.
What is a grillage
A grillage is a monolithic element of the base of a building that connects separate pillars or piles into a single system. It is made in the form of a strip foundation, on which the load-bearing and external enclosing structures of the building are installed. The tape evenly distributes the loads across the entire base of the building, which in turn transfers them to the ground.
Grillage arrangement diagram The grillage can be made not only in the form of a monolithic strip foundation. It is also made from wooden, metal and reinforced concrete products located between columnar supporting structures. Such a device in the form of beams is used much less frequently than a monolithic one.
There are hanging and recessed structures Depending on the height of the grillage foundation relative to the ground level, hanging and recessed versions of the device are distinguished. When constructing a recessed grillage, a monolithic design is selected. If a hanging one is made, then the grillage base can be made of horizontal beams.
A monolithic grillage is based on concrete and reinforcement. Reinforcement takes up the bulk of the time when constructing this type of foundation. When carrying out work on reinforcing a strip foundation, it is necessary to be guided by building codes and regulations 52-01-2003.
The grillage should serve as a reliable support and protect the structure from moisture. The pile-grillage foundation is suitable for the construction of buildings with no more than three floors.
Installation of a monolithic grillage
To make a monolithic grillage foundation, you will need to perform several stages of work.
- Installation of formwork.
- Grillage reinforcement.
- Concreting.
- Stripping.
- Waterproofing tape.
Installation of formwork
The formwork must be installed strictly at an angle of 90 degrees The grillage foundation is made suspended or buried in the ground. The design of the formwork directly depends on its shape.
Regardless of the design, the side walls of the formwork must be assembled at a strictly vertical level, and the angles must be 90°, unless the design provides for a different design.
When making a tape in the ground, you can use soil instead of formwork as a support for the future foundation. Above ground level, formwork is usually assembled from boards or plywood. It is knocked together or pulled together in such a way that the concrete does not squeeze out the boards and does not spread during the process of laying it. That part of the foundation that protrudes above the ground will be protected by such a structure.
If the hanging version of the grillage device is chosen, then it is necessary to provide in the formwork quality foundation. It needs to be calculated based on the load it must withstand. The load is determined by the mass of concrete and reinforcement. It is also necessary to take into account the mechanical effects on the structure from vibration of concrete during the pouring process.
The side walls of the formwork must be firmly assembled. For this, transverse ties, spacers, tubes with studs and other materials can be used that will ensure the reliability of the structure.
Poor quality formwork can lead to failure of the concrete laying process. This is unacceptable in construction, but often occurs due to negligence in this part of the work.
Grillage reinforcement
Structural reinforcement Reinforcement of pile cap or columnar foundation is one of the most critical stages of constructing the foundation for a building.
Periodic metal reinforcement is used as the main material for reinforcing foundations. Recently, it has begun to be replaced with composite fiberglass. It is worth noting that fiberglass reinforcement is not suitable for hanging structures. It is good where there is support on the ground.
Reinforcement is welded into beams The reinforcement is tied or welded in some cases into frames, so-called beams. There are several types of beams. The type of reinforcement, and therefore the type of beams, is determined at the design stage.
During self-construction, when there is no project and there is no opportunity to contact specialists, there is an option to use an online reinforcement calculator. It is advisable to find several such online programs on the Internet and make calculations in each in order to compare the data and determine the error in the calculations. Having calculated the reinforcement based on the entered foundation parameters, you can begin work.
The reinforcement of a monolithic grillage in its most common form consists of straight longitudinal and transverse rods, which are connected to each other by binding wire or welding. In order to properly connect the structure, clamps and U-shaped products are made from reinforcement. They are connecting elements in nodes reinforcement cage.
To find out how reinforcement frames and their components are made correctly, you need to familiarize yourself with the manual for the design of concrete and reinforced concrete structures from heavy concrete(without pre-tension).
Reinforcement of pile-grillage foundations is impossible without connecting the pile reinforcement to the grillage frame. When constructing a pile field at the reinforcement stage, vertical rods are made with allowances in height. When installing the reinforcement frame of a strip foundation, the rods released from the piles are bent at the required horizontal level and connected to the main frame. Thus, the integrity of the structure is achieved. For all the details on pouring a pile-grillage foundation, see this video:
You cannot heat metal reinforcement in order to bend it. For bending it is necessary to use special devices or a pipe bending machine.
Concreting tape
You need to pour concrete into the formwork without interruption to get a high-quality monolith The grillage foundation is poured with concrete at the same time without interruption in the work until it is completely completed. It is strictly forbidden to make breaks along the length of the foundation. The only permitted action is a gap in the height of the grillage. After pouring a 150-200 mm layer over the entire volume of the tape, a break in work is taken.
Before continuing construction work it is necessary to wait until the concrete reaches the minimum permissible strength. Then you need to clean off the top layer, the so-called concrete milk, and only after that continue concreting the tape.
It is important to carry out the work so that there are no pores in the concrete mass. It is required that the concrete fills the entire space in the formwork. There should not be a single air pocket left inside the grillage.
Stripping
It is important not to remove the formwork ahead of time You can neglect this process once and carry it out ahead of time in order to incur losses that will significantly affect the construction budget.
If the formwork is removed prematurely, the foundation may crack, which will leave virtually no options other than dismantling it. In this case, a new foundation will be required, and accordingly construction costs will increase significantly.
Concrete gains strength depending on its grade and ambient temperature. The ideal temperature is 20°C; in such conditions, concrete grades M200-300 will gain 100% strength in 28 days.
Data on concrete strength gain are presented in the table.
| Percentage of concrete strength depending on temperature | |||||||
|---|---|---|---|---|---|---|---|
| Concrete grade | Hardening time, days | -3°C | 0°C | +5°С | +10°С | +20°С | +30°С |
| 1 | 3 | 5 | 9 | 12 | 23 | 35 | |
| 2 | 6 | 12 | 19 | 25 | 40 | 55 | |
| M200-300 on Portland cement M-400 and M-500 | 3 | 8 | 18 | 27 | 37 | 50 | 65 |
| 5 | 12 | 28 | 38 | 50 | 65 | 80 | |
| 7 | 15 | 35 | 48 | 58 | 75 | 90 | |
| 14 | 20 | 50 | 62 | 72 | 90 | 100 | |
| 28 | 25 | 65 | 77 | 85 | 100 | - |
The table shows that at low temperatures it is advisable to use concrete with additives to quickly gain strength. This slightly increases its cost, but will also significantly speed up the construction process.
It is allowed to remove the formwork when the concrete has reached at least 50% strength.
Waterproofing tape
With a hanging grillage, you can use coating waterproofing. In the recessed version it is possible to lay roll waterproofing into the ground before pouring concrete and after stripping the upper part, completely cover the foundation. For more information about waterproofing a grillage structure, watch this video:
It is important to protect the base from moisture. If the foundation absorbs water, then winter time at sub-zero temperatures During the expansion of freezing water, microcracks will form in it. This must be avoided.
Mistakes when reinforcing and how to avoid them
Do not reinforce corners by crossing reinforcement There are a number of mistakes related to reinforcement that inexperienced builders make in order to save money or simply due to ignorance of building codes and regulations. Below are the most frequently repeated ones.
- Diameter reduction bored pile, according to some builders, should be accompanied by a reduction in the number of vertical reinforcement bars to which the grillage frame must subsequently be attached. Reducing the allowance of vertical bars.
- Reinforcement of corner sections by crossing straight reinforcement bars. Many people do this so as not to complicate the knitting of the frame.
- Failure to follow the steps for installing lintels when reinforcing the grillage. Skipping required connections. This often happens in order to save money.
- Deviation of the reinforcement cage from the central axis. This will lead to uneven load-bearing capacity of the foundation. Such things often happen due to simple negligence. Watch all the details of reinforcing a pile foundation in this video:
The solutions to the above errors are given below.
- The diameter of the pile should not be less than 300 mm, the number of vertical rods should be less than 4, the allowance for reinforcement under the grillage should be at least 0.5 m.
- To properly connect the beam assemblies, you should make bent U- and L-shaped parts with which you need to connect the corner elements.
- When installing the reinforcement frame, a step of 200 to 400 mm between the lintels must be observed. The exact step size is determined at the design stage.
- All measurements must be made using building levels so that the frame is aligned relative to the central axis.
Reinforcement is a significant part of the construction process. Everything is important: the quality of materials, the experience of the builders, and the availability of working documentation. 
Failure to comply with reinforcement rules can lead to the most serious consequences. This stage of construction is one of the most critical.
During construction work, any mistake leads to a decrease in the life of the building without the need for repairs. This is the best case scenario. At worst, even at the stage of construction of the building, it is subject to reconstruction.
To achieve maximum service life, it is necessary to comply with building codes and regulations, avoiding deviations from the design. Construction combines a set of measures that must be followed to achieve the desired result. If possible, it is better to entrust such work to professionals.
Quite often, a house under construction is built on a pile type of foundation; in this case, grillage reinforcement becomes relevant. pile type foundation.
The type of pile foundation is simply necessary in the case when construction work is carried out on weak and heaving soils, on construction site there are large differences in soil height or there are groundwater.
In addition, a pile foundation is the only solution if the construction of a house is planned in permafrost areas, as well as in many other cases.
In general, piles are used for these purposes, differing from each other both in the method of immersion in the ground and in the material used for their manufacture.
What unites them is that it is the grillage that connects them into a single solid and durable structure.
In turn, to give strength to the grillage itself, it is necessary to reinforce it, having first made a drawing and calculated all the expected loads during the subsequent operation of a private house.
Main features of the grillage
Immediately before moving on to the arrangement of the grillage itself, and, accordingly, to its reinforcement, it is necessary to decide on the type of pile foundation and the number of piles themselves.
Their minimum number can be from four pieces on the basis that each corner will have its own pile.
It is on this pile-type foundation that the grillage itself will subsequently be laid. It can be in the form of a single continuous slab or strip type.
In general, the main purpose of a foundation grillage is to tie together all parts of a pile-type foundation into a single whole to evenly distribute the load.
In the case when concrete beams are used as a grillage, it resembles a strip-type foundation, but the difference is that the grillage strip is never buried in the ground.
This is primarily due to the fact that in severe frosts the soil tends to bulge, and this, in turn, can lead to a violation of the integrity of the grillage itself, both the strip type and the solid slab.
The foundation grillage arrangement can be different.
So, it can be made of durable concrete and have a reinforcement frame; it can also be prefabricated from various elements manufactured at the factory, or combined.
Connect piles with various elements The grillage itself can be done using ordinary welding, as well as in monolithic sections.
When laying out the foundation for a pile-type house, you can use a variety of materials for the grillage.
If a strip-type foundation is assumed, then the grillage can be made from metal channels or I-beams.
However, even though the calculation of this type of strip foundation shows its high reliability, in economic terms it is not profitable and will be quite expensive.
In this case, the most preferable would be a grillage constructed in the form of a monolithic concrete structure with appropriate reinforcement.
Calculation of a foundation with a grillage
In order to correctly calculate a foundation of this type, it is first necessary to determine as accurately as possible the composition of the soil at the construction site, especially at the depth at which it is planned to build the foundation itself.
This is necessary, first of all, in order to calculate the length of the piles, plan their design, as well as the distance between the piles individually.
The load-bearing capacity of the future pile is also calculated.
When calculating a pile foundation with a grillage, it is also necessary to determine the expected loads that the house will exert directly on the piles themselves, as well as on the ground.
In order to calculate the total weight of the future structure, it is necessary to add together not only its weight, but also the weight of the roof and floors.
Natural loads are also taken into account, such as snow, the mass of people in the house, various equipment and furniture.
All subsequent calculations are made taking into account the total area of the entire house.
In most cases, a foundation with a grillage is installed for those buildings whose area will be at least three hundred square meters.
As a rule, the necessary calculations are carried out by specialists, since there are many different subtleties and nuances.
After the necessary calculation of the foundation of the house has been made, on the basis of which the number of piles, the distance between them and the depth of their installation are determined, a corresponding diagram and drawing must be drawn up.
It should be noted that screw piles are more economically profitable and can be equipped without the use of special equipment.
When carrying out work on laying a foundation for a house with a grillage, the structure must be reinforced, both for strip type and for solid monolithic slab.
Grillage reinforcement
In any case, a pile-type foundation must be reinforced. The piles themselves are reinforced primarily in order to give them adequate strength.
In turn, the grillage is reinforced to maximize its load-bearing capacity.
That part of the reinforcement that will protrude from pile structure, will be used as a connecting element between the pile itself and the grillage.
The fastening itself is usually carried out by welding.
To carry out reinforcement, it is necessary to use a previously drawn up drawing; in addition, the reinforcement diagram must be directly in front of your eyes.
It should be remembered that those grillage elements that do not have appropriate reinforcement will simply not withstand the loads during the construction of the walls and floors of the house.
In the case where strip grillages are installed, the reinforcement frame itself should be made of two separate belts.
They must be rigidly connected to each other using vertical metal rods with a cross-sectional diameter of up to eight millimeters.
This diameter is chosen due to the fact that these metal rods are practically not subject to load, but are intended mainly to give the appropriate shape to the frame.
A prerequisite is that each belt must consist of at least two rods.
The belts are connected to each other using rods located in a horizontal position and connected with ordinary knitting wire.
In the production of reinforcement cages for foundations with grillages at industrial enterprises, welding machines are used to fasten transverse connections.
However, transverse circles or squares with longitudinal rods are directly connected exclusively by knitting.
If the foundation is assumed to be constructed in the form of a continuous monolithic slab, then the reinforcement scheme remains exactly the same as in strip-type foundations.
In this case, the upper chord of the frame is made in the form of a mesh of reinforcement with a cross-sectional diameter of 10 to 14 millimeters, and reinforcement with a smaller diameter is used to arrange the vertical rods.
The cost of the foundation itself is mainly affected by the amount of concrete and reinforcement that are used to construct it.
In addition, the price includes lumber, which is necessary for the construction of formwork. Depending on their design, grillages can be high or low.
However, regardless of the type of structure chosen, the principle of grillage reinforcement remains the same.
In the case where a ruined type of foundation is assumed, its lower part should be flush with the ground.
In some cases, it is possible to lower it a few centimeters lower.
Between the piles it is necessary to build trenches in which appropriate cushions are made from carefully compacted sand and crushed stone.
This reinforcement frame must be rigidly connected to the pile heads and not reach the walls of the installed formwork by about five centimeters.
Only after this the foundation itself is poured with concrete. It should be noted that such a grillage is possible only if the house is built on non-heaving soil.
In all other cases, it is necessary to equip high grillages, and special attention should also be paid to the reinforcement of the entire structure.
Reinforcement of a pile-grillage foundation for a private house and the pile foundation itself are used when constructing a building in non-standard conditions. This could be a large number groundwater, strong changes in height, or weak soil that is not able to properly withstand the pressure of the building. This type is also used for construction in permafrost zones. Under such conditions, it is impossible or too expensive to use a monolithic or strip foundation.
Other types of foundation are solid, monolithic structures and thanks to this, the weight of the building is evenly distributed without the use of additional devices. The pile structure is divided into parts, each of which is subjected to different pressure, as a result of which some piles can sink more than others, thereby posing a threat to the integrity of the building. In order to combine individual piles into a strong and integral structure, regardless of their type, a grillage slab is used. With such a foundation arrangement, the main pressure falls on the grillage, which redistributes the load and transfers it to the piles.
The pile-grillage foundation is reinforced, then the slab is formed from concrete. For a private house, reinforcement is a mandatory element. The fact is that concrete itself is very durable material and perfectly withstands compressive loads. But when stretched or bent, it tends to crack and deform, since it is not flexible enough. In order to prevent this, the entire structure is reinforced with a reinforcing frame consisting of individual metal rods. The plasticity of the metal gives the foundation the necessary properties and makes it more durable and reliable.
Types of grillage
There are two main types of grillage:
Selection of fittings
The lower part of the grillage most often bears the heaviest loads, so the lower layer of the reinforcing frame is assembled from thick corrugated rods, their diameter must be at least 2 cm. The upper part of the reinforcement of a pile-grillage foundation for a private house mainly performs the function of redistributing pressure, therefore, for its formation, reinforcement up to 1 cm thick is sufficient. To perform reinforcing work, Various types fittings:
- A1 - reinforcement with a smooth surface and a relatively small diameter. Such rods can be used in places of the frame where heavy loads are not expected, as well as to create the foundation of the structure.
- A3 - reinforcement with an uneven surface. These are rods with a diameter of 1 cm. They have increased strength characteristics and a diameter of 1 cm. There are 2 main types of corrugated reinforcement: with a ring-shaped profile - for increased adhesion to concrete and with a crescent-shaped profile - to counteract tensile deformation. There may also be mixed options that offer the benefits of both types.
In order to reinforce a pile-grillage foundation for a private house, two types of connections are used - welding and wire knitting. Thus, when choosing metal rods, pay attention to how they will be attached to others. Only fittings marked “C” are suitable for welding.
Welding unsuitable reinforcement can lead to a loss of strength and elasticity in the material and an increased tendency to corrosion, which will negatively affect the condition of the entire foundation.
Reinforcement scheme for pile foundation grillage
When reinforcing the grillage of a pile foundation, a drawing must be drawn up before the start of construction work. When creating a drawing, it should be taken into account that in places where the grillage is connected to the piles, there are increased loads; such places require additional reinforcement by increasing the frequency of laying horizontal reinforcement by 2 times. The process of laying the reinforcement will differ depending on the type of grillage.
- For a strip-type grillage, creating a drawing for the reinforcement of a pile foundation grillage is quite easy. To perform this, you should take into account the width and height of the tape. The standard distance between horizontal rods is 8-10 cm. They are laid in two layers - upper and lower, which are connected to each other by sparser vertical rods.
- For a monolithic grillage, high-strength reinforcement is used. To do this, reinforcement with a diameter of 20-25 mm is laid across the entire area of the house. The laying step is from 10 to 15 cm, depending on the type of construction. In addition to the standard vertical and horizontal elements, the design of such a frame also contains, for additional reinforcement, cross-laid rods designed to maximize the strength of the pile foundation grillage reinforcement.
The drawing allows for the presence of only a lower layer of the reinforcing frame, since it is this layer, as in the case of a strip grillage, that takes on all the loads. The upper mesh is often absent completely or remains only in the form of thin additional rods.
To obtain the most accurate calculations, it is necessary to take into account not only the weight of the future structure, but also the weight of the roof, concrete floors and additional loads that will appear in the future. Furniture, equipment, precipitation and the number of people who will be in the building at the same time.
Thus, when performing the reinforcement-grillage of a pile foundation, the drawing gives you all the necessary information about the amount of materials needed for the work and the type of reinforcement.
Reinforcement of a pile-grillage foundation
Rods released from the piles are used to connect the reinforcing grillage of the frame and the pile structure. All elements are fastened together by welding. When forming the frame, you should strictly follow the drawn up drawing of the pile foundation grillage and ensure compliance with the standards. The reinforcement is laid in two layers, which must be fastened together with vertical rods. They may not be too thick and have a smooth surface, since they are practically not subject to load and are intended solely to create the base and shape of the frame.
Reinforcement of a pile-grillage foundation for a private house occurs in several stages:
- Construction of trenches between piles. Sand and fine crushed stone should be sequentially poured and compacted into these trenches. This is done so that the grillage pressure is subsequently transferred not directly to the ground, but to the supporting cushion.
Formwork assembly. Carefully ensure that there are no cracks or crevices on the surface of the formwork, this will lead to leakage of the solution.
Reinforcement of the lower part of a pile-grillage foundation for a private house. This part must be especially strong, since the main loads fall on the bottom of the grillage.
Installation of vertical rods and additional supporting elements.
Assembling the upper part of the frame.
Fastening all individual parts of the frame with wire and, if necessary, welding.
Pouring the structure with concrete.
Pouring concrete
After completing the formation of the reinforcement frame, you can begin pouring the slab with concrete. Concrete, when forming concrete base grillage, a brand no less than M250 or M300 must be used. Such concrete has sufficient strength and is used for pouring foundations, stairs, columns and other structures that require maximum reliability. The required amount of concrete mixture for construction work must be calculated taking into account the percentage of concrete shrinkage after hardening.
When reinforcing a pile-grillage foundation for a private house, it is extremely important to perform all calculations with maximum accuracy. A lack of materials necessary to continue the work can lead to an interruption of the construction process. Subsequently, this will negatively affect the strength characteristics of the foundation, since unevenly hardened concrete is prone to cracks and deformation. In turn, excess concrete is wasted money.
Concrete gains the necessary strength after 28 days, but you can walk on it after just a week. It is worth noting that a month after pouring, concrete sharply loses its hardening rate, but gradually becomes stronger over many years.
Basic mistakes
In order for the grillage to be as resistant to any negative factors as possible and to properly perform its functions, when carrying out work you should strictly adhere to the technology specified in the standards. You should also avoid common mistakes:
Not a complete formwork structure.
Welding fittings that are unsuitable for this purpose or fittings that are too small in diameter.
Leakage of concrete milk due to the lack of polyethylene coating of the poured structure.
Incorrect reinforcement of the pile foundation grillage; the drawing was made without the necessary calculations.
The distance between the horizontal bars is too large.
The absence of a pressure-absorbing cushion between the piles.
Often, when building a house, a pile type of foundation is used. Moreover, the relevance and popularity of reinforcing the grillage of a pile foundation today does not raise any doubts. In this article we will understand the main important stages, characteristics and features of this direction.
In what cases is it advisable to use a pile foundation?
First of all, this type of foundation becomes relevant in the case of construction on heaving and soft soils. Also, this option will be the best when significant differences in height are obvious at the construction site or there is groundwater. In addition, the construction of such a foundation becomes a necessity when building a house in permafrost areas.
What is a grillage and the process of its reinforcement in general?
In the cases described above, diverse piles can be used. They may differ regarding:
- The material used for their manufacture;
- The method of immersing them in the ground.
The grillage is the connecting element that unites them into a single strong and integral structure.
Reinforcement of the pile foundation, in turn, is carried out in order to impart the required strength to the grillage. To do this, a preliminary drawing must be drawn up and all the most important calculations regarding the upcoming loads during operation of the structure must be performed.
What features are typical for the grillage device?
- The norm for grillages is the presence of a so-called bending moment in the vertical plane. After all, it consists of beams laid on piles. At the same time, the span that lies between the supports is susceptible to the weight of various parts of the building, as well as other loads. It seems to be suspended in the air. For this reason, deflection appears;
- The grillage completely eliminates any impact from the ground. Therefore, it is quite easy to predict the occurrence of tension in it. For example, the lower part of the cross section in all cases turns out to be stretched in the spans located between the piles. The upper one is in areas where the structure rests on piles.
These features of the grillage are of decisive importance in the process of drawing up a reinforcement scheme for the grillage of a pile foundation. It is not surprising that much attention is paid to increasing the strength of the lower chord of the installed reinforcement cage in the areas between the piles. At the same time, it remains important to strengthen the upper belt at the support points.
Reinforcement scheme for pile foundation grillage
It should also be remembered that before proceeding with the installation of the grillage and its reinforcement, it is necessary to correctly and clearly determine the required type of pile foundation and the total number of piles required.
There should be at least 4 of them on the basis that each corner will have its own pile. It is on this pile-type foundation that the grillage will be laid in the future. Moreover, it can be in the form of a solid slab or it can be of a strip type.
Scheme of strip pile foundation
How to correctly select materials for a reinforcement frame and determine its parameters
In order to correctly calculate the required diameter of the reinforcement used, as well as the necessary parameters of the frame, it is necessary to correctly perform the calculation with mandatory consideration of temporary and permanent loads.
Let's take a closer look at the most important aspects:
- First of all, it is necessary to determine as accurately and clearly as possible the composition of the existing soil located at the construction site. It is worth approaching the depth at which the foundation is actually planned with special responsibility. Why is this so important? These points are of no small importance for calculating the length of piles, as well as planning them design features. In addition, these points will be important for planning the arrangement of the foundation.
- It is also necessary to correctly calculate the bearing capacity of the future pile being installed.
- It is necessary to determine possible loads that can affect not only the piles, but also the soil.
- In order to obtain the total weight of the future building, it is necessary to sum up not only its weight, but also the weight of the planned floors and roof.
- It will be useful to take into account possible natural loads (for example, the mass of people in the house, snow, various equipment, and furniture).
All further calculations must be carried out taking into account the total area of the building.
In general, in the most common cases, a grillage is chosen for buildings with an area of at least 300 square meters. Moreover, a construction engineer who has excellent knowledge and skills regarding reinforced concrete structures should calculate the reinforcement of a pile-grilled foundation.
After the calculation of the foundation of the building takes place (with the determination required quantity piles, as well as the distance between them, installation depth), an appropriate diagram and drawing must be drawn up.
Let's look at typical solutions and rules that are recommended to be followed:
- Several reinforcement bars of class AIII longitudinal type (diameter - 20 mm) and above must be laid in the stretched areas of the grillage being installed;
- Reinforcement with a diameter of 8 to 15 mm is placed in a compressed belt. The pitch between the rods of the longitudinal (working) reinforcement should be from 80 to 100 mm;
- In order to absorb transverse tensile forces, as well as to combine longitudinal reinforcement into a single frame, transverse rods are attached to it. In this case, use class AI smooth reinforcement with a diameter of 6-8 mm. Moreover, the distance between them should be at least 250 mm. However, it is usually 3/8 of the existing height of the grillage section.
If the grillage exceeds 150 mm, vertical bars must be installed in the existing reinforcement frame. Moreover, the step must correspond to the step of the transverse reinforcement.
In general, clamps are often used instead of separate transverse and longitudinal rods. They are reinforcement parts in the shape of an inverted letter “P” or in the shape of a closed rectangle.
Grillage reinforcement
In the process of carrying out work on laying the foundation for a building with a grillage, it is mandatory to carry out proper reinforcement of the structure.
Why are piles reinforced? In order to guarantee them the required strength.
What is the purpose of grillage reinforcement? In order to maximize its possible load-bearing capacity.
Moreover, that part of the reinforcement that tends to protrude from the pile structure will be used as a connecting element directly between the grillage itself and the pile.
Fastening, in turn, is carried out using welding in most cases.
In order to perform reinforcement, it is necessary to draw up a preliminary drawing. In addition, the reinforcement scheme is also important.
Strip foundation grillage diagram
Do not forget that the grillage elements, which are not properly reinforced, will not be able to withstand the loads during the construction of the floors of the house, as well as its walls.
1. In the case of installing strip grillages, the reinforcement frame must be made of two separate belts. Moreover, they must be connected to each other as rigidly as possible using vertical rods made of metal (with the required cross-sectional diameter - up to 8 mm). Why is this particular diameter relevant? This happens because these metal rods are actually not subject to load. Their main role is to give the frame the necessary shape.
Strip foundation
The required condition is that each belt must include at least two rods. Moreover, the belts must be connected to each other using rods that are positioned horizontally and connected using the so-called knitting wire.
When making reinforcement cages for foundations with a grillage within industrial enterprises, welding machines are used to fasten transverse connections.
But in this case, transverse circles or squares with longitudinal rods are connected only using the knitting method.
2. If the base is installed in the form of a solid monolithic slab, the reinforcement scheme will remain the same as for strip-type foundations.
In this case, the upper chord of the frame is made in the form of a kind of mesh of reinforcement, which has a cross-sectional diameter of 10-14 mm. For the purpose of arranging vertical rods, reinforcement with a smaller diameter is used.
Possible grillage design options
Depending on the design features, grillages can be low or high. Regardless of the type of structure, the same principle of reinforcing the grillage of a pile foundation is applied.
- In the case where it is planned to construct a foundation of the so-called ruined type, its lower part is placed at the same level with the ground. However, in some cases it can be allowed to drop down to a few centimeters below.
- To properly organize the trench between the piles, it is necessary to make cushions from compacted crushed stone and sand.
- After this, the direct installation of the formwork is carried out, as well as the assembly of the reinforcement cage.
- The reinforcement frame, in turn, must be rigidly connected with the existing pile heads. Moreover, it is necessary not to reach the walls of the installed formwork by approximately 5 cm.
- After the above steps, you can proceed to pouring the foundation with concrete.
However, it is worth keeping in mind that this grillage option will become possible if the building is erected on non-heavy soil. In other cases, an important condition will be the installation of a higher grillage with utmost attention to the reinforcement of the structure.
Methods of knitting reinforcement
Let's take a closer look at how to knit reinforcement for a pile foundation.
The most common method is tying reinforcement using special wire. For its part, electric welding is used quite rarely (only in the case of fittings that are marked with the letter “C”). Welding joints with conventional fittings is unacceptable. Indeed, due to exposure to high temperatures, it may lose its strength.
For the purpose of knitting reinforcement, only annealed round wire with a diameter of 1 mm is used. After all, unfired products have less plasticity and tend to bend poorly.
To speed up the mating process, use a special gun, which is equipped with a battery. However, it is logical to purchase it only if it is necessary to perform a large range of work. In addition, many appreciate it for its ease of working with viscous reinforcement in a variety of hard-to-reach places.
In general, reinforcement of a pile-grillage foundation is often performed using a different tool - a special hook. Moreover, professionals often make them themselves, but for one-time work, a purchased option will also be useful.
At the present stage, if desired, you can purchase screw (semi-automatic) as well as regular hooks.
Reinforcement tying scheme
Moreover, screw options help speed up the reinforcement process. At the same time, due to design features, after tightening they can leave quite long free ends of the wire used. Therefore, they tend to protrude from the concrete and begin to rust quite quickly.
What types of knots are considered the simplest and most convenient? The so-called “two loops” or “loop”. A loop is used to connect overlapping reinforcement, two loops are used in the case of butt joints. In practice, a loop is often used not only in the case of overlap joints, but also in the case of corner joints.
We should not forget that the final stage of installation of the required reinforcement cage should be the removal of the bosses on which the working reinforcement of the lower chord was installed. After this stage, the frame is suspended on a wire that wraps around the upper lintels of the formwork. After these operations, you can proceed directly to pouring concrete.
It is clear that reinforcing the grillage of a pile foundation is a rather complex multifaceted process that requires a thoughtful and competent approach. We hope that the tricks and tips in this article will help you complete all the work clearly and easily.