Reinforcement strip foundation drawings. Do-it-yourself strip foundation construction technology How to fill a T-shaped strip foundation
Most modern builders concrete the T-shaped foundation in exactly the same way as a hundred years ago: they construct a formwork for the supporting sole (broadening), pour the mortar, remove the formwork. Then repeat the same steps when pouring the foundation tape itself.
This time-tested algorithm is certainly good for large projects, but may not be the best way to solve the problem in small construction. You overpay a serious amount when you order a small amount of concrete, and small projects usually require very little. Simultaneous concreting of the base sole and the foundation strip makes it possible to order one standard mortar instead of two small batches.
It should be noted that it is easier to concrete the base plate and the foundation strip separately. If the sole turned out to be not even enough, errors can be corrected during the construction of the foundation tape. With simultaneous concreting, it is necessary to construct the formwork very carefully.
Rice. 1. Cast-off and cord. Correctly positioning the formwork for the T-shaped foundation will help the threads stretched between the cast-off boards. First, a long thread is attached, then a short one perpendicular to it, applying the 3-4-5 triangle rule. Since the stretched threads are only needed as guides, it is not necessary to place them at a certain height - it is important that they are at the same level in relation to each other.
Arrange the formwork like this. First, a cast-off is installed, between which the cords are pulled, which determine the position of the supporting sole (Fig. 1). Then the formwork of the broadening is installed. The formwork of the tape is mounted from above using metal strips and brackets (Fig. 2).
Rice. 2. Installation of formwork for concreting a T-shaped foundation
Formwork must be collapsible
When constructing the formwork, one should not forget that it will have to be removed. Poorly designed connections can turn formwork stripping into a nightmare.
Everything must be taken into account here: from which side (external or internal] it is easier to dismantle the shields, and how to dock them in the corners, and whether it is worth using long boards or is it better to use short ones and connect them with an overlay.
Concrete foundation pad
Hold concrete in formwork
Another difficulty with the simultaneous concreting of the base plate and the foundation strip is the distribution of concrete in the formwork.
When concreting a small foundation, a wheelbarrow may be required to distribute the solution around the perimeter of the formwork, and an electric vibrator will be very useful for compacting concrete. It will help get rid of voids and uneven distribution of the filler in the solution. However, one should also take into account the fact that vibration increases the pressure on the formwork, especially at the bottom and at the corners, which can lead to the destruction of forms. Anyone who has been involved in concreting has experienced similar problems first hand.
However, the main problem of simultaneous concreting- retention of the concrete mass at the level of the upper edge of the formwork of the support sole. You will not be able to curb this lava-like flow by sealing the top opening, because in this case the mortar will tear all the formwork (including fasteners) off the ground, leaving you with a concrete mess.
Therefore, the key point of simultaneous concreting is careful control of the upper cut of the sole formwork during mortar placement and vibration. As soon as the concrete starts to overflow, you need to move to another point and let the concrete set before adding an additional layer on top of it.
When you come back, you need to work both castings together with a vibrator to ensure good adhesion of the individual layers. This must also be done very carefully so that the formwork does not rise.
The shield allows you to lay the concrete mass in the formwork without splashing. If there is no assistant, prop up the shield and temporarily fix it.
Clean the formwork before the concrete has set. The formwork can be removed faster if you do not have to chip the hardened concrete to find fasteners. Another way to quickly dismantle the formwork is to use short boards in the form construction, connecting them with overlays.
Insert fittings into one of the pipes to the place of the intended bend.
Pass the bar into the second tube.
Bend the rod to the desired angle.
The outer corners of the formwork are easier to dismantle. When dismantling the formwork, you should start from one end and gradually move towards the other. From the side of the inner corners, it is advisable to design the formwork in such a way that dismantling starts from the central section. Then further dismantling can be done in both directions.
To compact the concrete mixture, a vibrator is used, which allows you to get rid of air inclusions and eliminates the working seams between the layers of concreting. It is better to use intermittent dipping of the tool into the concrete instead of constant vibration, which can cause excessive pressure on the formwork walls and make the concrete consistency too fluid.
When constructing a building, it is important to correctly select the types of main load-bearing structures. This will reduce the labor intensity of work, financial costs and terms of construction of the facility. One of the types of construction that makes it possible to simplify the process of building a building is a shallow strip foundation. During its construction, you need to take into account a large number of nuances, but with the observance of technology and proper selection, you can save a lot.
Application area
This type of tape has a rather limited scope. Do not dig foundations deep if:
The device of a shallow foundation at a high level of groundwater
- it is planned to build a building from light materials (wood, aerated concrete);
- on the site there is a high level of groundwater;
- The characteristics of the base soil are quite good, the soil has high strength characteristics.
When building a frame house or aerated concrete house, a shallow strip foundation is the best option. It will reduce the amount of excavation and increase the speed of construction. It is possible to make such a structure without carrying out additional measures to remove water from the site when groundwater is located at a distance of 1 meter or more from the surface of the earth. For a recessed tape, this value is much higher (50 cm more than the sole).
A shallow strip foundation is suitable for conditionally non-rocky and non-rocky soils, which include:
- rocks;
- coarse-grained bases (including those with dusty filling);
- coarse and medium gravelly sands;
- clay soils of firm consistency with natural moisture.
You can independently determine the composition of the soil on the site by extracting pits or by hand drilling. GOST “Soils. Classification".
Foundation types
The shallow foundation has two classifications. The first depends on the method of manufacture:
It is better to make a shallow strip foundation using monolithic technology, since in this case you do not have to worry about ensuring that the tape works together. When building a prefabricated structure for a house made of aerated concrete, it will be necessary to additionally provide for a monolithic belt along the edge, so monolithic work cannot be avoided in any case.
Depending on the type of section, there are:
Rectangular foundations have a lower bearing capacity, therefore they are more often used for the construction of frame houses. For building a house from heavier aerated concrete, it would be right to opt for a t-section.
This type differs from the rectangular one in the presence of a broadened base, which can significantly increase its bearing capacity even at a small depth. The shallow foundation in this case consists of a tape located horizontally (cushion) and a vertical part.
Foundation depth
To correctly design a support for a building, it is necessary to choose the depth of the foundation. For this type of tape, it will be higher than the depth of soil freezing for almost the entire territory of the country, which increases the risk of damage to the structure by frost heaving forces.
Frost heave is a phenomenon where water in the soil freezes and expands. In this case, the foundation tape is deformed and subjected to additional loads. The structure is starting to crack. That is why it was said above that a shallow foundation is mainly used for non-rocky soils.
Estimated Foundation Depth Table
The depth of laying is determined depending on the freezing, which is calculated according to the SN "Foundations and foundations" or is found in the tables. Minimum laying depth:
- when freezing to a depth of less than 2m - 50cm;
- when freezing less than 3m - 75cm;
- when freezing more than 3 m - 100cm.
It is also important to consider the location of groundwater. If the water is located closer than 2 measures from the expected sole mark, and the soils on the site are clay, loamy, sandy loam, fine or silty sands, it would be right to opt for a deep foundation with a drainage system.
Also, regulatory documents prescribe to choose the depth of laying the foundations of a house made of aerated concrete at least ½ of freezing for clays and loams with a deep location of water.
This is due to the increased heaving of this type of soil.
Protection methods
Before you build a shallow strip foundation with your own hands, you need to familiarize yourself with the technology for protecting it from negative external influences. Frost heave is caused by two factors:
To avoid this phenomenon, measures are taken to protect against these negative influences:
- Insulation of the house tape from aerated concrete over the entire height of the laying. Made using extruded polystyrene foam. Correctly using this particular material, the use of foam or mineral wool is highly discouraged.
- Additional insulation of the foundation due to the warm blind area of \u200b\u200bthe house. It can be made of concrete or asphalt concrete, while placing a heat-insulating layer under the material. As a heater, extruded polystyrene foam or expanded clay gravel is used. The thickness of polystyrene for most regions will be 100-150 mm, the thickness of the expanded clay layer is taken in the region of 30-50 cm.
- vertical waterproofing. The layer is provided for insulation. It is made of bituminous roll materials or mastic.
- Drainage of water from the foundation. This will require a stormwater device (from rainwater) and drainage (from underground moisture). Drainage pipes are laid 30-50 cm below the bottom of the tape and at a distance of no more than 1 m.
- Sand preparation device 30-50 cm thick. Coarse or medium sand is a non-porous material. Replacing part of the soil with it allows you to increase the reliability of the foundation.
The implementation of all these measures will reduce the likelihood of damage to the aerated concrete house structure by frost heaving forces in the winter.
Manufacturing technology
It is not much different from doing work on a buried tape. The device of a shallow strip foundation is made in the following order:
Strip foundation manufacturing technology
- The terrain is marked and a trench or pit of the required size is dug.
- Sand preparation is being arranged(it was mentioned earlier). When laying, it is necessary to ensure layer-by-layer compaction of the layer (by vibration, pouring or weights).
- Formwork is installed. For the type of foundation under consideration, the most optimal option is foam. After pouring, no additional work on insulation is required. Can be used as formwork boards.
- Structural reinforcement. For private houses, reinforcement can be performed without preliminary calculations. There are three types of reinforcement in the design: working longitudinal, constructive horizontal, constructive vertical. Structural reinforcement plays the role of a link between the working rods. The minimum diameter of the rods is 8 mm. Working reinforcement with a diameter of 12-16mm is laid in two rows: upper and lower. The total cross section of the working rods of a house made of aerated concrete or wood should be approximately 0.1% of the cross section of the foundation.
- Pouring concrete mix. It is performed in one step. If absolutely necessary, you can do it in layers, but this is undesirable. For foundation work, concrete B15-B25 is used, depending on the load.
- Vibrating concrete for compaction.
- Set concrete strength and care.
- Removal of formwork (if necessary).
- Foundation waterproofing.
- Warming (if necessary).
- Backfilling.
- Blind device.
To make a reliable foundation, it is necessary to carefully consider each stage of work: correctly select the depth of laying, reinforcement, concrete grade, and perform all necessary protection measures.
Shallow strip foundation: diagrams with photos
A shallow foundation protects the house from subsidence. We will tell you how to make such a strip foundation with your own hands.
T-shaped foundation concreting
Most modern builders concrete the T-shaped foundation in exactly the same way as a hundred years ago: they construct a formwork for the supporting sole (broadening), pour the mortar, remove the formwork. Then repeat the same steps when pouring the foundation tape itself.
This time-tested algorithm is certainly good for large projects, but may not be the best way to solve the problem in small construction. You overpay a serious amount when you order a small amount of concrete, and small projects usually require very little. Simultaneous concreting of the base sole and the foundation strip makes it possible to order one standard mortar instead of two small batches.
It should be noted that it is easier to concrete the base plate and the foundation strip separately. If the sole turned out to be not even enough, errors can be corrected during the construction of the foundation tape. With simultaneous concreting, it is necessary to construct the formwork very carefully.
Rice. 1. Cast-off and cord. Correctly positioning the formwork for the T-shaped foundation will help the threads stretched between the cast-off boards. First, a long thread is attached, then a short one perpendicular to it, applying the 3-4-5 triangle rule. Since the stretched threads are only needed as guides, it is not necessary to place them at a certain height - it is important that they are at the same level in relation to each other.
Arrange the formwork like this. First, a cast-off is installed, between which the cords are pulled, which determine the position of the supporting sole (Fig. 1). Then the formwork of the broadening is installed. The formwork of the tape is mounted from above using metal strips and brackets (Fig. 2).
Rice. 2. Installation of formwork for concreting a T-shaped foundation
Formwork must be collapsible
When constructing the formwork, one should not forget that it will have to be removed. Poorly designed connections can turn formwork stripping into a nightmare.
Everything must be taken into account here: from which side (external or internal] it is easier to dismantle the shields, and how to dock them in the corners, and whether it is worth using long boards or is it better to use short ones and connect them with an overlay.
Concrete foundation pad
Hold concrete in formwork
Another difficulty with the simultaneous concreting of the base plate and the foundation strip is the distribution of concrete in the formwork.
When concreting a small foundation, a wheelbarrow may be required to distribute the solution around the perimeter of the formwork, and an electric vibrator will be very useful for compacting concrete. It will help get rid of voids and uneven distribution of the filler in the solution. However, one should also take into account the fact that vibration increases the pressure on the formwork, especially at the bottom and at the corners, which can lead to the destruction of forms. Anyone who has been involved in concreting has experienced similar problems first hand.
However, the main problem of simultaneous concreting- retention of the concrete mass at the level of the upper edge of the formwork of the support sole. You will not be able to curb this lava-like flow by sealing the top opening, because in this case the mortar will tear all the formwork (including fasteners) off the ground, leaving you with a concrete mess.
Therefore, the key point of simultaneous concreting is careful control of the upper cut of the sole formwork during mortar placement and vibration. As soon as the concrete starts to overflow, you need to move to another point and let the concrete set before adding an additional layer on top of it.
When you come back, you need to work both castings together with a vibrator to ensure good adhesion of the individual layers. This must also be done very carefully so that the formwork does not rise.
The shield allows you to lay the concrete mass in the formwork without splashing. If there is no assistant, prop up the shield and temporarily fix it.
Clean the formwork before the concrete has set. The formwork can be removed faster if you do not have to chip the hardened concrete to find fasteners. Another way to quickly dismantle the formwork is to use short boards in the form construction, connecting them with overlays.
Insert fittings into one of the pipes to the place of the intended bend.
Pass the bar into the second tube.
Bend the rod to the desired angle.
The outer corners of the formwork are easier to dismantle. When dismantling the formwork, you should start from one end and gradually move towards the other. From the side of the inner corners, it is advisable to design the formwork in such a way that dismantling starts from the central section. Then further dismantling can be done in both directions.
To compact the concrete mixture, a vibrator is used, which allows you to get rid of air inclusions and eliminates the working seams between the layers of concreting. It is better to use intermittent dipping of the tool into the concrete instead of constant vibration, which can cause excessive pressure on the formwork walls and make the concrete consistency too fluid.
T-shaped foundation concreting
Most modern builders concrete the T-shaped foundation in exactly the same way as a hundred years ago: they construct a formwork for the support sole (widening),
T-shaped strip foundation
The base of the tape type is quite often used by individual developers for the construction of houses, baths, outbuildings, cottages and other structures. Its prevalence is associated with sufficient strength, reliability, availability of technology for independent work. Among the varieties of strip foundations, the T-shaped foundation is given a special place. It is used for various buildings. It is characterized by increased rigidity, due to the fact that it has the shape of the letter "T". This version of the support structure is made recessed or shallow. This is determined by the load on it, as well as the hydrogeological features of the construction site soil.
Varieties of strip foundations
The tape type foundation is a closed structure, which is built from different materials of your choice: reinforced concrete, prefabricated elements, stone or brick. Its parameters depend on the following factors:
- soil on the site;
- location of groundwater;
- the expected load on the base;
- climatic features of the region.
Varieties of strip foundations
The weight of the constructed structure is distributed along the entire perimeter of the supporting structure.
One-story and more buildings are erected on tape bases from the following materials:
Varieties of the strip foundation according to different classification criteria are presented in the table below.
The main task during construction is to choose an option that is economically and operationally suitable.
Tape-type bases have a resource of about 70 years (subject to technology), they are quite easy to repair. The scope of the various options is as follows:
- a shallow foundation is suitable for the construction of panel, panel, frame structures and log cabins on flat areas with loamy or sandy soils, on which it is allowed to lay floors;
- a shallow base with a depth of 0 to 1 m is suitable for the construction of buildings from various materials on non-rocky soils;
- the t-shaped base is expanded from below and is used for any buildings on different soils, if the site is not located on slopes or in a swampy area, and groundwater is deep;
- buried support structures are designed for the construction of buildings with a basement on various types of soil, even with high humidity;
- a monolith belt is a tape whose width is greater than its height, and it is used only if the soil has good bearing performance for the construction of frame or courtyard structures, log cabins.
Among the various types of strip foundation, you can choose the right option for different soils. The main problem is the action of heaving forces. If the estimated depth of penetration is more than 3 m, then it is recommended to give preference to a pile or in the form of a slab of a supporting structure, which will reduce the complexity of the work.
Do-it-yourself technology for building a T-shaped monolithic base
The technology for erecting a monolithic tape t-shaped foundation is similar to the construction of a tape. The difference lies only in the device of the extended lower part. Also, the formwork has a peculiar design so that the mortar does not leak out. To strengthen the base, reinforcement is also carried out.
T-shaped foundation with communications
The advantages of a T-shaped base are:
- ease of construction;
- sufficient strength;
- all work can be carried out without the use of special equipment;
- requires less financial and labor costs compared to deep and slab foundations, as well as less construction time;
- for construction, concrete is used, which is used to pour the reinforcing cage, or ready-made blocks, which speeds up the process.
They build a supporting structure for sheds, fences, houses from different materials. Due to the reduced thickness of the above-ground part, it is possible to save on concrete. At the same time, the area of distribution of the load from the building exceeds more than twice the corresponding parameter of the strip base.
The construction of the strip foundation occurs in 2 ways:
- with the installation of formwork in an excavated recess, in its width exceeding the same parameter of the base;
- pouring directly the trench, dug in the shape of the letter "T".
The latter option is not recommended by specialists, because the recessed part remains without a waterproofing coating, and this reduces the operating time by almost a third (by about 20-40%).
The technology of work provides for their implementation in 1 or 2 stages. In the latter case, the construction of the lower part (sole) occurs at the beginning, and then the construction of the tape.
The general algorithm of actions when working in stage 1 is as follows:
- determine the design of the foundation;
- calculate the dimensions of the sole and tape according to the bearing characteristics of the soil of the construction site, as well as depending on the depth of freezing and acting loads;
- carry out the marking of the building site;
- carry out earthworks;
- fill the bottom of the trenches with a sand cushion;
- formwork is installed;
- conduct reinforcement;
- pour concrete;
- apply a waterproofing coating, and if necessary, insulate, mount a drainage system.
Base parameters are calculated based on SNiP 2.02.01-83, which regulates the construction of building foundations, and using reference books (for example, V.S. Sazhina). They provide snow and wind loads for the region.
sole device
Work begins with marking. The sequence of actions is as follows:
- make a cast-off, which is perpendicular bars fixed on racks, with a height exceeding the same parameter of the base;
- arrange them in the corners according to the developed plan;
- to designate the outer planes of the walls along the upper bars, cords (ropes) are pulled around the perimeter;
- check the equality of the internal diagonals to get a square or rectangle.
Formwork installation and reinforcement
After marking the territory, earthworks begin:
- dig trenches, taking into account the margin of width for the installation of formwork and soles;
- make slopes;
- level the bottom of the recess;
- fill the trench with a sand cushion.
Land works should be carried out taking into account the following recommendations:
- the width of the trench in the presence of a basement or basement should take into account the place for mounting the formwork and provide free access for builders: the margin inward is from 0.5 to 0.8 m, and outward - 1.2 m;
- to avoid shedding at a depth of excavation equal to 1.5 m, the steepness of the slopes is made 1/1, and at 3 m it will be already 1/0.67;
- around the foundation trench, it is necessary to dig a 40x40 recess for the drainage system;
- the depth of the recesses must be done taking into account the thickness of the pillow, which is from 40 to 60 cm.
When the trenches are ready, then they proceed to the installation of the formwork and perform reinforcement:
- every 70 cm, vertical racks are driven into the ground along the lines marked with cast-off cords;
- boards are fixed to the stakes with screws or nails until the full height of the sole is reached;
- strengthen the structure with planks, nailing them to the top row;
- mount vertical reinforcing bars, the height of which is taken with a margin for connection with the overlying tape;
- fixed by welding or wire horizontal rods;
- pour the sole with concrete;
- ram it with a vibrator or manually;
- wait a few days for the concrete to partially harden.
Foundation tape on sole
Reinforcement bars are laid in at least two layers. The overlaps should be approximately 60 cm, and at the same time be offset from each other in the vertical and horizontal planes. The cross section of the rods used, depending on the design load, ranges from 8 to 16 mm. A knitting wire with a diameter of 1.2-1.6 mm is suitable for connecting the rods.
The erection of the tape part of the base
After the sole has been poured and the concrete has partially hardened, the formwork is installed under the top. Initially, according to the height of the tape, shields are made from boards or plywood (or other materials). Their length is determined from the convenience of handling them when performing work, and the thickness is determined by the level of future load created by concrete.
Subsequent actions for the construction of the foundation are carried out in the following sequence:
- mount the shields, leaning with their lower boards on the formwork structure of the lower part and combining them with the help of long beams (along the top and bottom);
- with the help of stretched cast-off ropes, as well as a level, the formwork is set in the required planes;
- shields located opposite each other are connected by horizontal ties;
- with the help of inclined struts, the formwork is fixed from the sides;
- inside the mounted structure, a reinforcing cage is laid in several rows, while it is connected to the sole bars;
- wet shields with water;
- pour the form with concrete in uniform layers, ramming it every 40-60 cm;
- for a uniform course of the solidification process, the base is covered with roofing felt or plastic wrap;
- periodically, the upper part of the monolith will be moistened with water (about a week or two, depending on climatic conditions).
When installing the formwork, special attention must be paid to the corners, connecting the panels there securely so that they do not disperse.
Concrete gains more than half its strength within about 7 days. Full solidification takes about a month, which is determined by temperature and humidity.
The formwork can be removed at least 3 days after the concrete has been poured. When it hardens, the basement and the underground part are recommended to be protected with a waterproofing coating. For these purposes, mastics, roofing material and other materials are used. Reliable protection against the destructive action of water will extend the life of the building under construction.
It is possible to install the formwork and reinforcement cage of the entire T-shaped base at once. You will still need to fill it in parts: first the sole, and only then the tape. This is due to the fact that the concrete of the lower part, if it does not harden enough, will be forced out. The tamping of the filled layers of the tape for the same reason will need to be carried out carefully.
Installation of a prefabricated foundation
The construction of a T-shaped strip foundation can be performed using reinforced concrete blocks. The technology for their installation is as follows:
- dig trenches below the freezing depth of the soil in the region;
- their bottom is covered with a pillow of sand, which is then rammed;
- stack blocks;
- connect them with each other with reinforcement;
- the joints are poured with concrete, having previously installed formwork in these places;
- they plaster the surface of the base, and after the applied coating dries, they waterproof and insulate.
The first row of the foundation is laid out with wider blocks (or trapezoidal) compared to those located above.
The use of blocks significantly speeds up the construction process, but requires the use of lifting equipment. Due to the presence of a large number of joints, the operating time of the foundation is reduced by about 3 times compared to monolithic counterparts. The standard dimensions of the blocks determine the choice of belt parameters.
The process of building a strip foundation of a t-shaped type is shown in the video below.
A T-shaped foundation is a reliable foundation that you can build yourself. The choice of concrete brand is determined by the future load on the base: material marked M100 and M150 is suitable for the construction of light structures, and from M200 to M400 for heavier ones. Waterproofing the sole and tape will help extend the life of the entire building.
Monolithic strip t-shaped foundation
Among the varieties of strip foundations, the T-shaped foundation is given a special place. It is used for various buildings.
Shallow strip foundation
A shallow or non-buried foundation requires careful and detailed consideration. It is obvious that such a design is less laborious in execution and economical due to the lower need for materials for construction and reducing the cost of earthworks. At the same time, in order to guarantee the reliability of the support, it is necessary to correctly select the type of structure, as well as calculate all the parameters. Subject to these conditions, foundations of this type will meet the requirements.
Classification of supports without significant penetration
Before proceeding with the construction of supports of this type with your own hands, familiarize yourself with the classification and nuances of the foundations of each type.
Support structure
There are main types of FMZ construction (shallow foundations):
If a pole is used for the walls of a light house or outbuilding, the individual poles are combined with a strapping or grillage to provide structural rigidity and more even load distribution.
Scheme of installation of a non-buried columnar foundation.
Plate supports are made with a thickness of 15-30 cm and are the most reliable. They are also suitable for installation on medium-heavy, water-saturated, weakly bearing soils.
Shallow slab foundation.
With a small mass of the structure, do-it-yourself construction of a more economical intermittent tape support is allowed. In other cases, it is recommended to lay the tape under the load-bearing or under all the walls of the building.
Tape FMZ with a rectangular section.
According to this criterion, FMZ are divided into rigid, capable of withstanding only the impact of compressive force, and flexible, also resistant to tension. Flexible supports include only structures made of reinforced concrete. Everyone else is tough
Preparation method
According to the method of production, an unburied foundation can be prefabricated (from ready-made blocks) or monolithic (filled).
Section shape
A shallow foundation can have various shapes of the tape section:
Base with a T-shaped section.
When manufacturing a trapezoidal structure, it is important to observe the load distribution angle (the angle between the perpendicular to the base and the inclined edge):
An increase in these values leads to an increase in tensile stresses.
Trapezoidal concrete blocks for prefabricated strip base.
The main stages in the manufacture of monolithic non-buried supports
“Do not dig foundations deep” is not an accurate enough recommendation, although it reflects the basic principle of building a FMZ with your own hands. For the reliability and durability of the support, accuracy and compliance with the technology at all stages of construction must be ensured.
We will consider the construction technology of the FMZ using the example of the production of tape structures. The manufacture of slab supports includes similar processes, but differs in nuances (calculation of the parameters of the foundation itself and its reinforcing elements).
Preparatory work
Preparation for the construction of the foundation includes digging a trench with your own hands or using equipment according to the markings made according to previously drawn up sketches and the installation of sand or sand and gravel backfill. An unburied foundation on a sand cushion will be more reliable if the backfill is carefully compacted by vibrotamping. In the construction of shallow supports, every opportunity should be used to increase the strength of the structure.
After that, a removable or fixed formwork is installed without fail to the entire required height. The build-up and layer-by-layer filling of the tape, which is sometimes recommended for supports of a different type, is not suitable for FMZ - they lead to the formation of seams and a decrease in the overall strength of the support.
Important: So that when pouring the mortar or subsequent ramming of concrete, the formwork does not deform and does not cause a change in the geometry of the base, it is important to securely fasten all elements during installation, paying special attention to the corners where the load will be maximum.
Reinforcement installation
The reinforcing frame for FMZ is calculated individually, taking into account the type of soil, the type of foundation and the existing loads, but there are also general principles by which a shallow foundation is reinforced.
- Reinforcement with a diameter of 14 mm or more has sufficient fracture and rupture strength.
- From the surface of the formwork to the rod and from the lower horizontal plane of the prepared trench to the reinforcement, distances of at least 5-7 cm must be maintained.
Trench with installed reinforcement for a shallow foundation.
- The frame consists of two pairs of parallel "threads" of reinforcement with an annular strapping that gives strength.
- The strapping is done with your own hands from the wire, preventing it from sagging between the reinforcement bars. It is undesirable to make a rigid ring by welding - in the places where the seams are made, the strength of the frame will be lower.
- The finished structure must be strong enough and rigid so as not to deform when pouring the solution.
Before filling the formwork with a mortar, it is better to perform a control markup in height, for example, by placing level marks on the corners of the tape and stretching a string between them.
It is optimal to fill the prepared channel evenly, supplying the solution alternately to different places, and not leveling the flow coming from one corner.
Pouring concrete into formwork.
Vibrotamping after pouring compacts the concrete and expels air from it. If it is impossible to use special equipment, it is possible to achieve shrinkage of concrete by evenly tapping the side walls of the formwork with your own hands with a hammer. Usually the result is immediately visible - the solution releases air, its level in the channel decreases slightly.
Waterproofing and water drainage
To ensure the durability of the structure, the unburied foundation is waterproofed with their own hands and atmospheric water is drained from the structure.
Waterproofing of the structure can be of two types:
- coating using bitumen or special mastic,
- pasting (roll materials are used).
The coating method is cheaper, but requires safety precautions due to the need to work with molten hot compounds.
Implementation of coating waterproofing.
Waterproofing with roll materials.
To protect the shallow foundation from atmospheric waters, a blind area is made around the perimeter of the structure.
Rice. 10. An example of a blind area device.
For private houses of 1-2 floors, a blind area 100 mm thick (sand or sand-gravel cushion, compacted soil, concrete layer) and 800 mm wide is sufficient. The slope of the blind area is provided by the method of filling and compacting the pillow materials and is carried out in the direction from the wall of the building.
Strip foundation not buried, not buried foundation
A shallow or non-buried foundation requires careful and detailed consideration. It is obvious that such a design is less laborious in execution and economical due to the lower need for materials for construction and reducing the cost of earthworks.
One of the most effective types of foundation, arranged for any structure - T-shaped strip foundation cost. Such a base is rigid, as there is a T-shaped profile. In the absence of water in the near layers of the soil, the T-strip foundation can not be deepened much. If the structure is massive, for example, a stone house, then the T-shaped strip foundation must be deepened by the amount of soil freezing. Our company has extensive experience in the construction of such foundations throughout the Leningrad region, and quality control of work at every stage allows us to guarantee the quality and exact timing of construction. To calculate the cost of the foundation, you can call us and get advice from an engineer on all your questions.
The price of a T-shaped strip foundation, prices in rubles
| tape, m * m | width height 300mm/600mm |
width height 300mm/900mm |
width height 300mm/1200mm |
width height 400mm/1500mm |
width height 400mm/1800mm |
|---|---|---|---|---|---|
| 6x6 | 67 000 rubles | 91 000 rubles | 120 000 rubles | 195 000 rubles | 224 000 rubles |
| 6x8 | 74 000 rubles | 108 000 rubles | 141 000 rubles | 247 000 rubles | 275 000 rub. |
| 8x8 | 80 000 rubles | 119 000 rubles | 161 000 rubles | 270 000 rubles | 330 000 rubles |
| 8x10 | 90 000 rubles | 127 000 rubles | 171 000 rubles | 293 000 rub. | 371 000 rubles |
| 10x10 | 100 000 rubles | 143 000 rubles | 200 000 rubles | 322 000 rubles | 390 000 rub. |
| 10x12 | 121 000 rubles | 195 000 rubles | 270 000 rubles | 375 000 rub. | 450 000 rubles |
| 12x12 | 133 000 rubles | 181 000 rubles | 303 000 rubles | 408 000 rubles | 507 000 rubles |
|
*Provided that the site has electricity, water and living conditions for the brigade. Included in the price: Planning and marking of the site for the foundation Earthworks, excavation, trenches The device of a sand cushion under the foundation Board formwork installation Rebar knitting Pouring concrete The cost of the foundation includes materials with delivery to your facility (within a radius of the city) We also carry out additional work on the installation of drainage systems, waterproofing and insulation of the foundation, we make wells for water supply, install septic tanks and treatment plants. ** You can find out the more exact cost of a turnkey strip foundation by calling us. |
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T-shaped strip foundation
The T-shaped strip foundation is laid in almost the same way as a conventional strip. The peculiarity lies only in the arrangement of a kind of formwork so that the concrete mixture does not flow out. It is important to achieve a perfectly even angle between the main foundation and the superstructure plane. The foundation structure is reinforced with reinforcement.
T-strip foundation can be built for houses, fences, sheds. The main advantage is the ability to save on materials, because the thickness of the above-ground part is less.
To avoid mistakes, it is better to entrust the T-shaped strip foundation to qualified builders. In our company you will be able to find both the qualified assistance of a team of builders and the necessary high-quality foundation materials.
The strip foundation has a non-standard geometry: its length is tens of times greater than the depth and width. Due to this design, almost all loads are distributed along the belt. On its own, a concrete stone cannot compensate for these loads: its bending strength is not enough. To give the structure increased strength, not just concrete is used, but reinforced concrete - this is a concrete stone with steel elements located inside - steel reinforcement. The process of laying metal is called strip foundation reinforcement. It is not difficult to make it with your own hands, the calculation is elementary, the schemes are known.
The quantity, location, diameters and grade of reinforcement - all this should be spelled out in the project. These parameters depend on many factors: both on the geological situation on the site and on the mass of the building being erected. If you want to have a guaranteed strong foundation, a project is required. On the other hand, if you are building a small building, you can try to do everything yourself, based on general recommendations, including designing a reinforcement scheme.
Reinforcement scheme
The location of the reinforcement in the strip foundation in cross section is a rectangle. And there is a simple explanation for this: this scheme works best.
Reinforcement of the strip foundation with a strip height of not more than 60-70 cm
Two main forces act on the strip foundation: from below, in frost, heaving forces press, from above, the load from the house. At the same time, the middle of the tape is almost not loaded. To compensate for the action of these two forces, two belts of working reinforcement are usually made: top and bottom. For shallow and medium-depth foundations (up to 100 cm deep), this is enough. For deep belts, already 3 belts are required: too high a height requires reinforcement.
In order for the working reinforcement to be in the right place, it is fixed in a certain way. And they do it with the help of thinner steel rods. They do not participate in the work, they only hold the working reinforcement in a certain position - they create a structure, which is why this type of reinforcement is called structural.
As can be seen in the reinforcement scheme of the strip foundation, the longitudinal bars of the reinforcement (workers) are tied up with horizontal and vertical supports. Often they are made in the form of a closed loop - a collar. It is easier and faster to work with them, and the design is more reliable.
What fittings do you need
For the strip foundation, two types of bar are used. For longitudinal, which carry the main load, class AII or AIII is required. Moreover, the profile is necessarily ribbed: it adheres better to concrete and transfers the load normally. For structural lintels, cheaper fittings are taken: smooth first class AI, 6-8 mm thick.
Recently, fiberglass reinforcement has appeared on the market. According to manufacturers, it has better strength characteristics and is more durable. But many designers do not recommend using it in the foundations of residential buildings. According to the regulations, it should be reinforced concrete. The characteristics of this material have long been known and calculated, special reinforcement profiles have been developed that contribute to the fact that metal and concrete are combined into a single monolithic structure.
How concrete will behave paired with fiberglass, how firmly such reinforcement will adhere to concrete, how successfully this pair will resist loads - all this is unknown and has not been studied. If you want to experiment - please use fiberglass. No - take iron fittings.
Do-it-yourself calculation of the reinforcement of the strip foundation
Any construction work is standardized by GOSTs or SNiPs. Reinforcement is no exception. It is regulated by SNiP 52-01-2003 "Concrete and reinforced concrete structures". This document indicates the minimum amount of reinforcement required: it must be at least 0.1% of the cross-sectional area of \u200b\u200bthe foundation.
Determination of reinforcement thickness
Since the strip foundation in the section has the shape of a rectangle, the cross-sectional area is found by multiplying the lengths of its sides. If the tape has a depth of 80 cm and a width of 30 cm, then the area will be 80 cm * 30 cm \u003d 2400 cm 2.
Now you need to find the total area of \u200b\u200bthe reinforcement. According to SNiP, it should be at least 0.1%. For this example, this is 2.8 cm 2 . Now, using the selection method, we determine the diameter of the bars and their number.
Quotes from SNiP that relate to reinforcement (to enlarge the picture, click on it with the right mouse button)
For example, we plan to use rebar with a diameter of 12 mm. Its cross-sectional area is 1.13 cm 2 (calculated by the formula for the area of a circle). It turns out that in order to provide recommendations (2.8 cm 2), we need three rods (or they also say “threads”), since two are clearly not enough: 1.13 * 3 \u003d 3.39 cm 2, which is more than 2.8 cm 2 recommended by SNiP. But three threads cannot be divided into two belts, and the load will be significant on both sides. Therefore, four are laid, laying a solid margin of safety.
In order not to bury extra money in the ground, you can try to reduce the diameter of the reinforcement: calculate under 10 mm. The area of this rod is 0.79 cm 2 . If we multiply by 4 (the minimum number of bars of working reinforcement for a tape frame), we get 3.16 cm 2, which is also enough with a margin. So for this version of the strip foundation, you can use class II ribbed reinforcement with a diameter of 10 mm.
Reinforcement of the strip foundation for the cottage is carried out using bars with different types of profile
Installation step
For all these parameters, there are also methods and formulas. But for small buildings, it's easier. According to the recommendations of the standard, the distance between horizontal branches should not be more than 40 cm. They are guided by this parameter.
How to determine at what distance to lay reinforcement? In order for steel not to corrode, it must be embedded in concrete. The minimum distance from the edge is 5 cm. Based on this, the distance between the bars is calculated: both vertically and horizontally, it is 10 cm less than the dimensions of the tape. If the width of the foundation is 45 cm, it turns out that there will be a distance of 35 cm between the two threads (45 cm - 10 cm = 35 cm), which corresponds to the standard (less than 40 cm).
The reinforcement step of the strip foundation is the distance between two longitudinal bars
If we have a tape of 80 * 30 cm, then the longitudinal reinforcement is located one from the other at a distance of 20 cm (30 cm - 10 cm). Since two reinforcement belts are required for medium-level foundations (up to 80 cm high), one belt from the other is located at a height of 70 cm (80 cm - 10 cm).
Now about how often to put jumpers. This standard is also in SNiP: the installation step of vertical and horizontal dressings should be no more than 300 mm.
All. Do-it-yourself reinforcement of the strip foundation was calculated. But keep in mind that neither the mass of the house nor the geological conditions were taken into account. We were based on the fact that these parameters were based on .
Corner reinforcement
In the design of the strip foundation, the weakest point is the corners and the junction of the walls. In these places, loads from different walls are connected. In order for them to be successfully redistributed, it is necessary to correctly bandage the reinforcement. Just connect it incorrectly: this method will not ensure the transfer of the load. As a result, after some time, cracks will appear in the strip foundation.
The correct scheme for reinforcing corners: either drives are used - L-shaped clamps, or longitudinal threads are made 60-70 cm longer and bent around the corner
To avoid this situation, when reinforcing corners, special schemes are used: the bar is bent from one side to the other. This "overlap" should be at least 60-70 cm. If the length of the longitudinal bar for bending is not enough, use L-shaped clamps with sides also at least 60-70 cm. The diagrams of their location and fastening of the reinforcement are shown in the photo below.
By the same principle, the adjoining walls are reinforced. It is also advisable to take the reinforcement with a margin and bend it. It is also possible to use L-shaped clamps.
Reinforcement scheme for adjoining walls in a strip foundation (to enlarge the picture, click on it with the right mouse button)
Please note: in both cases, in the corners, the installation step of the transverse jumpers is halved. In these places, they are already becoming workers - they are participating in the redistribution of the load.
Reinforcement of the sole of the strip foundation
On soils with not very high bearing capacity, on heaving soils or under heavy houses, strip foundations are often made with a sole. It transfers the load over a large area, which gives greater stability to the foundation and reduces the amount of subsidence.
So that the sole does not fall apart from pressure, it also needs to be reinforced. The figure shows two options: one and two belts of longitudinal reinforcement. If the soils are complex, with a strong tendency to winter baking, then two belts can be laid. With normal and medium soils, one is enough.
Reinforcement bars laid in length are working. They, as for the tape, take the second or third class. They are located from each other at a distance of 200-300 mm. They are connected using short pieces of rod.
Two ways of reinforcing the sole of the strip foundation: on the left for bases with normal bearing capacity, on the right - for not very reliable soils
If the sole is not wide (rigid scheme), then the transverse segments are constructive, they do not participate in the distribution of the load. Then they are made with a diameter of 6-8 mm, bent at the ends so that they cover the extreme bars. Tied to everyone with a knitting wire.
If the sole is wide (flexible), the transverse reinforcement in the sole is also working. She resists the ground's attempts to "collapse" her. Therefore, in this version, the soles use ribbed reinforcement of the same diameter and class as the longitudinal one.
How much rod do you need
Having developed a strip foundation reinforcement scheme, you know how many longitudinal elements you need. They fit around the perimeter and under the walls. The length of the tape will be the length of one reinforcing bar. Multiplying it by the number of threads, get the required length of the working reinforcement. Then add 20% to the resulting figure - the margin for joints and "overlaps". That's how much in meters you will need working fittings.
Now you need to calculate the amount of structural reinforcement. Consider how many cross jumpers should be: divide the length of the tape by the installation step (300 mm or 0.3 m, if you follow the recommendations of SNiP). Then you calculate how much it takes to make one jumper (add the width of the reinforcing cage with the height and double it). Multiply the resulting figure by the number of jumpers. Add 20% to the result (for connections). This will be the amount of structural reinforcement for reinforcing the strip foundation.
By a similar principle, consider the amount that is needed to reinforce the sole. Putting it all together, you will find out how much reinforcement you need for the foundation.
Technologies for assembling reinforcement for a strip foundation
Do-it-yourself reinforcement of the strip foundation begins after installation. There are two options:
Both options are not ideal and everyone decides how it will be easier for him. When working directly in the trench, you need to know the procedure:
- The longitudinal bars of the lower armored belt are laid first. They need to be raised 5 cm from the edge of the concrete. It is better to use special legs for this, but pieces of bricks are popular with developers. Reinforcement is also spaced 5 cm from the formwork walls.
- Using transverse pieces of structural reinforcement or molded contours, they are fixed at the required distance using a tie wire and a hook or a tie gun.
- Next, there are two options:
- If contours shaped in the form of rectangles were used, the upper belt is immediately tied to them at the top.
- If during installation cut pieces are used for transverse jumpers and vertical racks, then the next step is to tie up the vertical racks. After they are all tied, the second belt of longitudinal reinforcement is tied.
There is another technology for reinforcing a strip foundation. The frame turns out to be rigid, but there is a large consumption of the bar for vertical racks: they are driven into the ground.
The second technology for reinforcing the strip foundation - first, vertical racks are driven in, longitudinal threads are tied to them, and then everything is connected by transverse ones.
- First, vertical posts are driven in at the corners of the tape and at the junctions of the horizontal bars. Racks should have a large diameter of 16-20 mm. They are set at a distance of at least 5 cm from the edge of the formwork, checking the horizontal and vertical, they are driven into the ground by 2 meters.
- Then vertical bars of the calculated diameter are hammered. We determined the installation step: 300 mm, in the corners and at the junction of the walls it is half as much - 150 mm.
- Longitudinal threads of the lower reinforcement belt are tied to the racks.
- At the intersection of racks and longitudinal reinforcements, horizontal jumpers are tied.
- The upper reinforcement belt is tied up, which is located 5-7 cm below the upper surface of the concrete.
- Attached horizontal jumpers.
It is most convenient and fastest to make a reinforcing belt using preformed contours. The rod is bent, forming a rectangle with the given parameters. The whole problem is that they must be made the same, with minimal deviations. And it takes a lot of them. But then the work in the trench moves faster.
As you can see, reinforcing a strip foundation is a lengthy and not the easiest process. But you can cope even alone, without helpers. It will take, however, a lot of time. It is more convenient to work together with two or three people: both to carry the bars and to expose them.
Any building, regardless of its purpose, is unthinkable without a reliable foundation. The construction of the foundation is one of the most important and natural tasks of the entire construction cycle as a whole, and this stage, by the way, is often one of the most time-consuming and costly - often up to a third of the estimate is spent on it. But at the same time, any simplifications, unreasonable savings on the quality and quantity of the necessary materials, disregard for the current rules and technological recommendations should be absolutely excluded here.
Of all the variety of foundation structures, tape is the most popular, as the most versatile, suitable for most houses and outbuildings being built in the field of private construction. Such a base is highly reliable, but, of course, with its high-quality performance. And the key condition for strength and durability is the well-planned and properly carried out reinforcement of the strip foundation, the drawings and the basic principles of the device of which will be considered in this publication.
In addition to the diagrams, the article will provide several calculators that will help the novice builder in this rather difficult task of creating a strip foundation.
General concepts. Advantages of strip foundation
So, in short, a few general concepts about the device strip foundation. By itself, it is a continuous concrete strip, without gaps for door or gate openings, which becomes the basis for the construction of all external walls and capital internal partitions. The tape itself is buried at a certain calculated distance into the ground and at the same time protrudes from above with its basement. The width of the tape and the depth of its laying, as a rule, is maintained uniform throughout the entire length of the foundation. This form contributes to the most uniform distribution of all loads falling on the base of the building.
Strip foundations can also be divided into several varieties. So, they are not only poured from concrete, but also made prefabricated, using, for example, special reinforced concrete foundation blocks, or using rubble filling. However, since our article is devoted to reinforcement, in the future only a monolithic version of the foundation tape will be considered.
The strip foundation can be attributed to the universal type of foundations. This scheme is usually preferred in the following cases:
- When building houses from heavy materials - stone, brick, reinforced concrete, building blocks and the like. In a word, when it is required to evenly distribute a very significant load on the ground.
- When the developer plans to get a full-fledged basement or even a basement at his disposal, only a tape scheme can allow this.
- During the construction of multi-level buildings, with the use of heavy interfloor ceilings.
- When a building plot is characterized by heterogeneity of the upper layers of the soil. The only exceptions are completely unstable soils, when the creation of a strip foundation becomes impossible or unprofitable, and it makes sense to turn to another scheme. A strip foundation is also impossible in regions with permafrost.
A monolithic strip foundation has a considerable number of other advantages, which include durability, estimated for many decades, the relative simplicity and clarity of construction, ample opportunities in terms of laying engineering communications and organizing insulated floors on the first floor. In terms of its strength properties, it is not inferior to monolithic slabs, and even surpasses them, while requiring less material costs.
However, one should not think that the strip foundation is an absolutely invulnerable structure. All of the above advantages will be valid only if the parameters of the foundation being built for the house correspond to the conditions of the construction area, the design load, and have a built-in safety margin. And this, in turn, means that special requirements are always imposed on the design of the foundation (any, by the way). And the reinforcement of the tape in a series of these problems occupies one of the key positions.
The width of the foundation tape and the depth of its laying
These are two key parameters on which the very scheme of reinforcing the future foundation tape will depend.
But the degree of penetration into the ground strip foundations can be divided into two main categories:
- A shallow strip foundation is suitable for the construction of frame structures, small country houses and outbuildings, provided there is sufficiently stable, dense soil on the site. The sole of the tape is located above the freezing boundary of the soil, that is, it usually does not fall below 500 mm, excluding the basement.
- For buildings constructed from heavy materials, as well as in areas where the condition of the soil is not stable, deep tape is required. Its sole already falls below the freezing level of the soil, at least by 300 ÷ 400 mm, and if there is also a basement (basement) in the construction plans, even lower.
It is clear that the height of the foundation strip as a whole, including the depth of its occurrence, is by no means arbitrary values, but parameters that are obtained as a result of carefully performed calculations. When designing, a whole array of initial data is taken into account: the type of soils on the site, the degree of their stability both in the surface layers, and the change in structure as they deepen; climatic features of the region; presence, location and other features of ground aquifers; seismic characteristics of the area. Plus, the specificity of the building planned for construction is superimposed - the total load, both static, created only by the mass of the structure (of course, taking into account all its constituent elements), and dynamic, caused by operational loads, and all kinds of external influences, including wind, snow and others.
Based on the foregoing, it would be appropriate to make one important remark. The fundamental position of the author of these lines is that the calculation of the basic parameters of the foundation tape does not tolerate an amateurish approach.
Despite the fact that on the Internet you can find many online applications for carrying out such calculations, it would still be more correct to entrust the issue of designing the foundation to specialists. At the same time, the correctness of the proposed calculation programs is not in the least disputed - many of them fully comply with the current SNiP and are capable of really producing accurate results. The problem lies in a slightly different plane.
The bottom line is that any, even the most advanced calculation program, requires accurate input data. But in this matter, it is impossible to do without special training. Agree that it is correct to assess the geological features of the site for construction, to take into account all the loads that fall on the foundation tape, and - with their expansion along the axes, to provide for all possible dynamic changes - a non-professional simply cannot do it. But each initial parameter matters, and underestimating it may well then "play a cruel joke."
True, if it is planned to build a small country house or an outbuilding, then inviting a specialist designer may seem like an excessive measure. Well, at your own peril and risk, the owner can build a shallow strip foundation, using, for example, the approximate parameters that are shown in the table below. For light buildings, a heavily buried tape is not required (a large depth can even play a negative role, due to the application of tangential forces during frosty swelling of the soil). As a rule, in such cases they are limited to a maximum depth of the sole of 500 mm.
| Type of building under construction | Barn, sauna, outbuildings, small garage | One-story country house, including - with an attic | One- or two-story cottage, designed for permanent residence | Two or three story mansion |
|---|---|---|---|---|
| Average soil load, kN/m² | 20 | 30 | 50 | 70 |
| SOIL TYPES | RECOMMENDED DEPTH | TAPE INSTALLATIONS | (EXCLUDING THE GROUND | FOUNDATION PARTS) |
| Pronounced stony ground, flask | 200 | 300 | 500 | 650 |
| Dense clay, loam that does not disintegrate after being compressed by the force of the palm | 300 | 350 | 600 | 850 |
| Packed dry sand, sandy loam | 400 | 600 | Professional foundation calculation required | |
| Soft sand, silt or sandy loam | 450 | 650 | Professional foundation calculation required | Professional foundation calculation required |
| Very soft sand, silt or sandy loam | 650 | 850 | Professional foundation calculation required | Professional foundation calculation required |
| peat bog | Requires a different type of foundation | Requires a different type of foundation | Requires a different type of foundation |
We emphasize once again that these are only average values that cannot be considered as the ultimate truth. In any case, if an amateur builder uses such sources, he takes a certain risk on his own responsibility.
Now - about the width of the foundation tape.
It also has its own characteristics. Firstly, to ensure the rigidity of the foundation structure, it is customary to adhere to the rule that the total height of the tape should be at least twice its width - but this rule is not difficult to follow. And the second - the width of the tape in the sole area should be such that the distributed load is less than the calculated parameters of soil resistance, of course, also with a certain design margin. In a word, the foundation tape with a full load should stand stably, without sinking into the ground. In order to save materials, often to increase the area of \u200b\u200bsupport, the sole of the strip foundation is made with a broadening.
Probably, it makes no sense to give here formulas and tabular values of soil resistance for independent calculations. The reason is the same: not so much the difficulty in performing calculations, but the problems with the correct determination of the initial parameters. That is, again, it is better to turn to professionals on such issues.
Well, if a light structure or a country house is being built, then you can be guided by the fact that the width of the tape should be at least 100 mm more than the thickness of the walls being built. As a rule, when planning the foundation independently, they take round values that are multiples of 100 mm, usually starting from 300 mm and above.
Foundation tape reinforcement
If a specialist is engaged in the design of a strip foundation, then the finished drawing will, of course, include not only the linear parameters of the concrete belt itself, but also the characteristics of the reinforcement - the diameter of the reinforcing bars, their number and spatial arrangement. But in the case when a decision is made to independently erect a foundation for a building, when planning the structure, it is necessary to take into account certain rules established by the current SNiP.
What fittings are suitable for these purposes?
For proper planning, you need at least a little understanding of the assortment of reinforcement.
There are several criteria for classifying reinforcement. These include:
- Production technology. So, the fittings are wire (cold-rolled) and rod (hot-rolled).
- According to the type of surface, reinforcing bars are distinguished into smooth and having a periodic profile (corrugation). The profile surface of the reinforcement ensures maximum contact with the poured concrete.
- Reinforcement can be designed for conventional or prestressed concrete structures.
To create a reinforcing structure for a strip foundation, as a rule, reinforcement is used that is produced in accordance with GOST 5781. This standard includes hot-rolled products intended for reinforcing conventional and preloaded structures.
In turn, these fittings are distributed into classes, from A-I to A-VI. The difference mainly lies in the grades of steel used for the production and, therefore, in the physical and mechanical properties of the products. If low-carbon steel is used in the fittings of the initial classes, then in the products of high classes the parameters of the metal are close to alloyed steels.
It is not necessary to know all the characteristics of reinforcement classes during self-construction. And the most important indicators that will affect the creation of the reinforcing cage are shown in the table. The first column shows the reinforcement classes according to the two designation standards. So, in brackets there is a designation of classes, the digital designation of which shows the yield strength of the steel used for the production of reinforcement - when purchasing material, such indicators may appear in the price list.
| Reinforcement class according to GOST 5781 | steel grade | Rod diameters, mm | Permissible cold bending angle and minimum radius of curvature when bending (d - rod diameter, D - bending mandrel diameter) |
|---|---|---|---|
| A-I (A240) | St3kp, St3sp, St3ps | 6÷40 | 180º; D=d |
| A-II (A300) | St5sp, St5ps | 10÷40 | 180º; D=3d |
| -"- | 18G2S | 40÷80 | 180º; D=3d |
| AC-II (AC300) | 10GT | 10÷32 | 180º; D=d |
| A-III (A400) | 35GS, 25G2S | 6÷40 | 90º; D=3d |
| -"- | 32G2Rps | 6÷22 | 90º; D=3d |
| A-IV (A600) | 80C | 10÷18 | 45º; D=5d |
| -"- | 20HG2C, 20HG2T | 10÷32 | 45º; D=5d |
| A-V (A800) | 23X2G2T, 23X2G2C | 10÷32 | 45º; D=5d |
| A-VI (A1000) | 22H2G2AYU, 20H2G2SR, 22H2G2R | 10÷22 | 45º; D=5d |
Pay attention to the last column, which indicates the allowable bending angles and curvature diameters. This is important from the point of view that when creating a reinforcing structure, you come to manufacture bent elements - clamps, inserts, paws, etc. In the manufacture of conductors, mandrels or other devices for bending, it is necessary to focus on these values, since a decrease in the bending radius or exceeding the angle can lead to a loss of strength properties by the reinforcement.
Rods of class A-I are produced in a smooth version. All other classes (with some exceptions, which, however, are more dependent on the individual requirements of the customer) are with a periodic profile.
For a strip foundation in private construction, the best choice would be class A-III reinforcement, in extreme cases - A-II, with a diameter of 10 mm and above.
For the structural elements of the armored belt (clamps, jumpers), it is convenient to use a smooth rod of class A-I, with a diameter of 6 or 8 mm. The use of reinforcement of higher classes is unprofitable, due to its high cost with a clear lack of demand in such high physical and technical indicators.
"Classic" scheme of reinforcing the foundation tape. Number of longitudinal rods
To begin with, let's consider a typical reinforcement scheme for straight sections of the foundation tape.
It is based on a rectangle, with mandatory levels of reinforcement at the top and bottom, made of longitudinal reinforcement (pos. 1), which are interconnected by horizontal transverse (pos. 2) and vertical reinforcements, thereby creating a kind of “box-shaped” structure. Such an arrangement of the belts makes it possible to maximally compensate for two main multidirectional forces: from the total load created by the building, and from frost swelling of the soil. In this case, the central part of the tape is loaded the least, and if the foundation has a total height of up to 800 mm, then two belts are most often enough.
For higher belts, the arrangement of longitudinal belts in three or more tiers is used. But, as already mentioned, to calculate such foundations on your own is a rather risky task.
The illustration shows the linking of longitudinal rods into a three-dimensional structure using pieces of reinforcement. This approach is quite acceptable, however, it is not convenient. The work will go much faster and better if you prepare clamps according to the size of the armored belt on the conductor in advance, and then link all the details into a common design.
Pay attention to the illustration, in which the arrows show two dimensions: H - the height of the reinforcement belt and K - its width. It should be correctly understood that this is not the height and width of the tape at all. The metal parts of the foundation must necessarily be protected from oxygen corrosion by a layer of concrete. According to SNiP, the minimum layer is 10 mm, but for a strip foundation, 50 mm to the edge of the concrete structure will be optimal. This must be taken into account when planning, and during installation, simple devices will help to maintain the necessary clearances between the reinforcement and the formwork. So, you can set the desired distance from the bottom of the formwork by placing fragments of bricks or by installing special plastic racks under the lower rods.
And the required clearance from the side walls of the formwork can be observed if you use special fasteners - "stars" that are simply put on the reinforcing bars.
Now - closer to the question of how many rods of longitudinal reinforcement are still needed, and what diameter they should be.
| Reinforcement area | Minimum rebar diameter |
|---|---|
| Longitudinal working reinforcement on straight sections with a length of not more than 3 meters | 10 mm |
| The same, but with a section length exceeding 3 meters | 12 mm |
| Transverse reinforcement and clamps of compressed structural elements. | Not less than 0.25 of the diameter of the working reinforcement, and at the same time - not less than 6 mm |
| Transverse reinforcement and clamps in the area of bent knitted frames | 6 mm |
| Clamps for a tape knitted frame with a height of not more than 800 mm | 6 mm |
| The same, but with a knitted frame height of more than 800 mm | 8 mm |
Well, the number of longitudinal rods necessary to ensure the calculated strength of the foundation tape directly depends on its size and on the diameter of the reinforcement used. In accordance with the current requirements of SNiP, the total cross-sectional area of the longitudinal reinforcement rods must be at least 0.1% of the cross-sectional area of \u200b\u200bthe tape. Based on this, it is easy to make the necessary calculation. To make it even easier for the reader, the corresponding calculator is placed below.
