Foundation reinforcement is a process necessary to strengthen the structure and increase the life of the building. In other words, this is an assembly of a "skeleton", which plays the role of a protective component that restrains the pressure of the soil on the walls of the base. But in order to given function was implemented to the maximum extent, it is necessary not only to correctly calculate the reinforcement for strip foundation but also to know how to organize the progress of construction work.
The basis of the tape type foundation is a concrete mortar consisting of cement, sand and water. Unfortunately, the physical characteristics of the building material do not guarantee the absence of deformation of the building foundation. To increase the ability to withstand foundation shifts, temperature extremes and other negative factors, the presence of a metal in the structure is necessary.
This material is plastic, but provides reliable fixation, so reinforcement is a significant stage in the complex of works.
Reinforcement for strip foundation - steel bar with stiffeners
Reinforcement of the foundation is required in places where tension zones can occur. It is noted that the greatest tension appears on the surface of the base, which creates the prerequisites for reinforcement close to the upper level. On the other hand, in order to avoid corrosion of the frame, it must be protected from external influences by a layer of concrete.
Important! The optimal distance of reinforcement for the foundation is 5 cm from the surface.
Since it is impossible to predict the progress of deformation, tension zones can occur both in the lower part (when the middle bends down) and in the upper part (when the frame bends up). Based on this, reinforcement should pass from above and below with reinforcement with a diameter of 10-12 mm, and this reinforcement for strip foundations should have a ribbed surface.
This ensures perfect contact with the concrete.
Tensile zones of the strip foundation
The remaining parts of the skeleton (horizontal and vertical transverse bars) may have a smooth surface and a smaller diameter.
When reinforcing a monolithic strip foundation, the width of which usually does not exceed 40 cm, it is allowed to use 4 reinforcement rods (10-16 m) connected into a frame with a diameter of 8 mm.
Important! The distance between the horizontal bars (with a width of 40 cm) is 30 cm.
The strip foundation has, with a large length, a small width, so longitudinal tensions will appear in it, while there will be no transverse ones at all. It follows from this that transverse vertical and horizontal rods, which will be smooth and thin, are needed only to create a frame, and not to accept loads.
Reinforcement of corners must be given special attention
Special attention it is necessary to pay attention to the reinforcement of the corners: there are often cases when the deformation occurs not in the middle, but in the corner parts. The corners should be reinforced so that one end of the bent reinforcement goes into one wall, and the other into another.
Experts advise connecting rods with a wire. After all, not every type of reinforcement is made from steel that can be welded. But even if welding is acceptable, problems often arise that can be avoided by using wire, for example, overheating of the steel, leading to a change in properties, thinning of the rod at the welding site, insufficient strength of the weld, etc.
Scheme of the construction of the reinforcing structure
Reinforcement begins with the installation of formwork, the inner surface of which is laid out with parchment, which makes it easier to remove the structure in the future. The frame is created according to the scheme:
1. Reinforcing bars are driven into the soil of the trench with a length equal to the depth of the base. A distance from the formwork of 50 mm and a step of 400-600 mm should be observed.
2. Stands (80-100 mm) are installed on the bottom, on which 2-3 threads of the lower row of reinforcement must be laid. As supports, bricks mounted on an edge are quite suitable.
3. The upper and lower row of reinforcement are fixed together with the transverse jumpers to the vertical pins.
4. At the intersections, fastening is carried out by tying with wire or welding.
The video will introduce convenient way reinforcement knitting using a template:
Important! The distance to the outer surfaces of the future base should be strictly observed. Do it better with bricks. This is one of the most important conditions, because metal structures should not be based directly on the bottom. They must be raised above ground level by at least 8 cm.
After installing the fittings, it remains to make ventilation holes and pour the concrete solution.
You need to know!
Ventilation holes not only contribute to the improvement of the depreciation characteristics of the foundation, but also prevent the appearance of putrefactive processes.
Calculation of material consumption
To calculate the strip foundation, you need to know some parameters in advance. Let's look at an example. Suppose our foundation has a rectangular shape and the following dimensions: width - 3.5 meters, length - 10 meters, casting height - 0.2 meters, belt width - 0.18.
First of all, you need to calculate the total volume of the casting, for which you need to find out the dimensions of the basis as if it had the shape of a parallelepiped. To do this, we will perform a few simple manipulations: find out the perimeter of the base, and then multiply the perimeter by the width and height of the casting.
P \u003d AB + BC + CD + AD \u003d 3.5 + 10 \u003d 3.5 + 10 \u003d 27
V \u003d 27 x 0.2 x 0.18 \u003d 0.972
But on this account monolithic foundation does not end. We learned that the base itself, or rather the casting, occupies a rounded volume of 0.97 m3. Now you need to find out the volume of the inner part of the foundation, i.e. what is inside our tape.
We get the volume of the "filling": we multiply the width and length of the base by the height of the casting and find out the total volume:
10 x 3.5 x 0.2 = 7 (cubic meters)
We subtract the volume of the casting:
7 - 0.97 = 6.03 m3
The result: the volume of the casting is 0.97 m3, the internal volume of the filler is 6.03 m3.
Now you need to calculate the amount of reinforcement. Let's say the diameter will be 12 mm, in the casting - 2 horizontal threads, i.e. 2 rods, and vertically, for example, the rods will be located every half meter. The perimeter is known - 27 meters. So, we multiply 27 by 2 (horizontal bars) and we get 54 meters.
Vertical rods: 54/2 + 2 = 110 rods (108 intervals of 0.5 m and two at the edges). We add one more rod per corner and we get 114 rods.
Let's say the height of the rod is 70 cm. It turns out: 114 x 0.7 = 79.8 meters.
The final touch is the formwork. Suppose we will build it from boards 2.5 cm thick, 6 meters long and 20 cm wide.
We calculate the area of the side surfaces: we multiply the perimeter by the height of the casting, and then by 2 (with a margin, not taking into account the decrease in the inner perimeter against the outer one): (27 x 0.2) x 2 = 10.8 m2
Board area: 6 x 0.2 = 1.2 m2; 10.8/1.2 = 9
We need 9 boards 6 meters long. Don't forget to add connection boards (optional).
Result: 1 m3 of concrete is required; 6.5 m3 aggregate; 134 meters of reinforcement and 27 linear meters of boards (20 cm wide), screws and bars. Values shown have been rounded off.
results of painstaking settlement work
Now you know not only how to properly reinforce the strip foundation, but also how to calculate the necessary components. And this means that the foundation built by you will be reliable and strong, allowing the construction of monolithic structures of any configuration.
Even if you roughly calculate the cost of pouring a strip foundation for a private house of any size, it becomes clear that up to 30% of the total construction estimate is spent on the construction of the foundation. But this is the case if the developer buys absolutely everything - from concrete and its delivery and pouring to the labor of workers on the site. This also includes the cost of steel or fiberglass reinforcement and knitting of the reinforcement cage. But a correctly drawn up scheme for reinforcing a strip foundation or reinforcing a pile screw structure plus independently performed work (meaning all construction works, which can be done on your own) allow you to save the budget by 100-140%!
Basics of reinforcement
Reliable is the error-free implementation of the process of strengthening the concrete structure in accordance with the norms of SNiP 52-01-2003, SNiP II-21-75 and SN 511-78 and other regulatory documents. What are the most common mistakes that affect the reliability, strength and durability of the tape base:
- Reinforcing frame for concrete foundation tape low-rise building it is recommended to make from corrugated metal rods Ø 10-24 mm or from fiberglass rods;
- It is strictly forbidden to connect reinforcement intersections by welding, it is only possible to connect rods with soft knitting wire Ø 3-5 mm. Electric arc welding is ultra-high temperatures, under the influence of which the metal overheats and loses its strength properties by 150-200%, especially at the joints of perpendicular intersections;
- If there is a homogeneous soil on the foundation laying area, it is allowed to use thinner rods of metal or fiberglass reinforcement - Ø up to 14 mm. With heterogeneous soil layers, reinforcing rods must be at least 16 mm in diameter;
- Only corrugated rods are used - smooth rods adhere worse to concrete, and all mathematical calculations related to the strength and loads on the foundation are designed specifically for the use of corrugated rods. Smooth rods are allowed to be used in the reinforcement cage only for the formation of transverse fasteners, since in these areas the load on the concrete and the reinforcement cage is small;
- Longitudinal reinforcement bars in the body of the concrete strip must be located at a distance of ≥ 5 cm from the side, top and bottom walls of the formwork. If the reinforcement is bare, then corrosion will quickly eat it, while the concrete will collapse in parallel with the corrosion of the metal - crumble, crack, swell;
- A distance of 30-45 cm is observed between the transverse reinforcement;
- The reinforcement of the corners of the tape-type foundation is carried out according to a different scheme from the standard knitting. This issue will be discussed separately below;
- Also, the reinforcement of the strip foundation provides for the laying of longitudinal reinforcement every 40 cm along the height of the tape. That is, if the height of the foundation is 160 cm, then four longitudinal rows of rods must be laid.
Self-assembly of formwork
Properly mounted, it will not only save the construction budget by reducing the consumption of concrete mortar, but will also make the work of reinforcing the base much easier and faster.
- The material for assembling the decks (shields) of the formwork can be very different: if the height of the base is not more than 1.5 meters, then thick plywood, slabs (unedged boards), sheets of OSB, fiberboard or chipboard, slate, sheet metal, etc. . The main requirement for the formwork is that it can withstand the pressure of the mortar and soil. For foundations with a height of more than one and a half meters, it is recommended to do it only because of the high pressure on its walls;
- Preparatory work on the installation of formwork begins compacting the bottom of the trench. To do this, a sand cushion is made with a layer of 15 cm, moistened and rammed, and a 5 cm layer of concrete mortar is poured on top of the sand to level the sole. If through the body of the foundation will pass engineering Communication(water supply, sewerage, heating or communications), then holes for them are pre-equipped in the tape. To do this, in the right places in the formwork, embedded pipes are attached through which pipelines will pass;
- According to the project plan, the site is marked with pegs with a cord stretched between them along the outer width of the foundation. In order for the lower part of the formwork panels to collapse, the shields are bursting with slats or bars at a level of 70% of the height of the base. The length of the spacer should be about twice the height of the trench;
- Spacers are attached to the shields with screws or nails. With a base height of ≥ 1.5 meters, the formwork panels should be interconnected with soft steel wire with a step of 1 meter in a checkerboard pattern;
- The cracks in the formwork should not exceed 2-3 cm, so that the mortar does not seep through them into the ground, reducing the strength of the concrete tape.
From the inside, the surfaces of the formwork panels are recommended to be lubricated with engine oil or petroleum distillation products, so that the formwork can be more easily detached from the concrete during dismantling. This is done if the formwork will be used as a reusable structure.
Reinforcement weight calculator GOST 5781-82
Reinforcing cage installation
After the preparation of the trench and the installation of the formwork, the reinforcement of the shallow strip foundation begins. Reinforcing the foundation with fiberglass or iron reinforcement is technologically no different, so let's consider a more familiar option - knitting a frame from steel bars. For work you will need the following materials:
- Corrugated reinforcing bars Ø 14-18 mm (choice of diameter - according to the calculations in the project);
- Vertical and transverse smooth reinforcement Ø 10-12 mm;
- Soft knitting wire Ø 3-5 mm;
- Pliers, pliers, pincers, a narrow pry bar or other metal lever Ø 20-25 mm, or a special crochet hook that you can purchase or make yourself.
Important: fastening of steel or fiberglass reinforcement is carried out with annealed steel wire, as it stretches well and has a good margin of safety.
The first step to creating a reinforcement cage is to carry out calculations to determine the diameter of the rods, their length and weight. Calculating the correct reinforcement of the strip foundation is quite simple: the transverse rods are laid in increments of 30 cm, the longitudinal rods in increments of 40 cm, the vertical rods in increments of 50 cm. vertical rows of longitudinal reinforcement bars.
Let's say a house is being built 10 x 10 meters (base perimeter) with a foundation wall height of 120 centimeters:
- The length of one foundation wall is 1000 cm. The step of laying the transverse reinforcement bars is 30 cm, therefore 1000/33 = 33 (transverse reinforcement in one row);
- 33 x 3 = 99 (cross rods for one side);
- 99 x 4 = 396 (total number of reinforcing bars on all four sides).
In the same way, the number of fiberglass reinforcement bars is calculated.
Further actions: the total number of reinforcement (396 rods) is multiplied by the width of the tape (let's say the tape will be 0.6 meters wide): 396 pcs. x 70 cm = 237.6 meters - this is the total length of the reinforcement used in the frame. In the same way, the footage of the longitudinal rods is calculated:
- 1000 cm x 2 = 2000 cm (one row);
- 2000 cm x 3 = 6000 cm (one side);
- 6000 cm x 4 = 24000 cm (240 meters).
Calculation of vertical rods (knitting through a jumper, i.e., after 60 cm):
- 2 x 17 = 34 units per side;
- 34 x 4 = 136 units for the entire foundation;
- 136 x 1.20 m = 163.2 meters.
In order not to buy additional (in case of erroneous calculations) reinforcement bars, add 5-8% to the total result.
You can knit the frame both on the ground and in the trench, but if the trench is narrow, it will be inconvenient to do this. On the other hand, lowering a huge frame alone will not work - you need helpers.
Read more about do-it-yourself reinforcement of the tape-type base:
- The beginning of knitting is the lower transverse rods: they must be laid at a distance of 30 cm from each other, put two long rods on top, tie with wire at the intersections;
- Vertical rods are installed through one transverse rod and connected;
- Thus, two or three more (as many as needed) rows are knitted at a distance of 40 cm upwards;
- At the end of the assembly of the entire frame, four nodes should be obtained.
Now you need to learn how to properly connect them together, as well as correctly connect the rods at the corners of the foundation.
How to reinforce corners
The corners of the foundation are constantly subjected to multidirectional compressive forces, therefore, the reinforcement at the corners must be carried out in the same way and without errors, so that each corner evenly perceives the same loads, and does not create a separate local area in other bearing values. There are several methods for strengthening the corner structures of the foundation:
- With the help of a welded metal coarse mesh. Such a ready-made rigid structure has cells ≤ 200 x 200 mm, and the thickness of the reinforcing bars in the mesh can vary from 8 to 24 mm - this depends on the mass of the building and the length of the foundation. After 05-0.6 meters, horizontally laid rows of reinforcing mesh are connected with vertically arranged reinforcing bars, as when knitting a core frame, with an overlap at the corners of the frame of about 0.8 meters.
- Reinforcement with individual rods:
- With the help of L-shaped bent rods with an overlap of ≥ 60 cm;
- U-shaped rods usually reinforce right angles and foundation junctions;
- Reinforcement of adjunctions with L-shaped brackets.
The correct formation of corners is based on the observance of several recommendations:
- The length of the laps is calculated as 50 diameters of the reinforcement bars;
- When knitting corners with a width of more than 160 cm, the rods must be solid and bent along the corner;
- The distance between the transverse bars should not be less than 0.75 of the height of the tape, but not more than 50 cm;
- Reinforcement is attached to concrete with special paws, hooks, loops or a straight end. Welding and overhead cementing should not be used.
Self-reinforcing the foundation of any design for a novice master presents a certain problem, but if the above recommendations are followed, common mistakes can be avoided, and the foundation will turn out to be strong and durable.
Strip foundation reinforcement scheme updated: February 27, 2018 by: zoomfund
The strip foundation is one of the most common types of foundation for a house. In the process of its construction, great importance is given to the reinforcement of the formwork. Reinforcement allows you to increase the strength of the base and its resistance to stretching. This article will help you understand and understand what reinforcement is needed for a strip foundation and what details they pay attention to so that it lasts for many years.
After choosing the type of foundation, many are concerned about the question of what concrete should be, its composition and optimal proportions in order to produce a high-quality foundation. The builder should also pay attention to:
- number of floors of the future house;
- building weight;
- soil type;
- groundwater level and soil freezing.
Great importance is given to the quality of the concrete solution. Any brand of concrete consists of four components:
- Cement. The main component of concrete, which is best purchased in trusted hardware stores. Cement has a shelf life, so buying it in reserve is not recommended. For pouring a strip foundation, cement or portlant cement of the M400 brand is often chosen.
- Sand. Experts recommend using sand, which contains both large and small particles. It is best to choose river sand with a small admixture of quarry sand. The fraction of sand under the foundation is 2 - 2.5 mm.
- rubble. In the construction of small buildings, granite crushed stone of an average fraction from 20 to 40 mm is used.
- Water. Clean drinking water must be used. Water with a high content of salts and sulfates will reduce the quality of the concrete solution.
If there is a need to increase the properties of concrete, plasticizers are often added. Such chemical additives can affect the hardening, strength and fluidity of the mass. The ratio of plasticizers in the concrete solution is 0.2-0.3%.
Reinforcement requirements
To understand the importance of installing reinforcement, you need to understand what reinforcement is.
It is designed to increase the strength and reliability of the foundation. During operation, the base is subjected to loads:
- from the building itself
- during the movement of soils;
- from frost heaving.
Foundation reinforcement From these loads, the upper part of the base experiences a compressive load, and the lower one, in tension. It is in these parts that builders always settle the reinforcement, which takes on part of these loads. When choosing reinforcement for the foundation, pay attention to:
- rod diameter;
- resistance to corrosion;
- the need for welding;
- resistance to negative temperatures.
Specialized stores offer reinforcing bars with a diameter of 5 to 32 mm with a ribbed and regular smooth surface.
Ribbed ones create better adhesion to concrete, so they are used as the main elements. Smooth reinforcement performs the functions of an additional element and is installed on zones not subject to tension.
To reinforce the foundation, ribbed reinforcement with a diameter of 8-16 mm and smooth reinforcement of 6 mm are needed.
In the construction of the foundation, ribbed reinforcement of class A3 (A400) is most often used. When buying, you can see different markings of the elements. The letter "K" in the marking means that the rods are coated with a special anti-corrosion compound, and the letter "C" means that the rods can be welded.
To reinforce the foundation, ribbed reinforcement with a diameter of 8-16 mm is needed reinforcement requirements
To carry out high-quality and reliable reinforcement of the foundation, it is necessary to adhere to some rules:
- Make a purchase of rods in specialized stores that can provide quality certificates for products.
- The interlocked rods should not be deformed during pouring with concrete mix.
- To connect reinforcing elements, it is better to use a manual knitting method instead of welding rods.
- In addition, construction documents and codes for reinforced concrete structures describe the permissible distances between reinforcing bars:
- no more than 40 cm for longitudinal rods;
- no more than 30 cm for transverse rods;
- not less than 25 cm for elements located vertically.
According to experts, the diameter of the reinforcement for the strip foundation should be:
- for light houses on stable soil, a diameter of 8 mm is suitable;
- for loose and heaving soils and heavy buildings from 12 mm.
foundation reinforcement requirements Calculation of the number and diameter of reinforcement
During the calculation of the required diameter of the reinforcement, the indicator of the width and depth of the strip foundation is used. If the width of the foundation reaches 50 cm, and its depth is 100 cm, then the cross-sectional area of the foundation tape will be:
- 50 cm X 100 cm = 5000 cm2.
According to regulatory documents, the cross-sectional area of the reinforcement must be not less than 0.01% of the base, which means:
- 5000 cm2 X 0.01% = 5 cm2.
The result obtained is found in a special table for calculating the diameter of reinforcing bars. It turns out that to base a house with such a width and depth, you can use:
- 6 rods with a diameter of 10 mm;
- 8 rods with a diameter of 9 mm;
- 3 rods with a diameter of 14 mm.
- It should be borne in mind that if the length of the foundation is more than 3 meters, then 12 mm is the minimum allowable diameter for use.
The calculation of the amount of reinforcement is carried out independently, depending on the reinforcement scheme.
Calculation of the number and diameter of reinforcement Some reinforce the base with four bars, others use six. The reinforcement of the corners is also different. Someone makes them with L-shaped clamps, perhaps also U-shaped schemes and various variations.
To find out the number of longitudinal elements, when calculating, the perimeter of the house is calculated, the indicators of the walls are added to it, which are placed above the foundation tapes. The resulting number is multiplied by the planned number of longitudinal rods located on the same width of the tape.
Reinforcing bars differ not only in class and appearance, they also differ in their purpose:
Working longitudinal (horizontal)
Rods that are located along the base and take the main load from the compression and tension factors. To increase the strength of the foundation, they are installed in the lower and upper parts of the tape. The diameter of the elements of the lower reinforcement must be greater than the diameter of the upper rods.
Cross mounting
It is installed to link individual upper or lower working rods together. Ensures the integrity of work items and distributes the load between them.
Scheme of typical reinforcement of a strip foundation vertical
It is installed vertically and connects the upper and lower longitudinal reinforcement. Proper reinforcement of the strip foundation uses all these types of rods. Only together they will ensure the integrity of the reinforcing structure and evenly distribute the load.
How to reinforce the foundation?
The distance between the bars and the surface of the foundation should be 5 cm. The main load is taken by the horizontal bars, the transverse ones only connect the frame into a single whole. The lower layer of rods is settled on special stands.
Great importance is given to the reinforcement of corners. In these places, the rods are not simply connected, but separate curved L- or U-shaped clamps are used for this. At the corners, the rods are installed more often and denser than at the very base.
The reinforcement of a pile-strip foundation is no different from the reinforcement of a conventional strip foundation.
The main mistakes of foundation reinforcement:
- reinforcement of corners not with clamps, but with the usual crossing of rods;
- the location of the rods in the middle of the foundation;
Vertical reinforcement of the foundation - when there are only two bent rods in the corners of the foundation;
- uneven arrangement of reinforcement throughout the base.
How to knit reinforcing mesh yourself
Before starting work, it is better to familiarize yourself with. For this process, a knitting wire and a hook are purchased. Such a wire bends well, and its average diameter reaches 1.2-1.3 mm. You can buy a hook at a hardware store or make your own. For knitting, rods 5-6 meters long are used. The knitting technology for all foundations is the same, and if the diameter of the rods is more than 25 mm, then the rods are connected by welding.
Knitting reinforcement can be done in a place convenient for work, then place it in the formwork, and then install clamps at the corners of the base. To make knitting more convenient, do not use too long pieces of wire. Cut off 20 cm of metal thread and fold it in half. The overlap of reinforcing bars during binding reaches 2 cm.
Knitting reinforcement with a special device
In addition to conventional hooks, the construction market offers many additional devices and tools to not only speed up the process of knitting reinforcement, but to do it reliably and firmly:
Significantly reduces the time spent on tying rods. Additional spending on the tool will be required, but it will provide a more reliable tightening of the wire. In the gun, the wire is in a special drum, which is easy to replace. However, it has a weight of 2-3 kg and not all builders are comfortable working with it.
Rebar tying gun KW-0041 Semi-automatic and automatic rebar tying hook
Specialized tools that significantly reduce assembly time. The knitting of the rods can be done using ordinary pliers. Some builders at home use a screwdriver into which a bent nail is inserted.
Knitting reinforcement is an important stage when pouring a strip foundation and it is better not to save on high-quality tools.
How to knit reinforced mesh in a trench
Knitting a reinforcing cage in a trench is more difficult than in a free area. It is better to think over the connection scheme of the elements in advance, so as not to waste time on redoing the work in the future. Purchase rebar clamps from a specialized store. They will place the mesh above the formwork and ensure that the concrete solution is evenly applied to all the reinforcement.
It will not be possible for one person to work in a trench; an assistant is needed for such work. At the beginning, vertical bars are driven into the trench, horizontal working reinforcement is attached to them. At the end, they begin to harden the corners of the base.
Rebar welding for reinforcement Rebar welding for reinforcement
Welding reinforcing elements is faster compared to knitting rods, however, it significantly reduces the strength of the metal frame. After welding, the rods become more brittle, which affects the quality of the strip base. If a heavy building of several floors is being erected, and the area has problematic soil, it is better to abandon this method of connecting reinforcing bars.
For welding reinforcement, it is necessary to purchase special rods of class A500 and additional marking "C". Welding of reinforcement can occur in different ways:
- contact;
- bathrooms;
- butt;
- contact point.
- If the reinforcement is welded by contact, it is very important to control the current strength, on which the quality of the seam depends.
It is laid on the mortar between the brickwork. The work process starts from the bottom. Particular attention is paid to door and window openings, as cracks often occur in them. Individual elements of reinforcement can be connected with knitting wire.
"How to reinforce aerated concrete blocks?"
Produced with reinforcing mesh. For the location of the reinforcement, make grooves in the blocks with a wall cutter. The ditches are cleared of debris and the fittings connected with a special hook are laid. After laying the reinforcement, the grooves are filled with cement mortar.
Proper corner reinforcement should protect the foundation from cracks and ensure that the foundation resists tensile and compressive forces. The rigidity of the connection is provided both by the knitting method and by welding. Qualitative strength of the corner base is created by U- and L-shaped clamps.
Many believe that the cross section and the number of metal rods in the foundation does not play a special role, and they use everything that comes to hand, from knitting wire to metal pipes. But such connivance may have a bad effect in the future, both for the foundation itself and for the house standing on it.
In order for your future home to serve you for many years, it is necessary that the foundation of this house be sufficiently strong and durable, and the correct calculation of reinforcement for the foundation plays a huge role in this.
In this article, we will carry out the calculation of metal reinforcement, if you need to calculate fiberglass reinforcement, then you will need to take into account its features.
The calculation of reinforcement for the strip foundation of a private house is not as complicated as it seems at first glance, and comes down only to determining the required diameter of the reinforcement and its quantity.
Strip foundation reinforcement scheme
For the correct calculation of reinforcement in a reinforced concrete strip, it is necessary to consider typical schemes for reinforcing strip foundations.
For private low-rise buildings Basically, two reinforcement schemes are used:
- four rods
- six rods
What reinforcement scheme to choose? Everything is very simple:
According to SP 52-101-2003, the maximum distance between adjacent reinforcement bars located in the same row should be no more than 40 cm (400 mm). The distance between the extreme longitudinal reinforcement and the side wall of the foundation should be 5-7 cm (50-70 mm).
In this case, with the width of the foundation over 50cm, it is advisable to apply six-bar reinforcement scheme.
And so, depending on the width of the strip foundation, we have chosen a reinforcement scheme, now it is necessary to select the diameter of the reinforcement.
Calculation of the reinforcement diameter for the foundation
Calculation of the diameter of transverse and vertical reinforcement
The diameter of the transverse and vertical reinforcement must be selected according to the table:
In the construction of one-two-story private houses, as a rule, rods with a diameter of 8 mm are used as vertical and transverse reinforcement, and this is usually quite enough for strip foundations of low-rise private buildings.
Calculation of the diameter of the longitudinal reinforcement
According to SNiP 52-01-2003, the minimum cross-sectional area of longitudinal reinforcement in a strip foundation should be 0,1% from the total cross section of the reinforced concrete tape. It is from this rule that it is necessary to build on when choosing the diameter of the reinforcement for the foundation.
Everything is clear with the cross-sectional area of \u200b\u200bthe reinforced concrete tape, it is necessary to multiply the width of the foundation by its height, i.e. let's say you have the width of the tape 40 cm, and the height 100 cm(1 m), then the cross-sectional area will be 4000 cm2 .
The sectional area of the reinforcement must be 0,1% from the cross-sectional area of \u200b\u200bthe foundation, so you need the resulting area 4000 cm 2 / 1000 \u003d 4 cm 2 .
In order not to calculate the cross-sectional area of \u200b\u200beach reinforcement bar, you can use a simple plate. With it, you can easily choose the required diameter of reinforcement for the foundation.
The table contains very minor inaccuracies related to rounding of numbers, do not pay attention to them.
Important: When the tape length is less than 3m, the minimum diameter of the longitudinal reinforcement bars should be 10mm.
With a strip length of more than 3m, the minimum diameter of the longitudinal reinforcement should be 12mm.
And so, we have the minimum calculated cross-sectional area of \u200b\u200bthe reinforcement in the section of the strip foundation, which is 4 cm 2 (this is taking into account the number of longitudinal rods).
With a foundation width of 40 cm, it is enough for us to use a reinforcement scheme with four rods. We return to the table and look in the column where the values \u200b\u200bof 4 reinforcement bars are given, and select the most appropriate value.
Thus, we determine that for our foundation 40 cm wide, 1 m high, with a reinforcement scheme with four rods, the most suitable reinforcement with a diameter of 12 mm, since 4 rods of this diameter will have a cross-sectional area of \u200b\u200b4.52 cm 2.
The calculation of the diameter of the reinforcement for a frame with six bars is carried out in a similar way, only the values are already taken from the column with six bars.
It should be noted that the longitudinal reinforcement for the strip foundation must be of the same diameter. If for some reason you have rebars of different diameters, then the larger diameter rods must be used in the bottom row.
Calculation of the amount of reinforcement for the foundation
It often happens that the reinforcement was brought to the construction site, and when they begin to knit the frame, it turns out that it is not enough. You have to buy more, pay for delivery, and these are additional costs that are not at all desirable in the construction of a private house.
In order to prevent this from happening, it is necessary to correctly calculate the amount of reinforcement for the foundation.
Let's say we have a foundation scheme like this:
Calculation of the amount of longitudinal reinforcement
First you need to find the length of all the walls of the foundation, in our case it will be:
6 * 3 + 12 * 2 = 42 m
Since we have a 4-rod reinforcement scheme, it is necessary to multiply the resulting value by 4:
42 * 4 = 168 m
We have obtained the length of all longitudinal reinforcement bars, but do not forget that:
When calculating the amount of longitudinal reinforcement, it is necessary to take into account the launch of reinforcement during docking, because it often happens that reinforcement is delivered to a section of a long rod 4-6m, and in order to get the required 12m, we will have to join several rods. It is necessary to join the reinforcement bars with an overlap, as shown in the diagram below, the launch of the reinforcement must be at least 30 diameters, i.e. when using rebar with a diameter of 12 mm, the minimum start should be 12*30= 360 mm (36cm).
There are two ways to account for this launch:
- Draw up a diagram of the location of the rods and calculate the number of such joints
- Add about 10-15% to the resulting figure, as a rule, this is enough.
We will use the second option and in order to calculate the amount of longitudinal reinforcement for the foundation, we need to add 10% to 168 m:
168 + 168 * 0.1 = 184.8m
We have calculated the number of only longitudinal reinforcement with a diameter of 12 mm, now let's calculate the number of transverse and vertical rods in meters.
Calculation of the amount of transverse and vertical reinforcement for a strip foundation
To calculate the amount of transverse and vertical reinforcement, we again turn to the diagram, from which it can be seen that one "rectangle" will go:
0.35 * 2 + 0.90 * 2 = 2.5 m.
I deliberately took with a margin not 0.3 and 0.8, but 0.35 and 0.90 in order for the transverse and vertical reinforcement to go a little beyond the resulting rectangle.
Important: Very often, when assembling a frame in an already dug trench, vertical reinforcement is placed at the bottom of the trench, and sometimes it is also driven a little into the ground, for better stability of the frame. So this will need to be taken into account, and then it will be necessary to take into account not the length of the vertical reinforcement 0.9 m, but increase it by about 10-20 cm.
Now let's count the number of such "rectangles" in the entire frame, given that there will be 2 such "rectangles" at the corners and at the junction of the walls of the strip foundation.
In order not to suffer with the calculation and not get confused in a bunch of numbers, you can simply draw a foundation diagram and mark on it where your “rectangles” will be located, then count them.
Let's first take the longest side (12 m) and calculate the amount of transverse and vertical reinforcement on it.
As can be seen from the diagram, on the side of 12 m we have 6 of our “rectangles” and two parts of the wall of 5.4 m each, on which 10 more jumpers will be located.
Thus, we get:
6 + 10 + 10 = 26 pcs.
26 "rectangles" on one side of 12 m. Similarly, we count the lintels on the wall 6 m and we get that there will be 10 lintels on one six-meter wall of the strip foundation.
Since we have two 12-meter walls, and 3 6-meter walls, then
26 * 2 + 10 * 3 = 82 pieces.
Remember, according to our calculation, 2.5 m of reinforcement came out for each rectangle:
2.5 * 82 = 205 m.
Final calculation of the amount of reinforcement
We have determined that we need longitudinal reinforcement with a diameter of 12 mm, and transverse and vertical reinforcement will be 8 mm in diameter.
From previous calculations, we found out that we need 184.8 m of longitudinal reinforcement, and 205 m of transverse and vertical reinforcement.
It often happens that there are a lot of pieces of rebar of small sizes that will not fit anywhere. Given this, it is necessary to buy reinforcement a little more than it turned out in the calculation.
Following the above rule, we need to buy 190 - 200 m fittings with a diameter of 12 mm and 210-220 m fittings with a diameter of 8 mm.
If the reinforcement remains - do not worry, during the construction process it will come in handy more than once.
The strip foundation is one of the simplest and most reliable types of foundations that you can think of. One construction publication stated that a strip foundation, however, with reinforcement, can stand for at least 200 years. How they calculated this and by what kind of chronometer is unknown, but the fact that a reinforced strip foundation is reliable is a fact. The main thing is to correctly perform the reinforcement, which we will now do.
Why and how to reinforce the strip foundation
If we could know for sure what loads our foundation will be subject to in a year, two, ten or twenty years, it might not be worth reinforcing it. The fact is that the calculation is rather conditional. We bought a piano in the house - the load has changed, the forces and vectors of influence have changed. A new underground current arose - the same story. The foundation sank somewhere, and somewhere rose. Therefore, in order not to depend on the purchase of pianos and broken neighboring water pipes, the foundation must be reinforced.
By itself, concrete does not have such plasticity to respond to any changes in loads. For this, there is steel that holds the entire base structure together and can be ductile, while maintaining the rigidity that a strip foundation should have.
Reinforcement for the foundation. Which is better?
There is no special choice in structural reinforcement products, and it is not needed. Standard rolling bars do an excellent job of reinforcing any foundation, and their thickness and layout are selected depending on design features grounds. Whatever the reinforcement is, it is laid only according to two schemes:
longitudinal reinforcement occurs when it is necessary to minimize tensile loads, such reinforcement is placed below and above the foundation screed, for this
- use a rod brand A3 with a relief surface;
- longitudinal-transverse reinforcement is performed when anything is expected from the foundation, and especially in cases where its height exceeds at least 1.5 m in some places.
In the second case, more powerful class A1 reinforcement from a rolling rod is used, connecting the longitudinal with the transverse knitting wire. Welding is not used.
Calculation of reinforcement for a strip foundation
Everything is simple here. GOSTs and SNiPs will not let you fantasize, but it is necessary to reckon with the standards. Before pouring the strip foundation, it is necessary to check with the standards, and the standards say that the relative position of the reinforcement bars depends on which brand of concrete is used and on the fractions of the aggregate. Also of great importance is the method of laying and tamping. The recommended distance between the reinforcement bars with a foundation width of 40 cm is about 10 cm, provided that four bars with a diameter of 8-10 mm are laid. GOST recommends placing horizontal bars at a distance of 30 cm with the same width of the foundation.
When knitting reinforcement, it is very important to observe the distance to the outer surfaces of the foundation, to the formwork and cushion. You can control this in several ways, but the easiest way is with the help of bricks. It is necessary to ensure that the metal rods do not touch the ground, otherwise corrosion will nullify all reinforcement efforts. The minimum distance from the rod to the ground should be at least 6-8 cm. Only after that you can fall asleep a pillow.
How to make reinforcement of a monolithic strip foundation
This is the simplest and most academic case, when the reinforcement passes only along the bottom of the foundation. This is explained by the fact that the foundation buried to the depth of freezing is built when the soil is stable, and the building does not imply the presence of a second floor. In this case, the reinforcement is more of a safety feature. In this case, use A3 reinforcement and smooth A1 for cross knitting. All dimensions specified in the regulations, in this case, remain valid.
In the event that the soil on which the construction is being carried out is unreliable, and the load on the foundation is higher, more serious measures should be taken to strengthen the foundation. In these cases, the width of the foundation is one and a half to two times larger, and when reinforcing, the transverse rods are set in diameter equal to the longitudinal ones. In this case, the entire structure is connected with a knitting wire; the use of welding is also not welcome here. It is also recommended to increase the number of horizontal rods, reducing the distance between them to 20 cm.
We have reviewed the most simple circuits reinforcement of deep foundations, which are perfect for a fence on a strip foundation, for light structures and outbuildings with the prospect of increasing the load.
