Strip monolithic reinforced foundation - what is it, types, reinforcement

When building a private house, the first thing you need to do is make a high-quality foundation. The operational period of the entire house will depend on its quality and reliability. In most cases, a tape type of base is used. The reinforcement for the foundation of a private house serves as a tightening and strengthening element.

The foundation of any house takes on the entire load from load-bearing building structures. Therefore, it must be strong enough and able to withstand any type of load. Concrete itself is quite fragile and requires appropriate strengthening.

In this article we will look at why the reinforcement procedure is performed, what material is used for this, how the frame is knitted and reinforcement is performed. You will also find recommendations for selecting and purchasing products of appropriate quality.

Construction work before the start of the process

Before starting reinforcement, it is necessary to make a drawing of the foundation. It must support external walls and load-bearing internal partitions. Afterwards, the reinforcement frame is calculated.

Before immediately starting construction work on knitting the skeleton, you must:

Dig a trench according to the location and dimensions of the drawing.
Assemble the formwork inside the trench from suitable materials.
Arrange a sand cushion as a substrate to ensure uniform distribution of concrete.

Strip foundation

In low-rise private construction, strip foundations are the most common. This is, in fact, a reinforced concrete strip that stretches along the entire perimeter of the building. It is laid under all walls while maintaining shape and size along its entire length.

When compared with pile or slab foundations, the manufacture of a strip structure seems simpler and more accessible to perform.

At the same time, it is more labor-intensive and more expensive than the construction of a columnar foundation, which does not require a large amount of materials or special equipment.

The main elements for arranging a reinforcement frame

Its reliability and durability depend on a properly assembled structure.

Any strip foundation frame includes the following reinforcement elements:

Longitudinal.
Transverse.
Vertical.
Clamps.
Knitting wire.

The correct frame increases the load-bearing capacity of the structure. It also prevents the influence of deformation forces from the outside.

When is a strip foundation used?

The areas of application of strip foundations are
:

buildings made of stone, brick or concrete with a wall density of more than 1300 kg/cu.m. m.;
buildings with heavy floors (reinforced concrete, metal, monolith);
buildings built on areas with heterogeneous soils, as a result of which the settlement of the foundation may be uneven.

When making a basement or basement in a building, the strip foundation simultaneously becomes their walls.

Laying strip foundations usually begins in warm weather. This does not require the use of heavy construction equipment - the work is carried out using a concrete mixer and small-scale mechanization equipment.

Heaving, excessively moist and strongly freezing soils are not suitable for this type of foundation.

These conditions require a rigid, reliable and durable base that is resistant to transverse and longitudinal deformation. Such qualities are characteristic only of a pile-strip foundation.

What schemes exist?

There are two established schemes for longitudinal installation of reinforcement:

In four rods;
Six rods.

If we take the width of the base for the foundation to be more than 500 mm, then the second scheme is used. This depends on the standards, which require adjacent rods to be laid at intervals of 400 mm from each other.

The lateral longitudinal reinforcement should extend from the concrete walls by 50-70 mm. This helps maintain the protective layer of concrete on the frame.

When constructing a foundation of any height, two reinforcement belts are used:

Upper.
Lower.

Typical diagrams for the arrangement of corners and T-shaped junctions use clamps:

In the form of “G” elements.
In the form of “P” elements.

The figure shows a drawing of a reinforcement scheme for a strip foundation using G and P elements:

The bent elements must be a continuation of the main longitudinal rods and “layer” on them by 600-700 mm, but not shorter than 50 diameters of the reinforcement. The reinforcement spacing at the corner locations is calculated by the ratio: 0.75 x foundation height.

Detailed information on reinforcement is contained in SNiP 2.03.01-84 and SNiP 2.02.01-83.

Selection and calculation

When reinforcing, it is necessary to use class AIII reinforcement. It has a grooved surface. It is used for longitudinal and transverse whips, as well as for strengthening corners.

This type, compared to smooth, has better adhesion to concrete. Smooth class AI is used for vertical elements.

It is permissible to use only hot-rolled steel grades:

St3kp;
35GS;
35G2S;
32G2Rps;
22Х2Г2АУ;
22Х2Г2Р;
80C;
20ХГ2Ц.

Currently, in addition to standard metal rods, fiberglass reinforcement is used. Its strength is higher than that of steel. But this type is more often used in large-scale construction to reduce the load.

Simplified calculation plan:

To calculate the cross-section of the working rods, it is necessary to take 0.1% of the cross-sectional area of the foundation, namely, for a foundation with a length of:
more than 3 m - a cross-section must be used of at least 12 mm, but not more than 40 mm.
Horizontal reinforcement constitutes more than 25% of the thickness of the working rod (minimum value 6 mm).
Vertical rods calculated according to the height of the foundation:
more than 0.8 m, a cross-section of 8 mm or more is accepted.

These formulas are applicable only for the construction of small buildings. Large buildings in accordance with SNiP require taking into account the supply of reinforcement to ensure sufficient strength.

When planning a building of three floors or higher, or in the presence of moving soils, it is preferable to order calculations and diagrams from a specialized construction company.

Even more information about calculating reinforcement in the video:

Types of strip foundations

Having chosen a strip foundation as the basis for construction, you need to decide on its type.

According to their design characteristics, they are classified as follows:

monolithic reinforced strip foundations (the entire process of their arrangement from the first to the last stage is carried out on the construction site);
prefabricated strip foundations (for their construction, factory-made concrete blocks and reinforced concrete slabs are used, from which the cushion is made).

Prefabricated foundations are not only inferior to monolithic foundations in terms of strength and some other performance characteristics, but can also only be erected using special equipment.

According to the depth of occurrence, which is determined depending on the load, monolithic foundations can be:

shallow;
buried.

In both cases, it is a horizontally located reinforced concrete frame with increased rigidity. The cost of its production can reach almost 20% of the total construction budget.

The construction of a buried foundation is justified if the walls and ceilings of the building are made of heavy materials, as well as if the construction is carried out on heaving soil.

In addition, it is impossible to do without it in houses with basements or underground garages. Such a foundation is laid 20-30 cm deeper than the soil freezing mark. Under internal walls, the laying depth can be reduced.

Required tools and materials

Before you begin construction and installation work, you need to collect the necessary tools and equipment in advance:

Tape measure or other measuring tool to take local measurements;
An angle grinder (simply called a grinder) for cutting out reinforcement;
A specialized hook (you can make it yourself), pliers or a professional gun for knitting wire;
A special tool for bending rods.

Arrangement of formwork and cushions

OSB boards, wooden structures, plywood or fiberboard are used for formwork. The material must hold the concrete and not bend under its pressure. The higher the foundation, the stronger the material required.

Assembling the formwork in stages:

Stage 1. Installation of spacers around the perimeter of the trench (the length of the spacers is twice as long as the accepted height of the foundation). They should be located retreating from the bottom of the foundation by 70% of its height. In the future, they will hold the wooden base.
Stage 2. Installation of formwork from the selected material. It is worth fastening individual wooden elements from inside the formwork, so that you can disassemble it later without any problems. There should be no gaps of more than 0.3 cm in the finished base to prevent leakage of concrete and deformation of the finished structure.
Stage 3. Lubricating the inside of the formwork with technical oil before starting concrete work. This ensures easy removal of the formwork after the concrete mixture has hardened.

Next, a sand cushion is arranged. Its thickness varies within 200 mm. In this case, the sand should be compacted first. For quick compaction, just wet the sand with water.

Reinforcement for the foundation of a private house - how to knit

To strengthen the foundation of a private house, a special frame is made from reinforcing bars. After assembly, it is installed in the formwork and filled with concrete mixture. Rods can be connected in two ways:

Welding. This connection method allows you to create a rigid frame that will not deform under the influence of sufficiently strong loads. This method is used mainly in the construction of multi-storey buildings or industrial buildings;
Knitting. The rods are connected using wire. In this case, the structure will not be so rigid, which will allow small backlashes to appear under constant loads.

Which connection method should I choose? This will depend on many factors that will be taken into account at the design stage of the house.

How to reinforce correctly - step-by-step instructions

Tying the reinforcement for the frame is done either immediately in the formwork or outside it, followed by installation at the places of use.

Stages of knitting the “skeleton” of the foundation:

Stage 1. Laying out transverse rods with a length 100 mm less than the width of the foundation.
Stage 2. Laying out the two lower rods of longitudinal reinforcement. The lower belt is created in two stages.
Stage 3. Installation of vertical supports at joints with a height 100 mm less than the height of the finished foundation.
Stage 4. The upper belt is attached to the vertical frame, which is made using the steps of the first two stages.

Regardless of where the knitting takes place: directly in the formwork or separately with subsequent installation in the formwork, the sequence of steps is the same. If the parts of the frame are assembled separately, then they must be well connected to each other directly in the formwork.

All intersections of reinforcement must be tied with wire. Sometimes it is permissible to use plastic clamps. The use of a welding machine to connect elements is prohibited by building codes.

How to bend reinforcement correctly?

Correctly working with tools that are capable of bending metal bases for further use in the reinforcement process allows you to create correct and reliable bent skeleton elements.

There are two ways to bend a metal rod:

Hot bending - the bend must be heated to 700-900 degrees using a blowtorch, then bent to the desired angle with blows of a sledgehammer or hammer.
Cold bending – involves the use of a special machine. Some whips can be bent by hand (up to 8mm), or using a lever, but you need to control the bending angle.

The hot method makes the bend brittle. For further work, it is necessary to cool the finished product in the open air.

Uncover

If the diameter of the rods does not exceed 12 mm, a hacksaw or band saw can be used for cutting. If the diameter of the pins is more than 12 mm, it is better to use a grinder with a special attachment designed for “mild” steel.

An automatic tool helps speed up construction and installation work , but requires careful work to avoid injury.

Location

The reinforcement should move inward from the edge of the foundation by 50-60 mm. This will prevent corrosion of the metal inside the foundation and create a protective layer of concrete. It is not recommended to go deeper, since the frame will cease to perform its functions and withstand external environmental influences on the concrete.

To create a seamless frame, it is necessary to connect the vertical and transverse rods with one clamp.

To create a protective concrete layer at the bottom of the foundation, bricks must be placed under the frame at a distance of about 0.5 meters. In this case, deflections of the skeleton should not be allowed.

How to properly lay longitudinal reinforcement?

Longitudinal reinforcement must ensure uniform distribution of deformation forces throughout the entire foundation.

That is, it makes concrete workable. Clause 7.3.6 of SNiP 52-01-2003 states that the spacing between longitudinal reinforcing rods must be calculated based on their type (walls, floor slabs, beams, columns), as well as the height and width of the cross section.

But at the same time, the distance between the longitudinal rods should not be more than 400-500 mm. When laying, you should use whole rods without joints, extended by 1.5-2 meters in order to make bends at the corners. This will increase their strength.

Laying transverse

The rules for transverse reinforcement are discussed in clause 7.3.7 of SNiP 52-01-2003. Vertical and transverse reinforcement are placed at a distance of up to 300 mm from each other.

But this distance should not be less than half the height of the base. It takes on part of the lateral load, which acts on the concrete and prevents the formation of inclined cracks.

Knitting process

There is a specialized “knitting” wire for knitting. To choose the right material, you need to pay attention to its composition.

The composition of the binding wire is low carbon steel. It is distinguished by its white color.

In the tying process, it is enough to purchase wire with a diameter of 1.0 to 1.4 mm. If you use the minimum thickness, the material breaks easily. If you use thicker products during the installation process, it will be difficult to twist them.

To knit two elements of the frame, it is necessary to prepare cuts 250-500 mm long; to connect three pins, cuts of at least 500 mm are needed. The length cut depends on the diameter of the materials being bonded. When tying several elements, the tying wire should be folded in half.

The twist length should not be too long. 3-5 turns are enough to create a strong connection.

Base angles

To ensure a harmonious transition of two vectors of different loads, it is necessary to correctly reinforce the corners. In this case, bent elements are applicable.

If the longitudinal rods are long enough, it would be better to move the whips around the corner by 600-700mm. Solid elements will significantly increase the strength of individual clamps.

In this case, the pitch of the belt of vertical and transverse reinforcement should be ½ the pitch of the straight sections of the strip foundation.

Standard is not a rule

When arranging the foundation strip, a spatial frame is knitted from reinforcement. The following standard parameters are suitable for laying the foundation for a small one-story house (section of a small base 600×400 mm):

Reinforcement 12-14 mm is used on horizontal bearing guides;
Thin rods with a diameter of 8-12 mm are knitted with perpendicular crossbars, since there is no heavy weight load on them;
The pitch and distance between the crossbars must correspond to the loads, but not less than 200x200 mm and not more than 500x500 mm. Usually this distance is maintained with a value of 300x400x400 mm between the axes, where 300 is the length indicator.

Knitting corners is a rather important point (or rather, a knot). In addition to the spatial frame, you can lay several rods so that they form a triangle of the correct shape at the junction. The ends are made no shorter than 150 mm, bent and knitted with wire in two places parallel to the longitudinal rods. They are laid in the corners of the foundation, on the upper and lower tier of the frame.

Scheme of reinforcement of junctions.

Reinforcement of corners.

Reinforcement of obtuse angles.

Wire knitting techniques.

In some cases, additional rods with a diameter of 14-16 mm are placed around the perimeter of the entire base. This is done only when slightly larger loads are expected over the area of the entire frame. Proper tying of reinforcement for a strip foundation involves laying the metal in the center of the frame. If the base consists of four horizontally lying rods, then they are installed across, on the lower tier of the frame itself. The reinforcement must be tied into one whole with the main frame, reaching the very corners.

Possible errors and how to fix them

A small overlap of reinforcement or its absence in the frame is unacceptable, since the frame may move during the concreting process.

This may damage the finished product. It is better to leave allowances of 200 mm.

Welding elements or tying with unsuitable material, such as rope, is not permitted.

Welding makes the fastening unit fragile, and the rope does not provide sufficient strength to the connection.

Reinforcement of corners without overlaps. Reinforcing lap corners with whip can lead to rapid failure and uneven load transfer between the two parts of the foundation structure. To solve the problem, additional bent elements are included.