How to reinforce a strip foundation with your own hands correctly + photo

Mankind has accumulated vast experience in construction throughout its existence. The basis, the base of any building is a solid and reliable foundation. Today, the most common type of foundation is the one that allows the foundation, because it is this construct that evenly distributes the weight of buildings on the ground, which in turn affects the shrinkage process of the house. And the reinforcement of the strip foundation is a way to make the foundation of the structure stronger and more reliable.

Steel and concrete are the main load-bearing building materials. The properties of materials differ from each other. Comparative table of properties of some materials:

As you can see, steel is much stronger and more reliable than concrete, but at the same time, concrete is 80 times cheaper than steel. Therefore, a composite material reinforced concrete appeared. Since concrete works well in compression, the location of steel in reinforced concrete structures is in places subject to tension and bending.

Many believe that the foundation only works to compress and reinforce the strip foundation - money thrown to the wind. This is correct if the foundation is placed on rocky soils. But in most cases, the soil is not a solid monolith. There are many factors that make a bending base work:

• Soil heterogeneity. Different density of layers leads to uneven shrinkage.
• Erosion of soil by atmospheric precipitation or groundwater.
• Mobility of the surface layers of the soil.
• Frosty swelling. The close location of groundwater and negative temperatures cause clay soils to increase in size by 10-15% (swell). In this case, the base begins to squeeze the foundation up.

As a result, stress arises in concrete structures, destroying the material. Cracks and shrinkage of the foundation lead to the formation of cracks in the walls of the house, which spoils the appearance of the building or to its collapse. In other words, saving on reinforcing the foundation is more expensive for yourself, because repairing and restoring a house requires tangible cash costs.

Reinforcement technology is a process of creating a spatial reinforcement cage. It consists of the following elements:

• longitudinal reinforcement;
• transverse;
• vertical;
• reinforcing clamps;
• knitting wire.

Longitudinal reinforcement is laid along the long side of the foundation, and the length of the rod usually reaches 6 or 12 m. It is she who resists stretching. Longitudinal reinforcement is performed along the upper and lower edges of the reinforced concrete structure.

The laying pattern depends on the calculation of the required cross-sectional area of ​​the reinforcement. Such a calculation requires careful consideration of all loads on the foundation, including climatic ones from snow and wind, as well as the own weight of the foundation. The bearing capacity of the soil is taken into account according to geological studies (geological section). In GOST 5781-82, table 1 contains the cross-sectional area for each rod diameter, it remains to decide how many rods to place on the upper and lower sides of the foundation.

However, for those who decide to build a house on their own, with their own hands, you can do without calculations, using the recommendations of clause 10 and section 5 of the Manual "On the design of concrete and reinforced concrete structures made of heavy concrete without prestressing reinforcement." They indicate that the minimum cross-sectional area of ​​\u200b\u200bthe reinforcement is As \u003d µ * b * ho, where:

As is the cross-sectional area of ​​the reinforcement;

µ= 0.1% - percentage for bending structures;

b is the width of the section of the strip foundation;

ho is the height of the working area of ​​the section (equal to half the height of the foundation section).

The diameter of the upper rods can be equal to the diameter of the lower ones or taken smaller. The maximum distance between the axes of the longitudinal rods (step) is recommended to be taken no more than 1.5h or no more than 400 mm in beams and slabs, where h> 150 mm is the height of the foundation cross-section (clause 10.3.8 of the joint venture and clause 5.13 of the Handbook). Only in this case, the effective operation of concrete and reinforcement is ensured, and the width of the crack opening between the longitudinal bars is limited.

The minimum pitch of the rods (distance between the axes) is limited for reasons of convenience of laying and compacting the concrete mixture and is equal to:

• d + 25 mm - for the lower reinforcement row;
• d + 30 mm - for the top.

Consider an example:

It is necessary to reinforce the strip foundation 400 mm wide, 600 mm high. You need to calculate how many rods you need and choose the diameter. The minimum cross-sectional area of ​​​​the reinforcement is: As \u003d 40x30x0.1% \u003d 1.2 cm². The distance between the rods is 1.5x600 = 900 mm, therefore, we will take no more than 400 mm. That is, 2 rods are installed along the width of the section. We select the diameter of the reinforcement according to GOST 5781-82 table 1: two rods Ø 8 mm have an area As \u003d 2x0.503 \u003d 1.006 cm², which is less than the required 1.2 cm². Consider the following diameter Ø 10 mm. As \u003d 2x0.785 \u003d 1.57 cm². As a result, the layout of the rods looks like this: take the upper and lower reinforcement equal to Ø 10 mm and lay them in two rows.

Many builders today use the following rules to select the diameter of the rods: the diameter must be at least 10 mm if the side of the foundation is less than or equal to 3 m, and 12 mm for a side more than 3 m (see the Manual "Reinforcement of elements of monolithic reinforced concrete buildings" Appendix one). However, the rules of the manual have been developed for the design of monolithic reinforced concrete structures of multi-storey buildings, taking into account emergency loads and progressive collapse. Of course, for those who build a house with their own hands, the margin of safety will not hurt, but we are no longer talking about a reasonable consumption of reinforcement.

When installing reinforcement, one should not forget about the protective concrete layer - the distance between the side surface of the strip foundation and the reinforcement bar. The protective layer is necessary for several reasons: it protects the steel from the aggressive effects of air and groundwater. In addition, for the normal operation of reinforced concrete, the reinforcement must be inside the concrete. The minimum layer size depends on the operating conditions of the structure and for structures located in soils, foundations with a concrete preparation device, it is 40 mm and not less than the diameter of the working reinforcement (Table 10.1 of the SP and Table 5.1 of the Manual).

Read more about the calculation of reinforcement.

Transverse structural reinforcement

Structural transverse reinforcement means horizontal and vertical bars, which:

• Support longitudinal reinforcement in the design working position.
• Prevent the development of cracks.
• Perceive an unaccounted load, for example, lateral buckling of the foundation.

The diameter of the transverse reinforcement in knitted flexible frames is assumed to be at least 6 mm. In Appendix 1 of the Manual "Reinforcement of elements of monolithic reinforced concrete buildings", transverse reinforcement is recommended to be performed in the form of a closed clamp with a rod diameter of at least 8 mm.

Device for bending reinforcement clamps.

The distance between the rods (step) is taken no more than twice the width of the cross section and not less than 600 mm. As for the protective layer, the minimum distance between the rod and the concrete edge is 5 mm less than the minimum layer size for longitudinal working reinforcement, i.e. 35 mm.

Materials used

Reinforcement materials are accepted in accordance with GOST 5781-82. The fittings are made of low-alloy and carbon steel in accordance with GOST 380-2015. The surface of the rods can be smooth or with a periodic profile. Depending on the properties, the material is divided into the following classes:

• A 240 (A-I);
• A 300 (A-II);
• A 400 (A-III);
• A 600 (A-IV);
• A 800 (A-V);
• A 1000 (A-VI).

For the foundation, reinforcement with a sickle-shaped profile is needed.

The numerical code reflects the yield strength, for example 240 corresponds to 235 N/mm². Among them, only A 240 (A-I) is made with a smooth profile. In the range of products are limited to a diameter of 6 to 40 mm.

Frames can be welded or bonded. For bonding and reinforcement, low-carbon steel wire GOST 6727-80 is used, round (grade V-I) or ribbed (grade Vr-I), with a diameter of 3.0; 4.0.

Tip: The best solution for the foundation would be A400 (AIII) reinforcement, the use of higher grades is not justified, because. without prestressing, its strength potential will not be used 100%.

It should be noted that in recent years, fiberglass composite reinforcement has appeared in the construction industry. The material is durable and lightweight. The material has many advantages: easy installation technology, has high anti-corrosion properties.

Photo of composite reinforcement.

However, the material also has disadvantages. It has self-extinguishing characteristics during combustion, but at a temperature of 200 ° C it loses its properties. In addition, it does not bend well, which makes it difficult to use bent elements. Many professional builders refused to work with this material due to the lack of practical experience (foreign experience was not taken into account) and calculation recommendations.

But since July 2015, Appendix L has appeared in SP 63.13330.2012 with rules for the design and calculation of structures. For those who prefer to build with their own hands, there are design requirements for reinforcement.

Rules for reinforcing corners and junctions

Often at the construction site, reinforcement has to be made from remnants, so the rods are overlapped, welded, or special butt joints are used. When overlapping, the ends of the smooth profile reinforcement are bent in the form of paws, hooks and loops, and the ends with a periodic profile can not be bent. The distance between joined bars can be from zero to 4 reinforcement diameters. The length of the joint is calculated according to the design manual, but cannot be less than 15 bar diameters or 200 mm.

Butt welded joints are performed using clips, and in mechanical joints, threaded and crimp couplings are used.

Important! The rules prohibit reinforcing corners with a simple overlap, since in this case the corner will not be integral and motionless.

Angular and T-shaped junctions of frames are made in three ways: with paws, with additional curved clamps of L and U shapes.

Photo how to properly reinforce the corner.

Learn more about corner reinforcement.

Knitting armature

It would seem that welded frames are faster and more convenient to use. However, builders prefer to knit space frames. And there are reasons for this:

• Welding reduces the quality of the metal.
• Soil settlement during the production of foundations provokes additional stresses at the joints. Welding joints do not always cope with loads and are destroyed. Connected parts do not change position in space, but have a certain mobility.

Advice! If you need contractors, there is a very convenient service for their selection. Just send in the form below a detailed description of the work that needs to be done and you will receive offers with prices from construction teams and firms by e-mail. You can see reviews of each of them and photos with examples of work. It's FREE and there's no obligation.