Foundation beams: features and scope of their application

The building starts from the foundation. The earth "plays", therefore, the operational capabilities of the object depend on the strength of the foundation. Foundation beams are widely used due to their fundamental characteristics.

Foundation beams are a reinforced concrete structure that serves as the foundation of a building. They serve a dual purpose:

• are load-bearing elements in non-monolithic internal and external walls;
• they separate the wall material from the ground, performing the function of waterproofing protection.

The classical application of reinforced concrete beams (or randbeams) is carried out in the construction of industrial, agricultural facilities and public buildings. They serve as a support for the external and internal walls of buildings. With modern technologies at the stage of developing a building project, it is possible to use foundation beams in the construction of residential premises. The use of rundown beams is an alternative to a monolithic foundation structure, it is a prefabricated technology when laying the foundation of a building.

Beams are intended for:

• self-supporting walls of block and panel type;
• self-supporting brick walls;
• walls with hinged panels;
• solid walls;
• walls with door and window openings.

By destination in construction, FBs are divided into four groups:

• wall-mounted, they are mounted near the outer walls;
• connected, installed between the columns that form the layout of the building;
• ordinary beams are used to fasten wall and connected beams;
• sanitary ribbed products intended for sanitary needs.

The advantages of these reinforced concrete structures in comparison with monolithic technology are:

• shortening the construction time;
• facilitating the implementation of underground communications inside the building.

Today, due to its special characteristics, the use of foundation structures plays an important role. Their cost, according to calculations, is about 2.5% of the total cost of the building.

The widespread use of prefabricated foundation structures is a simple and inexpensive method of installation compared to strip foundations. Structures must be securely fastened. The glass type of foundation is classically used, when individual elements are supported on the steps from the side. If the height of the step and the beam do not match, then the installation of brick or concrete posts is provided for this.

When using columnar foundations, it is permissible to support from above. The columns are called support cushions. With a large base of the building, it is possible to create special niches in its upper part, into which standard randbeams are mounted. Models of trimmed beams are used in individual building cells and attached to the expansion transverse seam.

In the construction of frame structures, the use of foundation beams is advisable for the installation of external walls.The products are laid on the edge of the foundation, covered with concrete mortar. In order to prevent excessive moisture, as a rule, a solution of sand with cement is applied over reinforced concrete structures.

Installation of foundation structures is carried out only with the use of lifting equipment, since their weight ranges from 800 kg to 2230 kg. According to GOST standards, beams are made with holes provided for lifting and mounting. Thus, with the help of slinging holes or special factory mounting loops and special gripping devices, the beam is attached to the crane winch and placed in the intended place. Beams are mounted on pillars or piles, in exceptional cases - on sand and gravel bedding.

The structures are produced in accordance with the technical conditions GOST 28737-90, introduced by the State Construction Committee of the USSR in 1991. Time and practice have proven the quality of these products. According to the GOST of Soviet times, the manufacture of foundation structures is regulated in terms of the dimensions of structures, their cross-sectional shapes, marking, materials, acceptance requirements and procedures, quality control methods, as well as storage and transportation conditions.

Technical requirements: cross-sectional view, standard size, length and designation of a series of working drawings of beams - can be found in table No. 1 of GOST. The raw material for the manufacture of beams is heavy concrete. The length of the product, the type of reinforcement and the load calculation data influence the choice of the concrete grade. Usually beams are made of concrete of M200-400 grades. The technical characteristics of the product allow you to optimally ensure the load from the walls.

With regard to reinforcement, GOST allows:

• prestressed reinforcement for structures longer than 6 m;
• for beams up to 6 m, prestressed reinforcement at the request of the manufacturer.

Traditionally, factories produce all beams with prestressed steel reinforcement of class A-III. Having decided on the dimensions and cross-section of the product, it is necessary to correctly indicate the marking, especially for the basement options. It consists of alphanumeric groups separated by a hyphen. Typically, the marking consists of 10-12 characters.

• The first group of signs indicates the standard size of the beam. The first number indicates the type of section, it can range from 1 to 6. The letter set indicates the type of beam. The numbers after the letters indicate the length in decimetres, rounded to the nearest whole number.
• The second group of numbers indicates a serial number based on the bearing capacity. This is followed by information on the class of prestressing reinforcement (only for prestressed beams).
• The third group indicates additional characteristics. For example, in the case of increased corrosion resistance, the index "H" or the design features of the beams (mounting loops or other embedded products) are put at the end of the marking.

An example of a symbol indicating additional characteristics: replacement of slinging holes with mounting loops, production of concrete of normal permeability (N) and intended for use in conditions of exposure to a slightly aggressive environment: 4BF48-4ATVCK-Na. Three types of products define a set of letters:

• solid foundation beams (FBS);
• solid foundation beams with a cutout for laying lintels or skipping engineering structures (FBV);
• hollow foundation beams (FBP).

Quality control of foundation beams requires checking:

• compressive concrete class;
• tempering strength of concrete;
• the presence and ratio of reinforcement and embedded products;
• accuracy of geometric indicators;
• the thickness of the concrete cover to the reinforcement;
• shrinkage crack opening width.

In the technical passport of the purchased batch of randbeams, the following should be indicated:

• concrete grade for strength;
• tempering strength of concrete;
• prestressing reinforcement class;
• concrete grade for frost resistance and water permeability.

The fundamental model is a long, heavy concrete pile or column. Beams, depending on the width of the cross-sectional surface, are divided into types:

• for walls of buildings with column spacing up to 6 m (1BF-4BF);
• for walls of buildings with a column pitch of 12 mm (5BF-6BF).

Usually, the top beam has a flat platform of a certain size: from 20 to 40 cm wide. The size of the site depends on the types of wall material. The length of the product can reach 6 meters, but not less than 1 m 45 cm. In models 5 BF and 6 BF, the length is from 10.3 to 11.95 m. The height of the beams is 300 mm, except for 6BF - 600 mm. On the side, the beam has a T-shaped or truncated cone shape. This shape reduces the perceived loads.

Beams are distinguished by the type of sections:

• trapezoidal with a lower edge of 160 mm and an upper edge of 200 mm (1 BF);
• T-section with base 160 mm, upper part 300 mm (2BF);
• T-section with a supporting part, the lower part is 200 mm, the upper part is 40 mm (3BF);
• T-section with base 200 mm, upper part - 520 mm (4BF);
• trapezoidal with the lower edge of 240 mm, the upper edge - 320 mm (5BF);
• trapezoidal with the lower part of 240 mm, the upper part - 400 mm (6BF).

Indicators allow deviations: in width up to 6 mm, in height up to 8 mm. In the construction of residential and industrial buildings, the following types of foundation beams are used:

• 1FB - series 1.015.1 - 1.95;
• FB - series 1.415 - 1st issue. 1;
• 1FB - series 1.815.1 - 1;
• 2BF - series 1.015.1 - 1.95;
• 2BF - series 1.815.1 - 1;
• 3BF - series 1.015.1 - 1.95;
• 3BF - series 1.815 - 1;

• 4BF - series 1.015.1-1.95;
• 4BF - series 1.815 - 1;
• 1BF - series 1.415.1 - 2.1 (without prestressing reinforcement);
• 2BF - series 1.415.1 - 2.1 (prestressing reinforcement);
• 3BF - series 1.415.1 - 2.1 (prestressing reinforcement);
• 4BF - series 1.415.1 -2.1 (prestressing reinforcement);
• BF - RS 1251 - 93 No. 14 -TO.

Modern technologies allow the use of foundation beams for walls with strip glazing, with a brick basement up to 2.4 m high along the entire length of the beam. Traditionally, in the presence of brickwork in the area of ​​the basement and walls, foundation beams are necessarily used.

Individual series of foundation beams have their own standard sizes. They depend on the established standards for the dimensions of beams, approved by GOST 28737 - 90 to 35 m. Characteristics of beams of type 1BF:

• section dimensions 200x160x300 mm (upper edge, lower edge, model height);
• length of models - 10 variants of standard sizes from 1.45 to 6 meters are offered.

Characteristics of beams of type 2BF:

• section dimensions 300x160x300 mm. The thickness of the top crossbar of the T-bar is 10 cm;
• length of models - 11 standard sizes are offered from 1.45 to 6 meters.

Characteristics of beams of type 3BF:

• section dimensions 400x200x300 mm. The thickness of the top crossbar of the T-bar is 10 cm;
• length of models - 11 standard sizes are offered from 1.45 to 6 meters.

Characteristics of type 4BF:

• section dimensions 520x200x300 mm. The thickness of the top crossbar of the T-bar is 10 cm;
• length of models - 11 standard sizes are offered from 1.45 to 6 meters.

Characteristics of type 5BF:

• section dimensions 400x240x600 mm;
• length of models - 5 standard sizes are offered from 10.3 to 12 meters.

Characteristics of type 6BF:

• section dimensions 400x240x600 mm;
• length of models - 5 standard sizes are offered from 10.3 to 12 meters.

Since the prefabricated technology was developed for mass construction, its use in the construction of private residential buildings has two nuances:

• the use of models of planks made according to GOST standards, it is advisable to initially take into account atypical objects of individual construction in the project;
• large dimensions and weight of structures increase the cost of the building erection process due to the involvement of lifting equipment.

Therefore, when drawing up construction calculations, calculate these nuances. In case of difficulties with the involvement of special equipment and labor, use the construction of a grillage in a monolithic version.

• When choosing a model of beams, take into account the bearing capacity of the elements, that is, the maximum load of the structural solution of the walls. The bearing capacity of the beam is determined by the author of the project of the building being erected. This indicator can be specified at the manufacturer's plant or according to special tables for a specific series.
• Pay attention to the fact that beams that perform load-bearing functions should not have cracks, many cavities, sagging and chips.

For information on how to select and lay foundation beams, see the next video.