Reinforced concrete slabs are one of the most common types of floors. They provide high strength and allow you to install a rigid structure in the shortest possible time. Installation of floor slabs is a responsible task that requires certain knowledge in the field of construction. First things first.

Types of floor slabs

Before you start installing a horizontal structure, you need to select a type. Reinforced concrete prefabricated structures are produced in the form of:

• multi-hollow;
• flat (PT);
• tent panels with ribs located along the perimeter;
• with longitudinal ribs.

The most common choice is the use of reinforced concrete hollow-core. They are available in two types, depending on the manufacturing method:

• round hollow (PC);
• continuous molding (CB).

Scheme of a hollow-core floor slab with holes

Round hollow core slabs are time-tested products that have been used in construction for several decades. Many regulatory documents and installation rules have been developed for them. Thickness – 220 mm. Products are installed according to serial sizes, which creates inconvenience during individual construction.

The manufacturing technology of these slabs involves the use of reusable molds for pouring, and before manufacturing non-standard products, you will first need to prepare the formwork. Therefore the cost the right size may increase significantly. Typical PC slabs have a length from 2.7 to 9 meters in increments of 0.3 m.

Scheme of reinforced concrete products with dimensions

The width of reinforced concrete products can be:

• 1.0 m;
• 1.2 m;
• 1.5 m;
• 1.8 m.

Structures with a width of 1.8 m are purchased extremely rarely, because due to heavy weight The installation process in the design position is greatly complicated.

PBs are used in almost the same way as the previous type. But their manufacturing technology allows you to give the product any length. Thickness – 220 mm. The width is the same as the PC series. The disadvantage is little experience in use and poor regulatory documentation.

Flat PTs are often purchased as additional elements for hollow-core slabs. They are available in thicknesses of 80 or 120 mm and are smaller in size, allowing them to cover narrow corridors, storage rooms, bathrooms.

Supporting the slabs

The laying of floor slabs is carried out after the preparation of the project or diagram on which the products are laid out. Floor elements must be selected so that they are sufficiently supported brick wall or expanded clay concrete blocks and laying without gaps in width.

The minimum support for the PB and PC series depends on their length:

• products up to 4 m long – 70 mm;
• products longer than 4 m – 90 mm.

Visual diagram how to correctly and incorrectly support floor slabs

Most often, designers and constructors accept optimal value wall support 120 mm. This value guarantees reliability even with small deviations during installation.

It would be correct to arrange in advance load-bearing walls at home at such a distance that it is easy to lay the slabs. The distance between the walls is calculated as follows: length standard slabs minus 240 mm. The PC and PB series must be laid with support on two short sides without intermediate supports. For example, PC 45.15 has a size of 4.48 m, 24 cm is subtracted from it. It turns out that the distance between the walls should be 4.24 m. In this case, the products will lie with the optimal amount of support.

The minimum support of PT series products on the wall is 80 cm. Installation of such reinforced concrete slabs is possible with support points located on all sides.

The support must not interfere with the passage of ventilation ducts. Optimal thickness load-bearing internal brick wall - 380 mm. 120 mm on each side goes under the reinforced concrete floor, and 140 mm remains in the middle - standard width ventilation duct. In this case, it is necessary to lay it as correctly as possible. Shifting the product to the side vent will lead to a decrease in its cross-section and insufficient ventilation of the premises.

Summarizing what was said:

• PC and PB series up to 4 m are supported on both sides by at least 7 cm;
• PC and PB series more than 4 m - not less than 9 cm;
• PT series – at least 8 cm on two, three or four sides.

Slab storage

Product storage schemes different types

After the scheme has been developed and the products have been purchased, they need to be placed on the building site for convenient installation to the design position. There are rules for storing materials:

• elements must be laid under a canopy;
• the storage location must be located within the access area of ​​the crane;
• Support points are provided with pads.

Failure to comply with the last rule will result in a break in half. PC, PB and PT products operate in such a way that the appearance intermediate supports or a solid base leads to cracks. Laying is done in the following order:

• wooden blocks or boards are laid on the ground under the edges of the slab;
• I transfer the ceiling element onto the boards using a crane from the machine;
• boards or bars are placed again on the laid slab;
• unload the second slab from the machine;
• repeat points 3 and 4, maximum storage height is 2.5 m.

Masonry requirements

Scheme for calculating floor slabs

In order to correctly install floor slabs, you need to ensure that the special requirements for a brick wall are met:

• evenness of the masonry in the place where the floors are laid;
• laying in three rows until overlapping reinforcing mesh with a cell of 5 by 5 cm made of wire with a diameter of 3-4 mm;
• The top row of the frets on the inside should be bonded.

If the slabs are mounted on expanded clay concrete blocks, an additional monolithic belt. This design will help to evenly distribute the load from heavy floors onto expanded clay concrete blocks with less strength. The construction technology involves pouring a monolithic concrete strip 15-20 cm thick onto the blocks.

Laying floors

To carry out the work, a minimum of three people will be required: one performs the slinging, and two install them in the design position. If the installers and the crane operator cannot see each other, when installing the slab, another worker will be needed to give commands to the crane.

Scheme of laying reinforced concrete products

Fastening to the crane hook is carried out with a four-branch sling, the branches of which are secured at the corners of the slab. Two people stand on both sides of the support and control its evenness.

When installing a PC, pinching into the wall is carried out in a rigid way, that is, bricks or blocks are laid on both the top and bottom of the slab. When using PB series floors, it is recommended to use hinged fastening. To do this, the slabs are not pinched from above. Many builders install the PB series in the same way as PCs and buildings stand, but it’s not worth the risk, because the quality of the installation load-bearing structures human life and health depends.

Another important feature of the use of products from the PB series is that it is prohibited to make technological holes in them.

These punches are needed for heating, water supply and sewerage pipes. Again, many builders, even when constructing multi-story buildings, neglect this. The difficulty is that the behavior of this type of floor under load over time has not been fully studied, since there are no objects built quite a long time ago. The ban on punching holes has reasons, but it is rather preventative.

Slab cutting

Sometimes, in order to install a slab, it is necessary to cut it. The technology involves working with a grinder and a disc on concrete. PC and PT slabs cannot be cut to length, since they have reinforced reinforcement in their support zones. If you support such a cut slab, then one edge will be weakened and serious cracks will appear along it. It is possible to cut PB slabs to length, this is due to the peculiarities of the manufacturing method. A timber or board is placed under the cut site, which will make the work easier.

Separation along the length is carried out along the weakened part of the section - the hole. This method is suitable for PC, but is not recommended for PB, since the width of the walls between the holes is too small.

After installation, the holes in the support areas on the walls are filled with lightweight concrete or hammered mineral wool. This is necessary to provide additional strength in areas where the walls are pinched.

What to do if it was not possible to distribute the products evenly across the width

Sometimes the dimensions of the room do not correspond to the width of the products, in which case all the spaces are combined into one. This space is covered with a monolithic section. Reinforcement occurs with curved meshes. Along their length, they rest on the top of the ceiling and seem to sag in the middle of the monolithic section. For floors, concrete of at least B 25 is used.

The technology of prefabricated floors using bricks or blocks is quite simple, but requires attention to detail.

The reliability of supporting the floors on load-bearing walls ensures safe, reliable and long-term operation of the entire building. Structural stability depends on proper execution engineering structures. Therefore, the support of floor slabs on walls is regulated by SNiP.

Parameters that determined the amount of support

The depth of the ceiling on the walls depends on the following factors:

• purpose and type of buildings - residential, administrative, industrial;
• material and thickness of load-bearing walls;
• the size of the overlapped span;
• sizes reinforced concrete structures and their own weight;
• the type of loads acting on the floor (static or dynamic), which of them are permanent and which are temporary;
• magnitudes of point and distributed loads;
• seismicity of the construction area.

All the factors listed above must be taken into account when calculating the reliability of the structure. In accordance with current regulatory documents The support of the floor slab on a brick wall is taken from 9 to 12 cm, the final size is determined by engineering calculations during the building design process. With smaller overlaps, the heavy dead weight of the elements, combined with acting loads, will have a direct impact on the edge of the masonry, which can lead to its gradual destruction.

On the other hand, a larger overlap will be a kind of pinching reinforced concrete elements with the transfer of weight from the upper section of the wall to their ends. The result is cracking and slow destruction of the masonry walls. Also, when the ends of the products approach the outer surfaces of the walls, heat loss in reinforced concrete elements increases with the formation of cold bridges, leading to the formation of cold floors. The cost of parts is proportional to their length, so excessive pinching will lead to an increase in the cost of the structure.

Supporting unit for a floor slab on a brick wall

When erecting brick buildings with floors made of prefabricated reinforced concrete slabs, masonry is carried out in full thickness to the design bottom of the ceilings. Next, the bricks are laid only with outside walls to form a niche into which the slabs can be laid.

In support units, it is important to comply with the following conditions:

• the ends should not rest against brickwork, so for the overlap of 12 cm most often used in practice, the width of the niche is ≥ 13 cm;
• the mortar on which the slabs are laid is of the same brand as the masonry one;
• voids in the channels are sealed at the ends using concrete liners, which will protect the ends from destruction when compressed under loads. The production of concrete liners is carried out at factories with delivery upon purchase of slabs; in the absence of liners, channel voids are filled with B15 concrete directly at the construction site.

Slab reinforced concrete products are placed on the end brick walls with one side. In this case, the minimum support of the floor slab on the end walls is not standardized. But in order to avoid destruction of the product when squeezing the hollow channel, the installation must be carried out in such a way that the masonry laid above the ceiling does not rest on the outermost void of the structure and the shoulders of the moments acting from the load must be of minimal values.

Requirements for the installation of armored belts under floor slabs

In buildings with walls made of blocks made of lightweight concrete (aerated concrete, aerated concrete, foam concrete, polystyrene concrete), which have low strength characteristics, the floors must be supported by reinforced belts. The armored belt is installed around the entire perimeter of the building. The height of the reinforced belt for floor slabs is from 20 to 40 cm. The connection of the reinforced belts with the floor parts must be mechanically strong, for which anchor devices are used or joining with reinforcing bars of a periodic profile using electric welding.

The design has the following requirements:

• the belts should be arranged across the entire width of the walls; for external walls with a width of ≥ 50 cm, a reduction of ≤ 15 cm is permissible for laying insulation;
• reinforcement performed using engineering calculations must provide sufficient mechanical strength to absorb loads from the own weight of reinforced concrete elements and overlying structures;
• concrete ≥ class B15;
• the belt is a kind of cold bridge, so it is necessary to insulate it in order to prevent the destruction of aerated concrete blocks from accumulated moisture;
• reliable adhesion to load-bearing walls.

Supporting floor slabs on aerated concrete blocks load-bearing walls reinforced belts is carried out in compliance with the following standardized values:

• at the ends ≥ 250 mm;
• along the rest of the contour ≥ 40 mm;
• when supported on 2 sides of the span ≤ 4.2 m - ≥ 50 mm;
• the same for a span ≥ 4.2 m - 70 mm.

Aerated concrete blocks are not able to withstand high loads; the material begins to undergo various deformations. The armored belt, taking on all the loads, distributes them evenly, thereby ensuring that the structure does not collapse.

Installation of floor slabs on gas silicate blocks is also carried out with the obligatory installation of monolithic reinforced concrete belts. The required support values ​​correspond to the above values ​​for walls made of aerated concrete blocks.

During installation work, the following conditions must be met:

• maintaining the symmetry of laying elements in spans;
• the ends of the slabs must be aligned along the same line;
• all elements must be located in one horizontal level(control is carried out using building level), tolerance in the plane of the slabs ≤ 5 mm;
• the thickness of the mortar under the slabs is ≤ 20 mm, the mortar must be freshly prepared, without the beginning of the setting process. Additional dilution of the mixture with water is unacceptable.

It is unacceptable to lay rows of bricks or reinforcing mesh instead of an armored belt.

Floor slabs

Factory-made floor slabs are a very popular option for floors in individual housing construction, because... the alternative is a monolithic concrete floor - a much more labor-intensive thing, difficult for inexperienced private developers. Unlike a monolith, the slabs come with a factory-guaranteed maximum load, which is more than enough in a private home.

Description

There are two GOST standards for floor slabs in Russia:

• GOST 9561-91 “Reinforced concrete hollow-core floor slabs for buildings and structures. Technical conditions."
• GOST 26434-85 “Reinforced concrete floor slabs for residential buildings. Types and basic parameters."

These GOSTs are similar in content, and both GOSTs are valid. According to GOST 9561-91, floor slabs are divided into:

• 1PC - 220 mm thick with round voids with a diameter of 159 mm, designed for support on two sides;
• 1PKT - the same, for support on three sides;
• 1PKK - the same, for support on four sides;
• 2PK - 220 mm thick with round voids with a diameter of 140 mm, designed for support on two sides;
• 2PKT - the same, for support on three sides;
• 2PKK - the same, for support on four sides;
• 3PK - 220 mm thick with round voids with a diameter of 127 mm, designed for support on two sides;
• 3PKT - the same, for support on three sides;
• 3PKK - the same, for support on four sides;
• 4PK - 260 mm thick with round voids with a diameter of 159 mm and cutouts in the upper zone along the contour, intended for support on both sides;
• 5PK - 260 mm thick with round voids with a diameter of 180 mm, designed for support on two sides;
• 6PK - 300 mm thick with round voids with a diameter of 203 mm, designed for support on two sides;
• 7PK - 160 mm thick with round voids with a diameter of 114 mm, designed for support on two sides;
• PG - 260 mm thick with pear-shaped voids, designed for support on two sides;
• PB - 220 mm thick, manufactured by continuous molding on long stands and designed to be supported on two sides.

This list does not include PNO type floor slabs, which are found in reinforced concrete manufacturers. In general, as far as I understand, slab manufacturers are not required to comply with GOST (Government Decree No. 982 of December 1, 2009), although many produce and label slabs in accordance with GOST.

Manufacturers produce slabs different sizes, you can almost always find the size you need.

In most cases, floor slabs are made prestressed (clause 1.2.7 of GOST 9561-91). Those. the reinforcement in the slabs is tensioned (thermally or mechanically), and after the concrete has hardened, it is released back. The compression forces are transferred to the concrete, and the slab becomes stronger.

Manufacturers can strengthen the ends of the slabs that participate in the support: fill round voids with concrete or narrow the cross-section of the voids in this place. If they are not filled by the manufacturer and the house turns out to be heavy (the load on the walls at the ends increases accordingly), then the voids in the area of ​​the ends can be filled with concrete yourself.

The slabs usually have special hinges on the outside, by which they are lifted by a crane. Sometimes reinforcement loops are located inside the slab in open cavities located closer to the four corners.

Floor slabs in accordance with paragraph 1.2.13 of GOST 9561-91 are designated as: type of slab - length and width in decimeters - design load on the slab in kilopascals (kilogram-force per square meter). The reinforcement steel class and other characteristics may also be indicated.

Manufacturers do not bother with designating the types of slabs and in price lists they usually write only the type of slab PC or PB (without any 1PK, 2PK, etc.). For example, the designation “PK 54-15-8” means a 1PK slab with a length of 5.4 m and a width of 1.5 m and with a maximum permissible distributed load approximately 800 kg/m2 (8 kilopascals = 815.77 kilogram-force/m2).

Floor slabs have a bottom (ceiling) and top (floor) side.

According to paragraph 4.3 of GOST 9561-91, slabs can be stored in a stack with a height of no more than 2.5 m. Pads for the bottom row of slabs and gaskets between them in a stack should be located near the mounting loops.

Supporting the slabs

Floor slabs have a support zone. According to paragraph 6.16 of the “Manual for the design of residential buildings Vol. 3 (to SNiP 2.08.01-85)":

The depth of support of prefabricated slabs on walls, depending on the nature of their support, is recommended to be no less than, mm: when supported along the contour, as well as two long and one short sides - 40; when supported on two sides and a span of slabs of 4.2 m or less, as well as on two short and one long sides- 50; when supported on two sides and the span of the slabs is more than 4.2 m - 70.

The slabs also have a series of working drawings, for example, “series 1.241-1, issue 22”. These series also indicate the minimum support depth (it may vary). In general, the minimum depth of support for the slab must be checked with the manufacturer.

But there are questions regarding the maximum depth of support for the slabs. IN different sources given completely different meanings, somewhere it is written that 16 cm, somewhere 22 or 25. One friend on Youtube assures that the maximum is 30 cm. Psychologically, it seems to a person that the deeper the slab is pushed into the wall, the more reliable it will be. However, the limitation maximum depth There definitely is, because if the slab goes too deep into the wall, then bending loads “work” differently for it. How deeper slab enters the wall, the lower the permissible stresses from loads on the supporting ends of the slab usually become. Therefore, it is better to find out the maximum support value from the manufacturer.

Similarly, slabs cannot be supported outside of the support zones. Example: on one side the slab lies correctly, and on the other side it hangs, resting on the middle load-bearing wall. Below I have drawn it:

If the wall is built from "weak" wall materials like aerated concrete or foam concrete, then you will need to build an armored belt to remove the load from the edge of the wall and distribute it over the entire area of ​​the wall blocks. For warm ceramics, an armored belt is also desirable, although instead of it you can lay several rows of ordinary durable solid brick, which does not have similar problems with support. With the help of an armored belt, you can also ensure that the slabs together form a flat plane, so there is no need for expensive ceiling plaster.

Laying slabs

The slabs are placed on the wall/armoured belt on cement-sand mortar 1-2 cm thick, no more. Quote from SP 70.13330.2012 (updated edition of SNiP 3.03.01-87) “Load-bearing and enclosing structures”, paragraph 6.4.4:

Floor slabs must be laid on a layer of mortar no more than 20 mm thick, aligning the surfaces of adjacent slabs along the seam on the ceiling side.

Those. the slabs are leveled to create a level ceiling, and an uneven floor can then be leveled with a screed.

During installation, the slabs are placed only on those sides that are intended for support. In most cases, these are only two sides (for PB and 1PK slabs), so you cannot “pinch” the third side, which is not intended for support, with the wall. Otherwise, the slab clamped on the third side will not correctly absorb the loads from above, and cracks may form.

Laying of floor slabs must be done before construction interior partitions, the slabs should not initially rest on them. Those. first you need to let the slab “sag”, and only then build non-load-bearing interior walls (partitions).

The gap between the plates (the distance between the sides) may vary. They can be laid closely, or with a gap of 1-5 cm. The gap space between the floor slabs is then sealed with mortar. Usually the gap width is obtained “by itself” when calculating required quantity slabs, their size and distance to be covered.

After installation, floor slabs can be tied together using, for example, welding. This is done in earthquake-prone regions (Ekaterinburg, Sochi, etc.); in ordinary regions this is not necessary.

In places where it is difficult to select a floor slab or where it is impossible to install it correctly, a monolithic floor should be poured. It must be poured after installing the factory slabs in order to correctly set the thickness of the monolith. You need to make sure the installation is tight monolithic ceiling, especially if a ladder will rest on it. The space formed between the floor slabs does not always have a trapezoidal shape or a shape with slab protrusions on which you can rest. If the monolith turns out to be rectangular and is not supported by the beveled edges of the adjacent slabs, then it can simply fall out.

Insulation

The ends of floor slabs lying on external walls must be insulated, because reinforced concrete has high thermal conductivity and the slab in this place becomes a cold bridge. Extruded polystyrene foam can be used as insulation. I drew an example:

To carrier outer wall 50 cm thick includes a slab with a support of 12 cm, which is insulated at the end with EPS ( Orange color) 5 cm thick.

Covering is one of the structural elements buildings dividing it inner space to the floors. The ceiling is a load-bearing element, as it receives and transmits the load from its own weight, as well as from equipment and people to walls, supports, and crossbars. It is made of reinforced concrete slabs.

Based on their location in the building, they can be divided into:

1. Above the basement.
2. Interfloor.
3. Attics.

According to their design, they are divided into beam and beamless. They are factory-made from reinforced concrete and are divided into prefabricated monolithic, multi-hollow, made of heavy concrete and cellular concrete. Floors must meet such requirements as strength, soundproofing, rigidity, fireproofing and waterproofing.

Basically, reinforced concrete slabs from which floors are made are multi-hollow structures and are produced with polygonal, oval and round voids. Most widespread They use slabs with round voids PNO and PC in construction, the load-bearing capacity of which is 800 kg/m2. They are distinguished by high strength, complete factory readiness for installation, and manufacturability. Such slabs rest on two sides. They are laid on load-bearing walls. Floors made from such slabs are used with load-bearing wall spacings of up to 9 m. Durability, fire resistance, the required spatial rigidity, and the stability of the building are what distinguish such floors.

Common standards for hollow core slabs:

• length - 2.4-7.2 m;
• width - 1-1.8 m;
• thickness - 220 mm.

The base on which the slabs are laid can be from:

• bricks;
• reinforced concrete panels;
• aerated concrete;
• foam blocks.

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Depth of floor support and necessary equipment for work

Depending on the base on which, the depth of support is taken into account.

Also taken into account are the length of the slab, its weight, the thickness of the supporting wall, the permanent or temporary load on the slab from above, and the seismic resistance of the building. The calculations are quite complex and are done by specialists. For an individual developer, it is enough to focus on the parameters of the manufacturer that labels their products and strictly follow them. Strict adherence to manufacturers' recommendations will eliminate errors in the design and installation of hollow-core structures, otherwise the consequences will entail costly and labor-intensive steps.

• for large-panel walls - 50-90 mm;
• on brick walls - 90-120 mm;
• on aerated concrete base - 120 mm;
• on foam block walls - 120 mm;
• on external walls the support is specified up to 250 mm.

Necessary equipment, materials and tools:

1. anchors;
2. cement mortar;
3. level or level - to determine the height difference between working surfaces;
4. crossbars - support beams;
5. mounting crowbar;
6. plumb line - to check the verticality of the surface;
7. inventory scaffolds;
8. mooring cord;
9. slings;
10. truck crane with a lifting capacity of 25 tons.

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Installation of floors in brick buildings

A team of four people is required for installation work. The crane operator delivers it to the base (wall) - the slab. The rigger is busy strapping the slabs with a four-legged sling. Two installers, located on both sides of the supports of the mounted slab, accept it, unfold it and then coordinate its lowering into a given position using guiding actions. After using mounting crowbars, they perform a small straightening of the slab, even before removing the slings.

In brick buildings they are laid on walls and crossbars. The crossbars are laid on reinforced concrete pads using slings. They must be laid into brick walls during laying. Before placing the crossbars, you need to check the horizontality of the cushions. The difference between them, or rather, their surfaces, should not exceed 10 mm. Then the crossbars are brought to the desired position using mounting crowbars. The installers themselves are located on the scaffolding. The crossbar must be moved only perpendicular to the longitudinal axis, using the blade of a mounting crowbar. Otherwise, the stability of the walls that support the crossbar will be compromised. Afterwards, the verticality (plumb line) and horizontality (with a level) are verified, and only then the crossbar is fixed to the base. When this work is completed, the slings are removed.

The use of hollow core slabs is possible in buildings with either transverse or longitudinal load-bearing walls, because they are supported on two sides. Then follows the anchoring of the floor, which is the fastening of the laid floor slabs to the external walls and to each other. Anchors are usually placed at a distance of no more than 3 m from each other.

Before laying the floor slabs, the horizontalness of the working surfaces is again verified. The ridge of the wall masonry must be leveled. Because enough is enough big square hollow core slabs will react sensitively even to small unevenness of the base. The plates will simply sway. Identified irregularities are laid with additional insulation strips.

And only after that they lower the slabs onto the supports, where the cement mortar has already been placed. In order to obtain a single rigid horizontal floor, the slabs are connected to each other and to the external walls with steel anchors, which are secured to mounting loops. The ends of the floor slabs are connected to the brick wall with L-shaped anchors. They are then sealed with a mortar mixture to protect against corrosion.

When the slabs rest on interior walls, then composite anchors are used, obtained by connecting them by welding. The gaps that appear between the slabs are filled with bricks used in the main masonry. The slabs are laid on mortar mixture.

After laying the slabs, the ceiling is checked for horizontalness. If a discrepancy is detected between adjacent slabs, they are lifted using a crane and the mortar bed is trimmed, after which they are put back in place. When the alignment is completed, the slabs are secured with anchors, which are laid in the masonry. Adjacent slabs are connected to each other using mounting loops with anchors.

In hollow-core floorings, if the support is on an external base, the voids are filled with heavy concrete or concrete plugs to a depth of approximately 12 cm. This is done for the purpose of insulation. The same is done in hollow containers of slabs that rest on internal load-bearing walls. The voids are filled in order to prevent the destruction of the supporting parts of the slabs under the pressure of the structures located above, since it is their edges that are the most fragile.

The lintels that are load-bearing, that is, those that bear the main load from the floors, are installed by lifting them with slings using the mounting loops and laying them on the mortar mixture. Ordinary lintels are placed manually, taking into account the support area and horizontality.

And now we will tell you about the amount of support of a reinforced concrete hollow core slab on the wall. What should this value be and what does it depend on, and what is written about this in various literature, including normative ones.

Let's start by looking at what the slab consists of. We will now see a cross-section of a round hollow-core floor slab, and you will see that on one side the hole is wider than on the other. According to the series, the hole that is wider has a diameter of 159 mm, and on the other hand the hole is smaller, and this depends on the pipe itself, which is placed in the formwork at the factory during manufacture.

During manufacturing, the slab should come to your production site with a poured (“solidified”, that is, poured concrete mortar) on one side, and sometimes on both sides. If it comes to you not monolithic, you must definitely do it yourself. This must be done with M100 mortar, or concrete of the same grade as the slab itself. If this is not done, then the amount of load that the edge of the slab can withstand will be 17 kg / cm2, and this is very small. Therefore, make sure that these voids are filled as required by regulatory documentation.

When pouring is done at the factory (it is done during the hardening process of the slab), it is better. The second side of the slab has a smaller hole and can withstand a larger load, it can be 45 kg/cm2, it depends on the width of the support. If the width of the support is 100mm, then the load will be 45 kg/cm2, if the support is larger, the load will be approximately 30 kg/cm2, however, in general this is enough.

Therefore, almost all slabs must be filled with a monolith on the side where smaller hole, but as for where the hole is larger, it depends on the plant, so keep an eye on this during construction.

So, let's return to our question, what should be the amount of support on the wall and what does it depend on. Often we can meet different walls, if it is aerated concrete, then resting the slab on such walls without a monolithic belt is strictly prohibited. Why can’t this be done, even if the stove is supported entirely on a gas block? Even if it is 30 cm, this is wrong, since the deflection of the slab will increase, so the slab will chip off the edge of the block, and subsequently the plaster. And if you make a monolithic belt, then concrete will withstand stress better than a gas block.

If the house is being built from brick, then you don’t have to make a monolithic belt, but you need to know exactly what brand of brick and span size.

So, if you have a brick wall, then what determines the amount of support? Firstly, from the material on which they rest, and secondly, from the span of the slab.

There is such a series as 1.141-1, which produces slabs from PK30 to PK65. It states that a slab with a span of up to 4 meters must rest on the wall at least 70 mm, and if it is more than 4 meters, then it must rest on a minimum of 90 mm. You can also refer to the recommendations of the manufacturer's plant, and one of these plants recommends these characteristics to us. You can find slabs at the factory different heights, these can be slabs of 220mm, 320mm and 400mm. The depth of support depends on the length of the span; the larger it is, the greater the height of the slab must be taken, and for each height there is its own nomenclature for supporting the slab.

We can have three types of slab support: on concrete, brick and on a metal beam. Let's take standard height slabs, namely 220 mm. The factory describes the normal and minimum support value as follows: “For a slab with a height of 220 mm, the minimum support value for concrete and metal is 80 mm, for brick 100 mm. The normal amount of support for a slab with a height of 220 mm, for concrete and metal - 100 mm, for brick - 150 mm.

If we take the literature of Soviet times, when more attention was paid to science and practice, then the following is written there: “The length of support of the slabs on the brickwork is determined by local crushing and is taken to be no less than 75 mm for a span of up to 4 meters and no less than 120 mm for a span of more than 4 meters.” meters."

It turns out that the factory series and literature give us different numbers, and who should we trust? But in our opinion, it is better to believe the series, because if something happens, you will be able to present your claims to the plant.

To summarize: despite the fact that there may be deviations during construction, we suggest taking into account the following figures: for spans (slab length) up to 4 meters - the minimum support is 80mm, for spans of more than 4 meters - 120mm.

Supporting floor slabs on walls

Arrangement of support for floor slabs

• Important structural element
• Some calculations
• Individual construction

During the construction of a building, the following must be taken into account: important question, like supporting floor slabs.

Correct and incorrect support of floor slabs.

Important structural element

Floors #8211 load-bearing elements buildings made of reinforced concrete structures. They receive and distribute the loads from their weight and the people and equipment in the building onto walls and supports. With their help, the internal space of the structure is divided into floors, and the attic and basement spaces are also separated.

Scheme of laying floor slabs.

Floors in a building must meet many requirements. They must be strong, rigid, have good soundproofing characteristics, not burn and not allow water to pass through.

The material used for the production of floor slabs #8211 is reinforced concrete. Basically, these are multi-hollow structures with voids of different shapes: polygonal, oval, round. Most often in construction, elements with round voids are used. They are highly durable, technologically advanced and completely ready for installation. Their load-bearing capacity #8211 is 800 kg/m². They are laid on load-bearing walls located at a distance of about 9 m from each other. They rest on two sides. They are distinguished by fire resistance, rigidity, and long service life. Brick, aerated concrete, foam blocks and reinforced concrete panels are used as materials for the walls on which such overlapping elements will be laid.

Some calculations

To find the amount of support for the floor slab great importance has a base on which it is planned to be laid. It is imperative to take into account the length and weight of the structure, the thickness of the supporting wall, and the seismological stability of the building. In addition, the load and its nature must be taken into account, whether it will be temporary or permanent. Such calculations should be carried out by specialists. For an individual developer, when drawing up a project and installation, the main reference point is the manufacturer’s markings.

Design diagram for a square floor slab, supported along the contour

When using flat overlapping elements, the span can be calculated as follows: you need to sum up the thickness of this element and the distance between the two supports. As for the depth of support of the floor slab on the brick base, this value should be equal to the thickness of the structure itself, but not less than 70 mm. To calculate minimum thickness external wall, which will become the basis for floor slabs, it is necessary to take into account the thermal insulation layer and facing material on the end parts of the latter. Thus, a structure with a thickness of 140 mm must be supported by a base whose thickness is at least 300 mm.

Installation of frequently ribbed structures that have liners requires minimal deepening of the floor slabs onto the base #8211 150 mm. During installation, do not allow hollow liners to enter the wall. If the ribs are reinforced with two rods, then it is necessary to bend them through one on the support. If the rib has one rod, then the clamps will take shear stress.

Reinforced masonry structures #8211 are analogues of flat ones. Therefore, the minimum value of the support depth of these elements can be determined in the same way. They must be at least 90 mm thick and supported on two sides.

Individual construction

In specialized literature on construction work the definition of the necessary standards regarding the depth of support of floor slabs is given.

Supporting floor slabs on walls

This figure is within the range of 90-120 mm. To more accurately determine this value, certain calculations must be made, which take into account the length and weight of the structure, the thickness of the supporting wall and the material from which it is made. The expected load must also be determined.

For example, the use of a slab 6 m long requires a depth of support on a brick base of at least 100 mm. When using structures made of reinforced concrete or steel, the permissible depth is at least 70-75 mm; for walls made of foam blocks and aerated concrete #8211, at least 120 mm.

The support depth of the floor slab is determined:

- from the condition of the strength of the slab against local compression, that is, it must be such that the concrete of the slab in the area with which it rests on the wall does not collapse. Indicated in series for slabs, usually at least 90 mm, and taking into account the hands of the builders - 120 mm

- depending on the strength of the wall material. For a 380mm brick wall made of brick grade 75 and above, 120 is sufficient.

Is there any reason why they don't allow it anymore? In theory, 250 mm would sit more firmly on the wall.

The reason is that the operation of the stove changes. The slab becomes pinched in the wall and turns from a beam into a continuous one, which is not desirable and may turn out to be weaker. The support of the slab on a brick wall is usually 120-150mm.

The holes in the voids are covered with a solution, reason - possible deformation in the compression zone from the load. How to cover 250 mm? mystery)

When loads at the top level of the slab are less than 17 kg/cm2 (450 tons per 1 linear meter of a 380 mm thick wall), the voids in the slabs are not filled; when loads are more than 17 kg/cm2, the voids are filled with liners in the factory.

All of the above is for slabs of the 1.141-1 series.

The support of floor slabs in construction is a really important issue. Floors are load-bearing elements of a building and distribute the load of the entire weight along the walls and supports.

Building codes have special instructions on this matter for each type of floor. In addition, in a particular case, the basis where they will be laid is also of great importance. It is necessary to take into account the following parameters:

• length, weight of the structure
• thickness of the support wall
• stability of the building (including seismological).

Based on this, it is clear that calculations must be carried out by specialists.

There are calculations for square slab ceilings (depth 70 mm). When installing frequently ribbed structures that have liners - 150 mm. Reinforced masonry structures, like analogues of flat ones, must have a minimum support depth of 90 mm.

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Floor slabs

Factory-made floor slabs are a very popular option for floors in individual housing construction, because... alternative - monolithic concrete floor- a much more labor-intensive thing, difficult for inexperienced private developers. Unlike a monolith, slabs come with a factory-guaranteed maximum load, which is more than enough in a private home.

Description

There are two GOST standards for floor slabs in Russia:

• GOST 9561-91 “Reinforced concrete hollow-core floor slabs for buildings and structures. Technical conditions."
• GOST 26434-85 “Reinforced concrete floor slabs for residential buildings. Types and basic parameters."

These GOSTs are similar in content, and both GOSTs are valid. According to GOST 9561-91, floor slabs are divided into:

• 1PC - 220 mm thick with round voids with a diameter of 159 mm, designed for support on two sides;
• 1PKT - the same, for support on three sides;
• 1PKK - the same, for support on four sides;
• 2PK - 220 mm thick with round voids with a diameter of 140 mm, designed for support on two sides;
• 2PKT - the same, for support on three sides;
• 2PKK - the same, for support on four sides;
• 3PK - 220 mm thick with round voids with a diameter of 127 mm, designed for support on two sides;
• 3PKT - the same, for support on three sides;
• 3PKK - the same, for support on four sides;
• 4PK - 260 mm thick with round voids with a diameter of 159 mm and cutouts in the upper zone along the contour, intended for support on both sides;
• 5PK - 260 mm thick with round voids with a diameter of 180 mm, designed for support on two sides;
• 6PK - 300 mm thick with round voids with a diameter of 203 mm, designed for support on two sides;
• 7PK - 160 mm thick with round voids with a diameter of 114 mm, designed for support on two sides;
• PG - 260 mm thick with pear-shaped voids, designed for support on two sides;
• PB - 220 mm thick, manufactured by continuous molding on long stands and designed to be supported on two sides.

This list does not include PNO type floor slabs, which are found in reinforced concrete manufacturers. In general, as far as I understand, slab manufacturers are not required to comply with GOST (Government Decree No. 982 of December 1, 2009), although many produce and label slabs in accordance with GOST.

Manufacturers produce slabs of different sizes; you can almost always find the size you need.

In most cases, floor slabs are made prestressed (clause 1.2.7 of GOST 9561-91). Those. the reinforcement in the slabs is tensioned (thermally or mechanically), and after the concrete has hardened, it is released back. The compression forces are transferred to the concrete, and the slab becomes stronger.

Manufacturers can strengthen the ends of the slabs that participate in the support: fill round voids with concrete or narrow the cross-section of the voids in this place. If they are not filled by the manufacturer and the house turns out to be heavy (the load on the walls at the ends increases accordingly), then the voids in the area of ​​the ends can be filled with concrete yourself.

The slabs usually have special hinges on the outside, by which they are lifted by a crane. Sometimes reinforcement loops are located inside the slab in open cavities located closer to the four corners.

Floor slabs in accordance with paragraph 1.2.13 of GOST 9561-91 are designated as: type of slab - length and width in decimeters - design load on the slab in kilopascals (kilogram-force per square meter). The reinforcement steel class and other characteristics may also be indicated.

Manufacturers do not bother with designating the types of slabs and in price lists they usually write only the type of slab PC or PB (without any 1PK, 2PK, etc.). For example, the designation “PK 54-15-8” means a 1PK slab with a length of 5.4 m and a width of 1.5 m and with a maximum permissible distributed load of approximately 800 kg/m2 (8 kilopascals = 815.77 kilogram-force/m2).

Floor slabs have a bottom (ceiling) and top (floor) side.

According to paragraph 4.3 of GOST 9561-91, slabs can be stored in a stack with a height of no more than 2.5 m. Pads for the bottom row of slabs and gaskets between them in a stack should be located near the mounting loops.

Supporting the slabs

Floor slabs have a support zone. According to paragraph 6.16 of the “Manual for the design of residential buildings Vol. 3 (to SNiP 2.08.01-85)":

The depth of support of prefabricated slabs on walls, depending on the nature of their support, is recommended to be no less than, mm: when supported along the contour, as well as two long and one short sides - 40; when supported on two sides and the span of slabs is 4.2 m or less, as well as on two short and one long sides - 50; when supported on two sides and the span of the slabs is more than 4.2 m - 70.

The slabs also have a series of working drawings, for example, “series 1.241-1, issue 22”. These series also indicate the minimum support depth (it may vary). In general, the minimum depth of support for the slab must be checked with the manufacturer.

But there are questions regarding the maximum depth of support for the slabs. Different sources give completely different values, somewhere it is written that 16 cm, somewhere 22 or 25. One friend on Youtube assures that the maximum is 30 cm. Psychologically, it seems to a person that the deeper the slab is pushed into the wall, the more reliable it is will. However, there is definitely a limitation on the maximum depth, because if the slab goes too deep into the wall, then bending loads “work” differently for it. The deeper the slab goes into the wall, the lower the permissible stresses from loads on the supporting ends of the slab usually become. Therefore, it is better to find out the maximum support value from the manufacturer.

Similarly, slabs cannot be supported outside of the support zones. Example: on one side the slab lies correctly, and on the other side it hangs, resting on the middle load-bearing wall. Below I have drawn it:

If the wall is built from “weak” wall materials such as aerated concrete or foam concrete, then you will need to build an armored belt to remove the load from the edge of the wall and distribute it over the entire area of ​​the wall blocks.

Error 404

For warm ceramics, an armored belt is also desirable, although instead of it you can lay several rows of ordinary durable solid brick, which does not have similar problems with support. With the help of an armored belt, you can also ensure that the slabs together form a flat plane, so there is no need for expensive ceiling plaster.

Laying slabs

The slabs are placed on the wall/reinforced belt on a cement-sand mortar with a thickness of 1-2 cm, no more. Quote from SP 70.13330.2012 (updated edition of SNiP 3.03.01-87) “Load-bearing and enclosing structures”, paragraph 6.4.4:

Floor slabs must be laid on a layer of mortar no more than 20 mm thick, aligning the surfaces of adjacent slabs along the seam on the ceiling side.

Those. the slabs are leveled to create a level ceiling, and an uneven floor can then be leveled with a screed.

During installation, the slabs are placed only on those sides that are intended for support. In most cases, these are only two sides (for PB and 1PK slabs), so you cannot “pinch” the third side, which is not intended for support, with the wall. Otherwise, the slab clamped on the third side will not correctly absorb the loads from above, and cracks may form.

The laying of floor slabs must be done before the construction of interior partitions; the slabs should not initially rest on them. Those. first you need to let the slab “sag”, and only then build non-load-bearing interior walls(partitions).

The gap between the plates (the distance between the sides) may vary. They can be laid closely, or with a gap of 1-5 cm. The gap space between the floor slabs is then sealed with mortar. Typically, the width of the gap is obtained “by itself” when calculating the required number of slabs, their size and the distance that needs to be covered.

After installation, floor slabs can be tied together using, for example, welding. This is done in earthquake-prone regions (Ekaterinburg, Sochi, etc.); in ordinary regions this is not necessary.

In places where it is difficult to select a floor slab or where it is impossible to install it correctly, a monolithic floor should be poured. It must be poured after installing the factory slabs in order to correctly set the thickness of the monolith. You need to make sure that the monolithic floor is installed rigidly, especially if a staircase will rest on it. The space formed between the floor slabs does not always have a trapezoidal shape or a shape with slab protrusions on which you can rest. If the monolith turns out to be rectangular and is not supported by the beveled edges of the adjacent slabs, then it can simply fall out.

Insulation

The ends of floor slabs lying on external walls must be insulated, because reinforced concrete has high thermal conductivity and the slab in this place becomes a cold bridge. Extruded polystyrene foam can be used as insulation. I drew an example:

The load-bearing external wall, 50 cm thick, includes a slab with a support of 12 cm, which is insulated at the end with 5 cm thick EPS (orange color).

See also:

Supporting floor slabs

Naboka A. A. Construction of reinforced concrete interfloor covering on metal beams in the old foundation // StudArctic forum. Issue 1 (5), 2017, DOI: 10.15393/j102.art.2017.923

Main text

They refer to UNESCO statistics according to which more than 50% of all European residential buildings were built in the period before the 50s of the last century. The need for repair or reconstruction of a large number of residential buildings Now no one doubts it. This is how the regional program operates in St. Petersburg overhaul common property in apartment buildings in St. Petersburg, for which it is planned to allocate about 32 billion rubles from 2017 to 2019.

Carrying out such a volume of work requires the involvement of a large number of specialists in the field of design. The work contains design solutions for the installation of a new interfloor ceiling in order to facilitate, reduce labor costs and optimize the design process. It is worth noting that the design solutions given are not binding and, in the opinion of the author, are purely advisory in nature and may contain errors and inaccuracies. The application of a particular solution must comply with existing standards and be confirmed by calculations.

The building structures of the old housing stock are not only outdated, their layouts and quality engineering equipment do not comply with modern standards, but also physically - individual structures outlive their operational period and are not able to meet the strength and reliability requirements imposed on them at the time of construction. The main causes of physical wear and tear are both time, a long period of use, and operating conditions - untimely and improper care and repairs.

Defects and damage, as well as the reasons for their occurrence characteristic of a particular type of structure, can be found in.

We are interested in overlaps. The most common types of floors in old apartment buildings are floors on metal and wooden beams. Floor structures are shown in Figures 1 and 2.

Picture 1. The most common design of interfloor ceilings on wooden beams in the old foundation

Figure 2. The most common design of interfloor ceilings on metal beams in the old foundation

When carrying out a major overhaul, it may be discovered that the existing load-bearing beams are in poor condition and require replacement. Then there is a need to install a new floor. The simplest to perform is a reinforced concrete floor on metal beams using a profile sheet as permanent formwork. Further solutions for the arrangement of this floor will be considered.

First of all, you need to install the metal beams. It is better to use rolled profiles as load-bearing beams. Figure 3 shows a node for supporting a metal beam on a load-bearing brick wall of a house.

Figure 3(a). Beam support unit on brickwork

Figure 3 (B). Supporting unit for a beam on brickwork. Section A-A

Figure 3 (B). Supporting unit for a beam on brickwork. Section B-B.

Where, 1 is a stiffener; 2 - support sheet.

The stiffener is installed to ensure the stability of the beam and prevent bending of the I-beam flange. The support sheet is necessary to distribute the load on the brickwork.

Other options for the design of the support unit can be found in.

The span between load-bearing walls sometimes reaches 6 m or more, and it is not possible to deliver a metal beam to the mounting mark in one piece due to its large weight. Narrow entrances, the impossibility of installing lifting mechanisms and equipment for lifting beams - all these are the difficulties that builders encounter. Then it becomes necessary to make an equal-strength installation joint, shown in Figure No. 4.

Figure 4. Equally strong assembly joint of beams.

The most popular is the assembly joint, in which the top and bottom plates are the same in width and wider than the I-beam flanges. But in construction conditions for the convenience of carrying out welding work The upper plate can be made narrower than the I-beam shelf, then the lower one should be enlarged. (This is exactly the joint shown in Figure 4).

All metal elements must be protected from corrosion. A typical solution is a layer of GF-021 primer and 2 layers of PF-115 enamel. Fire protection measures for metal structures should also be taken into account.

After installing the beams, they begin to install a reinforced concrete slab along the top flange of the I-beam and inter-beam filling.

The predominant way to install reinforced concrete slabs in the old foundation is to use corrugated sheets as permanent formwork. (If the designer decides to use a profiled sheet also as working external reinforcement, the requirements specified in c. should be taken into account).

Profiled sheets should be joined together along the longitudinal edges with an overlap using self-drilling screws or rivets with a pitch of no more than 500 mm. They should be attached to load-bearing metal beams using metal screws in each corrugation on the outer supports and through the corrugation in the intermediate ones.

The profile flooring should be selected depending on the pitch of the beams so that it can withstand the load from the weight of the slab until it gains strength.

Figure 5 shows a possible floor reinforcement scheme.

Figure 5. Scheme of reinforcement of a floor slab using a profiled sheet.

The reinforcement consists of longitudinal rods laid in each corrugation of the corrugated sheet and upper reinforcing mesh with a pitch of 150-200 mm. The frame elements are connected either by welding or using steel wire.

Figure 6. Flooring on metal beams using profiled sheets as permanent formwork

Sound attenuation in reinforced concrete slab the overlap is too small, so to ensure comfortable conditions accommodation and noise reduction requires additional sound insulation. Available on the market wide choose heat and sound insulation materials and, depending on the budget, you can select the required material. To fix the material on the bottom shelf, use a profile sheet or separate profiles. As finishing You can use plasterboard facing panels.

At the end the overlap pie will look like shown in Figure 7

Figure 7. The final overlap pie

This overlap will allow you to implement any layout; however, the partitions should be made of lightweight materials, for example, gypsum plasterboard. WITH possible options partitions can be found in.

It is worth noting that the installation of such an overlap may be accompanied (depending on the type of initial overlap) by an increase in loads on the walls and foundation. When replacing floors on more than just one floor, an inspection should be carried out to ensure that the walls, foundation and base are able to withstand the design loads.

Conclusion.

A sharp increase in the volume of major repairs and reconstruction work carried out in the old building indicates the need to develop standard solutions.

The article contains design solutions and recommendations for the installation of a new floor, which received wide application during reconstruction rear. All accepted materials must be certified and comply with current regulatory documents.

Bibliography

1. Savyovsky, V.V. Repair and reconstruction of civil buildings / V.V. Savyovsky, O.N. Bolotskikh. - Kharkiv: Publishing House“Spirit level” 1999. – 287 p.

2. Decree of the Government of St. Petersburg dated December 8, 2016 No. 1127 (short-term plan for the implementation of the regional program for capital repairs of common property in apartment buildings in St. Petersburg in 2017, 2018 and 2019)

3. Rabinovich G.M. Twice born / G.M. Rabinovich. - Leningrad: Stroyizdat, (Leningrad branch Leningrad, Ostrovsky Square, 6) 1971. - 112 p.

4. Fizdel, I.A. Defects and methods for their elimination in structures and structures (2nd edition, supplemented and corrected) / I.A. Fizdel. – M.: Stroyizdat. 1970.

What is the support depth of floor slabs according to SNiP?

5. TsNIIproektstalkonstruktsiya. Series 2.440-1 Issue 1. Frame and hinge units of beam cages and junctions of crossbars to columns / TsNIIproektstalkonstruktsiya, VNIKTIstalkonstruktsiya Ministry of Montazhspetsstroy of the USSR, VNIPI Promstalkonstruktsiya - approved 12/15/1981 Gosstroy of the USSR ( State Committee Council of Ministers of the USSR for Construction Affairs)

6. JSC "TSNIIPSK im. Melnikov." STO 0047-2005 Steel-reinforced concrete floors with monolithic slab on steel profiled flooring. Calculation and design / JSC TsNIIPSK im. Melnikov", CJSC "Hilti Distribution Ltd" - M. 2005 - 63 p.

7. Knauf company. Product Catalog. Partitions - http://www.knauf.ru - product catalog Knauf. More details: http://www.knauf.ru/catalog/complete-systems/partitions/