Floors made of monolithic reinforced concrete floor slabs have long been known and have proven themselves in the construction of private and multi-storey buildings. To this day, they are in demand and popular, especially in the construction of cottages. large area. Reinforced concrete hollow-core floor slabs have a lot of advantages; the design of these slabs is such that, in addition to evenly distributing the load over the entire surface, they also additionally add rigidity and stability to the building.

General information and advantages of reinforced concrete slabs

The slabs are made of concrete, in which iron reinforcement is installed during pouring. The slabs along their length have circular longitudinal voids, which, in combination with reinforcement, gives the structure a huge advantage. The reinforced concrete slab is able to withstand bending, does not break under high loads, it is very durable at correct operation during construction. Factory-produced monolithic slabs meet all the requirements for floors; they are durable and resistant to high temperatures. It is very important that the reinforced concrete slab is a good sound insulator and, in addition, retains heat.

Equally important is the fact that the use of slabs in construction greatly speeds up and simplifies the process; they can be installed where no other flooring method is suitable. For example, laying the floors of a private house with an area of ​​more than 100 m² using pouring will take a lot of time, in addition, labor costs, as well as financial costs, will be much higher than when laying the floor with reinforced concrete slabs.

Correct selection of slabs and calculations

When laying the floor of the first floor, you need to understand that a large load will be placed on it, so it is important to correctly calculate the weight of the structure and take into account everything, right down to the total weight of the house and the furniture or equipment that will be installed in the premises. The thickness of reinforced concrete slabs is standard and equal to 220 mm, but the slabs can be designed for different weight loads depending on their brand. Here, the reinforcement of the slab and what grade of concrete it is made of play a role.

Reinforced concrete slabs are produced in lengths of 2.4-6.8 meters, the width of such slabs, depending on the length, is 1.2-1.5 meters, and their weight is 0.9-2.5 tons. This allows the use of small equipment during construction, cranes with a lifting capacity of up to 3 tons. It is not difficult to understand which slab you need; a marking is placed on the surface, for example, a PC 8-42-12 slab will be 4.2 meters long, 1.2 m wide, with a weight load of 800 kg/m².

Rules for installing slabs depending on the floor

When laying floor slabs, it is important to consider where they will be laid, since installation rules ground floor differ from laying floors between floors.

In the case of laying a basement floor, it is necessary to first carry out work to level the foundation, namely its upper edge. To do this, the upper edge of the foundation is not made of high formwork from boards; here it is necessary to pour a small layer of concrete to create a perfectly flat horizontal surface. Now a reinforced concrete slab can be laid on such a platform.

The slabs are laid taking into account their taper; it turns out that the lower part of the slab will fit smoothly with the adjacent row. There is a small seam at the top that needs to be sealed. cement mortar. This results in an almost flat floor surface in the shortest possible time. Depending on the type of floor you'll be laying, you may need to use a thin screed, but for most flooring materials, a slab without additional finishing is suitable.

In the case when a reinforced concrete slab is laid as a floor between floors, an additional reinforced concrete belt must be made on the walls made of bricks or blocks. This is something like a seismic belt, which is performed as follows. When the height of the walls is laid out to the required height, another row is laid, but one layer needs to be laid in order to leave an inner end around the entire perimeter, into which the slab will lie, and from the outside this place will be covered with brick. Before laying the slab, as in the first case, it is necessary to perform formwork and pour a thin layer of concrete with reinforcement. As a result, a niche is formed with a small gap for laying insulation materials, where the slab is laid. A thin layer of reinforced concrete increases the strength of the surface and evenly distributes the load from the slab along the walls.

Insulation

Floor slabs themselves serve good insulation, since they are located inside the house, there is no need to insulate them, however, it is necessary to insulate the ends. The slab has high thermal conductivity, which is undoubtedly good, because the slab on the upper floor conducts heat from below and thus the floor becomes warm. But the stove will receive cold from the ends, so you need to protect it with a layer of insulation. In the niche that was formed during the reinforcement process, where the slab adjoins the wall, it is necessary to lay insulation. Then this space, like the rest of the cracks, is filled with concrete.

It is necessary to carry out insulation, otherwise condensation will form in these voids, which the slab will absorb and gradually collapse. In addition to the destruction of the slab, humidity will appear in the room, and in places where there is reinforcement, rust will appear, which will not be covered with any putty.

Actually, this completes the process of creating floors and interfloor ceilings; now you can begin finishing the floor with materials. As already mentioned, you may have to apply a thin leveling layer of screed

With these types of work, construction equipment can greatly help you, for example

Reinforced concrete floors are characterized by high strength, rigidity and good sound insulation. Depending on the design, reinforced concrete floors can be prefabricated or monolithic.

Prefabricated reinforced concrete floors

Prefabricated reinforced concrete floors are assembled from ready-made factory reinforced concrete slabs, produced in a certain range of sizes. This range may be different for each manufacturing plant, but the length and width modules of the slabs are the same for all produced slabs. The length of the produced slabs ranges from 2m to 7.2m, while the length change module is 100mm. That is, slabs with a length of 2.1 m, 2.2 m, 2.3 m and so on can be produced. The width of the slabs can be 1m, 1.2m, 1.5m, 1.8m. The most common thickness of reinforced concrete slabs is 220mm. Industrially produced slabs have their own brand. For example, “PK 36-12-8t” will mean that the length of the slab is 3.6 m, width 1.2 m, design load 800 kg/m2, and “T” is the index of heavy concrete. It should be noted, however, that the actual dimensions of the slab are actually slightly smaller than those stated in the brand and in the house project. So our slab will have actual dimensions of 3580 x 1190 mm. This difference is due to the size of the gap between the floors and is necessary to maintain the design dimensions between the reference axes.

Iron plates concrete floors have a large weight from 0.7 to 2.5 tons, so a crane is required for their installation. An important nuance installation prefabricated floor is that the slabs for laying can be taken either from a truck or from a pre-stacked stack(s). And it is better to initially load or stack the slabs so that during the installation of the floor, the top slab is the first and the bottom is the last.

The support of the floor slabs on the wall or crossbar must be at least 120mm. Depending on the material of the walls, if they are insufficiently strong, it may be necessary to install reinforced concrete or brick reinforced belt, on which the slab will subsequently rest. The seams between the slabs are filled with concrete and carefully leveled.

Monolithic reinforced concrete floors

Monolithic floor with installed formwork

Monolithic reinforced concrete floors are erected directly at the construction site and form a single horizontal plane. The shape of the monolithic floor can be any, which removes the planning restrictions from the house design that are present in the case of the installation of fully prefabricated concrete floors. The process of erecting a monolithic slab consists of several stages - installing formwork, laying reinforcement cage, pouring cement, dismantling the formwork after gaining strength.

Formwork for a monolithic floor can be made from edged boards or plywood, with the latter being the most preferred option since it forms a flat surface with fewer seams. However, no less a good option There is also metal formwork, but not everyone has the opportunity to use it. Flat formwork elements rest on horizontal wooden or metal beams, under which they place vertical racks. It is highly advisable to use metal, height-adjustable stands, since with their help it will be easier to set the exact horizontal plane for pouring the slab. Metal racks can be rented. After assembly, the formwork must be absolutely rigid and withstand not only the weight of the reinforcement and poured concrete, but also possible additional loads during the pouring process.

When assembling the reinforcement frame of a monolithic floor, it is necessary to ensure its even spatial geometry. The first layer of reinforcement should be raised above the formwork plane by 20-50mm. This distance is called the protective layer of concrete and can vary depending on the thickness of the ceiling and its design parameters. The protective layer is necessary to prevent corrosion of the reinforcement and ensure the fire resistance of the structure. In order to lift the reinforcement above the formwork, it is installed on special plastic clamps, which can be designed for different thicknesses of the protective layer of concrete, the cross-section of the reinforcement, and have a wide variety of shapes. The second layer of reinforcement is raised above the first with the help of supporting reinforcement elements.

PROBLEM OF CHOICE

Currently, floors in private houses are made of wood and reinforced concrete. Both wooden and reinforced concrete floors have several solution options. The choice of flooring material is primarily determined by the structures of the building itself (for example, in houses with wooden walls and wooden floors), and also depends on the purpose of the floor, the capabilities of the developer and the characteristics of the construction site.

For example, between the first residential floor and an unheated basement, it is best to install a reinforced concrete floor, which is more resistant to moisture and easier to use. Between the residential floor and the attic, a light wooden floor would be appropriate, which would not create additional load on the walls and foundations. In a house with an attic, in which it was decided to make the floor above the first floor wooden, under the rooms with wet conditions (shower, bath, toilet) located on this floor, it will be necessary to install a fragment of reinforced concrete floor.

The decision-making may also be influenced by the conditions of the construction site, in particular, the possibility of access for transport and construction equipment. In cases of cramped conditions in a small area, it is better to abandon prefabricated reinforced concrete floors, giving preference to solutions that can be implemented using manual labor or small-scale mechanization means - winches or manual (electric) hoists.

The choice of material and design of the floor also depends on the characteristics of the soil at the construction site. For example, if at the level of the base of the foundations there are soils with low bearing capacity, it is better to make floors with low dead weight - wooden ones, which transfer small vertical loads to the foundations.

WOODEN COVERS

Wooden floors have long prevailed in private construction due to the availability of the material. The load-bearing element in the structure of a wooden floor is beams.

Depending on the characteristics of the beams, wooden floors can be divided into the following types:
- floors with beams made of solid wood;
- floors with beams of composite section;
- ceilings with beams on two levels.

Section dimensions wooden beams depend on the span (the distance between the supports, that is, the distance between the load-bearing walls) and the pitch of the beams in plan. These parameters are determined by the designer through calculations when designing the floor. The composition of the floor and the number of its elements depends on the design of the floor and the method of filing the ceiling.

Floor covering boards can rest directly on floor beams or on joists laid on the beams. In the first case, the ceiling provides little protection from impact noise created when people move along the ceiling. If floor boards are laid on joists, then soundproofing pads are placed between the joists and beams.

The ceiling structure can be made from wooden flooring(rolling) laid between the beams. The beating (in the form of shields or individual boards) is supported on cranial bars nailed to the beams. Until recently, the finishing of the ceiling was made of plaster over shingles, which was pressed onto the lower surface of the shingle.

A more progressive solution is to line the ceiling with plasterboard slabs, which are attached directly to the lower plane of the load-bearing floor beams. This is also better in terms of fire safety requirements, since two layers of ordinary ceiling plasterboard or one layer of fire-resistant plasterboard will provide all the requirements for fire resistance of load-bearing materials wooden structures ceilings

Floors with spaced beams (that is, the beams are located in two levels with a shift between them in plan) are probably the most suitable solution: the floor boards rest on the upper beams, and the ceiling lining is attached to the lower ones. In this case, there is no need to lay logs under the floor boards. The beams used here are of smaller cross-section, so the load on them is reduced. Such a ceiling does not transmit the sounds of impact noise, since the beams are not connected to each other.

Beams in floors can be made of solid wood or glued beams, the cross-section of which consists of several elements glued together, can be used. Glulam beams have greater strength than solid wood beams and are capable of covering large spans; they are less susceptible to moisture (they do not change size when air humidity changes), but their cost is higher.

The cross-section of composite beams can be designed in the form of a T-beam or an I-beam. Such beams are made from boards 30-50 mm thick. For their production, less wood is spent in volume than for solid beams, but the load-bearing capacity of these beams is no lower.

Today, ready-made wooden I-beams, in which the horizontal elements are made of laminated veneer lumber and the vertical elements are made of OSB boards, are becoming increasingly popular.

Options for sections of wooden floor beams: a - solid beam; b - glued beam; c - T-section beam; g - I-beam; d - ready I-beam with a stack of OSB boards

Traditional wooden floor: 1 - load-bearing beams; 2 - cranial bars 50x50 mm; 3 - ceiling flooring (panel roll); 4 - plaster on shingles; 5 - soundproofing gasket; 6 - lag; 7 - floor made of boards; a - beam pitch

Wooden floor with beams on two levels: 1 - floor beams; 2 - ceiling beams; 3 - floor boards; 4 - plasterboard ceiling lining; a - beam pitch

I-beams with an OSB-plate stand have high load-bearing capacity with low weight

Advantages wooden floors:
- low weight, which contributes to less consumption of materials for foundation construction;
- performing the entire range of work on installing the ceiling manually, including supplying material to the installation site;
- quick and easy installation;
- low cost. Disadvantages of wooden floors:
- susceptibility to rotting with constant moisture, which requires good ventilation of structures, as well as surface treatment with biological protection agents (antiseptics);
- easy flammability of wood requires surface treatment with fire retardants (means that increase fire resistance) and protection from open fire by cladding or applying fire-retardant paints and varnishes to their surface;
- the difficulty of making floors with large spans (more than 6 m), which entails a significant consumption of materials due to the need to increase the height cross section load-bearing beams, and therefore the thickness of the floor itself;
- impossibility of making wooden floors under rooms with wet conditions (bathrooms, showers, toilets, laundries);
- the need to install a heat-insulating seam in places where the ceiling adjoins the chimney ducts from stoves, fireplaces and boilers.

REINFORCED CONCRETE FLOORS

Reinforced concrete floors can be divided into three main types:
- floors made of prefabricated reinforced concrete slabs;
- floors made of monolithic reinforced concrete;
- combined (prefabricated-monolithic) floors.

Prefabricated floors are made from factory-made hollow-core reinforced concrete slabs, which are produced mainly with a width of 1.0; 1.2 and 1.5 m. Their thickness is 220 mm. The length of prefabricated slabs varies - from 2.4 m to 9.0 m. These slabs are very heavy, 1 m2 of such a slab weighs about 300 kg. To install these floors, there must be free space near the house, which is required not only for the delivery of slabs by car, but also for placing a truck crane, with the help of which the slabs are laid in place.

Monolithic reinforced concrete floors are made in the form of a flat or, less commonly, ribbed slab. The ribs of the slab can protrude upward or downward. To construct these floors, it is necessary to arrange formwork and perform reinforcement from steel rods. Floors with a flat slab usually have a thickness of 200 mm with a span of no more than 4.5 m (otherwise the consumption of materials increases sharply). Such floors are very heavy: 1 m2 weighs about 480 kg.

To produce monolithic ribbed slabs, less material consumption is required (reinforcing steel and concrete mixture), but the formwork for them is somewhat more complicated, which increases the labor costs for its manufacture. But such slabs can cover spans of up to 6 meters or more. The weight of 1 m2 of such floors is less than that of floors with a solid slab 200 mm thick (it depends on the span of the slab and the pitch of the rib beams). If the ribbed beams of ribbed floors protrude upward, it is more difficult to lay the floors. Ribbed floors, in which the beams protrude downwards, require a suspended ceiling.

Combined prefabricated monolithic floors made from prefabricated elements and monolithic concrete. They may have different designs. One of the simplest options is to install a monolithic slab along load-bearing metal beams from a rolled profile - channel or I-beam.

A monolithic reinforced concrete slab in such floors can be located above the beams or rest on their lower chords. When making such floors, you can do without the manufacture of removable formwork, which is necessary for laying the concrete mixture. In this case, permanent formwork made of galvanized steel profiled sheet is used.

This design makes it possible to perform monolithic slab smaller thickness, which reduces the consumption of concrete and reinforcement. There is also no need to install and dismantle formwork. However, such ceilings require a different approach to the construction of the floor or ceiling. In addition, floors using steel beams need protection from open fire in the form of plastering the beams metal mesh, facing with plasterboard or painting with fire-retardant paints.

Monolithic floors: 1 - flat slab; 2 - ribbed slab with beams protruding downwards; 3 - ribbed slab with beams protruding upward; a - beam pitch

Prefabricated monolithic floor with a slab along the upper chord of the beams: 1 - monolithic slab; 2 - steel beams; a - beam pitch

Prefabricated monolithic floor with a slab along the lower belt of beams: 1 - steel beams; 2 - monolithic slab; 3 - permanent formwork from corrugated sheet; 4 - concrete; 5 - reinforcing mesh; a - beam pitch

Teriva prefabricated monolithic floor: 1 - floor beams; 2 - hollow blocks; 3 - monolithic concrete; a - beam pitch

Advantages of reinforced concrete floors:
- rigidity of the floor, increasing the reliability of the building structure;
- high strength of the material, allowing it to withstand increased loads;
- good fire resistance, meeting all the requirements of current fire safety standards; better resistance to moisture than wooden structures.

Disadvantages of reinforced concrete floors:
- a significant mass of the floor, transmitting a large force to the foundations, which requires greater consumption of materials for their construction;
- the need to install monolithic distribution belts under floor supports in walls made of materials with low strength (cellular concrete, porous ceramic blocks);
- a long time for constructing the floor, which is associated with the implementation of formwork, reinforcement, and the acquisition of the required strength by concrete, which is achieved only after 28 days;
- the need to construct formwork and temporary supports for it;
- the need to use cranes when making floors from precast reinforced concrete slabs;
- when making monolithic floors, mechanisms are needed to supply concrete to the place of installation and the use of vibrators to compact the concrete mixture;
- space is required for the access of vehicles transporting structures, concrete mixture or materials for its preparation.

FREQUENTLY RIBBED COVERS

The frequently ribbed reinforced concrete floor does not require formwork: the space between the load-bearing beams is filled with hollow blocks, after which the entire structure is filled with concrete

Frequently ribbed ceilings deserve special mention. From a constructive point of view, they are also prefabricated monolithic floors. The idea is that the space between the floor beams is filled with hollow blocks, after which the entire structure is poured on top with a layer of concrete. In Europe, this is the most popular type of flooring in private construction.

Purlin beams are a reinforced concrete strip with a cross-section of 120 x 40 mm, into which a reinforcement frame is mounted in the form of a spatial truss. The length of the beams is 2.2-8.0 m. The beams are laid in increments of 600 mm and supported by load-bearing walls. Hollow liner blocks are placed between the beams, supported on their longitudinal edges.

The installation of such an overlap does not require continuous formwork. Temporary supports for beams consist of 50 mm thick boards laid at trench spacing of 600 mm. 1 m2 of such a floor weighs about 260 kg, that is, much less than a monolithic or prefabricated one.

Blocks can be made of concrete - the products differ greater mass(22 kg) and a lower price, or from expanded clay concrete - these blocks are lighter (only 14 kg), they provide more high level heat and sound insulation, but their price is higher. Block size - 520x240x210 mm.

Concrete is laid on top of the structure of beams and blocks, which fills the spaces between the beams and forms a ribbed monolithic slab 30 mm thick. If necessary, reinforcement mesh is laid on top of the blocks.

Elements of prefabricated reinforced concrete floors are manufactured at the factory, therefore, during design, standard elements are used according to current catalogs and reference books.

Prefabricated reinforced concrete floors are divided into three main groups: in the form of decking (slabs), large-panel And beam

1. Ceilings in the form of decking consist of flat or ribbed elements of the same type, placed closely; connect them by filling the gaps with cement mortar. Reinforced concrete deck slabs differ in the type of cross-section (solid, hollow-core and ribbed) and the method of reinforcement (with conventional or prestressed reinforcement).

· Solid reinforced concrete slabs for floors are the most durable among other types of reinforced concrete slabs used for floors. Their lower smooth surface, serving as a ceiling, forms a plane ready for finishing, and floors are laid on the upper surface. Solid floor slab is used for interfloor floors in buildings with a cross arrangement load-bearing walls and support around the perimeter, or on three sides. The design load that solid slabs must withstand is 600 kgf/m². They are used, as a rule, for the construction of interfloor ceilings of multi-apartment buildings. panel houses. Solid slabs also have their disadvantages - they are inferior to hollow-core floor slabs in terms of sound and thermal insulation.

· Void, or else - multi-hollow, floor slabs - perhaps the most common type. Such slabs can have a length sufficient to cover 12-meter spans. They are used for constructing floors in buildings with longitudinal load-bearing walls.

Depending on the span length, they can be 160 mm high (for spans up to 4 m) and 220 mm (for spans over 4 m). The floorings have longitudinal round, oval or vertical voids.

To the benefits hollow-core floor slabs should be attributed to the relative simplicity and speed of their installation, low cost and ability to withstand specified loads almost immediately after installation, good heat and sound insulation qualities.

· Ribbed panels require even less concrete and steel for their production than hollow flooring. Such slabs are made with ribs in one or two directions with a solid slab at the top or bottom. Laying the panels edge down improves the use of concrete in the compressed area, but due to the downward protruding beams it creates a non-flat ceiling, which limits its use in residential buildings. They find application in attic coverings or in industrial construction. When laying ribbed panels with the ribs up, a smooth ceiling surface is obtained, but the lack of a flat top complicates the installation of a clean floor.

2. Large-panel floors consist of room-sized elements.

Large panels are produced solid ( single-layer, layered and with liners ) , hollow , ribbed , tent with a raised midsection and folded . Floors made of large load-bearing panels are also used, the lower surface of which is the ceiling; a floor of several layers is laid on top.

By design interfloor large-panel reinforced concrete floors can be with layered floor, separate type (with a separate floor, ceiling or two separate load-bearing panels) and with laminated floor and split ceiling . All these floor structures have a relatively small mass (less than 300 kgf/sq.m.); Standard sound insulation is ensured by a layered floor structure or the presence of a continuous air gap in the thickness floors.
Floor panels They produce solid, hollow (with round voids) and tent-shaped ones. The load-bearing single-layer panel is reinforced concrete slab constant cross section with a lower surface ready for painting and a flat upper surface.

Large panels are also used to make separate type ceilings, in which separate ceiling and floor panels are laid with a gap to create a closed air space between them. Floor elements are separated by spacers or a continuous layer of soundproofing material from the ceiling slabs and walls. The separate type of floors has increased sound insulation properties compared to solid floors. No joints in floor panels within the room increases their sound insulation and provides more high quality ceiling finishing. At installation of floors separate type, which uses the soundproofing ability of the air gap between the upper and lower communication floor panels, as well as when installing layered floors, it is possible to ensure the standard soundproofing ability with a floor mass of less than 300 kgf/sq.m.

3. Floors on reinforced concrete beams mainly used in low-rise industrial buildings. The supporting structure is reinforced concrete T-section beams, on the supporting flanges of which gypsum concrete slabs or lightweight concrete roll-up slabs reinforced with wooden slats are laid. Overlappings of this type require little metal consumption, but are labor-intensive to manufacture. Prefabricated reinforced concrete interfloor slabs beam type consist of T-profile beams and filling between them. The filler here is a roll of gypsum concrete or lightweight concrete slabs 80 mm thick and 395 mm long, reinforced with wooden slatted or timber frames, and in attic floors - lightweight concrete slabs 90 mm thick and 395 mm long, reinforced with welded steel mesh. The seams between the beams and slabs are filled with cement mortar and rubbed. Attics and basements floors They must be insulated and soundproof between floors. To do this, use expanded clay or sand bedding, layered coatings with elastic gaskets. At the same time, it is desirable that heat and sound insulation is not carried out at the expense of increasing the weight of building structures.
Since the elements beam floors They have a relatively light weight and are used on buildings equipped with low-capacity cranes (up to 1 t).

ü When installation of reinforced concrete floors In sanitary facilities, a waterproofing layer is included in the floor structure. To do this, 1-2 layers of roofing felt are usually glued on top of the decking or panels using bitumen mastic.

ü To construct the ceiling of balconies, solid reinforced concrete slabs are usually used, which are clamped into the brickwork of the wall and welded to the reinforcement outlets from the underlying concrete lintel. It is also possible to use special embedded elements and attach them to floor slabs. To cover loggias, you can use hollow-core slabs, which have a console on the outer edge with embedded metal plates for attaching fences.

ü For bay window ceilings that have different outlines in plan, it is advisable to use monolithic reinforced concrete structures, which are easy to do directly on the construction site.

According to forum participant ontwerper from Moscow, it’s not that difficult to do on your own. He cites well-known and little-known considerations for their manufacture as arguments. In his opinion, making ceilings with your own hands is beneficial for several reasons:

1. Availability of technologies and materials;
2. Convenience and practicality from architectural and engineering points of view;
3. Such floors are durable, fireproof and have noise-insulating properties;
4. Financial feasibility.

Monolithic works

Before pouring concrete, ontwerper advises to carefully think through the entire process and, first of all, order concrete from the factory. It is better than homemade - there is control over the quality and quantity of fillers that improve the concrete and prevent it from delaminating for a long time. The composition must consist of heavy aggregates, have a strength class of B20-B30 (M250-M400), and frost resistance of F50.

Don’t be lazy and check the documents for the release parameters, grade and time until the concrete sets.

If you need to supply concrete to the second, third floor or over a long distance, you will not be able to do this without a concrete pump, and rolling concrete with shovels along endless gutters is a very difficult and inconvenient task.

IN winter time concrete can be ordered with anti-frost additives, taking into account that additives usually increase the time of strength gain, some of them provoke corrosion of reinforcement, but this is acceptable if the additive is factory-made.

ontwerper prefers not to carry out construction in winter, and does not recommend it to you. As a last resort, do not prepare the solution yourself; use industrial concrete.

Installation of formwork

The main purpose of formwork is to withstand the mass of freshly poured concrete and not deform. To calculate the strength you need to know that one 20 centimeter layer of concrete mixture presses on square meter formwork with a force of 500 kg, to this you need to add the pressure of the mixture when it falls from a hose, and you will understand that all structural elements must be reliable.

To make it, ontwerper recommends using 18-20mm laminated (coated) or plain plywood (but it sticks more strongly). For beams, crossbars and formwork posts, timber with a thickness of at least 100x100 mm should be used.
After assembling it, it is necessary to check the horizontalness of all structures. Otherwise, you will waste a lot of time and money fixing errors in the future.

Reinforcement

The lower one is along the span, the lower one is across the span, the upper one is across the span, the upper one is along the span.

span– the distance between the supporting walls (for a rectangular slab on the short side). The lowest row is placed on plastic crackers specially designed for this; their height is 25-30mm. The top row overlaps it across and is knitted with wire at all intersections.

Then the next step is the installation of a mesh separator - parts made of reinforcement with a certain pitch, it can be done at will. On the dividers - knit the top one across, - knit the top one along it, - knit with wire at all intersections. The top point of the frame (top of the upper rod) should be 25-30 mm below the top edge of the formwork wall, or the thickness of the concrete is 25-30 mm above the top reinforcement.

After the reinforcement is completed, the frame should be a rigid structure that should not move when concrete is poured from the pump. Before pouring, check that the pitch and diameter of the reinforcement correspond to the design.

Pouring concrete

After all the preparation, you need to take and distribute the concrete over the entire area and vibrate it. It is best to fill the slab entirely at one time; if this is not possible, place cuts - intermediate walls inside the formwork contour that limit concreting. They are made from steel mesh with a cell size of 8-10 mm, installing it vertically and attaching it to the frame reinforcement. Under no circumstances should you make cuts in the middle of the span and do not make them from boards, PPP.

Curing

After pouring the slab, you need to cover it to prevent precipitation from entering, and constantly water the outer surface to keep it moist. After about a month, you can remove the formwork, and in case of emergency, this can be done no earlier than after a week and only remove the panels. To do this, you need to carefully remove the shield and back up the slab with a stand. The racks support the stove until it is completely ready, about a month.

Strength of monolithic floor: calculation

It comes down to comparing two factors:

1. Forces acting in the slab;
2. The strength of its reinforced sections.

The first must be less than the second.

Walls on a monolithic floor slab: calculating the loads

Let us calculate the constant loads on a monolithic floor slab.

Self-weight of a monolithic floor slab with a load safety factor of 2.5 t/m3 x 1.2 = 2.75 t/m3.
- For slab 200mm - 550kg/m3

Own weight of a floor with a thickness of 50mm-100mm – screed – 2.2t/m2 x 1.2= 2.64t/m3
- for floor 50mm - 110kg/m3

Bring partitions made of bricks measuring 120mm to the area of ​​the slab. The weight of 1 linear meter of a partition with a height of 3m is 0.12m x 1.2x1.8 t/m3 x 3m = 0.78t/m, with a step of partitions 4m long it turns out to be approximately 0.78/4 = 0.2t/m2. Thus, the reduced weight of the partitions = 300 kg/m2.

Payload for the 1st group of limit states (strength) 150 kg/m3 - housing, taking into account the reliability factor of 1.3, we will accept. Temporary 150x1.3= 195kg/m2.

The total design load on the slab is 550+110+300+195=1150kg/m2. For sketch calculations we will accept a load of - 1.2t/m2.

Determination of moment forces in loaded sections

Bending moments determine 95% of the reinforcement of flexural slabs. Loaded sections are the middle of the span, in other words, the center of the slab.

Bending moments in a square slab of reasonable thickness, hingedly supported - not restrained along the contour (on brick walls) for each of directions X,Y can be roughly defined as Mx=My=ql^2/23. You can get some values ​​for special cases.

• Slab in plan 6x6m - Mx=My= 1.9tm;
• Slab in plan 5x5m - Mx=My= 1.3tm;
• The slab is 4x4m in plan - Mx=My= 0.8tm.

These are forces that act both along and across the slab, so you need to check the strength of two mutually perpendicular sections.

Checking strength to the longitudinal axis

When checking the strength to the longitudinal axis of the section by bending moment (let the moment be positive, i.e. belly down), the section has compressed concrete on top and stretched reinforcement on the bottom. They form a power couple that perceives the momentary force coming to it.

Determination of effort in this pair

The height of the pair can be roughly determined as 0.8h, where h is the height of the slab section. We define the force in the reinforcement as Nx(y)=Mx(y)/(0.8h). We get a representation of the 1 m width of the slab section.

• Slab in plan 6x6m -Nx(y)= 11.9t;
• Slab in plan 5x5m - Mx=My= 8.2t;
• The slab is 4x4m in plan - Mx=My= 5t.

For these efforts, select reinforcement of class A-III (A400) - a periodic profile. The calculated tensile strength of the reinforcement is R=3600kg/cm2. cross-sectional area of ​​the reinforcing bar with diameter Ф8=0.5cm2, Ф12=1.13cm2, Ф16=2.01cm2, Ф20=3.14cm2.

The bearing capacity of the rod is equal to Nst=Ast*R Ф8=1.8t, Ф12=4.07t, Ф16=7.24t, Ф20=11.3t. From here you can obtain the required reinforcement spacing. Step = Nst/ Nx(y)

• Slab in plan 6x6m for F12 reinforcement Step=4.07t/11.9t=34cm;
• Slab in plan 5x5m - for F8 reinforcement Step = 1.8/ 8.2 = 22cm;
• Slab in plan 4x4m - Ф8 Step=1.8/5=36cm.

This is strength reinforcement in each of the X and Y directions, i.e. a square grid of rods in the tensile zone of concrete.

In addition to strength, it is necessary to reduce the formation of cracks. For slabs of houses and residential premises with a span of up to 6 m, 200 mm thick, supported along the contour (i.e. on four sides) at any a/b ratio, you can take lower working reinforcement from A III rods in two directions with a step of 200x200 with a diameter of 12 mm, upper ( constructive) - the same from F8, thinner and smaller should not be.

All this is a special case of the general approach, demonstrating the specifics of the task, but to implement it it is necessary to look deeper and turn to specialists.

Posted by FORUMHOUSE member ontwerper.

Editor: Adamov Roman