The device of monolithic reinforced concrete floors. The construction of wooden floors between floors: detailed construction technology. Formwork for a monolithic floor slab - installation features

The most reliable (but not always expedient) option for interfloor overlapping is a monolithic overlap. It is made of concrete and reinforcement. Read about the rules for installing monolithic floors in this article. Analysis of the characteristics of types and applications, the device of monolithic ceilings.

In what cases is it necessary to install monolithic ceilings

Monolithic reinforced concrete floor is the most reliable, but also the most expensive of all. existing options. Therefore, it is necessary to determine the criteria for the expediency of its device. In what cases is it advisable to install monolithic ceilings?

1. Impossibility of delivery/installation of precast concrete slabs. Subject to a conscious rejection of other options (wooden, lightweight Terriva, etc.).
2. Complex configuration in plan with an "unfortunate" location internal walls. It, in turn, does not allow decomposing a sufficient number of serial floor slabs. That is, it is required a large number of monolithic areas. The cost of a crane and formwork is not rational. In this case, it is better to immediately go to the monolith.
3. Unfavorable operating conditions. Very heavy loads, extremely high humidity values ​​that cannot be completely solved by waterproofing (car washes, swimming pools, etc.). Modern floor slabs are usually prestressed. Tensioned steel cables are used as reinforcement. Due to their very high tensile strength, their cross section is very small. Such plates are extremely vulnerable to corrosion processes and are characterized by brittle rather than ductile fracture.
4. Combination of overlapping functions with the function of a monolithic belt. Supporting precast concrete slabs directly on light block masonry is generally not allowed. A monolithic belt device is required. In cases where the cost of the belt and the prefabricated floor is identical or exceeds the price of the monolith, it is advisable to dwell on it. When resting it on a masonry with a depth equal to the width of the belt, the device of the latter is usually not required. An exception may be difficult soil conditions: subsidence of the 2nd type, seismic activity, karst formation, etc.

Determination of the required thickness of a monolithic floor

For bendable plate elements, decades of application experience reinforced concrete structures, the value is experimentally determined - the ratio of thickness to span. For floor slabs, it is 1/30. That is, with a span of 6m optimum thickness will be 200mm, for 4.5mm - 150mm.

Understatement or vice versa, an increase in the accepted thickness is possible based on the required loads on the floor. At low loads (this includes private construction), it is possible to reduce the thickness by 10-15%.

VAT of slabs

For determining general principles reinforcement monolithic floor it is necessary to understand the typology of his work through the analysis of the stress-strain state (SSS). The most convenient way to do this is with the help of modern software systems.

Let's consider two cases - free (hinged) support of the slab on the wall, and pinched. Plate thickness 150mm, load 600kg/m2, plate size 4.5x4.5m.

Deflection under the same conditions for a pinched slab (left) and a hinged slab (right).

The difference in moments Mx.

The difference in the moments of Mu.

The difference in the selection of the upper reinforcement according to X.

The difference in the selection of the upper reinforcement according to W.

The difference in the selection of the lower reinforcement according to X.

The difference in the selection of the lower reinforcement according to W.

Boundary conditions (character of support) are modeled by superimposing the corresponding links in the support nodes (marked in blue). For hinged support, linear movements are prohibited, and for pinching, rotation is also prohibited.

As can be seen from the diagrams, when pinched, the work of the support area and the middle area of ​​the slab differ significantly. AT real life any reinforced concrete (prefabricated or monolithic) is at least partially pinched in the body of the masonry. This nuance is important in determining the nature of the reinforcement of the structure.

Reinforcement of a monolithic floor. Longitudinal and transverse reinforcement

Concrete works great in compression. Reinforcement - tensile. Combining these two elements, we get a composite material. Reinforced concrete in which strengths each component. It is obvious that the reinforcement must be installed in the tension zone of the concrete and absorb the tensile forces. Such reinforcement is called longitudinal or working. It must have good adhesion to concrete, otherwise it will not be able to transfer the load to it. For working reinforcement, rods of a periodic profile are used. They are designated A-III (according to the old GOST) or A400 (according to the new one).

The spacing between rebars is the spacing of the reinforcement. For floors, it is usually taken equal to 150 or 200 mm.
In case of pinching in the support zone, a support moment occurs. It generates a tensile force in the upper zone. Therefore, the working reinforcement in monolithic ceilings is located both in the upper and lower concrete zones. Particular attention should be paid to the bottom reinforcement in the center of the slab, and the top one at its edges. And also in the area of ​​​​leaning on internal, intermediate walls / columns, if any - it is here that the greatest stresses arise.

To ensure the required position of the upper reinforcement during concreting, transverse reinforcement is used. It is located vertically. It can be in the form of supporting frames or specially bent parts. In lightly loaded plates, they perform a constructive function. At high loads, the transverse reinforcement is involved in the work, preventing delamination (cracking of the slab).

In private construction in floor slabs, transverse reinforcement usually performs a purely constructive function. The supporting transverse force (the "shear" force) is taken up by the concrete. An exception is the presence of point supports - racks (columns). In this case, it will be necessary to calculate the transverse reinforcement in the support zone. Transverse reinforcement is usually provided with a smooth profile. It is designated A-I or A240.

To maintain the upper reinforcement during concreting, bent U-shaped parts are most widely used.

Filling the ceiling with concrete.

Calculation of a monolithic floor example

Manual calculation of the required reinforcement is somewhat cumbersome. This is especially true for determining the deflection, taking into account the opening of cracks. The norms allow the formation of a crack in the tensile zone of concrete with a strictly regulated opening width. They are completely invisible to the eye, we are talking about fractions of a millimeter. It is easier to simulate several typical situations in a software package that performs calculations strictly in accordance with current building codes. How to calculate the device of monolithic floors?

The following loads are taken into account:

1. Self-weight of reinforced concrete with a design value of 2750kg/m3 (with a standard weight of 2500kg/m3).
2. The weight of the floor structure is 150 kg/m2.
3. Partitions weight (average) 150 kg/m2.

General view of the calculation scheme.

Scheme of plate deformation under load.

Mu moments diagram.

Plot of moments Mx.

Selection of upper reinforcement according to X.

Selection of upper reinforcement according to U.

Selection of the lower reinforcement according to X.

Selection of the lower reinforcement according to U.

The spans were assumed to be 4.5 and 6 m. The longitudinal reinforcement is given:

• class A-III fittings,
• protective layer 20mm

Since the area of ​​support of the slab on the walls was not modeled, the results of the selection of reinforcement in the extreme plates can be ignored. This is a standard nuance of programs that use the finite element method for calculation.

Pay attention to the strict correspondence of bursts of moment values ​​with bursts of the required reinforcement.

The thickness of the monolithic slab

In accordance with the calculations performed, it can be recommended that for the installation of monolithic ceilings, in private houses, the thickness of the ceiling is 150mm, for spans up to 4.5m and 200mm up to 6m. Exceeding a span of 6m is undesirable. The diameter of the reinforcement depends not only on the load and span, but also on the thickness of the slab. Reinforcement often installed with a diameter of 12 mm and a pitch of 200 mm will form a significant margin. You can usually get by with 8mm in 150mm increments or 10mm in 200mm increments. Even this reinforcement is unlikely to work to the limit. The payload is taken at the level of 300 kg / m2 - in housing it can be formed, perhaps, by a large closet completely filled with books. The actual load in residential buildings, as a rule, is significantly less.

The total required amount of reinforcement is easy to determine based on the average reinforcement weight coefficient of 80kg/m3. That is, for a floor device with an area of ​​​​50m2 with a thickness of 20cm (0.2m), 50 * 0.2 * 80 \u003d 800 kg of reinforcement (approximately) will be needed.

In the presence of concentrated or more significant loads and spans, it is impossible to use the diameter and pitch of the reinforcement specified in this article for a monolithic ceiling device. A calculation will be required for the corresponding values.

Video: Basic rules for the installation of monolithic floors

Monolithic floors

reinforced concrete slabs, monolithic ones are also popular among private developers. Their advantages include not only the solidity and durability inherent in the same plates, but also the ability to cover rooms of any configuration. At the same time, the disadvantages include a large mass of plates, requiring a reinforced base and wall materials of increased strength, and the need to assemble the formwork. Therefore, many self-builders, including the craftsmen of our portal, prefer a lightweight variety - monolithic ceilings on a profiled sheet, which will be discussed in the material. Consider:

• What is a monolithic overlap on a profiled sheet.
• Technology of the device of steel-reinforced concrete floors.
• The experience of the portal participants in the installation of unsupported monolithic ceilings according to the profiled sheet.

Monolithic overlap on a profiled sheet

Initially, NIIZhB (Research Institute of Concrete and Reinforced Concrete) of the USSR Gosstroy developed a method for pouring monolithic reinforced concrete floors with steel (SPN) for industrial buildings and structures. The first recommendations for the design of monolithic reinforced concrete floors with SPN were developed in 1987, after almost two decades, STO 0047-2005 appeared, in fact, a slightly updated version of the first version. However, for those who want to understand the technology and make calculations on their own, without resorting to the services of a pro, our old-timers are advised to first study the training manual from the Land of the Soviets.

Yury

If you want to understand without extra costs, read the recommendations for the design of monolithic reinforced concrete floors with steel profiled decking, NIIZhB, 1987.

The essence of the technique lies in the fact that the corrugated board serves both as an external reinforcement of the plate, as well as the finishing layer.

When talking about industrial premises, such exterior finish more than enough. According to the developers of the service station, lightweight ceilings along the profile, compared to a conventional monolithic slab, have a number of advantages:

• Reducing the amount of steel on beams - by 15%.
• Reducing labor costs - by 25-40%.
• Reducing the mass of the plate - by 30-50%.
• Increasing the rigidity of floors (to horizontal loads).
• Simplification of communications wiring - placement of highways in corrugations.
• The absence of wooden formwork - an increase in the speed of work.

The use of steel-reinforced concrete floors in the construction of industrial and private buildings is permissible under the following basic conditions:

• slightly aggressive and non-aggressive operating environment;
• humidity conditions up to 75%;
• the temperature in the room is not higher than + 30⁰С;
• used concrete without potassium chloride and other chlorine-containing additives.

That is, the main contraindication to this type of overlap is high humidity, which is why they are usually used as interfloor and are not used between the basement and the first floor or the basement and the first floor.

al185 FORUMHOUSE Super Moderator

The profiled sheet in the base will rot, who are interested in the timing, look with a search. On the protection of the wheel arches, galvanized self-tapping screws rust in a couple of months.

For pouring slabs, it is allowed to use both heavy and light concretes, but the compressive strength class for heavy concrete on fine-grained aggregates is from B15 (M200), for lightweight concrete on porous aggregates - from B12.5 (M150). The minimum layer of concrete above the profile flooring is 30 mm, if a finishing screed is provided, if without a screed - from 50 mm. The flooring is made of load-bearing profiled sheets (H), with a corrugation height of 44 mm.

For the reinforcing cage, reinforcing bars of a periodic profile, class A-III, and class Bp wire are used. If an overlap with a stairway is planned, then it is necessary to reinforce the reinforcing cage around the perimeter and install side formwork. steel beams power frame either rolled or composite profiles.

Technology for the installation of steel-reinforced concrete floors

In the original version, the profiled sheet is laid not only on the walls, but also on the frame of steel beams (girders), which is the carrier. The number and parameters of the beams are calculated individually, based on the dimensions of the overlapped span and the expected loads, the average step is from 1.5 to 3 m, but each sheet should have three support points - in the center and along the edges. Single-layer reinforcement - mesh, wire diameter from 3 mm, pitch 200 × 200 mm, thickness of the protective layer over the mesh is at least 15 mm.

Profiled sheets are laid across the long side of the span, with wide corrugations down, along the length on the overlap runs, at least one wave, butt-to-width. Between themselves, the waves are fixed with rivets or self-tapping screws with a step of no more than 500 mm. In order for the profile and runs to work as one system, the flooring is fixed with rod anchors that are welded to the beams. Next to the load-bearing walls, the anchor must pass through each wave, on intermediate beams through one. In addition, the flooring is fixed to the beams by means of self-tapping screws or dowels.

However, the use of steel beams is not the most attractive option for self-builders, so many of the craftsmen of our portal prefer Alternative option- unsupported monolithic overlap along the profile sheet.

The experience of the portal participants in the installation of unsupported monolithic ceilings according to the profiled sheet

winder

Overlapping on a professional sheet can be without I-beams or channels.

Instead of a frame, a bearing profiled sheet is used with a wave height of 60 mm or more, a thickness of 0.7 mm, and reinforced reinforcement - lower, upper, transverse and mesh. In this case, the profiled sheet is a non-removable formwork, and the reinforced reinforcing cage takes the main loads. The sheets are laid with a narrow corrugation down and, just as in the method with beams, they are oriented in waves across the long side of the span. It turns out a kind of ribbed monolithic overlap, only the ribs are formed not by removable formwork, but by corrugations. Unlike a steel-reinforced concrete slab supported by beams, this slab is not recommended to be poured with lightweight concrete, and the compressive strength class should be increased to B22.5 (M300).

winder

It is reinforced concrete that holds the load, neither foam concrete nor expanded clay concrete have the necessary strength. Strengthening the reinforcement in this case is useless.

When pouring, be sure to carefully vibrate the solution. If necessary, props are placed from below, which are removed after the concrete has gained strength.

One of our craftsmen decided to use the profiled sheet not only as a formwork, but also as an additional power frame.

worodew

I make a monolithic ceiling according to the H75 profiled sheet, 0.7 mm thick. In order not to lose its bearing capacity, after pouring, I decided to include it in joint work with concrete. I did this: with a puncher (drill 6 mm) in each ridge, I punched holes through a meter and inserted pieces of wire 6 mm thick, 10 mm long into them, and instead of stars, I put and tied reinforcement on it, plus a mesh on top. Even stiffness has increased, I compare before and after knitting reinforcement.

Spans of 3.6 and 2.0 m, in a wave reinforcement 12 mm, on top - a wire mesh 5 mm thick, with a cell of 100 × 100 mm. From below, the waves were closed with gas block trimmings and sealed the cracks mounting foam, one bottle was enough for 70 m². The flooring rests only on external walls and on a load-bearing wall in the middle. The slab was poured with a concrete pump, the ceiling thickness was 130 mm, the area was 76 m², about 7 m³ of mortar (M300) was taken. After a few hours, it was possible to cut off the bumps, focusing on the rule, the next day I moistened the slab and polished it.

The underfloor heating system is usually mounted in a finishing screed, but if desired, you can combine a warm floor and a monolithic ceiling along a profiled sheet.

Toha71

Is it possible to install TP pipes directly into the poured slab? Will the presence of TP pipes in it not weaken such an overlap? And if possible, how much thickness to add under the 20 pipe? As I understand it, the TP must be placed between the layers of reinforcement so that the top layer of reinforcement in concrete is not “drowned” for its normal operation? I would like to try once and pour the concrete evenly so that only the finishing self-leveling floor remains and you do not have to load the slab with an additional screed.

The method has the right to life, subject to an increase in the thickness of the overlap and the presence of certain experience.

Sometimes in private housing construction, such a variant of floors is used - monolithic reinforced concrete, based on metal beams(paired channels, I-beams, square pipe, etc.).

The advantages of such an overlap is that due to the fairly often located beams (from 1 m to 2.5 m on average), the overlap itself can be made quite thin (but not less than 50 mm). Such an overlap is reinforced in one layer, which also gives considerable savings.

The main disadvantage is that, according to fire safety requirements, metal structures must be coated with a special flame retardant, and this is an expensive pleasure.

In this article, we will consider two questions: how to make a reinforced concrete floor and how to choose metal beams.

Where should you start? From the floor plan analysis. Let's say we have a floor of 4x8 m. It is more rational to place the beams along the short side of the slab, i.e. the length of the beams will be 4 meters (not counting the depth of support on the walls). The shorter the beam, the less metal we will spend on it, and the less frequently these beams can be placed. Of course, this is not a hard and fast rule, just rational advice.

The load from the weight of the partitions (it is advisable to place the beams under the partitions to avoid excessive load on the lightweight floor),

The own weight of the floor.

Then you need to set the pitch of the metal beams. Here, a monolithic overlap comes to the fore. If we make the step of the beams too frequent, we risk causing an overrun of both metal and reinforced concrete. If the distance between the beams, on the contrary, is too large, this will cause an increase in the reinforcement in the slab, an increase in the thickness of this slab (in this case, the load on the beams will increase significantly), which means that the section of the beams will also increase. Therefore, always before starting the calculation, it is necessary to analyze and select the optimal distance between the floor beams. The calculations below are applicable under the following conditions: there must be the same distance between all beams; the condition L 1/L 2 > 2 must be satisfied, where L 1 is the length of the beam, L 2 is the distance between adjacent beams.

In principle, there are several ways to calculate this type of overlap.

The first way (more time-consuming, especially without sufficient experience, but sometimes necessary). You can specify the profile of metal beams (for example, you already have metal of a specific profile); then, given the thickness of the floor and the step of the beams, you can collect the loads and perform the calculation of the beam. At the same time, performing the calculation, in several approaches you can determine the maximum allowable distance between the beams, at which the conditions of strength and deformability are met. After that, you can proceed to the calculation of the floor and determine its thickness and reinforcement. If everything went well, fine. If the thickness turned out to be greater than you specified, the calculation will need to be repeated from the beginning - until all parts of the problem converge.

Second way. The calculation begins with a reinforced concrete floor. We set the step of the beams and the thickness of the slab, collect the loads and perform the calculation of the slab. If necessary, we adjust the spacing of the beams and the thickness of the slab to the most economical results. We collect the load on the beam from the resulting span and select the section of the beams.

We will consider the second way with an example.

The calculation is carried out for conditionally a dedicated strip of slab 1 m wide.

It is necessary to block the room with a plan size of 6x10 m. Above the ceiling there will be living rooms - a temporary load of 150 kg / m 2. Slab materials: class B15 concrete, design concrete resistance Rb = 7.7 MPa, hot-rolled rebar of a periodic profile of class A400C, design resistance of rebars s Rs = 365 MPa.

The minimum floor thickness must be greater than L /35, where L is the distance between the beams.

We set the step of the beams - 2.5 m, the direction of the beams - along the short side of the room, the thickness of the reinforced concrete. ceilings - 80 mm (which is more than 2.5 / 35 \u003d 0.071 m \u003d 71 mm), the distance from the bottom edge of the slab to the working reinforcement is 35 mm.

We collect loads on 1 m 2 of overlap.

Type of load:	normative, kg / m 2	safety factor	calculated, kg / m 2
Partition weight load (average)
Floor own weight 2500*0.08

To calculate the overlap, it is necessary to find the maximum bending moment that occurs in the extreme span of the slab, and is equal to: М = qL 2 /11 ( see formula 6.169 reference book "Design of reinforced concrete structures”, Golyshev A.B.).

In our case, q = 6241 m, L = 2.5 m - the distance between the beams, then M = 624 * 2.5 2 / 11 \u003d 355 kg * m.

For slabs reinforced with mesh in the lower zone(without top reinforcement), the following condition must be met:

αm > αR (See Section 3.18 of the Concrete Design Guide and reinforced concrete structures made of heavy and light concrete without prestressing). α R value find from tables s 18 allowances. For class AIII (A400C) reinforcement and class B15 concrete αR = 0.440.

We find α m \u003d M / R b bh 0 2 \u003d 355 / (770000 * 1 * 0.045 2) \u003d 0.228, where

b = 1 m - strip width s floor for which the calculation is performed;

h 0 \u003d 0.08 - 0.035 \u003d 0.045 m - the distance from the upper zone of the plate to the center of gravity of the working reinforcement.

Condition αm = 0.228< αR = 0,440 выполняется. Из таблицы 20 пособия при αm = 0,228 находим значение

Find the area of ​​the working reinforcement of the plate:

As \u003d M / (R s * ζ * h 0) \u003d 355 / (36500000 * 0.87 * 0.045) \u003d 0.000248 m 2 \u003d 2.48 cm 2. We accept rebar with a diameter 8mm in increments of 200 mm (5 rods per 1 meter of slabs s, with an area of ​​​​2.52 c m 2).

For self-examination, you can use the table from the reference book Linovich L.E. for the selection of thickness and reinforcement of the floor, depending on the load. This table shows the results for single-span slabs. Our slab is considered multi-span (the number of spans is equal to the number of beam steps), and it works much better due to multi-span. Therefore, the results of the calculation according to the example should be better (more economical) than in the table from the reference book.

We proceed to the calculation of the beam (see the book Ya.M. Likhtarnikov "Calculation of steel structures” pp. 60-61 or the book Vasiliev A.A. "Metal structures" §24). First of all, it is necessary to determine the linear load on each beam. The load on 1 m 2 of the floor turned out to be 540 (624) kg / m 2, and we took the step of the beams 2.5 m. Then the load per 1 linear meter of the beam is:

standard 540*2.5 = 1350 kg/m;

calculated 624*2.5 = 1560 kg/m.

The span of the beam in the clear is 6 m. The depth of support on each side is 0.2 m. Then the estimated length of the beam is 6 + 2 * 2 * 0.2 / 3 = 6.3 m.

Let's find the maximum moment in the beam section according to the formula M = qL 2 /8, where q is the load per 1 running meter of the beam, L is the estimated length of the beam.

Standard moment M n \u003d 1350 * 6.3 2 / 8 \u003d 6698 kg * m,

design moment M p \u003d 1560 * 6.3 2 / 8 \u003d 7740 kg * m.

Determine the required moment of resistance:

W tr \u003d M p / 1.12R \u003d 7740 / (1.12 * 21) \u003d 329 cm 3. According to the assortment (for example, a reference book by Ya.M. Likhtarnikov Calculation of steel th structures, Appendix VI), we select an I-beam No. 27 (modulus W = 371 cm 3, moment of inertia I = 5010 cm 4).

We check the strength of the beam from the condition:

σ= M/1.12W \u003d 7740 / (1.12 * 371) \u003d 18 kN / cm 2, which is less R \u003d 21 kN / cm 2 - the condition is provided.

Let's check the stiffness of the beam.

M n * L / (10EI) \u003d 6698 * 630 / (10 * 21000 * 5010) \u003d 0.004 \u003d 1/250 - the condition is met (although at the limit).

Thus, the selected beam passes according to the calculation. But it turned out to be quite powerful. To reduce the beam section, you need to specify a smaller step of the beams and recalculate the problem from the beginning. The smaller the step of the beams (the distance between the beams), the less load they have, which means the smaller the cross section will be.

The diagram of the overlapping device, the characteristics of which we determined during the calculation, see the figure below.

Attention! For the convenience of answering your questions, a new section has been created "FREE CONSULTATION".

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Comments

1 2 3

0 #65 Irina 23.01.2013 09:25

Quoting Dmitry:

what ceilings are possible during the construction of walls from aerated concrete blocks. And is it possible to replace metal beams with something else when installing monolithic ceilings.

Any overlap is possible (prefabricated, monolithic, wooden, etc.), the main thing is to avoid large spans and perform wall calculations in accordance with SNiP (DBN) "Stone and reinforced masonry structures".
You can not make beams at all, but simply make the floor monolithic, only thicker and with more powerful reinforcement. You can also make a ribbed monolithic floor, or use prefabricated reinforced concrete. beams.

0 #71 Maxim 05.03.2013 20:36

Quoting Irina:

It would be better not according to calculations, but according to SNiP (DBN) "Loads and Impacts" - in different cities it is different. And it is given for 1m2, which greatly simplifies the calculation.
And yet, if your ceiling is on an extension to a higher part of the house, then a snow bag may form, this must also be taken into account. If so, please describe in detail.

For my 4th zone, the Middle Urals, the load is already 240 kg per square meter !! and how I counted these 800 kg of my calculated ones ...)

The building is separate.

0 #76 Irina 18.04.2013 11:04

Quoting Andrew:

Hello, I need the opinion of an experienced person.
Overlapping is made, the room is 6 * 6.5 wide, materials: I-beam height 120mm laying step 1200mm (overlapped in width, i.e. 6m), between I-beams concrete to the full height (120mm) in concrete reinforcement 10mm with a step of 120mm in length, (across between I-beams cage through 400mm reinforcement 10mm) from the bottom there was formwork plywood and aged on racks for a month.
Question: what load can this flooring withstand (payload)
Thanks for the answer.

Andrey, I have experience in design, and not in the scientific analysis of what was done wrong. For a span of 6m, I-beam No. 12 is clearly not enough. Its shelves for supporting reinforcement of 10mm are also not enough (you need a minimum of 100mm). Reinforcement pitch 400mm is too large, no more than 200mm is needed. With such initial data, the calculation will not give an answer, because calculation assumes that everything is designed correctly.

0 #77 Andrey 24.04.2013 23:01

Quoting Irina:

Andrey, I have experience in design, and not in the scientific analysis of what was done wrong. For a span of 6m, I-beam No. 12 is clearly not enough. Its shelves for supporting reinforcement of 10mm are also not enough (you need a minimum of 100mm). Reinforcement pitch 400mm is too large, no more than 200mm is needed. With such initial data, the calculation will not give an answer, because calculation assumes that everything is designed correctly.

Hello! Thanks for the answer.
Reinforcement pitch 400mm is transverse between I-beams (support 25mm), parallel to the I-beams is reinforcement with a pitch of 120mm with a diameter of 10mm from one wall to another (10 pieces in each span)
http scheme
The overlap is standing, there are no cracks, but I'm interested in what kind of load it can withstand.

The design of the floor and materials for it are selected based on the characteristics of the designed building.

Overlappings can be of two types: wooden and reinforced concrete. The latter have the greatest advantages due to their high reliability, since wood is highly flammable and concrete is not a combustible material. At the same time, the concrete floor slab is heavy, so the impact on the walls of each floor of the building is very high. When designing buildings, it is necessary to foresee the necessary thickness and strength of the walls, which will have to correspond to the chosen type of flooring. In addition, to increase the thermal insulation properties, expanded clay is added to concrete, and not crushed stone.

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Types of reinforced concrete and monolithic floors

Reinforced concrete floors have the following types:

For prefabricated floors, the size of the panels is selected based on the size of the building.

• monolithic;
• prefabricated, that is, factory prefabricated plates;
• often ribbed, in the manufacture of which lightweight concrete or hollow blocks and reinforced concrete beams are used.

Prefabricated ready-made slabs must be installed using a crane. We can also note the advantages in the size of the floors: for reinforced concrete slabs, they can be any, and wooden floors should have standard sizes. The installation of monolithic reinforced concrete floors does not require the implementation of various works related to loading and unloading. The surface of the products is very high quality, since the technology does not provide for the presence of seams on monolithic floors. There are the following types:

1. Beam monolithic.
2. Beamless.
3. With fixed formwork.
4. With the use of flooring (steel profiled).

The monolithic device allows you to get smooth surfaces, ready for further use, so it is more common in construction than others. It is not required to purchase beams, so the consumption of materials is less. The corrugated board during installation allows you to get a very high-quality plate. When using the second option, additional consumption of materials is also not required in order to process the floor.

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The principle of installation of formwork systems

Multi-story buildings are now designed to complex layouts and configurations by having the load-bearing slabs of framing systems supported by beams that support a monolithic slab. At the same time, interfloor monolithic ceilings perform the functions of a hard disk, which gives the building special strength and reliability. Modern technologies devices of monolithic ceilings make it possible to ensure the rigidity of each floor of the building, therefore, to install bearing walls in this case is not necessary.

The dynamic growth in the construction of buildings using monolithic slabs is associated with the introduction of formwork technology.

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The concept and types of slab formwork, their design

One of the most inexpensive floors, but at the same time quite reliable.

The formwork for a monolithic floor slab is a structure, the installation of which is associated with obtaining a shaping surface of the floor. The use of formwork increases the possibilities of building design and obtaining various geometric shapes, which allows for more modern design each floor building structures. The formwork is a type of temporary structure that forms the necessary surface of a monolithic floor, so it is dismantled after the concrete has hardened. The design of a monolithic floor assumes the existence of a formwork life cycle, which means the number of times it is used, providing for the preservation of strength and geometric shape.

The height at which the slab is located above the base determines the type of prop used in the formwork. Telescopic racks are divided into individual and frame ones, which provide for a ceiling height of 4.5 m and 3 m. For very high heights, it is advisable to use formwork towers, while the ceiling thickness can reach 1000 mm, while in the first case - 300 mm . Obtaining complex configurations of monolithic floors depends on the use of a wooden glued beam, the length of which can be different. includes the following parts:

1. Plywood.
2. Cover beams.
3. Racks of a formwork of overlapping.
4. Tripods.
5. Uniforks.

These parts have the following functional features and characteristics:

• Plywood determines the quality of the surface, forming the lower part of a monolithic floor, with laminated plywood being the most popular;
• The beams carry the load of the floor structure of each floor of the building, transferring it to the formwork racks of the monolithic floor. Plywood is laid on the beams;
• The telescopic rack of the ceiling formwork serves to transfer the load of the structure from each to its base;
• The tripod must ensure a stable vertical position of the formwork stand;
• The unifork is a connecting link between the formwork prop and the monolithic floor beam.

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The technology of the monolithic overlap device on a profiled sheet

For overlapping, corrugated board marked with the letter H is used - bearing.

Modern technologies for the installation of monolithic ceilings using corrugated board are associated with the use of fixed formwork in the process of pouring slabs. Concrete is poured according to the classical principle associated with the dismantling of floor foundation panels that hold the concrete in the hardening process. The technology used with the use of fixed formwork and profiled sheet allows the construction of garages, utility blocks, terraces, etc. This is due to higher strength due to giving the metal profile to concrete the shape that will provide the greatest degree of resistance to deformation, which will make the overlap very reliable and durable. Studies have shown that the consumption of reinforcement in this case is much less than as a result of the use of other technologies, since the overlap is ribbed in cross section. The consumption of concrete is less, as well as reinforcement, however, the strength of structures using a profiled sheet does not differ from other types of monolithic floors.

The technology of overlapping with the use of corrugated board allows you to get a slab of low weight. Therefore, such a slab is used in the construction of houses with brick walls, or built using concrete blocks.

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Materials used and necessary tools

In the process of manufacturing monolithic floors, the following types of materials will be needed:

The undeniable advantage of corrugated board is its relatively low weight, which greatly speeds up and facilitates installation.

1. Fittings.
2. Beams.
3. Concrete.
4. Boards for fixed formwork.
5. metal columns.
6. Steel wire.
7. profiled sheet.
8. Film or roofing felt.
9. Film for waterproofing.
10. Insulation.

The performance of all work will be associated with the use of such types of special tools as:

1. Self-tapping screws with reinforced drill.
2. Electric drill.
3. Screwdriver.
4. Fasteners.
5. Concrete pump.

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Preparatory work

The technology using corrugated board involves, in the process of planning work, calculating the strength of the future floor, taking into account each floor, if the building structure is multi-storey. Since manufacturing is associated with various difficulties, it is better to entrust this work to professionals. After all the loads for the future floor are determined, beams with metal columns should be prepared, determining all the necessary parameters of these materials by calculations. Depending on the type of profiled sheet, the beams are placed at a predetermined distance from each other, taking into account their pitch, so that the concrete slab is firmly and reliably poured.

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Installation of profiled sheet

Depending on the height of the profile, the installation step of the beams is selected - the higher the profile, the smaller the step. In any case, at least 3 beams should go on a sheet of profiled sheet.

For example, beams can be laid at a distance of no more than 3 m. A profiled sheet of the TP-75 brand with a thickness of 0.9 mm is required. The length of the corrugated board should take into account that 3 beams will serve as a support for it, which will prevent the sheet from deforming in the future. The pressure in short spans will be less and the concrete will be easier to pour. The profiled sheet must be attached to a metal base, which is associated with difficulties, therefore, special tools are needed, namely self-tapping screws with a reinforced drill and fasteners with a parameter of 32 mm. Thanks to the reinforced drill, the self-tapping screw will be easier to enter the channel even without pre-drilling, so this fastener is called armor-piercing.

Screw the screws with a screwdriver, you can use an electric drill if you set it to low speed, as the technology involves a large number of attachment points for the profiled sheet. In this case, it is necessary to ensure that each fastening and the base beams are in contact, since the entire structure will have a very large load. The formwork in this case requires very reliable, since the concrete will give the structure a considerable weight. The next step is fixing the joints of individual profiled sheets. In this case, smaller screws are used, for example, having a length of 25 mm, so they are screwed in with a pitch of 25 mm. After fixing, proceed to the preparation of reinforcement.

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Making a frame from reinforcement

To fix the corrugated flooring from the tools you only need a screwdriver.

The reinforcement frame, which will be located inside the monolithic ceiling, will make the concrete as strong as possible, which will prevent compression and bending of the slabs. Only a specialist can foresee that, due to fixed formwork, additional strength of a monolithic ceiling will not be achieved, therefore, laying reinforcement requires skill. The overlap must have a three-dimensional structure, which is created by making a frame of reinforcement, including longitudinal bars having a thickness of 12 mm, placed in the hollows of the profiled sheet. Both longitudinal and transverse elements are used, made from 10 and 5 mm reinforcement bars. The connection of the frame elements from the reinforcement occurs with the help of welds, or with the use of steel wire. Welded seams make the entire reinforcement structure stronger.

However, the connection can be made faster, therefore, in practice, steel wire is most often used to connect the components of the reinforcement frame. If the building is planned to be multi-storey, then the interfloor stairwells and communication channels are planned in advance and then formwork is performed around them. After the completion of all work, in this case, it will not be necessary to perform additional work related to the opening, but only to cut out a part of a thin profiled sheet where interfloor openings are planned.

The formwork is made of wood, as it is the cheapest material, while the boards require a protective film layer, roofing material can be used.