Reinforcement techniques are ubiquitous in almost all areas of construction. It is used to make steps for stairs, concrete porches, and monolithic slabs for floors. The essence of reinforcement is the organic combination of different materials into a single whole. For example, reinforcement and concrete. Concrete by its nature has very high strength, but is too fragile to fracture. The metal that makes up the reinforcement is elastic. Therefore, the combination of these two materials creates a certain synergy, that is, the properties of reinforced concrete are much better and more useful than the properties of concrete or metal separately. Reinforced concrete is able to withstand such vibrations and vibrations that ordinary concrete will never survive. At its core, reinforcement plays the role of a kind of skeleton for concrete products, because without it it would simply crumble into pieces at the first load.
What you need to know about floor reinforcement
Reinforcing steel rods are used to reinforce concrete. Its thickness varies from 8 to 14 mm with a slab thickness of up to 150 mm. When purchasing ready-made floor slabs, it is necessary to take into account the fact that they are produced in factories as solid, ribbed and hollow. The last option is especially popular. This is due to the fact that, thanks to the voids inside the concrete monolith, such slabs have relatively low weight, excellent thermal insulation, poor sound permeability, and also withstand deformation well.
Floor slabs are produced from heavy grades of concrete. Their standard sizes are characterized by three values: length - 4, 5 or 6 m, thickness - 140, 180 or 220 mm, permissible load - 150, 190 or 230 kg/m2.
It should be understood that when laying purchased slabs, they always form joints, which can be stepped, which negatively affects the evenness of the surface formed by them. If we reinforce a monolithic floor slab with our own hands, we will get a uniform and even surface without joints.
What are the possibilities of reinforcement
The use of structures made of reinforced concrete allows not only to insulate the building, but also to significantly speed up the process of its construction. The relatively small mass of slabs with reinforcement reduces the load on the foundation. The structure itself is quite durable and can withstand not only prolonged and significant stress, but also serious exposure to fire. In the event of a fire, reinforced concrete floor slabs hold up a building for an hour, while wooden ones collapse within 25 minutes.
The use of monolithic floor slabs with reinforcement makes it possible to erect buildings and structures with any degree of complexity. With their help, you can easily correct the geometric features of the room, as well as create non-standard floors, both in size and shape. Since the supports for such slabs are not only the walls of the building, but also various arches with columns, the planning possibilities increase significantly.
How to make a monolithic floor slab with your own hands
In the construction literature you can find a very simple formula with which you can easily calculate the thickness of the floor. Take the span length and divide it by 30. The result obtained is the optimal thickness of the future slab. The classic scheme for reinforcing slabs involves placing working rods in the upper and lower parts of the slab. This redistributes the load of all reinforcement and rod stops. If the slab thickness is less than 80 mm, it will be quite enough to use a wire mesh rather than a reinforcing rod. You just need to make sure that it is inside the monolith. To do this, the mesh is raised 2.3 cm above the surface to be poured.
The reinforcing rod is tied together with wire or welded. The first method is faster and more convenient. For tying, a special hook is used, which you can make yourself, or you can buy it in a store. In the case where the slab has a thickness of about 150 mm or even more, two layers of reinforcement will need to be made. The layers are made one above the other, fastening them together with jumpers. The size of the resulting cells should vary from 150 to 200 mm. For normal strength, when making a floor slab yourself, you should use a rod with the same cross-section. To further increase the strength, you can tie the reinforcement with rods from 40 to 150 mm long to the main structure.
The distribution of the load over the entire structure occurs in such a way that its main share falls on the lower layer of reinforcement. In this case, the top layer is subject to compressive forces like concrete. Reinforcement is made by pouring concrete into the formwork over the entire surface of the floor.
In general, the entire process of creating a concrete floor slab is divided into three components: installation of formwork, reinforcement and pouring concrete. Let's look at them all.
Creating formwork
The formwork for pouring a monolithic floor resembles a horizontal “deck” made of special moisture-resistant plywood, the thickness of which is 18-25 mm, or a tightly knit edged board 40 mm thick. It is installed on reliable supporting beams made of wooden beams (80-100x100 mm), located horizontally.
Horizontal timber beams are supported by strong vertical posts, which can be ready-made, special (telescopic) or prepared independently from solid timber 100x100 mm, round timber with a diameter of 80-100 mm, as well as durable metal pipes or channels.
To determine the need for materials for the construction of formwork, you need to calculate the area of the entire floor and its thickness. The latter ranges from 10 to 20 cm, depending on the width of the span and the load planned for future operation. The strength of the formwork must be such as to withstand the weight of concrete and the reinforcement that will be embedded in it without the slightest deformation. With a floor thickness of 20 cm, the weight of the resulting slab is about 500 kg per m2. The surface of the formwork is best made from ordinary or laminated 20 mm plywood. When using plywood with a laminated coating, you will get a perfectly smooth ceiling that does not require a large amount of finishing work. The installation height of the formwork is determined using a level or building level. To do this, mark a horizontal line, which should correspond to the height of the future ceiling, along the perimeter of the entire span.
When using telescopic stands, they are installed primarily at the edges, using tripods and uniforks (crowns). Beams in the longitudinal direction are installed along the racks at a distance of 2 m. Only after this can intermediate racks be installed. You don't have to make tripods for everything. Usually it is enough to equip 30 - 40% of the racks with this design. The distance between the intermediate supports is determined by calculating the power of the floor and the thickness of the racks themselves. On average, no more than 1 m2 of formwork should be allocated per rack with a load of 900–1200 kg.
If you decide to use homemade racks, then their length should correspond to the installation height of the lower part of the longitudinal beams. Install homemade racks in 1 m increments on a solid base or thick pieces of board with sufficient area. Transverse ones are placed along the longitudinal logs at a distance of 0.5 m from each other, and sheets of thick plywood are laid on top of them. The upper surface of this structure must be strictly horizontal and meet a pre-fixed level.
When using edged boards for the top of the formwork, they must be aligned closely, and a thick plastic film or roofing felt should be placed on top of them. Along the entire perimeter of the board formwork, a side of uniform height corresponding to the thickness of the ceiling is mounted. It needs to be securely connected at the corners.
How to independently reinforce a concrete floor slab
Steel reinforcement of class A3 is produced by hot rolling. It ranges from 8 to 14 mm in diameter with a smooth or ribbed surface. It is best suited for creating a monolithic reinforced floor yourself. The first mesh is mounted in the lower part of the proposed slab, and the second, respectively, in the upper part. The formwork must be positioned in such a way that both grids are inside the slab monolith. The distance from the top mesh to the surface must be at least 2 cm. The reinforcement must be tied into the mesh with knitting wire, forming cells with sides of 200 or 150 mm. Today there are special machines for knitting reinforcement, but this can also be done with a regular hand crochet.
Using a welding machine is advisable only when you know how to operate it well, since inept actions can lead to thinning of the rods at the welding sites, which will certainly lead to destruction. There should be no breaks along the entire length of the mesh, therefore, if the length of the rods is insufficient, they should be overlapped by at least 50 cm. In this case, all joints should be placed in a checkerboard pattern. Along all edges of the mesh, they are tied into U-shaped figures. Rods should only be bent if absolutely necessary, without heating. Overheating the metal disrupts its internal structure, which can lead to a broken rod. In those places where additional loads are expected, they are reinforced in a special mode with additional rods. When reinforcing, one should also take into account the places where utility lines will pass. If possible, it is better to immediately leave holes in them by inserting a piece of pipe. The entire area of support on walls and columns especially requires reinforcement. In the latter case, the reinforcements should be volumetric.
Pouring concrete mixture
After the entire mesh of reinforcement is connected, you can start pouring it. The best way to do this is to use a concrete pump. If the amount of work is not very large, then it is quite possible to cope without it. In this case, you will need at least two assistants who will mix the concrete in a concrete mixer and lift it to you for pouring. During the process of filling the formwork with concrete mortar, it is necessary to periodically compact the mixture. A special construction vibrator is best suited for this, but if you don’t have one, you can simply rhythmically tap the formwork or open parts of the reinforcing mesh with a hammer from time to time.
During the hardening process, significant shrinkage of concrete occurs, which, with an accelerated drying process, can lead to the appearance of microcracks. In this regard, the flooded slab needs to be watered with water for several days, especially in hot weather. However, you need to know that water should be sprayed from a hose with a sprinkler nozzle or watering can, since a direct stream can damage the surface of concrete that has not yet set. Sometimes, to avoid the appearance of cracks, a special polymer mesh is placed under the very bottom layer, and the rest of the structure is built on top of it. In other cases, a polymer mesh is used as the main reinforcing element. This is done where it is impossible to build reinforcement from rods and even wire.
Complete hardening of the concrete will occur no earlier than after 3 to 4 weeks. Until this time, you should not carry out any work on site or dismantle the formwork. After this period, the formwork is dismantled and a concrete floor slab is obtained, which serves as a rough ceiling for the rooms underneath. In this way, you can even create curved floors of any configuration.
When building your own house or cottage, it is quite possible to create your own concrete floor slabs with reinforcement inside. This structure is much more reliable and durable than a wooden one, but it should only be built on strong concrete or brick walls. The use of lightweight concrete blocks or wood as wall material eliminates this possibility, since such walls may not support the weight of the reinforced concrete floor.
The construction of high-rise and low-rise buildings is impossible to imagine without floor elements. When constructing multi-storey buildings, ready-made slabs are mainly used, and when constructing small houses on private plots, craftsmen practice making their own floors. When performing such work, it is necessary to correctly reinforce the monolithic floor slab.
Design Features
A concrete structure reinforced with metal rods has higher quality characteristics than a slab entirely cast from concrete. In addition, rods are connecting parts, so the creation of a monolith is always carried out using reinforcement.
Strengthening solid floor slabs with reinforcement is carried out using rods with a diameter of 8 mm to 14 mm, taking into account that the thickness of such a slab will not exceed 15 cm. Moreover, the cross-section of the rods may vary depending on the type of structure.
If you decide to purchase ready-made slabs, you should note that there are several types of such elements:
- Solid (solid);
- Ribbed;
- Hollow.
However, it should be understood that when laying any finished slabs, joints always form, and this has a detrimental effect on the evenness of the surface. If you make the floor slab yourself, you can forget about this trouble.
Advantages of reinforced concrete floor elements
To perform the roof or horizontal overlap between floors, a monolithic floor slab is used. Interfloor reinforcement of slabs allows you to achieve many positive qualities from the finished structure, including:
- High-quality noise insulation;
- Good thermal insulation;
- Light pressure on the base;
- Uniform distribution of load on the walls of the building;
- Ability to withstand significant weight.
In addition to the advantages of the floor slab itself, the advantages of the execution technology should also be noted:
- You can do the work yourself, without using the services of professional contractors;
- You don’t have to hire heavy construction equipment to make the slab;
- It becomes possible to build a building with unusual geometry, since not only walls, but also columns can serve as support for the slab.
Basic calculations and selection of materials
To begin with, we should consider the most common example of reinforcement of a monolithic floor slab: working rods in the lower part of the slab, working rods in the upper part of the element, rods that redistribute the load, wire rods and stands. Naturally, there are other design schemes.
Whatever drawing is chosen, care must be taken to correctly calculate the planned load on the concrete structure. The thickness of the floor slab is calculated based on the proportion of 1 to 30, therefore, to calculate the thickness of the concrete, you should divide the span length by 30.
If the thickness of the concrete structure exceeds 15 cm, double reinforcement will have to be performed. Reinforcement meshes must be placed one on top of the other and connected with special wire. The minimum mesh size is 15x15 cm, the maximum is 20x20 cm.
In order to ensure good resistance to the slab, it is best to use metal rods of the same diameter. Additional reinforcement can be done with rods 0.4-1.5 m long. The reinforcement scheme assumes that the main load falls on the bottom row of rods, and the compressive load falls on the top row. The reinforcement frame for a solid floor slab must be made for the full length of the structure, and not for part of it.
Also, do not forget that you need to use formwork - an important element when concreting a slab. To make formwork, you can use wood (boards measuring 5x15 cm) or cheap plywood. The main thing is to securely fix the formwork frame, since the mass of concrete mortar used during pouring can be equal to 300 kg per square meter of slab. The most suitable supports for such formwork are telescopic racks, which are very easy to work with. They have a high load-bearing capacity (can support up to 2 tons), unlike wooden beams, which often have knots or microscopic cracks.
Self-reinforcement of the structure
As mentioned earlier, when performing overlapping, proper calculation of reinforcement is especially important. To create a reinforcement frame with your own hands, it is best to use hot-rolled metal rods of class A3. Their cross-section can be from 8 to 14 mm - the choice is determined by the design load.
If reinforcement is carried out on a monolithic floor slab, SNiP assume a two-layer frame. Both metal meshes must be placed in the thickness of the concrete. The minimum protective layer created by the formwork box should be 1.5 cm. In order to make a mesh, the rods must be connected with knitting wire. We must not forget that the cell size can only be 15x15 cm or 20x20 cm.
The rods used to make the mesh must be solid and cannot have cracks or breaks. If the length of the rods is not sufficient, additional rods are tied to them with an overlap (its length should be equal to 40 diameters of the reinforcement used). That is, if D12 rods are used in the work, then the overlap will be equal to 480 mm. The joints of the rods are placed in a checkerboard pattern. The edges of the reinforcement in the two resulting meshes are connected by U-shaped reinforcement.
The manufacturing technology assumes that the working basis is the lower metal mesh, which takes the tensile load. As for the upper part of the frame, it takes compressive loads.
When calculating and designing, additional reinforcement reinforcements must be taken into account, however, there are also standard standards that should be taken into account:
- When performing the lower reinforcement network, the reinforcements are placed between the load-bearing rods in the center;
- When preparing the upper mesh, additional rods are installed above the base supports;
- Reinforcement will be needed at points where excavations and loads accumulate: it is carried out using separate rods 0.4-2 m long (the choice of length is determined by the width of the spans).
If an unconventional pattern of reinforcement of a monolithic floor slab (with a column) is performed, then at the points of intersection of the metal frame with the supports, the reinforcement will be completely different. At intersections, special spatial reinforcements are created.
The finished floor frame is poured with concrete mixture using a special device. After laying, the solution is compacted using a deep vibrator. The maturation process of a monolith involves its shrinkage. To avoid cracking of the slab, the structure must be moistened for the first 3-4 days after pouring. Concrete will gain power in 28 days.
Video about reinforcement of a monolithic floor slab:
To create a reliable floor, it is necessary to properly make reinforcement, which will provide strength under bending loads and evenly distribute the pressure on the foundation. Monolithic floor slabs will cost less because they do not require lifting equipment on site. You can make preliminary calculations for small spans yourself using the formulas of regulatory documents
Types of floors
Depending on the design of the floor frame, wooden and reinforced concrete are installed. The latter, in turn, are divided into:
- standard reinforced concrete slabs of various designs;
- monolithic ceiling.
The advantage of ready-made reinforced slabs in professional production in accordance with SNiP requirements: lower weight due to the presence of cavities formed during pouring. According to the number and shape of the internal structure, the slab can be:
- multi-hollow - with round longitudinal holes;
- ribbed - complex surface profile;
- hollow – narrow, shaped panels are used as inserts.
Ready-made floor slabs justify their use in large-scale construction, for example, in the construction of high-rise buildings. But they have their own disadvantages when installing:
- presence of joints;
- use of lifting equipment;
- suitable only for standard room sizes;
- inability to create shaped ceilings, openings for hoods, etc.
Installation of slab floors is expensive. You have to pay for transportation by a special vehicle, loading and installation with a crane. In order not to call special equipment twice, it is advisable to immediately install the slabs on the walls from the machine. If we consider the individual construction of small cottages and houses, then experts recommend making the floors yourself. Concrete mortar is poured directly on site. The frame formwork and reinforced mesh are pre-constructed.
Advantages and disadvantages of solid reinforced floors
The reinforced concrete floor is made in the same way as ready-made slabs from 2 materials:
- iron rods;
- cement mortar.
Concrete has high hardness, but it is brittle and cannot withstand deformation and is destroyed by impacts. The metal is softer and tolerates bending and torsion well. When these two materials are combined, durable structures are obtained that can withstand any load.
Advantages:
- absence of seams and joints;
- smooth, continuous surface;
- the ability to make floors for any shape and size of premises;
- installation and assembly of fittings is carried out directly on site;
- a reinforced concrete monolith strengthens the structure and binds the walls together;
- there is no need to seal joints and align transitions after installation;
- the local large load on the floor is evenly distributed over the foundation;
- It is easy to make various openings between floors for stairs and communication wells.
The disadvantages of reinforcement include high labor costs for assembling the reinforcing mesh and the long process of drying and hardening of concrete.
Calculation of slab thickness and number of rows of reinforcement
Calculation of floor parameters must be done based on the requirements of SNiP. 30% is added to the design dimensions for strength, or rather the numbers are multiplied by a safety factor of 1.3. When calculating, only load-bearing walls and columns standing on the foundation are taken into account. Partitions cannot serve as support.
Floor thickness
An approximate calculation of the thickness of the floor relative to the distance between the walls is the ratio of 1:30 (respectively, the thickness of the slab and the length of the span). A classic example from reference literature is the width of the room is 6 meters, that is, 6000 mm. Then the overlap should have a thickness of 200 mm.
If the distance between the walls is 4 meters, according to calculations, you can install a 120 mm slab. In practice, such reinforcement of a monolithic floor slab is suitable only for a non-residential attic where there will be no bulky furniture. It is advisable to make the remaining floors (ceilings) 150 mm with two rows of reinforced mesh. You can save on the second row by installing the rod at 8 mm in increments of 2 times larger.
With a span of more than 6 m, deflections and other loads increase significantly. All floor dimensions and drawings must be made by specialists. Approximate calculations cannot take into account all the nuances.
Reinforcing mesh
According to the recommendations of SNiP, in residential buildings the ceiling should have 2 rows of reinforcing mesh. Depending on the design thickness, the top row may have a smaller reinforcement cross-section and a larger mesh size. The dimensions recommended by experts for spans of 6 m and 4 m with a standard load of a residential building are shown in the table.
The calculation is based on the maximum distance between the walls. The same thickness of flooring is laid over rooms on the same floor; the calculation is made based on the room with the maximum dimensions. Calculated values are rounded up.
Bar joints
The mesh is made from wire rod - hot-rolled round section of low-carbon steel 3A. This means that the metal has high ductility and will hold the concrete floor well under large stationary loads and vibrations from earthquakes, the operation of heavy equipment, and weak soil.
The length of the rod may not be enough to create a continuous ceiling. To do this, docking is done using the overlay method. The rolled products are laid side by side at a distance of 10 diameters and tied with wire. For a rod 8 mm thick, the double connection is 80 mm (8 cm). Similarly for rental F12 – the joint is 48 cm. The joining of the rods is shifted and should not be on the same line.
For connection, you can use welding, laying the seam along. In this case, the flexibility of the design is lost.
Mesh installation
The mesh rods are tied together with 1.5–2 mm wire. Each intersection is tightly twisted. The distance between the meshes is approximately 8 cm. This is ensured by an 8 mm rod cut to size. The tie should be at the intersection points on the bottom grid.
It is necessary to leave a gap of 2 cm under the lower reinforcement for pouring a layer of concrete. To do this, plastic conical clamps are installed on the formwork at intervals of 1 m.
Trims and holes for hoods and stairs
To connect the ceiling with the walls around the perimeter, a box is created - side formwork. It is installed vertically and serves as a boundary for the spreading of concrete. The perimeter piping runs along it, reinforcing the corners. After the slab hardens, this box is removed, leaving a flat end.
The formwork is installed at a distance of 2 cm from the ends and longitudinal rods after completion of the assembly of the reinforcing mesh and ensures the location of the metal inside the concrete. Its distance from the wall plane is 15 cm for brickwork and cinder block. Aerated concrete is less durable, the overlap of the ceiling is 20 cm. This distance on the wall before pouring is covered with a special composition that dampens vibration. This layer significantly increases the strength of the building.
Similar formwork is placed in places where holes should remain. These are mainly stairs between floors, pipe outlets, ventilation systems and communication wires. They will be covered with a mesh and will not be flooded.
Floor slab drawing
A drawing is made to ensure proper assembly of the floor. Using it you can calculate the consumption of all materials, from tying wire to the amount of cement.
Algorithm of actions:
- 1. Before drawing up a drawing, you should take measurements of all rooms and the outer perimeter of the house if there is no design. They are made from the axis of the wall.
- 2. Mark all holes that will not be filled.
- 3. The contours of all load-bearing walls and parts of the intermediate ones are drawn. A detailed diagram of the strapping, mesh, and reinforcement is made, indicating the thickness of the rod, joints and connections.
- 4. The drawing indicates the size of the cells and the location of the outermost longitudinal rod from the edge of the fill.
- 5. The dimensions of the corrugated sheet for the lower plane of the slab are calculated.
When creating a grid diagram, in most cases the number of cells is not an integer. The reinforcement should be shifted and the same reduced cell sizes near the walls obtained.
Based on the overlap area, the number of plastic fasteners is calculated and how much rolled stock will be used for inserts between the meshes.
The cement composition is calculated based on the thickness of the floor and its area.
The reinforcement above and below must be covered with mortar with a minimum thickness of 20 mm. When air enters, corrosion forms on the metal surface and destruction begins. When creating a floor thicker than 15 cm, with reinforcement in 2 layers, more mortar is distributed at the top.
The drawing also serves to calculate the amount of formwork, support columns and wooden beams to create a lower supporting plane - a platform for pouring the floor.
Any developer can install the rods on the clamps and tie all the intersections with wire. To guarantee safety, it is better to entrust the calculations of floors and the creation of a house project to professionals.
The process of reinforcing a monolithic slab
After all the calculations have been completed and the drawing has been prepared, they begin to install the formwork along the entire length of the floor. For it, boards measuring 50x150 mm, beams and plywood are most often used. The correctness of the construction of structures is monitored using a level or level. The next step is laying the bottom row of reinforcement according to the project. All connections of the metal frame are made in a checkerboard pattern.
As a result, it should turn out that the entire space between the reinforcement and the formwork is filled with concrete. To do this, the mesh is placed on stands and secured with knitting wire.
Under no circumstances should welding be used to connect elements.
The second row of reinforcement is laid on the first layer. All elements are placed on special stands.
The next step is to fill the formwork first with a liquid and then with a thicker layer of concrete (most often grade M200). The first layer should resemble sour cream in consistency, and air bubbles are carefully removed from it using a shovel. To prevent cracking of concrete, it is moistened with water for the first 2-3 days. When the entire structure hardens (at least 30 days must pass), the formwork is removed.
The issue of reinforcement of monolithic slabs is relevant for any type of construction, be it a slab foundation or a concrete floor in a brick building. This is explained by a huge margin of safety, unpretentiousness to environmental conditions and the versatility of this type of building structures. Capable of withstanding heavy loads for many decades, they nevertheless require a qualified approach to their design and construction.
Below we will consider a number of reasons why you cannot simply take and pour a slab without calculations and a drawing of the reinforcement, how to do it correctly, and all this will be clearly reflected in a real, widespread example.
Scheme
During operation, the monolithic slab can withstand uneven distribution of loads. From above it is pressed by the summing vector of gravity, the load of the walls and the elements of the building and interior located above it. If the upper surface of the slab is affected by a compressive force, then the lower (or the only one, if the reinforcement is single-span) layer of the reinforcing mesh is affected by the tensile force acting on the rupture.
Such an item as the reinforcement of a monolithic floor slab must be given the closest attention, along with the choice of concrete, placement of the slab on walls or columns, load calculation, etc.
The design reinforcement scheme may differ depending on what type of stove:
- beam,
- working in two directions.
And profile slabs:
- flat,
- flat with capitals,
- ribbed,
- empty.
For small slabs up to 6x8 meters in size, beam type, that is, supported by at least three walls and the load predominantly in one direction (from top to bottom, interfloor floor or foundation), simple single-span reinforcement and a flat, continuous fill profile are quite suitable.
For more difficult slabs, for example, for long spans used in the construction of hall floors or supported by columns, it is necessary to calculate the load and use a lightweight configuration, for example, ribbed slabs with multi-span reinforcement.
The reinforcement diagram of a monolithic slab is as follows— a mesh is formed from steel reinforcement with a diameter of at least 8-10 mm with a pattern in the form of squares or rectangles, and the distance between the two nearest reinforcement bars should not exceed 0.5 meters, otherwise the reinforcement simply will not withstand the impact of the gap, deforming the slab.
With a small slab thickness (up to 150mm), for beam flat slabs it is quite possible to limit oneself to single-span reinforcement.
Slab thickness taken in proportion to the long part as 1 to 30, that is, with a slab length of 6 meters, the recommended slab thickness is 200 millimeters. A further increase in thickness does not make sense and will only negatively affect the load-bearing capacity of the floor, increasing the weight and load on the iron frame.
There is also a requirement for slab filler- its grade must be no lower than M200; grades lower simply cannot provide the design strength of the floor.
In addition to reinforcing the entire surface of the slab it is necessary to strengthen the places where there will be an increased load on the slab- this is the entire area that touches the supporting elements, the geometric center, the location of the holes and the location of the calculated increased load.
It is also necessary to remember that the distance from the outer edge and from the end of the slab to the reinforcement must be at least 25mm. This will ensure that the reinforcement is protected from external influences that negatively affect the reinforcement metal.
Is it possible to build a monolithic foundation slab on your own? Follow the link and find out.
With your own hands
Taking into account the drawn up diagram, reinforcement can be done on your own. Complex reinforcement schemes are calculated using specialized software and qualified specialists, however, a monolithic slab for a low-rise building with a small area (up to 6x8 meters) can be calculated, reinforced and concreted with your own hands.
Initially, it is necessary to weld the mesh from the reinforcement. The recommended pitch is 150-200mm with a reinforcement diameter of 10-15mm and concrete grade not lower than M350. Reinforcing bars running perpendicularly to each other are connected with knitting wire with a diameter of 15-30 mm, but ready-made reinforcing mesh is also available for sale.
Be sure to take into account the margin in length and width, because the slab needs to rest securely on something. For foam concrete and aerated concrete the width of the supporting part must be at least 250mm, for brick and silicate masonry- no less than 150mm. The higher the density of the wall material, the smaller the width required.
If the reinforcement is multi-span, then the meshes are separated from each other by special clamps or simply bars, which should be securely strengthened between the reinforcement meshes. This is done so that when concrete is poured, lighter blocks of wood do not shift and jump to the surface, and special clamps already have this fastening.
The distance between reinforcement spans is set to a maximum of 0.125 m, and the clamps themselves are located at a distance of 0.4-1 m, and in places of high load the step is reduced, and in other places it is 1 meter. It is advisable to install the clamps one after another, in a checkerboard pattern. That is, the grids are spaced no more than 125mm apart from each other and are securely fastened to each other with a large number of clamps or bars.
By the way, reinforcement of a monolithic foundation slab is practically no different from reinforcement of floors, in addition, thinner reinforcement (with a diameter of 5 mm or more) can be used for multi-span reinforcement. The slab foundation, in the same way, during operation, will withstand heavy loads, plus the weight of the entire building, so it must be reinforced. Additionally, the foundation is also affected by soil swelling forces if construction is carried out on soils with high water content.
After installing the reinforcement mesh and installing formwork and waterproofing, concrete is poured and 10-14 days later, after the concrete has gained strength, further construction continues on the reinforced monolith.
Example
For the interfloor covering of a two-level house, it was chosen monolithic reinforced concrete slab with a design thickness of 200mm. The external walls of the house are one and a half bricks thick (~380mm), height 2.90m, house dimensions 6x6m.
As a floor slab A single-span, flat, simple design with a reinforcement pitch of 150 mm is quite suitable. The reinforcement drawing for a monolithic slab will be presented in the form of 0.15 x 0.15 m squares with additional reinforcement along the perimeter of the floor.
After installation of the formwork for the slab, it is made on site rebar mesh with a diameter of 10mm, grade 25g2s, class A3. This reinforcement is a very common item in the product range; it is made by hot rolling, and class A3 means that the reinforcement is grooved and notched. This profile, unlike round reinforcement, provides better adhesion of concrete to metal structures.
Slab width and length, with the external dimensions of the building being 6000x6000mm and the supporting part on the external walls of 200mm will be 5640mm (6000mm minus 380mm and plus 200mm on each side). Additionally, 4 rods are added along each face of the monolith with a cross-section in the form of a rectangle elongated from top to bottom. This will strengthen the slab and distribute the load more evenly over its entire surface.
Total length of reinforcement will be: 48 * 2 * 6m = 288m. With a mass of 1 linear meter = 0.617 kg, the total weight of the reinforcing structure, excluding knitting wire, will be: 288 * 0.617 kg = 177.7 kg.
Calculation of the required volume of concrete shows that for 1 square meter of such flooring you will need about 0.2 m3 of M350 concrete. For a 6x6 meter slab, the volume of concrete will be 7.2m3. Concrete weight will be: 36 * 0.2 * 2400 kg/m3 = 17280 kg. Adding the weight of the reinforcement, we get weight of the entire floor slab: 17280 + 177.7 = 17457.7 kg.
Summarize: calculations of reinforcement for complex, large and highly loaded monolithic slabs should only be carried out by qualified specialists. But a simple design, for example, for low-rise construction, is quite possible to calculate independently and make it yourself. Despite the high cost of such a floor, its use is justified, especially in cases where the foundation or floor will be subject to high loads, which only a reinforced monolithic slab can successfully withstand.
How to properly reinforce a slab foundation?
The main element that determines the strength of a structure is the foundation. That is why, before starting construction activities, you should decide on the type of foundation, the materials used, and perform calculations. When giving preference to a solid foundation for the construction of a future facility, be sure to reinforce the monolithic foundation slab.
To carry out measures to strengthen structures, you will need steel reinforcement combined into a rigid frame. This will improve the strength characteristics of the base and increase the service life of the building installed on a monolithic foundation.
In this article we will dwell in detail on how to properly reinforce a foundation slab. Let us consider the stages of construction activities that allow us to form a reliable and durable foundation of the building.
The construction of any house is impossible without a strong and reliable foundation, which is the basis for the entire structure
Monolith formation technology
The set of measures for constructing a monolithic base includes the following steps:
- marking and cleaning the site;
- extraction of earth for a foundation pit of the required size;
- formation of a drainage system;
- backfilling and compaction of the sand and gravel base;
- performing waterproofing;
- assembly and fixation of formwork;
- installation of reinforcement frame and;
- concreting.
The reliability of a monolithic base is determined not only by the quality of the concrete solution, but also by correctly performed reinforcement. Let's look at this operation in more detail.
About the need for reinforcement
Before carrying out construction activities, be sure to understand how the reinforcement of a monolithic foundation slab is performed. The erroneous position of skeptics and amateurs, who believe that hardened concrete mortar without reinforcement with reinforcement has high strength and can withstand the weight of the structure, is completely unfounded. This is absolutely not true.
Reinforcing the foundation with metal reinforcing bars will strengthen the supports of the future structure and prevent the formation of cracks in the concrete structure
The need for reinforcement is associated with the characteristics of concrete, which perfectly withstands compressive loads, but is susceptible to bending moments and tensile forces.
When constructing a building on a monolithic foundation, the loads on the foundation are distributed unevenly. The result is the occurrence of a bending moment, causing cracks to appear and a violation of the integrity of both the base and the entire building. Remember that the compressive forces are absorbed by the concrete mass, and the steel reinforcement compensates for the bending moment. Reinforcement of the foundation slab eliminates the impact of negative factors.
Reinforcement with steel rods allows:
- increase the strength characteristics of a monolithic base that can withstand increased forces compared to a conventional slab without reinforcement;
- prevent the possibility of building shrinkage associated with insufficient foundation strength;
- prevent deformation of the solid concrete slab under the influence of soil reaction.
Current standards regulate the mechanism for reinforcing monolithic foundations used for the construction of various objects. Reinforcing concrete with steel reinforcement makes it possible to ensure a high degree of reliability of the foundation of a future building.
The construction of a monolithic slab must fully meet all requirements for loads and soil type at the construction site
Calculation part
A solid foundation slab will ensure the stability of the building being constructed if the reinforcement scheme for the monolithic foundation slab is correctly drawn up.
A correctly calculated monolithic foundation will ensure the stability of the structure on problematic soils with closely spaced aquifers. The calculation will allow you to form a reliable basement foundation for the building. By drawing up a drawing of the foundation and performing calculations, you can determine the parameters of the foundation and calculate the need for reinforcement. By giving preference to a not deeply buried slab located at soil level, there is no need to dig a deep pit, which is associated with significant financial costs.
Saving money and reducing labor costs is ensured by creating a foundation with the following characteristics:
- The depth of the pit is 0.3-0.5 m.
- The thickness of the concrete slab is 0.15-0.3 m.
To carry out construction, a slab foundation reinforcement scheme is required. It is easy to develop it yourself, knowing the dimensions and design features of the building. An independently developed drawing will allow you to estimate the cost of construction activities and professionally approach the implementation of reinforcement work.
Such a slab is completely filled with concrete mixture; before pouring, a reinforcement cage is installed, which strengthens the structure many times over.
Knowing the dimensions of the base and, focusing on the interval between steel bars and the weight of one linear meter of reinforcement, it is not difficult to calculate the number of steel rods of the required assortment.
Let us consider the algorithm for calculating the need for reinforcement located in increments of 20 cm using the example of a base having overall dimensions of 900x700 cm:
- The need for longitudinal rods of one frame level is determined by dividing the length of the slab by the distance between the rods - 900:20 = 45 rods (7 meters long). The amount of longitudinal reinforcement on both sides will be 45x2=90 elements;
- the total number of transversely located elements is determined similarly: 700:20x2=70 rods (9 meters long);
- we calculate the total footage of the reinforcement rods: 90x7+70x9= 1260 meters;
- We determine the mass of reinforcement necessary to strengthen the foundation, knowing the weight of a linear meter of steel bar. For example, for a rod with a diameter of 14 mm, a linear meter of which weighs 1.21 kg, we obtain: 1260x1.21 = 1524.6 kilograms.
Rods are ordered in tons. Based on the obtained value, you should order a slightly increased number of rods, taking into account the waste associated with cutting the material.
Diagram of a reinforced monolithic concrete slab