The most popular floors in the construction of low-rise individual buildings are reinforced concrete hollow slabs. But their installation requires lifting equipment, which negatively affects the final cost of the work. Among other things, off-the-shelf platforms are used for buildings with simple shapes.
A number of developers prefer to do the flooring on their own using reinforced concrete. This method is most suitable for objects that must have the wrong geometry. All this allows you to abandon the standards and erect buildings that are complex in architectural terms.
Why is it necessary to reinforce the slab
Reinforcement of the floor slab is carried out taking into account the technological subtleties. This allows you to use the product for several decades. When pouring, thin ceilings are obtained that do not have seams, and the floors in this case do not require laborious and expensive repairs when performing interior decoration.
Reinforcement of the floor slab allows reducing the weight of the structure in comparison with the finished reinforced concrete slabs, but this does not negatively affect the strength. The load on the foundation is reduced, because lighter building materials are used. One cannot but mention strength. Concrete and iron create a solid foundation. The platform is used to overlap large-span and loaded structures.
Additional advantages of reinforcing
Reinforcement of the floor slab is also carried out to ensure reliability. Designs gain high resistance to stress through the use of reinforcement. They gain the ability to undergo a load of up to 800 kg / m 2 . In this way, the products also manage to impart fire resistance, because the materials used are not combustible.
The stove does not support combustion, withstands exposure to open flames for a long time. Overlapping costs do not exceed the cost of the factory product. The price will be determined by the equipped area.
Features of the work
Carrying out work on the reinforcement of floor slabs involves the use of technology that gives ample opportunities in the issue of room planning. The platform at the same time turns out to be quite durable, it withstands high loads, does not contribute to the development of fungus and insects, as well as harmful bacteria. Work is carried out according to the rules. Do not save on building materials, because the ceiling can be deformed, which will lead to the destruction of the slab and the entire building.
With the help of a removable formwork, the ceiling is filled, inside there should be reinforcement. Steel rods are connected by wire. But you can use welding equipment. The frame is positioned so that it is completely recessed in concrete mortar. The fittings take the load on themselves, and the solution eliminates the flow of oxygen, which negatively affects the metal.
About additional items
When drawing up a reinforcement scheme, auxiliary reinforcement should be taken into account. It should be located in the center of the platform, where the concentration of loads occurs, as well as in the place where the overlap contacts the holes. Auxiliary reinforcement should also be at the point of contact of the monolith with internal walls, columns and arches.
As for the concentration of loads, then in this case we are talking about heavy equipment or a fireplace. Additional elements are installed at the exit of the stairs to the upper floor, as well as at the point of passage of chimneys or ventilation elements.
Step-by-step instruction
Reinforcement of the prefabricated floor slab is carried out after calculating the thickness of the reinforcement, which will depend on the length of the floor. If the step between the bearing supports is 5 m, the thickness of the platform should be equal to 170 mm. In the calculation, a ratio of 1 to 30 should be used. But with a thickness of the structure less than 150 mm it cannot be allowed to operate. If the thickness of the overlap has a minimum thickness, then the remaining elements must be laid in one layer. With an increase in this parameter, the number of layers also increases to two.
For mortar, concrete of grade M-200 or higher should be purchased. This brand combines affordable value and excellent features. The class of compressive strength should be equal to 150 kgf / cm 2 . The diameter of the used steel rods can reach 14 mm, the minimum parameter is 8 mm. If metal rods are located in 2 layers, then the diameter of the metal of the first row should be larger than that located on top.
Work on the fence
Having considered the reinforcement drawings of a monolithic floor slab, which are proposed in the article, you can start work. At the next stage, the technology involves the installation of formwork made of moisture-proof plywood or boards. These materials can be combined. The supports should be well fixed, because the weight of the cast structure is 300 kg per square meter. The supporting elements can be telescopic jacks . They allow you to set the desired height with high accuracy. Supports withstand loads up to 2.5 kg.
Work on the formwork
The scheme of reinforcing the floor slab is proposed in the article, however, its compliance is not a guarantee of success. You must follow the rules at every stage of the work. For example, with regard to formwork, it is a removable structure, which consists of 150 x 25 mm boards. They will not be able to provide a perfectly flat ceiling surface, because in the thickness of the lumber an error is allowed. Irregularities can be hidden under the plaster. This is true if you plan to work on suspended ceilings. If the presence of a flat surface is fundamentally important, instead of boards, you can use laminated 22-mm plywood. However, such formwork will cost more.
It is more economical to use edged boards as the basis, on top of which 8 mm plywood is laid. Before reinforcing a monolithic slab, you can prepare 150 x 50 mm boards that are installed around the perimeter of the room and will be a formwork. The distance between the transverse bars is 800 mm or less. Under them, telescopic racks or supports are installed strictly according to the level.
150 x 25 mm boards are laid out on top of the frame. Their fastening to the base is not required, otherwise, after completion of work when dismantling the formwork, difficulties may arise. Plywood sheets should be placed on top of the boards. In order for the formwork material to be used for other purposes, the structure should be covered with a plastic film. Cloths should be laid with an overlap of 200 mm. When working, it is important to avoid jams.
Specialist advice
If the plate will act as a flooring under the roof, instead of side boards, you can use the sides of the brick or cellular blocks. After completing the work on the manufacture of the slab, the formwork must be dismantled, not broken. All fasteners for this should be located on the outside.
Fittings
The example of reinforcing a monolithic floor slab described in the article provides for the use of a mesh that binds independently. The rods should be laid along the length, and tears should be avoided. If there is a need for a garter, the metal elements must be laid with an overlap of 0.5 m. In the place where the rods intersect, they must be fixed with a wire or welding machine. Spot welding is recommended when using fittings of impressive diameter. Thin rods in this process may become thinner, which will reduce the strength of the metal and lead to a loss of the bearing capacity of the plate.
Having considered the drawing of the reinforcement of the floor slab, you can begin to work. However, it is important to stock up on tools and materials, among which a special hook should be highlighted. It is used for knitting. But its application will require certain skills. As part of the construction of your home, you can do with pliers. Metal cards will facilitate the process. They are stacked with an overlap of 2 cells. Fixation is carried out using wire.
The steel frame must not lie on the bottom of the formwork. It is set to battle tiles, stones or bricks. If the thickness of the reinforced concrete slab is more than 150 mm, then another layer of the lattice is knitted. The second layer should be located at some distance from the first, while on top the layers are covered with concrete mortar.
Settlement
Before starting work, it is necessary to calculate the reinforcement of a monolithic slab. In this case, you can take into account the area of the building, which in the example will be 6 x 6 m. The transverse walls are taken into account here.
The plate thickness will be equal to 160 mm. The cross-sectional area, taking into account the steel reinforcement, is 14 cm 2 . The design will be based on concrete grade B200. In this case, the calculation of the reinforcement of the floor slab will look as follows: Rb = 117 kg / cm 2 , Rbin = 14.3 kg / cm 2 , Eb = 3.1 * 10 '5 kg / cm. The used fittings correspond to the class A-500C. Further calculations are as follows: Rs = 4500 kg / cm 2 , E2 = 5.5 * 10 '5 kg / cm. If we use AKP-SP fiberglass reinforcement in the work, the calculations will look different: Rs = 12,000 kg / cm 2 , E = 5.5 * 10 '5 kg / cm.
Reinforcement Example
If you do not have enough experience, you can consider a specific example of reinforcing a floor slab. The pressure on the structure will be vertically down, and distributed throughout the area. The upper part of the reinforcing cage will take on compressive loads, while the lower - tensile. The rods should be laid in the formwork and interconnected by wire. Thick rods are used for the bottom mesh.
If the plate has a thickness ranging from 180 to 200 mm, a distance of between 100 and 125 mm should be maintained between the nets. To do this, you can use clamps from the scraps of reinforcement. Long rods are bent in the form of the letter L and are arranged in increments of a meter.
In those areas that require reinforcement, the distance should be reduced to 40 cm. As a rule, these are the connection points with the supports, the central part and the maximum load points. Reading the instructions for reinforcing a dwg-format floor slab, you can find out that a 25-cm layer of concrete should be poured under the lower mesh. To maintain this size under the reinforcing units, it is necessary to lay out plastic supports, which can be found in the hardware store. They are sometimes replaced by wooden bars, fixed to the base of the formwork using self-tapping screws. The upper mesh of the frame is filled with the same layer.
Hollow core reinforcement
Reinforcement of a hollow core slab should not be accompanied by making additional holes for communication networks. It is better for this to purchase plates, the reinforcement of which was carried out by prestressing reinforcement. Otherwise, the bearing capacity of the product will be reduced.
Having become acquainted with GOST 9561-91, you can learn about a number of exceptions in the manufacture of certain types of hollow panels. They are allowed not to use reinforcement of tensile reinforcement. Such panels have a thickness of 220 mm, and their length is 4,780 mm. The diameter of the holes in this case varies from 140 to 159 mm. In the calculation of reinforcing a ribbed floor slab, it is necessary to include data on the concrete resistance to compression (11.5 MPa), which is 117 kgf / cm 2 . The fittings used are in accordance with class AIII. The calculated tensile strength is 355 MPa.
If the concreting of the beams will be carried out separately from the floor slab, then their calculation will not differ from that used in the case of ordinary reinforced concrete beams of rectangular cross section. If concreting is carried out simultaneously, then the beams can be considered as beams of T-section.