Typical prefabricated reinforced concrete products are mainly used as load-bearing elements of floors in civil and industrial buildings of mass construction - plates.
Reinforced concrete floor slabs are subdivided:
By type of cross section (fig. 2.1) - solid, hollow-core, ribbed, box-shaped;
By the number of layers (see fig. 2.1) - single-layer, two-layer, three-layer;
According to the support options - on four sides (along the contour), on three sides, on two opposite sides, at the corners (on the columns of the frame);
Prefabricated floors made of reinforced concrete slabs are used mainly in buildings of wall and frame structural systems, resting them, respectively, on walls and beams (crossbars) (Fig.2.1 a, b). In some cases, the slabs are supported directly on the columns of the frame, as well as on other floor slabs (Fig. 2.2 c, d).
Multi-slot reinforced concrete floor slabs(table 2.1, fig. 2.3) subdivided into types:
1pc- 220 mm thick with round voids with a diameter of 159 mm, designed to be supported on both sides;
1PCT
1PAC - then same, for support on four sides (along the contour);
2pcs- 220 mm thick with round voids with a diameter of 140 mm, designed to be supported on both sides;
2PKT- the same, for support on three sides;
2PZ
ZPK- 220 mm thick with round voids with a diameter of 127 mm, designed to be supported on both sides;
ZPKT- the same, for support on three sides;
ZPKK- the same, for support on four sides (along the contour);
4pcs- 260 mm thick with round voids with a diameter of 159 mm and cutouts in the upper zone along the contour for supporting on both sides;
5pcs- 260 mm thick with round voids 180 mm in diameter, designed to be supported on both sides;
6pcs- 300 mm thick with round voids with a diameter of 203 mm, designed to be supported on both sides;
7pcs- 160 mm thick with round voids with a diameter of 114 mm, designed to be supported on both sides;
Rice. 2.1. The main types of reinforced concrete floor slabs:
a - solid single layer; b - solid two-layer; c, d - solid three-layer; d - void; e - two-layer hollow; g - ribbed: h - ribbed (trough) sanitary-technical; and - ribbed type "PI"; k - ribbed insulated with a lower shelf; l - ribbed type "TT"; m - ribbed folded; n - box-shaped.
Table 2.1. Reinforced concrete hollow-core floor slabs (according to GOST 9561-91)
Note. For the length of the slabs, the size of the side of the slab that is not supported by the supporting structures of the building is taken for slabs intended to be supported on two or three sides; the smaller of the dimensions of the slab in plan - for slabs with support along the contour.
PG - 260 thick with pear-shaped voids, intended for support on both sides;
PB - 220 mm thick, manufactured by continuous molding on long stands and designed to be supported on both sides.
These types of hollow-core slabs are intended for use in residential and public buildings:
With walls made of bricks, stones and blocks;
With walls made of large panels;
With monolithic concrete walls;
Frame constructive system.
Plates 1PC can also be used for industrial buildings. The use of 7PK type slabs is limited to low-rise residential buildings.
Wide application of hollow-core slabs in construction (Figure 2.4) largely determine their merits:
Strength, stiffness and crack resistance;
Small reduced thickness due to the high voidness of the sections, reaching 50%;
Sufficient sound insulation of the floor, provided by the mass of the slabs in combination with the floor structure;
High fire resistance of the floor;
High level of prefabrication of prefabricated elements, which provides a smooth ceiling and an acceptable surface for flooring;
The possibility of a device in the plates of utilities.
Hollows in slabs designed to be supported on two or three sides, are located in the direction of the length of the plates. In slabs supported on four sides, voids are located parallel to either side of the slab.
Plates are made with grooves or grooves on the lateral edges for the formation of intermittent or continuous dowel, providing joint operation of floor slabs for shear in horizontal and vertical directions.
Plates designed to be supported on two or three sides with a length of more than 4.8 m have pre-stressed reinforcement.
Reinforcement of the ends of the plates, necessary when transferring the load is achieved by reducing the cross-section of the voids on the supports (on the one hand) and filling the voids with concrete (on the other side).
Slabs can have (in accordance with the design of a particular building) embedded parts, outlets of reinforcement, local cutouts, holes, and other additional structural details. For lifting and mounting plates, mounting loops or special gripping devices (holes) are provided in them.
Hollow-core slabs are made of heavy concrete of classes B15-B25 and structural lightweight concrete of dense structure with an average density of at least 1400 kg / m 3.
Hollow-core slabs with support on two sides (beam slabs) are calculated in the longitudinal direction for bending as free-lying single-span beams. According to the calculated values of bending moments and transverse forces, the required amount of longitudinal and transverse reinforcement is assigned. The longitudinal working armature with a diameter of 10-18 mm of classes A-IV and A-V is included in the lower grid. The transverse reinforcement is installed in the extreme edges of the section, and, if necessary, on average, according to the results of the calculation for the shear force. An example of reinforcing a hollow core slab is shown in rice. 2.5.
In the manufacture of plates of the PB type, modern continuous formwork method on heated long stands. The forming machine with targeted concrete mix moves at a speed of 0.6-3.5 m / min. Addressable heating of the track guarantees the maturation of concrete up to 70% strength in 16 hours, after which a computer-controlled diamond disk cuts the reinforced concrete tape into slabs of any given length (2.4-9 m), including trapezoidal in plan. The nominal width of such slabs is 1.2 or 1.5 m. Reinforcement is performed with prestressing rods of wire reinforcement of classes VI and VR-I with a diameter of up to 8 mm or seven-wire rope reinforcement of class K-7 with a diameter of up to 15 mm.
Rice. 2.5. Reinforcement of the hollow core slab: a - cross section; b - longitudinal section; 1 - bottom welded mesh; 2 - longitudinal working reinforcement; 3 - vertical flat welded frames; 4 - mounting loop; 5 - top welded mesh; 6 - protective concrete layer; 7 - distributor fittings.
Hollow-core slabs are used in the floors of stone and monolithic concrete buildings with longitudinal-wall and cross-wall structural systems (fig. 2.6).
The role of ceilings as hard disks is in the perception of all vertical and horizontal loads falling on them, as well as in ensuring the unity of the load-bearing frame when the forces of the building are perceived by the walls of the building. Therefore, the slabs have anchor links between themselves and with the load-bearing walls. (see fig. 2.6).
If necessary, the device of vertical communications between the slabs or between the wall and the slab, leave a gap of up to 300 mm, which is subsequently embedded in concrete with the installation of flat reinforcing frames (nodes 5,6, 9 - fig. 2.6).
In buildings with monolithic concrete walls, hollow-core slab floors can be made according to carved or uncut schemes (fig. 2.7). At the same time, the design of the joints of the floors with the walls should ensure the unhindered passage of the vertical reinforcement of the walls through them.
Table 2.2 Solid reinforced concrete floor slabs for large-panel buildings (according to GOST 12767-94)
| Plate thickness, mm | Type of slabs when resting on the supporting structures of the structure | ||
| on four sides | on three sides | on both sides | |
| 1P | - | - | |
| 2P | - | 2PD | |
| RFP | 3PT | 3PD | |
| 4P | 4PT | 4PD | |
| 5P | 5PT | 5PD | |
| 6P | 6PT | 6PD |
With free support on the walls (sectional diagram), the floor slabs must have support protrusions that extend beyond the wall edge to a depth sufficient for anchoring the longitudinal reinforcement of the slabs, but not less than 70 mm. In this case, the connection of the slabs at the ends, in addition to the indicated method, can be carried out by embedding the reinforcement cages in the voids of the slabs ( rice. 2.7 a).
With a rigid connection to the walls (continuous scheme), floor slabs must have reinforcing outlets - straight, looped, hooks. The rigidity of the nodes is achieved by welding the upper and lower outlets of the reinforcement (fig. 2.7 b), combining looped outlets and anchoring them with horizontal reinforcing bars (Fig.2.7 c, d).
Rice. 2.7. Interfacing of hollow core slabs with monolithic concrete walls:
a - freely supported slabs on the inner wall (split diagram); b, c - rigid joints of floor slabs with internal walls; d - the same, with an outer wall; 1 - inner wall; 2 - outer wall; 3 - hollow-core slab; 4 - plug; 5 - reinforcing cage; 6 - straight reinforcement outlet; 7 - loop reinforcement outlet.
In low-rise buildings and apartments on two levels, it becomes necessary to arrange stairways in the ceilings. These openings can be designed without any additional vertical supporting structures using rolled steel profiles supported by walls or main floor slabs. (fig. 2.8).
Reinforced concrete solid floor slabs for large-panel buildings subdivided into types according to their thickness and pattern of support on wall panels (Table 2.2).
The thickness of the slabs is taken from 100 to 200 mm. The most widely used slabs are made of heavy concrete with a thickness of 160 mm.
Slabs are supported on the walls on four sides (along the contour), on three or two opposite sides. Based on this, the working reinforcement of the slabs is located in two or one direction. Slabs with a length of more than 4.8 m, designed to be supported on both sides, have, as a rule, prestressed reinforcement.
Coordination dimensions of the slabs: length 3.0-7.2 m (through 0.3), width 1.2-6.6 m (through 0.3). The length of the slab is taken: when it is supported on four sides - the smallest of the dimensions of the slab in the plan; when it is supported on three or two sides - the size of the side of the slab not supported by the supporting structure. According to the transportation conditions, one of the dimensions of the slab should not exceed 3.6 m.
Plates have (fig. 2.9):
Steel embedded parts, outlets of fittings and other structural elements for connection with adjacent building structures;
Channels for hidden electrical wiring, sockets for boxes and sockets, plastic boxes with anchors for fixing luminaires;
Rice. 2.8. Arrangement of openings for intra-apartment stairs in ceilings with hollow-core slabs: a - when adjacent to one wall; b - when adjacent to two walls; A, B, C, D - nodes.
Holes and openings for the passage of utilities.
The side faces on the sides of the plates of the PD and PT types, intended for joining in the span (without leaning on the walls), are performed with closed or open recesses, the shape of which ensures the joint operation of the mating plates for shear in the horizontal and vertical directions after the grouting of the joints between the plates ... The slabs can have recesses for the formation of dowels also on the sides, supported by the wall panels.
The depth of the platform for supporting the slabs on the outer walls is 90 mm (fig. 2.10). The nominal size of the depth of the platform bearing on the inner walls is equal to half the thickness of the wall panel minus 10 mm, except for the cases when the plates are supported on the walls of the staircase, where the plates are supported for the entire thickness of the walls. The support of the floor slabs on the walls is carried out using a cement-sand mortar. All steel connections of floor slabs to each other and to external wall panels are welded. At least two ties are provided on each side of the floor slab.
Overlapping buildings with reinforced concrete frames are solved using three types of products:
Hollow-core slabs with a height of 220 mm;
Ribbed slabs with a height of 300 or 400 mm;
Plates type "TT" and "T".
Rice. 2. 9. Reinforced concrete solid floor slab, type PT for large-panel buildings:
1 - embedded corner for joining plates for welding; 2 - sling loop; 3 - loop outlet for connecting plates; 4 - hole for the ventilation block; 5 - hole for communications; 6 - hidden wiring channel; 7 - box for fixing the lamp.
Hollow-core slabs for buildings with reinforced concrete frames of the 1.020.1 series are designed to cover spans 3.0; 6.0; 7.2; 9.0 m (fig. 2.11). Coordination dimensions in width - 3 m (only for a span of 6 m); 1.5; 1.2; 0.9 m.Along with them, ribbed (trough) slabs, also 220 mm high and 1.5 m wide, are used as plumbing plates in the places of passage of vertical engineering communications.
Hollow-core slabs are laid on the shelves of crossbars or stiffening diaphragms over a 10 mm thick layer of cement mortar. Flat reinforcing cages are installed in the seams between the slabs and poured with cement-sand mortar. Intercolumnar slabs of the frame floors are also installed on the shelves of the crossbars (stiffness diaphragms) along the internal axes of the buildings and, using reinforcing assembly products, are connected to each other by arc welding (node B - see fig. 2.11).
Rice. 2.10. Scheme of the assembly plan and joints of the floor slabs:
1 - floor slab; 2 - outer wall panel; 3 - inner wall panel; 4 - connecting rod; 5 - freeze-out concrete; 6 - connecting bracket; 7 - cement mortar; 8 - mounting loop; 9 - loggia floor slab.
Ribbed reinforced concrete floor slabs with a height of 300 mm are intended for floors of multi-storey public and industrial buildings for various purposes with a column pitch of 6 m with a maximum load on the slab up to 26 kPa (2600 kgf / m 2). The shapes, sizes of the slabs and their purpose are indicated in tab. 2.3 and on Figure 2.12.
The slabs can have holes with a diameter of 400, 700 and 1000 mm, cutouts in the shelves, recesses on the outer edges of the longitudinal ribs for installing concrete dowels between adjacent slabs, additional embedded parts.
The ribbed slabs are installed "dry" on the ledger shelves or stiffening diaphragms and welded to the ledger shelves.
Slabs are made of heavy concrete with an average density of 2200 kg / m 3 or lightweight concrete of dense structure with a density of at least 1600 kg / m 3.
Rice. 2.11. Hollow-core slabs with a height of 220 mm and their location in the ceilings of frame buildings: a, b - in the span of girders 3 m; c, d - in the span of crossbars 6 m; d, e - in the span of crossbars 7.2 m; g, h - in the span of the girders 9 m; 1 - row plate; 2 - intercolumnar (tie); 3 - intercolumnar near-wall; 4 - sanitary ribbed plate; 5 - transverse crossbar; 6 - longitudinal girder; 7 - reinforcing cage; 8 - column; 9 - connecting rod.
Ribbed reinforced concrete floor slabs 400 mm high are intended for floors of industrial buildings for various purposes with a frame column pitch of 6 m with a maximum load on the slab up to 52 kPa (5200 kgf / mg 2).
Plates, depending on the way they are supported on the crossbars of the building frame, are divided into two types (table 2.4):
1P - with support on the shelves of the crossbars;
2P - leaning on the top of the crossbars (fig. 2.13).
Plates of type 1P are provided in eight standard sizes (1P1-1P8), type 2P - one standard size (2P1).
Reinforced concrete prestressed slabs of type "TT" and "T"(Figure 2.14) intended for floors of public and industrial buildings with a column pitch of 9 m (coordination length of slabs).
Rice. 2.12. Ribbed slabs with a height of 300 mm and their location in the floors of frame buildings:
a, b - in the span of the crossbars 3 m; c, d - in the span of crossbars 6 m; e, f - in the span of the girders 9 m; 1 - ordinary plate; 2 - ordinary and intercolumnar (tie); 3 - intercolumnar wall; 4 - additional solid section slab; 5 - transverse crossbar; 6 - longitudinal transom; 7 - reinforcing frame; 8 - embedment concrete.
Table 17.5. Reinforced concrete ribbed floor slabs 300 mm high
Slab "TT" with two ribs in the longitudinal direction has a width of 3 m and can be used both as an in-line and as an inter-column (tie) slab. Slab "T" with one edge has three standard sizes: 1.5m wide - row -
vaya and intercolumnar; 1.3 m - ordinary additional; 1.7 m - intercolumnar wall. The height of all slabs of type "TT" and "T" 600 mm - corresponds to the height of the crossbars of the reinforced concrete frame. The support is carried out on the shelves of the crossbars by the thickened ends of the plates with trimming of the longitudinal ribs (Fig.2.14 d), which allows you to solve the overlap without protruding individual elements.
Differ in architectural expressiveness coffered ceilings public buildings made of reinforced concrete slabs with not only longitudinal, but also transverse (sometimes diagonal) ribs of the same height (Figure 2.15). In this case, two types of slabs are used - ordinary and side (intercolumnar). The overlap is solved on a square grid of columns with a pitch of 6 or 7.5 m. The modular dimensions of the width of the slabs and the pitch of their ribs are assumed to be 1.5 m. Ordinary slabs rest on the crossbars only on two sides, the side slabs on three. The supporting parts of the slabs have undercuts from below to the height of the girder flange.
Rice. 2.14. Slabs of type "TT" and "T" and their location in the floors of frame buildings:
a - in the span of the crossbars 3 m; b - in the span of crossbars 6 m; c - in the span of the crossbars 9 m; d - unit for supporting the slab on the crossbar; 1 - row and column slab 3 m wide; 2 - the same, 1.5 m wide; 3 - ordinary additional plate; 4 - intercolumnar wall; 5 - ri-gel at the end of the building; 6 - fine-grained concrete.
The overlap is one of the structural elements of the building, dividing its internal space into floors. The overlap refers to load-bearing elements, as it perceives and transfers the load from its own weight, as well as from equipment and people to walls, supports, crossbars. It is made of reinforced concrete slabs.
By location in the building, they can be divided into:
- Above the basement.
- Interfloor.
- Attic.
By their design, they are divided into girder and non-girder. They are prefabricated from reinforced concrete and are divided into precast-monolithic, hollow-core, made of heavy concrete and aerated concrete. Ceilings must meet requirements such as strength, soundproofing, rigidity, fireproofing and waterproofing.
Basically, the reinforced concrete slabs from which the floors are made are hollow-core structures and are produced with polygonal, oval and round voids. The most widespread in construction are slabs with round voids PNO and PC, the bearing capacity of which is 800 kg / m2. They are distinguished by high strength, full factory readiness for installation, manufacturability. Such plates are supported on two sides. Lay them on load-bearing walls. Overlappings made of such slabs are used with a spacing of load-bearing walls up to 9 m. Durability, fire resistance, the required spatial rigidity, and building stability are what distinguishes such overlappings.
Common standards for hollow core slabs:
- length - 2.4-7.2 m;
- width - 1-1.8 m;
- thickness - 220 mm.
The base on which the slabs are laid can be from:
- bricks;
- reinforced concrete panels;
- aerated concrete;
- foam blocks.
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Floor bearing depth and necessary equipment for work
Depending on the base on which, the value of the bearing depth is taken into account.
The length of the slab, its weight, the thickness of the supporting wall, permanent or live load on the slab from above, and the seismic resistance of the building are also taken into account without fail. The calculations are quite complex and are done by specialists. An individual developer, on the other hand, only needs to be guided by the parameters of the manufacturer, marking his products, and strictly follow them. Strict adherence to the manufacturer's recommendations will save you from mistakes in the design and installation of hollow structures, otherwise the consequences will entail costly and time-consuming steps.
- on large-panel walls - 50-90 mm;
- on brick walls - 90-120 mm;
- on aerated concrete base - 120 mm;
- on foam block walls - 120 mm;
- on external walls, support is negotiated up to 250 mm.
Necessary equipment, materials and tools:
- anchors;
- cement mortar;
- level or level - to determine the difference in heights between the working surfaces;
- crossbars - support beams;
- assembly crowbar;
- plumb line - to check the verticality of the surface;
- inventory scaffolds;
- mooring cord;
- slings;
- truck crane with a lifting capacity of 25 tons.
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Installation of floors in brick buildings
A team of four is required for installation work. The crane operator feeds the base (walls) - the slab. The rigger is busy slinging the slabs with a four-leg sling. Two installers, being on both sides of the supports of the mounted slab, take it, unfold it and then coordinate its lowering to a given position by directing actions. After mounting crowbars, they perform a small straightening of the plate, even before removing the slings.
In brick buildings, they are laid on walls and crossbars. Crossbars are laid on reinforced concrete cushions using slings. They must be laid in brick walls during masonry. Before placing the crossbars, it is necessary to check the levelness of the pillows. The difference between them, or rather their surfaces, should not exceed 10 mm. Then the crossbars are brought to the desired position with assembly crowbars. The installers themselves are located on the stage. The crossbar must be moved only perpendicular to the longitudinal axis, using the blade of the mounting crowbar. Otherwise, the stability of the walls that support the crossbar will be violated. After that, the verticality (plumb) and horizontal (level) are verified, and only then the crossbar is fixed to the base. When this work is completed, the slings are removed.
The use of hollow core slabs is possible in buildings with either transverse or longitudinal load-bearing walls, because they are supported on two sides. This is followed by the anchoring of the floor, which is the fastening of the laid floor slabs to the outer walls and to each other. Anchors are usually placed at a distance of no more than 3 m from each other.
Before laying the floor slabs, the horizontal alignment of the working surfaces is again verified. The ridge of the wall masonry must be leveled. Because a sufficiently large area of hollow ceilings will be sensitive to even small irregularities in the base. The plates will just rock. The identified irregularities are laid with additional insulation strips.
And only after that they are lowered onto the supports of the slab, where the cement mortar has already been placed. In order to obtain a single rigid horizontal overlap, the plates are connected to each other and to the outer walls with steel anchors, which are fixed to the mounting hinges. The ends of the floor slabs are connected to the brickwork with L-shaped anchors. Then they are sealed with a mortar mixture in order to protect against corrosion.
When the slabs are supported on internal walls, composite anchors are used, obtained by welding them together. The gaps between the slabs are filled with bricks used in the main masonry. Plates are laid on a mortar mixture.
The ceiling after laying the slabs is checked for horizontalness. If a mismatch is found between adjacent slabs, they are lifted with a crane and the mortar bed is trimmed, and then put back in place. When the alignment is completed, the plates are secured with anchors, which are laid in the masonry. The adjacent slabs are connected to each other by the mounting loops with anchors.
In hollow floorings, if the support is on an external base, the voids are filled with heavy concrete or concrete plugs by about 12 cm. This is done for the purpose of isolation. The same is done in hollow slab containers, which are supported by internal load-bearing walls. The voids are filled in order to prevent the destruction of the supporting parts of the slabs under the pressure of the structures located above, since it is their edges that are the most fragile.
The lintels, which are load-bearing, that is, those on which the main load from the floors falls, are installed by lifting and laying them on the mortar with slings for the mounting loops. Ordinary jumpers are placed manually, taking into account the area of support and horizontality.
The reliability of the support of the ceilings on the load-bearing walls provides a safe, reliable and long-term possibility of operating the entire building. The constructive stability of engineering structures depends on competent execution. Therefore, the support of floor slabs on the walls is regulated by SNiP.
Parameters that determined the amount of support
The depth of the overlap on the walls depends on the following factors:
- purpose and type of buildings - residential, administrative, industrial;
- material and thickness of load-bearing walls;
- the size of the span to be covered;
- dimensions of reinforced concrete structures and their own weight;
- the type of loads acting on the floor (static or dynamic), which of them are permanent and which are temporary;
- values of point and distributed loads;
- seismicity of the construction area.
All the factors listed above are necessarily taken into account when performing calculations of the reliability of the construct. In accordance with the current regulatory documents, the support of the floor slab on the brick wall is taken from 9 to 12 cm, the final size is determined by engineering calculations during the design of the building. With less overlaps, the heavy dead weight of the elements, together with the existing loads, will have a direct effect on the edge of the masonry, which can lead to its gradual destruction.
On the other hand, a larger overlap will already be a kind of pinching of reinforced concrete elements with the transfer of weight from the upper section of the wall to their ends. The result is cracking and slow destruction of the wall masonry. Also, when the ends of the products approach the outer surfaces of the walls, an increase in heat loss in reinforced concrete elements occurs with the formation of cold bridges, leading to the formation of cold floors. The cost of parts is proportional to their length, so excessive pinching will increase the cost of the structure.
The node for supporting the floor slab on a brick wall
When erecting brick buildings with precast concrete slabs, the laying is carried out in full thickness up to the design bottom of the ceilings. Further, the bricks are laid only on the outside of the walls to form a niche into which the slabs can be laid.
It is important to observe the following conditions in the support nodes:
- the ends should not rest against the brickwork, so for the overlap most often used in practice of 12 cm, the width of the niche is ≥ 13 cm;
- the mortar on which the slabs are laid is of the same brand as the masonry;
- the voids in the channels are sealed from the ends with the help of concrete inserts, which will protect the ends from destruction when squeezed under loads. The production of concrete liners is carried out in factories with delivery upon purchase of slabs; in the absence of liners, the channel voids are filled with B15 concrete directly at the construction site.
On the end brick walls, slab reinforced concrete products also fall on one side. In this case, the minimum support of the floor slab on the end walls is not standardized. But in order to avoid the destruction of the product when the hollow channel is squeezed, the installation should be carried out so that the masonry laid out above the overlap does not lie on the extreme void of the structure and the shoulders of the moments acting from the load should be of minimum values.
Requirements for the device of armored belts for floor slabs
In buildings with walls made of blocks made of lightweight concrete (aerated concrete, aerated concrete, aerated concrete, polystyrene concrete), with low strength characteristics, the overlap must necessarily rely on reinforced belts. Armopoyas is arranged around the entire perimeter of the building. The height of the armopoyas under the floor slabs is from 20 to 40 cm. The connection of the reinforced belts with the details of the floor must be mechanically strong, for which anchoring devices or joining with reinforcing bars of a periodic profile using electric welding are used.
A number of the following requirements are imposed on the design:
- belts should fit the entire width of the walls; for external widths ≥ 50 cm, a decrease of ≤ 15 cm is permissible for laying insulation;
- reinforcement, made using engineering calculations, must provide sufficient mechanical strength to take the loads from the dead weight of reinforced concrete elements and upstream structures;
- concrete ≥ class B15;
- the belt is a kind of cold bridge, therefore, its mandatory insulation is necessary in order to prevent the destruction of aerated concrete blocks from accumulated moisture;
- reliability of adhesion to load-bearing walls.
The support of the floor slabs on the aerated concrete blocks of the bearing walls along the reinforced belts is carried out in compliance with the following standardized values:
- at the ends ≥ 250 mm;
- along the rest of the contour ≥ 40 mm;
- when supported on 2 sides of the span ≤ 4.2 m - ≥ 50 mm;
- the same with a span of ≥ 4.2 m - 70 mm.
Aerated concrete blocks are not able to withstand high loads, the material begins to undergo various deformations. Armopoyas, taking on all the loads, evenly distributes them, thereby ensuring that the structure is not destroyed.
Installation of floor slabs on gas silicate blocks is also performed with the obligatory installation of monolithic reinforced concrete belts. The required support values correspond to the values given above for walls made of aerated concrete blocks.
During the installation work, the following conditions must be met:
- compliance with the symmetry of the laying of elements in the spans;
- the ends of the plates must be aligned in one line;
- all elements must be located in the same horizontal level (control is carried out using a building level), the permissible deviation in the plane of the plates is ≤ 5 mm;
- mortar thickness under the boards ≤ 20 mm, the mortar must be freshly prepared, without starting the setting process. Additional dilution of the mixture with water is inadmissible.
It is unacceptable to lay rows of bricks or reinforcing meshes instead of an armored belt.
Building a house is fraught with many nuances that many novice builders do not even know about. In particular, one of these "pitfalls" is the floor assembly, which is a whole technology responsible for the durability of the house.
That is why it is necessary to approach the solution of this problem with full responsibility, at least to become familiar with the consequences of negligence.
Acquaintance with floor nodes
The node for supporting the floor slab on a brick wall is nothing more than a junction of two planes: vertical and horizontal. Many private developers play this moment in different ways, but this does not always work out correctly, and even more so reliably.
Therefore, in order to avoid the adverse consequences associated with expensive repairs, it is necessary to prepare in advance.
Types of materials used for floors
By themselves, these floors are made of reinforced concrete slabs, the most reliable of the materials available.
But there are some differences in the production process, this is due to the type of structure:
- Aerated concrete.
- Prefabricated monolithic- the most popular of all.
- Made on the basis of heavy concrete... This type refers to many materials, since impurities of heavy concrete are present in various products.
- Hollow.
All of the above-described floors of brick buildings are used in certain conditions, depending on the construction plan, the load carried out and the dimensions of the span.
They should be divided into two categories:
- Interfloor ceilings in a brick house are used for multi-level houses. They are mounted in a load-bearing wall on a special lining, which ensures reliable fixation of the product. In this case, the depth with which the ceiling will lie on the wall is very important.
- The attic type does not experience such high loads, therefore it is mounted into the wall without lining.
For your information! If you decide to build a multi-storey brick house with your own hands, you should give your preference to an overlap made of precast concrete slabs. They have not only increased strength, but also a huge bearing capacity, as well as, if I may say so, affordable installation.
Supporting node - find a solution
To support the floor slabs on brick walls to withstand high loads, there is little use of durable materials; the most subtle approach is required here.
- Firstly, it is necessary to correctly calculate the bearing node. Keep in mind that it can only be implemented on a load-bearing wall, but cannot in any way be connected with a partition.
Note! Each product (building material) has its own marking, which indicates its specific features: seismic resistance, bearing capacity, and others. This applies not only to reinforced concrete slabs, but also to bricks used as load-bearing structures. For example, double sand-lime brick M 150 is not the best solution for the construction of a multi-storey building.
- Secondly, all calculations and a plan for solving the problem must be verified with GOST 956-91 and additional project documents. Otherwise, you may be denied construction.
For example, look at the marking of the PK 42.15-8T slabs, where PK is an overlap with round voids, 42.15 is the dimensions of the product in decimeters (length 4180, width 1490). The number 8 is the maximum permissible load on the slab, which is 800 kgf / m2, and the letter T following the 8 is the index of the heavy concrete used for the production of this slab.
There is also a certain standard for how the support of floor slabs on a brick wall should look like - from 90 to 120 mm. It is this size that should be maintained, adjusting to it.
There are two main points to keep in mind:
- The reliability of the foundation of the house, which must be designed for high loads. It is necessary to avoid those places where the foundation can be weakened, which will lead to uneven shrinkage of the structure, as a result of which - curvature of the floor.
- In no case should the width of the foundation be less than that of the brickwork. In this case, the deformation of the bearing walls is inevitable - the load of the floor will affect the bricks and weaken the cement mortar.
It is also necessary to focus on the thickness of the slab in relation to the thickness of the load-bearing wall. And this is provided that high-quality building bricks are used that comply with standards and GOSTs.
Fixing floor slabs
Anchoring floor slabs in a brick house is used to strengthen the structure, increase strength and reduce the likelihood of material deformation. This method is extremely difficult to implement on your own, so it is better to entrust it to professionals, although the price can be unpleasantly high. The main thing in the construction business is reliability and durability.
One thing to be aware of is that it is possible to locate the anchors through the slab. However, there is also a limit - 3 meters from each other, this is a permissible maximum.
For your information! The anchor is also used to fasten precast concrete slabs together.
Now you understand what is the node supporting the floor slab on the brick wall, what is connected with it and what it affects. That is why you can protect yourself from any unfavorable moments even at the design stage.
Conclusion
It is important not only to lay the slabs correctly, but also to build a foundation, to withstand the drying time of the mortar, to lay bricks with a minimum seam thickness, as stated in the instructions. All this can be done by yourself, but if in doubt, it is better to entrust the work to professionals.
Floor slabs
Factory floor slabs are a very popular option for floors in IZHS, because the alternative - a monolithic concrete floor - is a much more time-consuming thing, difficult for inexperienced private developers. Unlike the monolith, the slabs come with a factory-guaranteed maximum load, which is more than enough in a private house.
Description
There are two GOSTs on floor slabs in Russia:- GOST 9561-91 “Reinforced concrete hollow-core floor slabs for buildings and structures. Specifications. "
- GOST 26434-85 “Reinforced concrete floor slabs for residential buildings. Types and basic parameters. "
- 1PK - 220 mm thick with round voids with a diameter of 159 mm, designed to be supported on both sides;
- 1PKT - the same, for support on three sides;
- 1PCK - the same, for support on four sides;
- 2PK - 220 mm thick with round voids with a diameter of 140 mm, designed to be supported on both sides;
- 2PKT - the same, for support on three sides;
- 2PCK - the same, for support on four sides;
- 3PK - 220 mm thick with round voids with a diameter of 127 mm, designed to be supported on both sides;
- 3PKT - the same, for support on three sides;
- 3PCK - the same, for support on four sides;
- 4PK - 260 mm thick with round voids with a diameter of 159 mm and cutouts in the upper zone along the contour, intended for support on both sides;
- 5PK - 260 mm thick with round voids with a diameter of 180 mm, designed to be supported on both sides;
- 6PK - 300 mm thick with round voids with a diameter of 203 mm, designed to be supported on both sides;
- 7PK - 160 mm thick with round voids with a diameter of 114 mm, designed to be supported on both sides;
- PG - 260 mm thick with pear-shaped voids, designed to be supported on both sides;
- PB - 220 mm thick, manufactured by continuous molding on long stands and designed to be supported on both sides.
This list does not include floor slabs of the PNO type, which are found in manufacturers of precast concrete elements. In general, as far as I understand, board manufacturers are not required to comply with GOST (Government Decree No. 982 dated December 1, 2009), although many produce and mark boards in accordance with GOST.
Manufacturers produce slabs of different sizes, you can almost always find the size you need.
Floor slabs in most cases are prestressed (paragraph 1.2.7 GOST 9561-91). Those. the reinforcement in the slabs is stretched (thermally or mechanically), and after the concrete has set, it is released back. Compression forces are transferred to the concrete, the slab becomes stronger.
Manufacturers can strengthen the ends of the slabs that participate in the support: fill round voids with concrete or narrow the cross-section of the voids in this place. If they are not filled by the manufacturer and the house turns out to be heavy (the load of the walls on the ends increases accordingly), then the voids in the area of the ends can be filled with concrete yourself.
Plates usually have special loops on the outside, for which they are lifted by a crane. Sometimes the reinforcement loops are located inside the slab in open cavities located closer to the four corners.
Floor slabs in accordance with clause 1.2.13 of GOST 9561-91 are designated as: slab type - length and width in decimeters - design load on the slab in kilopascals (kilogram-force per square meter). The steel grade of the reinforcement and other characteristics may also be indicated.
Manufacturers do not bother with the designation of the types of plates and in the price lists they usually write the type of plate only PC or PB (without any 1PC, 2PC, etc.). For example, the designation "PK 54-15-8" means a 1PC slab 5.4 m long and 1.5 m wide and with a maximum permissible distributed load of about 800 kg / m 2 (8 kilopascals = 815.77 kgf / m 2 ).
Floor slabs have bottom (ceiling) and top (floor) sides.
According to paragraph 4.3 of GOST 9561-91, the slabs can be stored in a stack with a height of not more than 2.5 m. The pads for the bottom row of plates and the gaskets between them in the stack should be placed near the mounting loops.
Supporting the plates
Floor slabs have a support zone. According to clause 6.16 "Guidelines for the design of residential buildings, Vol. 3 (to SNiP 2.08.01-85) ":The depth of support of precast plates on the walls, depending on the nature of their support, is recommended to be taken at least, mm: when supporting along the contour, as well as two long and one short sides - 40; when resting on two sides and a span of plates of 4.2 m or less, as well as on two short and one long sides - 50; with support on both sides and a span of plates of more than 4.2 m - 70.
The slabs also have a series of working drawings, for example, "series 1.241-1, issue 22". In these series, the minimum bearing depth is also indicated (it can vary). In general, the minimum bearing depth of the slab must be checked with the manufacturer.
But there are questions with the maximum depth of support of the plates. Different sources give completely different meanings, somewhere it is written that 16 cm, somewhere 22 or 25. One friend on Youtube assures that the maximum is 30 cm. Psychologically, it seems to a person that the deeper the stove is pushed into the wall, the more reliable will be. However, there is definitely a limit to the maximum depth, because if the slab enters the wall too deeply, then bending loads "work" differently for it. The deeper the slab enters the wall, the usually lower the allowable stresses from loads on the support ends of the slab. Therefore, it is better to find out the value of the maximum support from the manufacturer.
Similarly, the slabs must not be supported outside the support zones. Example: On one side, the slab is lying correctly, while the other side hangs down from the middle load-bearing wall. Below I have drawn this:
If the wall is built of "weak" wall materials such as aerated concrete or foam concrete, then you will need to build an armored belt to remove the load from the edge of the wall and distribute it over the entire area of the wall blocks. For warm ceramics, an armored belt is also desirable, although instead of it you can lay several rows of ordinary durable solid bricks, which do not have such support problems. With the help of an armored belt, it is also possible to ensure that the plates together form a flat plane, therefore, expensive ceiling plastering is not required.
Laying slabs
Plates are placed on the wall / armopoyas on a cement-sand mortar with a thickness of 1-2 cm, no more. Quote from SP 70.13330.2012 (updated version of SNiP 3.03.01-87) "Bearing and enclosing structures", clause 6.4.4:Floor slabs must be laid on a mortar layer no more than 20 mm thick, aligning the surfaces of adjacent slabs along the seam from the side of the ceiling.
Those. the slabs are leveled to create an even ceiling, and the uneven floor can then be leveled with a screed.
During installation, the plates are placed only on those sides that are provided for support. In most cases, these are only two sides (for PB and 1PK slabs), so you cannot "pinch" the third side with a wall, which is not intended for support. Otherwise, the plate clamped from the third side will not correctly perceive the loads from above, and cracks may form.
Floor slabs should be laid prior to the construction of interior partitions; the slabs should not initially rely on them. Those. first you need to let the slab "sag", and only then build non-load-bearing interior walls (partitions).
The gap between the plates (the distance between the sides) can be different. They can be laid close, or with a gap of 1-5 cm. The space of the gap between the floor slabs is then sealed with mortar. Usually the gap width is obtained "by itself" when calculating the required number of slabs, their size and the distance to be covered.
After laying, floor slabs can be tied together using, for example, welding. This is done in earthquake-prone regions (Yekaterinburg, Sochi, etc.), in ordinary regions it is not necessary.
In places where it is difficult to pick up a floor slab or it is not possible to mount it correctly, a monolithic floor should be poured. It must be poured after installing the factory plates in order to correctly set the thickness of the monolith. You need to make sure of the rigidity of the installation of a monolithic floor, especially if a staircase will rest on it. The space between floor slabs is not always trapezoidal or with slab protrusions on which to lean. If the monolith turns out to be rectangular and does not hold on to the beveled edges of adjacent slabs, then it can simply fall out.
Warming
The ends of the floor slabs lying on the outer walls must be insulated, because reinforced concrete has a high thermal conductivity and the slab in this place becomes a cold bridge. Extruded polystyrene foam can be used as insulation. Drew an example:
The load-bearing outer wall 50 cm thick includes a plate with a support of 12 cm, which is insulated from the end with EPS (orange) 5 cm thick.