Supporting the slab on a load-bearing wall. Supporting the floor slab on the wall: permissible limits, SNiP. Types of floor slabs
When building a house, any developer faces the question of choosing an interfloor floor. The three most common types of floors are wooden, monolithic reinforced concrete and prefabricated reinforced concrete, mounted from flat hollow-core slabs. It is this type of flooring, as the most popular and practical for low-rise construction, that will be discussed in this material. From this pro interfloor ceilings in a private house you will learn:
- What is the difference between hollow-core floor slabs (PC) and floor slabs made using the formless molding(PB).
- How to lay floors correctly.
- How to avoid installation mistakes.
- How to store floor slabs.
How to choose a hollow core slab
At first glance at hollow-core floors it may seem that they differ from each other only in length, thickness and width. But specifications hollow core floor slabs are much wider and are described in detail in GOST 9561-91.
Hollow core slab, private house.
Hollow-core interfloor slabs differ from each other in the method of reinforcement. Moreover, reinforcement (depending on the type of slabs) can be performed using prestressed reinforcement or without prestressed reinforcement. More often, floors with prestressed working reinforcement are used.
When choosing floor slabs, you should pay attention to the following: important point, as the permissible number of sides on which they can be supported. . Usually you can only support on two short sides, but some types of slabs allow support on three or four sides.
- PB. Provides support on two sides;
- 1pc. Thickness – 220 mm. The diameter of the round voids is 159 mm. Allows support on two sides only;
- 1PKT. Having similar dimensions, it allows support on three sides;
- 1PKK. Can be leaned on four sides.
Floor slabs also differ in their manufacturing method. There is often a debate about what to prefer – PC or PB.
Andrey164 User FORUMHOUSE
The time has come to cover the basement floor of the building with floor slabs, but I can’t decide what to choose - PC or PB, PB has a better surface finish than PC, but I heard that PB is used only in monolithic frame houses and country houses, and the end of such a slab cannot be loaded with a wall.
Sasha1983 User FORUMHOUSE
The main difference between the plates lies in the technology of their manufacture.
PC (thickness from 160 to 260 mm and typical load-bearing capacity of 800 kg/sq.m.) is cast in formwork. PB brand panels (thickness from 160 mm to 330 mm and typical load-bearing capacity from 800 kg/sq.m) are manufactured using formless continuous casting (this allows for a smoother and more even surface than PC panels). PBs are also called extruder ones.
PB, due to prestressing of the compressed and tensile zones (prestressing of the reinforcement is done at any length of the slab), is less susceptible to cracking than PC. PCs with a length of up to 4.2 meters can be produced without prestressed reinforcement and have a greater free deflection than PB.
At the request of the customer, PB can be cut to individual specified sizes (from 1.8 to 9 meters, etc.). They can also be cut lengthwise and into individual longitudinal elements, as well as making an oblique cut at an angle of 30-90 degrees, without losing its load-bearing capacity. This greatly simplifies the layout of such floor slabs on a construction site and provides greater freedom to the designer, because the dimensions of the building box and load-bearing walls are not tied to standard sizes PC.
When choosing interfloor slabs For PCs (more than 4.2 meters long), it is important to remember this feature - they are prestressed with special stops at the ends of the slab. If you cut off the end of the PC, then the stop (cut off together with the end of the PC and the vertical reinforcement) will not work. Accordingly, the working reinforcement will cling to the concrete only with its side surface. This will significantly reduce the load-bearing capacity of the slab.
Despite the better quality smooth surface, good geometry, lower weight and high load-bearing capacity, this point should be taken into account when choosing a PB. Hollow holes in the PC (depending on the width of the slab, with a diameter of 114 to 203 mm) make it possible to easily punch a hole in it for a sewer riser with a diameter of 100 mm. While the size of the void hole in the PB is 60 mm. Therefore, to punch a through hole in a PB brand panel (so as not to damage the reinforcement), you should check with the manufacturer in advance on how best to do this.
Floor slabs for a private house: installation features
PB (unlike PC) does not have mounting loops (or you have to pay extra for their installation), which can complicate their loading, unloading and installation.
It is not recommended to use the “folk” method of installing the PB, when the fastening hooks cling to the end of the hollow hole. In this case, there is a high probability that the hook will be torn out of the hole due to the destruction of the end of the slab, or the hook will simply slip off. This will cause the slab to fall. Also, at your own peril and risk, you can use a method in which a crowbar is inserted into the hollow holes of the PB (two crowbars on one side of the slab) and hooks cling to them.
Installation of PB slabs is allowed only with the use of soft chocks or a special traverse.
ProgC User FORUMHOUSE
To pull the joist out from under the slab, when laying it, leave a gap of 2 cm to the adjacent slab. Then we move the already laid slab with a crowbar to the adjacent one.
Max_im User FORUMHOUSE
Personal experience: I laid slabs at my construction site using this method. The gap was left at 3 cm. The slabs lay on cement-sand mixture 2 cm thick. The mixture acted as a lubricant, and the plates were easily moved with a crowbar to the distance I needed.
Also, when installing floor slabs, it is necessary to comply with the calculated values of the minimum depth of support for the slab. The following numbers can be used as a guide:
- brick wall, minimum support depth is 8 cm, maximum support depth is 16 cm;
- reinforced concrete – 7 cm, maximum support depth – 12 cm;
- gas and foam concrete blocks– minimum 10-12 cm, optimal support depth – 15 cm;
- steel structures– 7 cm.
It is not recommended to support the floor slab more than 20 cm, because as the depth of support increases, it begins to “work” like a pinched beam. When laying floor panels on walls built with gas and foam concrete blocks, it is necessary to install a reinforced concrete armored belt, which is described in detail in the article:. Read also our article, which explains in detail. We wish you to successfully apply the acquired knowledge on your construction sites!
Before installing the slabs, it is recommended to seal the ends of the hollow holes. The voids are sealed to prevent water from getting inside the panel. This also increases the strength at the ends of the slabs (this applies to a greater extent to PC than to PB) if load-bearing partitions are supported on them. The voids can be filled by inserting half a brick into them and “filling” the gap with a layer of concrete. Typically, voids are sealed to a depth of at least 12-15 cm.
If water does get inside the slabs, it must be removed. To do this, a hole is drilled in the panel, in the “void,” from below, through which water can flow out. This is especially important to do if the floors have already been laid, and the house went into winter without a roof. In cold weather, water can freeze inside the hollow hole (since there is nowhere for it to flow out) and tear the slab.
Sergey Perm User FORUMHOUSE
I had slabs laid on the floor for a whole year. I specially drilled holes in the “voids” with a hammer drill, and a lot of water flowed out. Each channel must be drilled.
Before laying floor slabs, it is necessary to select a truck crane with the required lifting capacity. It is important to take into account the accessibility of access roads, the maximum possible reach of the boom of the truck crane and the permissible weight of the load. And also calculate the possibility of laying floor panels not from one point, but from both sides of the house.
zumpf User FORUMHOUSE
The surface on which the floor slab is laid must be flat and free of debris. Before laying the panel, it is “spread out” cement mixture, so-called mortar “bed”, 2 cm thick. This will ensure its reliable adhesion to the walls or armored belt. Also, before installing the panels and before applying the solution to the wall, you can lay reinforcing rod with a diameter of 10-12 mm.
This method will allow you to strictly control the vertical mixing of all slabs when laying them (since the panel will not fall below the rod). The rod will not allow it to be completely squeezed out from under itself cement mortar and lie down “dry”. It is not allowed to place slabs in “steps”. Depending on the length of the slabs, the discrepancy between the ends should not exceed 8-12 mm.
A serious mistake during installation is covering two spans at once with one slab, i.e. it rests on three walls. Because of this, loads unforeseen by the reinforcement scheme arise in it, and under certain unfavorable circumstances, it may crack.
If such a layout cannot be avoided, to relieve stress, a cut is made with a grinder along the upper surface of the panels, exactly above the middle partition (wall).
Another point that you should pay attention to is how to block a flight of stairs between floor slabs if there is nothing to support them on. In this case, you can run two channels parallel to the slabs, and place one across, along the edge of the opening, tie the reinforcement cage in the form of a mesh with a cell of 20 cm and a rod diameter of 8 mm, etc. Place formwork and pour monolithic site. There is no need to tie the channel to the floor slabs. In this case, they rest on two short sides and are not subject to loads from the support unit of the flight of stairs.
How to properly store floor slabs on site
Ideally, if the panels are brought to the site, they should be installed immediately. If for some reason this cannot be done, the question arises: how to properly store them.
To store the slabs, it is necessary to prepare a solid and level area in advance. You can't just put them on the ground. In this case, the lower slab may rest on the ground, and, due to the uneven load, it will break under the weight of the upper slabs.
Products should be stacked in a stack of no more than 8-10 pieces. Moreover, spacers are placed under the bottom row (from timber 200x200 mm, etc.), and all subsequent rows are placed through spacers - a 25 mm thick inch board. The spacers should be located no further than 30-45 cm from the ends of the slabs, and they should be positioned strictly vertically one above the other. This will ensure uniform load redistribution.
, and read about e. The video reveals everything
Building a house is a very difficult process, which is fraught with a sufficient number of pitfalls. These include support units for floor slabs. This installation technology, on which the strength and service life of the house depends. In such conjugations, horizontal and vertical plane fits together.
It happens that when building a private house, it is not possible to make the joint of building elements efficiently. This, in turn, dictates in the foreseeable future the incurrence of costs for very expensive repairs or serious destruction of structures.
TYPE OF COVERING MATERIAL
Today, most of them are made of reinforced concrete. This circumstance is dictated by the fact that reinforced concrete is an extremely durable material, and its reliability has been tested not only by calculations, but also by time. The structure of the floors varies. Meet:
- plates with cells;
- prefabricated monolithic structures;
- monoliths made of heavy concrete;
- multi-hollow slabs.
The nature of the conditions for the use of slabs can be very different and depends on a number of factors: the dimensions of the building, the magnitude of the load, etc.
Floors in brick house are divided into following types:
- Floors between floors.
- Attic floors.
The first type is used for houses that are characterized by a multi-level structure. Support plate brick wall lies on a special lining. This ensures that the product is securely fixed. What is important is the depth to which the slab rests on the wall.
If there is an attic type, then significant loads are not observed, and there is no need for lining.
A special feature of such ceilings is that they insulate from unwanted noise and save heat. It is necessary to use heat insulators not only from the attic side, but also at the junctions of the walls and the ceiling.
SEARCHING FOR SOLUTIONS FOR THE SUPPORT UNIT
The support unit must withstand significant loads. It is not enough that materials with a safety margin are used in construction; additional measures must also be taken.
1. It is necessary to carry out the correct calculation of the support unit. It should be borne in mind that such calculations can only be carried out in relation to load-bearing structures, but not partitions.
2. To determine the minimum support of the floor slab on a brick wall, it is necessary to check all calculations with GOST 956-91 and the building design.
Each plate has its own marking. In the document, for each brand there is a figure characterizing the maximum load on the slab. There is a standard that characterizes the amount of support of slabs on a wall with brickwork. It ranges from 90 to 120 mm. These parameters should be adjusted to.
This indicator is important both at the construction and design stages.
The reinforced concrete floor, consisting of slabs, can be considered a load-bearing element of the building. Divided by plates inner space multi-story building into floors, and basements are separated, as well as attic spaces. Each slab receives the load from the equipment, people, and furniture located on it and transfers it, including its weight, evenly to the walls.
In specialized construction literature, a definition of the standard is given - what should be the minimum unlocking of a floor slab on a brick wall. This indicator is defined as 100 - 150 mm. For example, for a hollow slab 6 m long, the expected support on the brick should be at least 100 mm.
To more accurately determine the slab support area, additional specific calculations should be made. They must take into account the length of the slab, the material of manufacture, its total weight, and also determine what the expected load on it will be. These calculations should also take into account the thickness of the brick wall to support the slab.
What should be the minimum support for a floor slab on a brick wall to ensure the reliability and durability of the structure? This is a serious question; the stability of the building to loads and the safety of the people in it depend on its solution. That is why the depth of application of flat reinforced concrete products on brickwork is regulated by construction regulations regulatory documents(SNiP).
The strength of the entire house structure depends on the quality of installation of floor slabs.
About hollow reinforced concrete products
It is difficult to understand the issue if you do not know what floor slabs are. This structural elements permanent buildings, made of reinforced concrete, for the construction of floors between floors. There are voids inside along the entire slab various shapes
, more often round. Products are manufactured according to standard projects - series of drawings, which indicate design features and sizes. The length of the elements is 1.5-12 m. Modern technologies
production allows you to cut slabs of the required length in increments of 100 mm. The width of the product is made into 4 types: 1000, 1200, 1500 and 1800 mm.
The standard distributed load for which each element is designed is 800 kg/m2. The slab can have a thickness of 16-33 cm depending on the design and length, the most common size is 22 cm. Floor slabs are practically irreplaceable products. The alternative is either monolithic reinforced concrete. The tree loses reinforced concrete in terms of bearing capacity, and the structure monolithic design
- the process is complex and expensive.
What determines the minimum distance for support? Regulatory documents establish the minimum length of support for the end part hollow core slab on a brick wall - 9 cm. Similar solution
accepted by design engineers with justification and calculations. Factors influencing the depth of overlap:- The parameters for supporting the slab depend on the type of future structure.
- overall span size and length of reinforced concrete product;
- the magnitude of the distributed and point load on the concrete floor;
- types of loads - static, dynamic;
- thickness of load-bearing brick wall;
type of building - residential, administrative or industrial.
If you study the series by which floor elements are produced, they indicate 2 types of sizes:
- Modular. This is the theoretical width of the span where the element should be placed.
- Constructive. This is the net length ceiling slab from one end to the other.
The question arises - why is the size of the support so small, because the slab can be laid at 20-30 cm, as long as the width of the fence allows it. But this will not be support, but pinching reinforced concrete element, since its end also bears part of the load from the wall built above. In such a situation, both the slab and the load-bearing partition will not work correctly, which will lead to slow destruction and cracking brickwork.
Conversely, due to too little overlap, the heavy slab, along with the entire load, will begin to act on the edge of the masonry and eventually collapse it.
Therefore, the minimum support of 9 cm is rarely used in practice; usually 10-12 cm is accepted.
There is another reason why the edge of the ceiling should not be too deep inside the enclosing structure. The closer the end of the slab is to outer surface, the more heat is lost in such structural unit because concrete conducts heat well. The result will be a bridge of cold, which will cause cold floors in the house.
Support unit design
During construction brick building with floors made of flat concrete elements, the full-thickness masonry of the fence is carried out to the design level of the bottom of the ceiling. Then the brick is placed only from the outer part so that a niche is formed where the slab will lie. The process is accompanied by the following:
- If the depth of support is 12 cm (exactly half a brick), then the niche is made at least 13 cm wide so that the end part of the slab does not rest against the brickwork.
- Before installing the ceiling, a layer of cement-sand mortar of the same grade that was used during the construction of the masonry is laid on the base.
- Since the edge zones of the slabs will absorb part of the load from the wall erected above, the voids at the end are tightly sealed with concrete liners so that the product does not collapse from compression.
//www.youtube.com/watch?v=-Ol8NGMGQGc
As a rule, manufacturers of reinforced concrete products provide concrete liners at the factory. If this has not been done, the voids must be filled concrete mixture grade M200 under construction site conditions.
IN end walls In buildings, the floor slabs rest on the external fences not only with their ends, but also with one side part. Here the depth of support is not standardized, but for reliability, this unit should be designed in such a way that the load from the brickwork does not fall on the first void of the product. Otherwise, squeezing the hollow part may cause its destruction. The support arm should be minimal; its size depends on the design of the slab.
Comments:
During the construction of a building, such an important issue as the support of floor slabs must be taken into account.
Building codes have special instructions on this matter.
Important structural element
Floors are load-bearing elements of a building made of reinforced concrete structures. They receive and distribute the loads from their weight and the people and equipment in the building onto walls and supports. With their help, the internal space of the structure is divided into floors, and the attic and basement spaces are also separated.
Floors in a building must meet many requirements. They must be strong, rigid, have good soundproofing characteristics, not burn and not allow water to pass through.
The material used for the production of floor slabs is reinforced concrete. Basically, these are multi-hollow structures with voids of different shapes: polygonal, oval, round. Most often in construction, elements with round voids are used. They are highly durable, technologically advanced and completely ready for installation. Load bearing capacity theirs is 800 kg/m². They are laid on load-bearing walls located at a distance of about 9 m from each other. They rest on two sides. They are distinguished by fire resistance, rigidity, long term operation. Brick, aerated concrete, foam blocks and reinforced concrete panels are used as materials for the walls on which such overlapping elements will be laid.
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Some calculations
To find the amount of support for the floor slab great importance has a base on which it is planned to be laid.
When using flat overlapping elements, the span can be calculated as follows: you need to sum up the thickness of this element and the distance between the two supports. As for the depth of support of the floor slab on the brick base, this value should be equal to the thickness of the structure itself, but not less than 70 mm. To calculate minimum thickness outer wall, which will become the basis for floor slabs, it is necessary to take into account the thermal insulation layer and facing material on the end parts of the latter. Thus, a structure with a thickness of 140 mm must be supported by a base whose thickness is at least 300 mm.
Installation of frequently ribbed structures that have liners requires a minimum deepening of the floor slabs onto the base - 150 mm. During installation, do not allow hollow liners to enter the wall. If the ribs are reinforced with two rods, then it is necessary to bend them through one on the support. If the rib has one rod, then the clamps will take shear stress.
Reinforced masonry structures are analogues of flat ones. Therefore, the minimum value of the support depth of these elements can be determined in the same way. They must be at least 90 mm thick and supported on two sides.
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Individual construction
In specialized literature on construction work the definition of the necessary standards regarding the depth of support of floor slabs is given. This figure is within the range of 90-120 mm. For more precise definition of this value, certain calculations must be made, which take into account the length and weight of the structure, the thickness of the supporting wall and the material from which it is made. The expected load must also be determined.
For example, the use of a slab 6 m long requires a depth of support on a brick base of at least 100 mm. When using structures made of reinforced concrete or steel, a depth of at least 70-75 mm is permissible, for walls made of foam blocks and aerated concrete - at least 120 mm.
On the wall is one of the indicators of the reliability, safety and long service life of the building. From proper installation a lot depends on the slabs, so all the rules and regulations are regulated government agencies. There is a special document - SNiP, which has compiled a set of these standards.
Purpose of floors
Floors are one of the main load-bearing structures of a building, so they are given enough attention during construction. Main function reinforced concrete floors- transfer and distribution of load on its own weight, and then on other elements of the building.
By location data building construction are divided into interfloor, above-basement and attic. The slabs are manufactured in a factory and come in several types:
- prefabricated monolithic;
- multi-hollow;
- made from heavy grades of concrete.
The main requirements that high-quality floors must have are strength, rigidity, fire resistance, sound and water resistance.
Most floor slabs are made with voids; this design is considered the most optimal in terms of weight and quality. Laying takes place on the load-bearing walls of the building, the pitch of which can be up to 9 m.
Parameters for support amount
The maximum and minimum support of the slab floor on the wall is determined by the following factors:
- The purpose of the building is residential, industrial, administrative.
- The material from which the load-bearing walls are made and their thickness.
- The size of the overlapped span between the walls.
- The size of the reinforced concrete floor slab and its weight.
- Seismic indicators of the building location.
In accordance with SNiP data, the support of floor slabs on walls is from 9 to 12 cm, depending on the factors described above. The final size is determined by engineers when designing the building. It is important to correctly calculate the amount of overlap, otherwise the pressure of the ceilings can lead to gradual cracking and destruction of the building.
Supporting unit for a slab on a brick wall
When constructing brick buildings, the masonry is carried out close to the future ceiling, and it is important to leave small niches for installing ceilings. The support unit for the floor slab on the wall is created taking into account the following conditions:
- The ends of the slabs should not rest on the brickwork. For example, with an overlap of 12 cm, the width of the niche should be 13 cm;
- the composition of the mortar for laying and fixing the floors must be identical;
- voids formed in the channels should be filled with concrete liners. They are manufactured at the factory along with the plates.
The minimum support of floor slabs on a brick wall is not standardized if the reinforced concrete product is placed on one side of the end walls. The installation is carried out so that the masonry, which will be higher than the ceiling, does not fall on the formed extreme voids.
Floor installation
The installation of floors is carried out by a team of four people:
- crane operator who delivers the slab,
- a rigger who rigs slabs,
- two installers involved in coordinating the slab and placing it in place.
Supporting floor slabs on a brick wall is one of the most important procedures that requires strict compliance with standards.
Before installation work It is imperative to level the ridge of the brickwork. If this is not done, the slab will be unstable. The gaps that appear between the slabs are sealed with cement mortar.
Features of installation of floors for buildings made of aerated concrete
The support of the slab ceiling on the wall is carried out on the ring reinforced belt, which is mounted along its perimeter. Such a monolithic concrete strip covering the entire building is required if the support value is less than 12 cm. Recommended following parameters for armored belt:
- thickness 12 cm;
- width 25 cm;
- the support depth is the same as for reinforced concrete floors.
Combined with durable reinforced concrete slabs the reinforced belt creates a rigid structure that provides sufficient resistance to the structure of emergency impacts, temperature changes and shrinkage deformations.
If the amount of support of the ceiling on the wall is more than 12 cm, then the building does not need an additional reinforced belt. In such cases, it is enough to construct a reinforced belt from a ring anchor along the outer perimeter of the slabs.
Calculation of the support parameter
Regulates the amount of support of floor slabs on the walls of SNiP (otherwise, a set of norms and rules), which distinguishes the following types of slab sizes:
- modular - the width of the span into which the structure is installed;
- constructive - the actual size of the ceiling slab from one end to the other.
For example, if the modular floor length is 6.0 m, then the actual length is 5.98 m. To obtain a room size of 5.7 m, a slab should be installed with a support of 12 cm. The optimal calculation of the support of the floor slab on the wall is also important for maintaining warmth in the room. If the end is too close to the outer surface of the wall, cold air will penetrate inside. This design gives a cold floor in winter.
Floor covering
Installation of floor slabs for ground floor is the simplest. In order to achieve a flat surface for laying reinforced concrete structures, the upper edge of the foundation should be leveled. Then formwork boards are placed along the upper edge of the poured foundation. This design is poured concrete mortar. This creates a perfectly flat pad for installing the slabs.
Installed on a smooth surface, the slabs form a flat ceiling, in which you only need to seal the seams, after which it is ready for finishing.
Sealing seams between floors
After optimal size the support of the floor slabs on the walls was determined, and the reinforced concrete structures installed, you should start sealing the seams between them.
For this, a sand-cement mortar is used if the gaps are small. If there are large gaps, use the following methods:
- From wooden boards formwork is constructed into which the mortar is subsequently poured.
- Large gaps can be sealed with fragments of reinforcement, fragments of bricks and other materials. They are compacted into the cracks, which are then covered with concrete mortar.
It is important to seal the voids formed when installing slabs immediately. This makes it much easier Finishing work, which will be produced upon completion of construction.
From correct calculation The amount of support of the ceiling on the wall determines the future strength and durability of the structure. That's why this process is regulated by SNiP rules and is carried out by experienced designers.
