Weight of a hollow floor slab. Hollow-core floor slabs. monolithic and hollow structures, sizes, prices
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Reinforced concrete floor slabs do not occupy a dominant place in the overall construction estimate, but in terms of mass indicators this structural element cannot be discounted. At the project development stage, it is necessary to clearly calculate what loads the walls and base of the building can bear, and then make a choice in favor of one or another type of interfloor covering.
Types of reinforced concrete floor slabs
The variety of modifications of this building element is relatively small, all of them are standard, as they are produced exclusively in accordance with GOST standards. All existing types of reinforced concrete products meet safety requirements for the construction of high-rise, low-rise or industrial buildings.
- A solid floor slab is a monolithic product that does not have large internal voids. The weight of a slab with a thickness of 120 mm is from 4300 to 7100 kg. Moreover, the higher the grade of concrete, the greater the strength and weight of the floor element. The weight of a 160 m thick floor slab is up to 8700 kg.
A type of solid floor slabs is additional elements. The length of such products is standard for full-size slabs (1.8 - 5 m), but the width is much smaller, as is the weight (up to 1500 kg).
- Hollow (lightweight) floor slabs have less weight, since their body is pierced with technological holes of a certain shape. These are mainly round chambers with a diameter of 140 to 159 mm (PK1, PK2); there are types of hollow slabs with ellipsoidal chambers (PG) and different shapes (PB).
The presence of voids in the body of the slab allows the weight of standard 6-meter floors to be reduced to 3 tons. The advantage of hollow slabs is their good heat and sound insulation characteristics.
- Ribbed reinforced concrete products can be classified as monolithic, since they do not have internal cavities. These are slabs with enhanced load-bearing capacity, which they received thanks to side solid-cast ribs. Standard 6-meter slabs weigh from 1500 to 3000 kg, and industrial 12-meter “giants” reach 7000 kg.
- A floor slab made of polystyrene concrete is a lightweight version of a floor slab, where thermal insulation material is used as a filler. The strength of such slabs is slightly lower than classic reinforced concrete products, but is sufficient for loads of 400-500 kgf/cm2. The weight of polystyrene concrete slabs is two times lower than classic solid ones, while the insulating qualities are several times higher than those of conventional reinforced concrete products.
How much do different floor slabs weigh?
The weight of the slabs depends on many factors, in particular on the brand of concrete used, the number of reinforcing elements, samples, voids and other factors.
| Type of concrete products | Marking | Dimensions (m) | Weight, kg) |
| Full-bodied | PRTm-3 | 1600x400x80 | 85 |
| TP-43-8 | 4300x800x220 | 1400 | |
| PTP 24-12 | 2400x1200x120 | 840 | |
| Ribbed | 1P7-2 | 5550x740x400 | 1500 |
| 2PG-5 | 5970x1490x250 | 1230 | |
| 1P3-1 | 5550x1490x400 | 2650 | |
| Hollow | PK26.10-8 | 2580x990x220 | 78 |
| PK30.15-8 | 2980x1490x220 | 790 | |
| PK50.12-8 | 4980x1190x220 | 1320 | |
| Polystyrene concrete | 36.10.3 | 3600x1000x300 | 1150 |
| 42.12.3 | 4200x1200x300 | 1610 | |
| 51.15.3 | 5100x1500x300 | 2450 |
Floor slabs are reinforced concrete horizontal structures that act as an attic or interfloor partition in a building. Modern construction uses products of this type in a wide variety of buildings, both individual and industrial, regardless of the number of floors.
Reinforced concrete floor slabs are produced in various sizes and weights, which accordingly affects the characteristics and properties. Most of the products are produced in standard dimensions, but custom production is possible in accordance with the calculations and requirements of the customer.
Regardless of the type and parameters, a reinforced concrete slab is made from high-quality light/heavy concrete, with mandatory reinforcement with a reinforcement cage.
The reinforcement is pre-tensioned mechanically or thermally and released after the concrete has hardened. This makes the slabs more durable (the reinforcement in this case is called stressed).
The ends of the slabs directly involved in the support are reinforced in different ways - with additional reinforcement, special structural elements; in hollow-core slabs, holes can be filled with concrete or the cross-section of the voids can be narrowed. All types of slabs are equipped with special hinges on the outside, necessary for working with the crane during the installation process. The loops can be located on top or inside the product in open cavities.
All reinforced concrete slabs are made in strict accordance with GOST, in the established dimensions, from properly prepared material, which guarantees compliance with technical specifications. When a reinforced concrete floor is designed, slabs with the necessary parameters and properties are selected.
Main Functions and Applications
A standard reinforced concrete slab is a flat, rectangular piece of concrete with a frame of steel rods on the inside and special hinges on the outside. Typically, such slabs are used for installing floors of various buildings and structures. There are a large number of products that differ in weight, size, and parameters.
Main characteristics of flooring with reinforced concrete slabs:As a floor, the slab takes on the full weight of the remaining parts of the structure, absorbs the load-bearing load and distributes it evenly further. The correctness of calculations and the selection of appropriate slabs directly affect the strength, reliability and durability of the entire building.
- Strength – due to the need to withstand severe design load-bearing loads
- Rigidity - noticeable bends must be excluded in the floor structure even under heavy loads, and therefore the acceptable value is considered to be 1/200 of the span for attic floors and 1/250 of the span of interfloor floors
- Thermal protection – especially important for residential buildings
- Sound insulation – to ensure optimal protection of the room from external sounds
- Fire resistance – within acceptable limits
- Cost-effective – it is desirable to combine minimal weight with low thickness and high strength/stiffness characteristics
- Industrial design of all elements, ease of installation
- Formation of floor structures and building coverings. Most often, slabs are used in such structures in a certain way: the edges of the product rest on the purlins/walls, the middle part takes the load (only dispersed, placing heavy massive objects is prohibited - no columns, etc.).
- To carry the load and ensure the spatial rigidity of the building - the slabs are embedded into one solid disk, rigidly connected to the walls, which is especially important in seismic zones.
- Arrangement of exploitable and flat roofs - hollow-core slabs are most often used for buildings and structures. Communications are laid in such slabs (but not in the seams).
- The use of used slabs in performing a variety of tasks (except for the main ones - it is better not to make floors from them) - constructing paths, fences, fences, bridges, access roads, temporary roads, used as a load-bearing structure for arranging a floor on the ground, etc. d.
The total cost of floor slabs (sizes, weights may vary) is up to 20% of the total cost of building a building. Therefore, in this case, the issue of choosing products with optimal properties at a suitable cost is relevant.
On the one hand, saving on quality can cause rapid destruction of the structure, on the other hand, there is no point in overpaying for exceeding parameters that are not relevant in operation.
Advantages
Prefabricated reinforced concrete floor slabs have certain advantages and disadvantages. There are many more advantages of using them in the installation of various buildings, which is why different types of products are actively used in the construction of certain objects.
The main advantages of floor slabs:- Correct geometric dimensions, evenness and smoothness of the slabs - which greatly facilitates calculations, installation, and further finishing of surfaces.
- Simplicity of construction - no mounting supports or formwork are needed, the slabs can be easily and simply mounted into any structure.
- Speed of work completion - immediately after installation, the slabs can be used (rather than waiting, as in the case of pouring concrete, 28 days).
- Possibility to load the slab immediately after installation is completed.
- Excellent soundproofing and thermal insulation characteristics.
- High levels of strength, reliability, rigidity.
- Easier installation of various communications - when a prefabricated reinforced concrete floor is made from hollow-core slabs, in the holes of which cables, pipes, etc. can be laid.
Among the disadvantages of using slabs in construction, it is worth noting only the need to use special equipment for installation and possible problems with delivery. But these disadvantages are conditional, since many enterprises are engaged in the production of slabs, not only in Moscow, but also in the regions, and renting a crane is not difficult.
Types of slabs
All technical characteristics of the slabs are specified in GOST 9561-91. There is a huge variety of products, varying in weight, length, height, thickness. But they are all divided into several groups, each of which has its own specification and scope of application.
Void and multi-void
This type of reinforced concrete slabs is most often found and used in different types of structures. Hollow-core slabs are good for the construction of both single-story and multi-story buildings. Often, hollow core slabs are also used to create massive industrial facilities; they are used to protect heating mains.
The main difference between hollow-core slabs and other products is the presence of through holes (voids) in the monolith. The products are made with a smooth flat surface, a reinforcement frame is laid inside for strengthening, and there are holes along the entire length of the rectangle, which can be of different shapes: oval, round, semicircular.
During the installation process, the technological voids are filled with air, which simultaneously provides several effects.
- Significant savings in material for the production of plates, which accordingly affects the cost of the product.
- High levels of noise and thermal insulation, which significantly improves the operational characteristics of the building.
- The ability to lay various pipes, wires, and other parts of communication lines in the holes.
- A significant reduction in the weight of the slab itself, which reduces the weight of the building, is necessarily taken into account in the calculations.
The installation method of the slabs may differ: 1 PKT has three supporting sides, 1 PKK has four. Also, when choosing, pay attention to the size of the internal voids - the smaller the diameter, the stronger and more durable the panel will be, but its weight will also increase. So, for slabs 1 PKK and 2 PKT, the width, height, length, and number of supporting sides are identical, but the diameter of the holes in the first case is 159 millimeters, in the second – 140 millimeters.
The strength of the slab largely depends on its thickness - standard hollow-core reinforced concrete floor slabs are 22 centimeters. There are also panels 30 centimeters thick; lightweight ones can be 16 centimeters in height (and poured from lightweight concrete).
The load-bearing capacity of hollow core slabs is about 800 kg/m2. This is quite enough for one-story buildings and not very heavy structures. Massive buildings are assembled from slabs with stressed reinforcement, the strength of which reaches 1250 kg/m2.
The standard ceiling is as follows: length up to 1.5-1.6 meters, width 1, 1.2, 1.5 or 1.8 meters, weight from half a ton (the lightest) and up to 4 tons (the most massive products). Slabs with round voids are very convenient to use, they are supplied in different standard sizes, so choosing the best option for any building will not be difficult.
Ribbed U-shaped
Ribbed reinforced concrete floor slabs are made with a special element - two longitudinal stiffeners. Most often, such products are used in the installation of non-residential premises as load-bearing elements for the subsequent installation of water supply networks and heating plants.
Reinforcement of reinforced concrete floor slabs is carried out using steel reinforcement in a stressed or unstressed state. The plates become resistant to bending and are as durable as possible. Usually they are not installed between floors of residential buildings, since then the problem of finishing the ceiling arises (it turns out ribbed, not very aesthetically pleasing).
Ribbed slabs are produced in two heights - 30 or 40 centimeters.
Products 30 centimeters thick are used as jumpers between the attic and the upper floor of the building. In the installation of massive industrial and commercial structures, slabs with a height of 40 centimeters are most often used.
The width of the ribbed slabs can be 1.5 or 3 meters, the length is 6, 12 or 18 meters (very rare). Weight can vary from 1.5 to 3 tons, in the most exceptional cases the weight of the product reaches 7 tons.
Monolithic ribbed tents
Reinforced concrete ribbed panels are produced in accordance with GOST 21506 or 27215. Tent floor slabs are flat elements designed to absorb the operational loads of the building and transfer them to the structures located below.
The load-bearing capacity of this type of slab is approximately 400-500 kg/m2. Thanks to the presence of longitudinal stiffening ribs, slab floors are particularly resistant to vibration loads, and therefore they are very often used in regions with increased seismic activity.
- Height – 22, 30, 40 centimeters
- Width – 120, 150 centimeters
- Length – 6 or 12 meters
The main advantage of this type of product is its much lighter weight compared to similar panels. Thus, a slab measuring 6x1.5x0.3 meters will weigh only one and a half tons, since the thickness of the floor at the base of the slab is only 5 centimeters.
Classification of slabs by purpose:- PP – for covering buildings as a roof for structures without an attic. The slabs are made prestressed, there are no openings in the flange.
- PR – for installation of floors on objects, produced with non-stressed reinforcement.
- PG – suitable for covering objects; these are additional slabs with non-stressed reinforcement.
- PV - panels with a special opening in the shelf for a roof fan or ventilation shaft.
- 1P – products for supporting crossbars on shelves.
- 2P – panels for resting on crossbars from above.
Specifications
Hollow-core and solid floor slabs can be made in various sizes and several design options, which accordingly affects the properties and is necessarily displayed in the markings.
Classification and labeling
Marking of slabs is carried out in accordance with GOST. Numbers and letters are printed on the side of the slab and display all specifications: information about dimensions, weight, load-bearing capacity, production date, etc.
What do the markings on the plates mean:- The first letters indicate the type: PB – solid concrete slabs; PC – hollow; NV, NVK, 4НВК – ribbed reinforced concrete products.
- The third letter indicates the presence of an additional side to support the product: T indicates the presence of three sides, K - four.
- The first 2 digits at the beginning are the length of the slab, displayed in decimeters.
- The second two numbers are the width (more often it is indicated by 1-2 real centimeters).
- The next group of alphanumeric designations indicates various additional parameters (presence of mounting loops, product class, etc.).
- The first digit of the marking indicates the thickness of the product: 1 means 10 centimeters, 2 equals 12 centimeters, 3 means 14 centimeters, 4 means 16, 5 means a slab with a thickness of 18 centimeters, 6 means 20 centimeters.
- 1P-6P – the slab rests on 4 sides.
- 3PT-6PT – on 3 sides.
- 2PD-6PD – rest on 2 sides.
Thus, the marking PC 51.15-8 on the slab indicates that this is a hollow-core floor, the length of the product is 54 decimeters (5.4 meters), the width is 15 decimeters (1.5 meters).
In addition, the dimensions and characteristics, according to GOST 12767-94, can be encrypted in the name of the slab itself. Usually, not in the markings, but in the regulatory documents, it is determined that the slabs have structural elements for installation and connection of products with metal/reinforced concrete elements. In addition to mounting loops, the slabs provide channels for laying communications.
Weight
The weight of floor slabs can vary and directly depends on the size and the presence/absence of voids inside. The indicator can vary from 960 to 4820 kilograms. The weight determines the method of installation of the structure. Most often, slabs are installed using cranes with a lifting capacity of 5 tons.
It is worth remembering that the weight of slabs, even with the same markings, may differ within small limits, both initially and under the influence of certain factors. For example, if the panel is exposed to rain, it will weigh more.
Dimensions
Modern reinforced concrete floor slabs are produced in different sizes.
Standard sizes of floor slabs:- Length – from 1.6 to 15 meters
- Width – 0.6, 1.5 meters, as well as 1.8, 2.4
- Thickness – 22 centimeters
Thanks to the options already available, you can easily design almost any building. If necessary, it is possible to make custom-made slabs.
Precast concrete products from heavy and light concrete with voids are usually made in the range of 2.4-6.6 meters in length (depending on what series), in width from 0.6 to 2.4 meters, the thickness is the same everywhere (22 centimeters), the standard weight is 900-2500 kilograms.
Solid slabs are most often produced in the following standard sizes: 2.6-4.2 meters long (if the thickness is 12 centimeters), sometimes 6.6 meters long (if the thickness is 16 centimeters). The width of standard panels is 1.2-2.4 meters. Products up to 16 centimeters thick are considered heavy and guarantee excellent sound insulation. If you choose reinforced concrete products with a thickness of 12 centimeters, you need to take care of additional sound insulation.
To perform floors with standard spans of 9, 12, 15 meters, 2T floor slabs of the following dimensions are used: height 6 meters along the edge, width 3 meters.
All floors have a specified load-bearing capacity, which is the main parameter. The load-bearing load is affected by the size and configuration of the slabs. So, in the case of multi-hollow panels, the calculations are influenced by the different shapes of the voids, length, and width of the product. Reinforcement of hollow core slabs is implemented in the lower part, which directly affects the strength. Less commonly, reinforcement is performed in the upper part of the slab.
The load on floor and bottom slabs is calculated during the design process. Depending on the type of concrete and the geometric parameters of the slab, the indicator ranges from 800 to 1450 kgf/sq.m.
Floor slabs (types and types corresponding) are made from cement grade M300 or M400. Thus, cement grade M400 can withstand loads equal to 400 kg/m3 per second. This does not mean that this will always be the case: the panel will withstand the maximum load for some time, but not all the time. M300 cement can withstand lower loads, but offers greater ductility and resistance to deflection.
Thanks to reinforcement, the load-bearing capacity increases. The hollow core slab is reinforced with steel rods of class A3 or A4, which have anti-corrosion properties and resistance to temperature changes in the range from -40 to +50 degrees.
During the production process, the reinforcement is used under tension - it is tensioned in the mold, then a mesh is installed that transfers the tension from the elements in tension to the entire body of the panel. After pouring and hardening of concrete, the tension reinforcement is cut off.
Thanks to reinforcement, reinforced concrete floor slabs become capable of withstanding heavy loads without deflection or sagging. Double reinforcement is performed at the ends so that they do not sag under their own weight and well support the load of the upper load-bearing walls.
Manufacturing technology
Different types of floor slabs are produced in different ways. PG and PC slabs are cast in formwork, PB is created on a conveyor line using a continuous method. Thanks to this, PB slabs are smoother and more even, and can be of any length.
The slabs produced in formwork are created quite simply - prestressed or non-prestressed reinforcement is placed in special forms, concrete of a certain grade is poured, they wait until it dries and hardens, the reinforcement is cut (if we are talking about prestressed reinforcement) and the panels are supplied for sale. PB slabs are continuously poured on a conveyor and then cut into panels of the required length.
PG and PC slabs, in turn, make it possible to freely lay communications in holes of at least 114 millimeters, without fear of destruction of the entire structure. The PB has a narrower hole (about 60 millimeters), so to install communication risers, you have to cut the ribs and weaken the entire structure. The calculation of a reinforced concrete floor slab must take all this into account.
Approximate prices
The cost of floor slabs varies within significant limits. It all depends on the production method, the brand of concrete used, the amount of reinforcement, and the delivery distance from the factory. Custom-sized panels are much more expensive.
Average prices for standard slabs:- PC 30.12-8 – from 5000 rubles
- PC 30.15-8 – from 5500 rubles
- PC 40.15-8 – from 7500 rubles
- PC 48.12-8 – from 7000 rubles
- PC 51.15-8 – from 9500 rubles
- PC 54.15-8 – from 10,000 rubles
- PC 60.12-8 – from 8000 rubles
- PC 60.15-8 – from 10,500 rubles
Installation
High-quality and correct installation must be carried out in strict accordance with the plan, which indicates the parameters for supporting the slabs on the walls. If the support area is insufficient, the structure may collapse; if it is excessive, heat loss will increase.
- For reinforced concrete - 7.5 centimeters
- For steel structures - 7 centimeters
- For blocks made of gas/foam concrete - 15 centimeters
- On a brick - 9 centimeters
The maximum depth of embedding panels into walls should be no more than 16 centimeters (light blocks/bricks) or 12 centimeters (reinforced concrete/concrete).
Before installation begins, all voids in the panels are sealed to a depth of at least 12 centimeters using lightweight concrete. The panels are not laid “on dry”; before laying, a layer of mortar with a maximum thickness of 2 centimeters is laid, which ensures uniform load transfer.
If installation is carried out on fragile or light blocks, a concrete monolithic reinforced belt is placed under them, which does not allow the blocks to be pressed, but requires proper external insulation.
During installation, be sure to monitor the deviation of the difference in the indicators of the front surfaces of adjacent slabs. This is done at the seams. Placing panels in “steps” is unacceptable. Dismantling it later is more difficult than doing everything right right away.
- Up to 4 meters – maximum 8 millimeters
- 4-8 meters – maximum 10 millimeters
- 8-16 meters – maximum 12 millimeters
Supporting the slabs
Each floor slab has a certain support depth, which is regulated by SNiP 2.08.01-85. Depending on the type of support, the depth may vary.
What should be the depth of support:- Along the contour, two long / one short side - 4 centimeters
- On two sides and a span of 4.2 meters, on two short / one long - 5 centimeters
- On two sides with spans greater than 4.2 meters - 7 centimeters
In the series of working drawings of the panels, the minimum support depth is indicated, and information can also be clarified with the manufacturer. The maximum support depth can be different - from 16 to 25 centimeters. The slabs should not be supported too strongly, as this will negatively affect the slabs’ ability to withstand bending loads. The deeper the panel goes into the wall, the lower the permissible stresses from loads on the ends will be.
It is prohibited to support slabs outside the support zones. Walls made of light, fragile materials are reinforced with an armored belt. For warm ceramics, laying solid, durable bricks is allowed.
Laying slabs
Floor slabs are laid on an armored belt/wall using a solution of sand and cement up to 2 centimeters thick. The surfaces of adjacent slabs should be aligned along the seam - leveled to make the ceiling or floor even (to avoid a large layer of flooring later and make finishing easier).
During the installation process, the slabs are placed exclusively on those sides that can be used for support. Usually these are 2 sides (for 1PC and PB), the third side cannot be “pinched” by the wall if it is not intended for support. This can lead to the fact that the solid slab will not be able to correctly absorb loads from above, and cracks will appear.
The installation of floor slabs is carried out before the construction of interior partitions; the slabs do not rest on them. The slab must stand for some time (“sag”), and then non-load-bearing interior partitions are created.
The gap between the panels can be different - some people place them tightly, while others consider a gap of up to 5 centimeters to be optimal. The gap space is sealed with mortar. The slabs can be tied by welding, which is important in seismic zones.
Insulation
The ends of the floors, which are located on the external walls, must be insulated. Particularly important is the insulation of the attic floor using a reinforced concrete slab, which has a high thermal conductivity and acts as a cold bridge. Usually they are insulated with extruded polystyrene foam 5 centimeters thick.
Properly produced and laid floor slabs ensure high quality, reliability, strength and durability of the structure. With their help, you can quickly and efficiently install floors of various buildings and structures.
Reinforced concrete hollow slabs are manufactured in accordance with State Standard 9561-91 and are used to cover spans of residential and public buildings.
Almost no construction project is complete without the use of these products. If for arranging foundations with FBS concrete blocks there is an equivalent replacement in the form of a poured foundation, pile foundation, etc., then there is practically no alternative to hollow core floor slabs. Any other solutions (monolithic reinforced concrete structures or wood floors) are inferior either in strength or in ease of manufacture.
From this article you will learn:
- what is the difference between PC and PB boards,
- how to calculate the permissible load on a panel,
- what causes deflections in floor slabs and what to do about it.
Differences between PC and PB hollow core floor slabs
In recent years, the PC floor slabs introduced into circulation back in Soviet times have been replaced by new generation products - hollow formless molded bench panels of the PB brand (or PPS, depending on the project).
If PC reinforced concrete slabs are manufactured according to drawings of the 1.141-1 series, then there is no single document on the basis of which bench panels are produced. Typically, factories use shop drawings provided by equipment suppliers. For example, series 0-453-04, IZH568-03, IZH 620, IZH 509-93 and a number of others.
We have summarized the main differences between PC and PB boards into one table.
| PC | PB |
|---|---|
| Thickness | |
| 220 mm, or 160 mm for lightweight PNO slabs | From 160 mm to 330 mm depending on the project and required length |
| Width | |
| 1.0; 1.2; 1.5 and 1.8 meters | The most common are 1.2, but there are also stands with a width of 1.0 and 1.5 meters |
| Length | |
| For lightweight PNOs up to 6.3 meters with a certain pitch, individual for each manufacturer. For PC - up to 7.2, less often up to 9 meters. | Since the slabs are cut to length, it is possible to produce the required size to order in increments of 10 cm. The maximum length can reach 12 meters depending on the height of the panel. |
| Typical 800 kgf/m2, upon request it is possible to produce a load of 1250 kgf/m2 | Although most often they produce a load of 800, the technology makes it possible to make slabs and any other load from 300 to 1600 kgf/m2 without additional costs. |
| Smoothness and evenness | |
| Still, the technology is old and all the molds are already worn out, you won’t find ideal slabs, but downright bad ones are rare. In appearance it's a solid 4. | They are manufactured on the latest benches and smoothed with an extruder. As a rule, slabs look much better, although there may be some exceptions. |
| Reinforcement | |
| Up to a length of 4.2 - simple mesh; longer panels are made prestressed, because the use of tension allows you to achieve the required strength grade at lower costs. | Prestressed at any length. Depending on the project, the strings can be either 12k7 or 9k7 ropes or VR-1 wire. |
| Concrete grade | |
| M-200 | From M-400 to M-550 |
| Sealing holes | |
| Typically performed at the factory. If you have not done this, be sure to fill it with M-200 concrete | Sealing of holes is not required, since the design provides for sufficient strength of the end sides even without additional reinforcement |
Load on hollow core slabs
In practice, the question often arises of what load a reinforced concrete hollow-core floor slab can bear, and whether it will break under this or that stress.
In any case, the load-bearing wall should not rest on it. Capital (load-bearing) walls can rest strictly either on foundation blocks or on the same walls of the lower floors.
Where the panel overlaps the load-bearing wall, it is additionally strengthened - the void holes at the ends are filled with concrete, and on the sides it is not recommended to overlap by more than 100 mm, i.e. until the 1st void.
The load can be distributed or point. For a distributed load, everything is simple - calculate the area of the slab in m2, multiply by the load according to the marking (usually 800 kg/m2) and subtract the own weight of the slab. So for PC 42-12-8 we have area = 5m2. Multiply by 800 = 4 tons. And subtract its own weight = 1.53 tons. The remaining 2.5 tons will be the permissible distributed load. You can, for example, fill it with a 20 cm thick concrete screed.
For point loads, it is difficult to make a similar calculation, since the load-bearing capacity of the slab in the case of point pressure depends not only on the weight of the body, but also on the point of application. So the edges of the panel are much stronger than the center. It is usually recommended not to exceed the rated load by more than 2 times, i.e. up to 1.6 tons in the absence of other influences.
In practice, it is more often necessary to calculate the combined load from different sources, such as screed, furniture, people, non-load-bearing partitions. Here you should trust the experience of Soviet research institutes, which adopted the “8” standard load, i.e. sufficient for all "standard" use cases.
Their calculations are based on the following considerations:
- own weight = 300 kg/m2
- screed + poured floors = 150 kg/m2 (approximately 6-7 cm.
- furniture + people = 200 kg/m2
- walls/partitions = 150 kg/m2
If in your case these indicators are significantly exceeded, it may be worth considering purchasing panels with higher load-bearing capacity.
Hollow-core floor slabs, due to the reinforcement and properties of concrete, distribute the weight of the object pressing on them over a larger surface than the actual contact area. So, for example, if your partition has a width of 100 mm, and there are no other loads near it, then this pressure will be distributed over a larger surface and will not go beyond the limits laid down in the calculations of the maximum standards.
It should also be remembered that in addition to constant (static) loads, there are also variable (dynamic) loads. For example, a weight standing on the floor will have a significantly less destructive impact than one that has fallen from a cabinet. Therefore, dynamic loads on the panels should be avoided whenever possible.
Deflections of floor slabs
Sometimes buyers are faced with a situation where reinforced concrete floor slabs have different deflections, including in the opposite direction. You should know that according to SNiP 2.01.07-85 “Loads and Impacts”, deflection of more than 1/150 of the length of the product is not a defect. So for the most problematic PB 90-12, the permissible deflection is as much as 6 cm.
Reverse deflection most often occurs when cutting off the last PB floor slab on a stand, when its length is significantly less than the length range for which the stand was originally prepared. For longer slabs, more tension is given, etc. the main reinforcement goes along the bottom surface of the slab; when cutting a short slab, this excess compression force seems to bend the slab.
To avoid this situation, buyers should carefully inspect the products before purchasing. As a rule, a reinforced concrete slab with a large deflection is not difficult to notice in a stack of other hollow-core slabs. It should be recognized that these cases are still rare and practically never occur among good manufacturers.
The answer to the question about the permissible support of panels on walls can be found in our article
4583 09/16/2019 4 min.Floor slabs are a very popular and inexpensive material that allows you to complete the construction of a garage, basement, or build a floor. To obtain such a product, reinforced concrete is used, which today is actively used in various branches of construction.
Hollow slabs serve as an excellent solution for roofing or as interfloor partitions.
Description of material
The production process is carried out in accordance with GOST 23009-78. This standard also requires special markings, which include dimensions, concrete grade and withstand load.
You can learn about how to use hollow core slabs assortment from this
The installation process is carried out using special equipment. But it is not recommended to use hollow slabs in aggressive environments. Therefore, before installing them, it is necessary to perform a qualitative calculation of the possible load on the walls.
The video shows hollow-core floor slabs and their technical characteristics:
When you have previously installed the frames for the technological holes, you can carry out direct pouring. Materials and working time must be distributed in such a way that the concrete filling process occurs continuously. Filling must be done until the formwork is completely filled.
When these steps have been completed correctly, compaction must be done using a deep vibrator for this purpose. Now you just have to wait 30 days for the concrete to completely harden. At the same time, treat the surface with water throughout the entire time.
Reinforced concrete hollow-core floor slabs are used in accordance with GOST specified
The video shows the load-bearing capacity of hollow-core floor slabs:
Price
Today, hollow floor slabs are available in a wide range. For this reason, it will not be possible to indicate the cost of each product. Let's consider the price (price) of the PK24-10-8 slab, it is 2,200 rubles, but the PC 90-15-8 slab will cost you 18,990 rubles.
Calculations
The presented products are characterized by their sizes and thickness. It is these parameters that influence their resistance to loads. To determine the load that the floor slab can withstand, you must first prepare a drawing of the house. After this, calculate the mass of everything that will be carried by the ceiling. Here it is worth considering plasterboard partitions, floor insulation, cement screed, parquet flooring. Now the resulting value must be divided by the total number of slabs.
The video shows the calculation of a hollow-core floor slab:
Let's look at load calculation using a specific example. Let's assume that a PC 60-15-8 plate will be used. According to GOST 9561-91 its weight will be 2850 kg. First, it is worth determining the area of the bearing surface of the product: 6 m × 1.5 m = 9 m2. To determine the load that the calculated area can withstand. As a result we get: 9 sq. m × 800 kg/sq.m = 7200 kg. We now get the mass of the plate itself: 7200 kg – 2850 kg = 4350 kg.
To determine the total load, it is necessary to take into account all floor coverings and insulation. In general, the resulting value should not exceed 150 kg/m2. As a result, 9 m2 of slab will have the following load: 9x150 = 1350 kg. The total load is determined as follows: 4350 kg – 1350 kg = 3000 kg.
The video shows what load a hollow core slab can withstand:
Series 1.141 1
Today this material is in great demand in the construction of residential and public buildings. The brand includes numbers and symbols that indicate the size of the panel and the design load. Such products are characterized by high levels of strength and durability, and the frost resistance level is F50. When making slabs I use heavy concrete, which is equipped with liners. In product labeling this is indicated by the letter A.
Hollow floor slabs are in great demand today when arranging residential buildings. But before using them, it is necessary to accurately calculate all the necessary parameters. This is the only way you can determine the advisability of using such material in certain conditions.
Anyone who has at least once dealt with the construction of a house knows how important hollow reinforced concrete slabs or floor panels are. Hollow-core concrete floor slabs, in fact, make up about 90% of the total weight of the house. Floor slabs (PC) can vary greatly in both weight and size, depending on the specific purposes for which they are used.
Structural features of hollow core slabs
As you might guess, the inside of reinforced concrete floor slabs (RC) are hollow, which is why they are labeled for sale as multi-hollow. But the holes inside such slabs, contrary to misconception, can have not only oval, but also round, square and other shapes.
Scheme of supporting a hollow core slab However, in most cases, floor slabs (PCs) have cylindrical hollow circles inside.
Interestingly, floor slabs (PC) can be either unreinforced or reinforced. Reinforced concrete floor slabs (PC) will be reinforced.
Such floor slabs (PCs), although they have a significantly greater weight, which ultimately increases both the load on the building and the cost of construction, however, have a large margin of safety. The installation of floor slabs, namely the installation method itself, depends on what support the slabs will be placed on, because support is also an important criterion.
For example, if the support of the slab is not stable enough, this can lead to unpleasant consequences, which, of course, must be avoided.
Scheme of laying a hollow core slab on the second floor Characteristics of hollow core slabs
Size
Its final cost also depends on the size of the hollow core PC; in addition to parameters such as width and length, weight is also important.
PC sizes vary as follows:
- the length of the PC ranges from 1180 to 9700 millimeters;
- The width of the PC ranges from 990 to 3500 millimeters.
The most popular and in demand are hollow-core panel slabs, the length of which is 6000 mm and the width of 1500 mm. The height or thickness of the panel is also important (it would be more correct to talk about height, but builders, as a rule, say “thickness”).
So, the thickness that hollow-core panels can have is always the same value - 220 mm. Of course, the weight of the floor panel is also of great importance. Concrete floor slabs must be lifted by a crane with a minimum lifting capacity of 4-5 tons.
Comparative table of coordination sizes of hollow core floor slabs The length and weight of the panels are of utmost importance for construction; length is an even less important indicator than weight.
Weight
As for such an important parameter as weight, everything is very clear the first time: the range of products produced in Russia ranges from 960 kilograms to 4.82 tons. Weight is the main criterion by which the method by which the panels will be installed is determined.
Typically, cranes are used, as noted above, with a lifting capacity of at least 5 tons (of course, cranes must lift weight with some margin).
The weight of panels with the same markings may differ, but only slightly: after all, if we consider the weight with an accuracy of one gram, anything can affect it.
Comparative characteristics of the main brands of hollow core slabs If, for example, a product is caught in the rain, then it will a priori be slightly heavier than the product that was not exposed to rain.
Types of loads
To begin with, it should be noted that any overlap requires the presence of the following 3 parts:
- The upper part, with the floor where people live. Accordingly, the panel will be loaded by the floor covering, various insulating elements and, of course, concrete screeds - the main component of the load;
- The lower part, with the presence of the ceiling, its decoration, and lighting fixtures. By the way, you shouldn’t be skeptical about the availability of lighting fixtures. Firstly, the same LED lamps require partial destruction of the plate with a hammer drill to lay the cable. Secondly, if you take large rooms, with columns and halls, huge crystal chandeliers can hang there, which will give a greater load than any other device or type of decoration. This must also be taken into account;
- Structural. It unites both the upper and lower parts at once, as if supporting them in the air.
A hollow core slab is a structural slab that supports both the upper and lower parts of the floor in the air!
By the way, you should not discount the dynamic load. It, as you might guess, is created by people themselves, as well as the things they move. All this affects the properties and states of the panel.
Diagram of a hollow core slab with holes For example, if moving a heavy piano in a small two-story house from one place to another once is normal, then daily movement will create a much greater negative impact on the hollow-core slab. It is unlikely to fall, but there may be serious problems with ventilation later.
Based on the type of load distribution, they are divided into 2 groups:
- distributed;
- point.
To understand the difference between these two types, it is worth giving an example. The same huge crystal chandelier, which weighs one tone - this is a point load. But a suspended ceiling with a frame over the entire surface of the slab is already a distributed load.
Construction of a technological line for the production of hollow core slabs But there is also a combined load, combining point and distributed. For example, a bathtub filled to the top. The bathtub itself stands on legs, and its pressure on the legs is a type of distributed load. But the legs standing on the floor are already a point load.
Its cost directly depends on the weight of the hollow core slab.
It's complicated, but you can figure it out. And it is necessary! After all, calculations for floors and hollow core slabs during construction will still need to be made.
Brands of hollow core slabs
As a matter of fact, hollow core slabs don’t even have brands as such. We are talking about markings that reflect some parameters. It is enough to give a small example.
Scheme of laying a hollow core slab on a crossbar Let's say the panel has the following markings: PC 15-13-10 PC - means hollow core slab; all digital designations indicate any technical parameters.
15 would mean that the panel is approximately 15 decimeters (1.5 meters) long. Why approximately? It’s just that the length can be 1.498 meters, but on the marking the manufacturer has the right to round this figure to 1.5 meters (15 decimeters). The number 12 means that the product is 10 decimeters wide. The last digit (in this case 10) is the most important indicator.
This is the load that the material can withstand (maximum permissible). In our case, the maximum load will be 10 kilograms per 1 dm². Usually builders calculate the load per square meter, here it will be 1000 kilograms per 1 m². In general, everything is not so difficult.
The panel brand always looks like PC-XX-XX; if sellers offer other options, then you should be wary.
Load calculation
Calculation of limiting impact
Calculation of the limiting impact is a mandatory condition when designing a building. The dimensions and other parameters of the panels are determined by the old, good Soviet GOST number 9561-91.
Construction of a hollow core slab with a reinforced screed In order to determine the load that will be exerted on the product, it is necessary to indicate on the drawing of the future structure the weight of absolutely all elements that will “press” on the ceiling. Their total weight will be the maximum load.
First of all, you need to consider the weight of the following elements:
- cement-sand screeds;
- gypsum concrete partitions;
- weight of flooring or panels;
- thermal insulation materials.
Subsequently, all the obtained indicators are summed up and divided by the number of panels that will be present in the house. From here you can get the maximum, maximum load on each specific product.
Calculation of optimal load
It is clear that the maximum permissible level is a critical indicator, which cannot be brought to under any circumstances. Therefore, it is best to calculate the optimal indicator. For example, a panel weighs 3000 kg. It is needed for an area of 10 m².
It is necessary to divide 3000 by 10. The result is that the maximum permissible load value will be 300 kilograms per 1 m². This is a small indicator, but you also need to take into account the weight of the product itself, for which the load was also calculated (let’s say its value is 800 kilograms per 1 m²). From 800 you need to subtract 300, the result is 500 kilograms per 1 m².
Now you need to roughly estimate how much all the loading elements and objects will weigh. Let this figure be equal to 200 kilograms per 1 m². From the previous indicator (500 kg/m²) you need to subtract the resulting one (200 kg/m²). The result will be a figure of 300 m². But that's not all.
Diagram of a hollow core slab with waterproofing Now from this indicator it is necessary to subtract the weight of furniture, finishing materials, and the weight of people who will constantly be in the room or house. “Live weight” and all elements, their load, let it be 150 kg/m². From 300 you need to subtract 150. As a result, the optimal permissible indicator will be obtained, the designation of which will be 150 kg/m². This will be the optimal load.
Advantages of hollow core slabs
Among the advantages of these products are the following:
- relatively small load on the perimeter of the entire building, in contrast to the same solid products;
- high strength indicators, despite the fact that the panels at the bottom are hollow;
- reliability;
- settlement of the house will be much less intense than when using solid products (in fact, this advantage comes from the relatively low weight);
- relatively low cost.
In general, hollow-core panels are one of the most important building materials. Today it is produced by only a few factories throughout vast Russia. The main thing, as noted above, is not to be deceived when purchasing.
Diagram of the arrangement of reinforcement blocks in a hollow-core floor slab Sometimes (this is rare, but still) sellers try to sell low-quality panels, so-called lightweight ones. For example, they may have markings indicating that the product is designed for a load of 500 kilograms per square meter, but in reality this parameter is several times lower.
This is not even fraud, it is a criminal offense that should be punished to the fullest extent of the law. After all, if you buy a panel designed for a smaller load, there is a serious risk of building collapse. This situation can be observed not only in the provinces, but even in Moscow or St. Petersburg.
In general, you need to be extremely careful when purchasing such products. It is important to remember that any design mistake can even have tragic consequences.
Video
You can watch a video where experts talk in detail about the features of different types of hollow core slabs.