For an opening in the ceiling under the stairs, even during the construction of the building, a gap in width is left standard plate made of reinforced concrete. Since the opening for the stairs on stringers and bowstrings usually occupies a much smaller area than a standard reinforced concrete slab, the space remaining after the opening is equipped is subsequently filled with concrete.

Installation of metal beams for the opening in the ceiling under the stairs

When creating an opening under the stairs, place along the interfloor slabs steel beams. They are installed in the same way as when making a staircase in wooden floor. Metal beams welded together. The metal frame obtained in this way should rest on the walls of the building, just like the reinforced concrete interfloor slabs. When the frame of the profiles is installed in its place, they begin to reinforce the areas to be poured with a monolith. The lower surface of the formwork is formed by a shield, which is made on the floor of the lower floor and lifted to the installation site using ropes. Already at the installation site, this shield is attached to the beams supporting the formwork. Such beams can be made from boards placed on edge, or from thick reinforcing bars.

Wire loops are placed on the beams, and mounts are inserted between their branches. After this, they begin to twist the wire, thereby attracting and pressing the formwork panel to the adjacent floor slabs. To prevent the possibility of laitance leakage, the shield is covered plastic film. When the formwork is secured, reinforcement and pouring begin. concrete mixture. The assembly wire twists of the formwork are left inside the concrete monolith.

Installation of a metal frame for an opening in the ceiling under the stairs

When making a metal frame from profiles, it is recommended that their “horns”, that is, the shelves of the profiles lying lengthwise, be placed in the middle of the ceiling. Then it will be easier to produce a monolithic section. For transversely lying profiles, it does not matter where the horns are directed. But if the opening in the ceiling under the stairs is planned to be finished with wood or other material, then it is also better to direct these horns inside the areas being poured with concrete.

To hide the metal frame, it must be raised relative to the bottom surface of the floor slabs by twenty to thirty millimeters. Then the cement poured into the formwork will flow under metallic profile, closing the steel frame. To ensure that the cement does not begin to fall off over time, it is recommended to weld several short pieces of metal to the bottom flange of the profile and attach a special plaster mesh to them.

Construction of a beamless structure for an opening in the ceiling under a staircase

There are also more economical option devices for staircase openings, when instead of a welded structure, a so-called beamless structure is used. It does not contain longitudinal beams, and the opening itself is framed with metal corners. These corners rest on the edges of adjacent floor slabs with their shelves. In this case, the entire weight of the monolithic section and the staircase itself will be transferred directly to the interfloor slabs. This method This method is only suitable for fairly narrow staircases, and this method is not suitable for constructing a wide staircase opening.

The technique for making openings in the ceiling along the stairs on bowstrings and on stringers is almost identical. That is, the openings themselves, options for resting the bowstring on the lower and top beams the same as for stairs on stringers.

In houses made of brick, concrete or concrete blocks, the floors are usually made of reinforced concrete. They provide exceptional strength and earthquake resistance to the structure, and are also very durable and do not burn, which is important. There are several ways to construct reinforced concrete floors. The most common and universal is laying factory-made floor slabs. Such slabs are ordered from concrete factories and then installed using a crane and a team of workers. In cases where using a crane on a construction site is difficult, or when the house has a non-standard layout and it is difficult to lay out finished slabs, a monolithic floor slab is being installed. In fact, you can fill a monolithic slab not only when there is evidence for it, but also simply because you consider it more appropriate. In this article we will tell you how to lay floor slabs and how to pour a monolithic slab. Not all work can be done independently, but it is still worth familiarizing yourself with the technology, if only to control the process on the construction site.

DIY monolithic floor slab

Monolithic flooring has a number of advantages compared to flooring made from ready-made reinforced concrete slabs. Firstly, the structure is strong and monolithic without a single seam, which ensures an even load on the walls and foundation. Secondly, monolithic filling allows you to make the layout of the house more free, since it can rest on columns. Also, the layout can involve any number of corners and crannies for which it would be difficult to select floor slabs standard sizes. Thirdly, it is possible to safely equip a balcony without an additional support plate, since the structure is monolithic.

You can install a monolithic floor slab yourself; you don’t need crane or a large team of workers. The main thing is to follow the technology and not skimp on materials.

Like everything related to construction, monolithic flooring begins with a project. It is advisable to order the calculation of a monolithic floor slab from a design office and not save on it. It usually involves calculating the cross-section of the slab for the bending moment at maximum load. As a result you will receive optimal sizes for the floor slab specifically in your home, instructions on what reinforcement to use and what grade of concrete. If you want to try to perform the calculations yourself, an example of calculating a monolithic floor slab can be found on the Internet. We will not focus on this. Let's consider the option when a regular country house with a span of no more than 7 m, so we will make a monolithic floor slab of the most popular recommended size: from 180 to 200 mm thick.

Materials for the manufacture of monolithic floor slabs:

• Formwork.
• Supports for supporting the formwork at the rate of 1 support per 1 m2.
• Steel reinforcement with a diameter of 10 mm or 12 mm.
• Concrete grade M 350 or separately cement, sand and crushed stone.
• Bending device for reinforcement.
• Plastic supports for fittings (clamps).

Technology for pouring a monolithic floor slab includes the following steps:

1. Calculation of the floor slab if the span is more than 7 m, or the project involves supporting the slab on a column/columns.
2. Installation of deck type formwork.
3. Reinforcement of the slab with steel rods.
4. Pouring concrete.
5. Compacting concrete.

So, after the walls have been kicked out required height, and their level is almost perfectly level, you can begin arranging a monolithic floor slab.

The construction of a monolithic floor slab assumes that concrete will be poured into horizontal formwork. Sometimes horizontal formwork is also called “deck”. There are several options for its arrangement. First - ready-made rental removable formwork made of metal or plastic. Second - production of formwork on site using wooden planks or sheets moisture resistant plywood . Of course, the first option is simpler and preferable. Firstly, the formwork is collapsible. Secondly, it offers telescopic supports, which are needed to support the formwork at the same level.

If you prefer to make the formwork yourself, please note that the thickness of the plywood sheets should be 20 mm, and the thickness edged boards 25 - 35 mm. If you knock down panels from edged boards, then they need to be tightly adjusted to each other. If gaps are visible between the boards, then the surface of the formwork should be covered waterproofing film.

Installation of formwork is carried out in this way:

• Vertical support posts are installed. It can be telescopic metal racks, the height of which can be adjusted. But you can also use wooden logs with a diameter of 8 - 15 cm. The step between the racks should be 1 m. The racks closest to the wall should be located at least 20 cm from the wall.
• Crossbars are placed on top of the racks (a longitudinal beam that will hold the formwork, an I-beam, a channel).
• Horizontal formwork is laid on the crossbars. If not ready-made formwork is used, but home-made one, then the longitudinal beams are laid on top cross beams, on which sheets of moisture-resistant plywood are placed on top. The dimensions of the horizontal formwork must be adjusted perfectly so that its edges rest against the wall without leaving gaps.
• The height of the pillar supports is adjusted so that the upper edge of the horizontal formwork coincides with the upper edge of the wall masonry.
• Vertical formwork elements are installed. Taking into account the fact that the dimensions of a monolithic floor slab must be such that its edges extend 150 mm onto the walls, it is necessary to construct a vertical fence exactly at this distance from the inner edge of the wall.
• IN last time The horizontal and even position of the formwork is checked using a level.

Sometimes, for the convenience of further work, the surface of the formwork is covered with a waterproofing film or, if it is made of metal, lubricated with machine oil. In this case, the formwork can be easily removed, and the surface concrete slab will be perfectly smooth. Usage telescopic stands preferable for formwork wooden supports, since they are reliable, each of them can withstand a weight of up to 2 tons, microcracks do not form on their surface, as can happen with wooden log or timber. Renting such racks will cost approximately 2.5 - 3 USD. per 1 m2 of area.

After arranging the formwork, it is installed reinforcement cage from two grids. For the manufacture of reinforcement frames it is used steel reinforcement A-500C with a diameter of 10 - 12 mm. These rods are used to knit a mesh with a mesh size of 200 mm. To connect longitudinal and transverse rods, 1.2 - 1.5 mm knitting wire is used. Most often, the length of one reinforcing rod is not enough to cover the entire span, so the rods will have to be connected to each other lengthwise. To make the structure strong, the rods must be connected with an overlap of 40 cm.

The reinforcing mesh should extend onto the walls by at least 150 mm if the walls are made of brick, and by 250 mm if the walls are made of aerated concrete. The ends of the rods should not reach the vertical formwork along the perimeter by 25 mm.

Reinforcement of a monolithic floor slab is carried out using two reinforcing meshes. One of them - the bottom one - should be located at a height of 20 - 25 mm from the bottom edge of the slab. The second - the top - should be located 20 - 25 mm below the top edge of the slab.

In order for the lower mesh to be located at the required distance, special plastic clips. They are installed in increments of 1 - 1.2 m at the intersection of the rods.

The thickness of the monolithic floor slab is taken at the rate of 1:30, where 1 is the thickness of the slab, and 30 is the span length. For example, if the span is 6 m, then the slab thickness will be 200 mm. Considering that the grids should be located at a distance from the edges of the slab, the distance between the grids should be 120 - 125 mm (from a slab thickness of 200 mm we subtract two gaps of 20 mm and subtract 4 thicknesses of reinforcing rods).

To space the meshes at a certain distance from each other, they are made from 10 mm reinforcing rod using a special bending tool. special clamps - stands as in the photo. The upper and lower flanges of the clamp are 350 mm. The vertical size of the clamp is 120 mm. The installation step of the vertical clamps is 1 m, the rows should be staggered.

Next step - end clamp. It is installed in increments of 400 mm at the ends of the reinforcement cage. Serves to strengthen the support of the slab on the wall.

Another important element - connector of upper and lower mesh. You can see what it looks like in the photo. It is necessary so that the spaced grids perceive the load as one whole. The installation step of this connector is 400 mm, and in the area of ​​support on the wall, within 700 mm from it, in steps of 200 mm.

Pouring concrete

It is better to order concrete directly from the factory. This makes the task much easier. In addition, pouring the mortar from a mixer in an even layer will ensure exceptional strength of the slab. The same cannot be said about the slab, which was poured manually with breaks to prepare a new portion of the solution. So it is better to pour concrete immediately in a layer of 200 mm, without interruptions. Before pouring concrete into the formwork, it is necessary to install a frame or box for technological holes, for example, a chimney or ventilation duct. After pouring, it must be vibrated with a deep vibrator. Then leave to dry and gain strength for 28 days. During the first week, the surface must be moistened with water, only moistened, and not filled with water. After a month, the formwork can be removed. The monolithic floor slab is ready. For the installation of floor slabs, the price includes the cost of reinforcement, concrete, rental of formwork and ordering a mixer machine, as well as a concrete pump. In fact, it comes out to about 50 - 55 USD. per m2 of flooring. You can see how the floor slab is poured with concrete in the video demonstrating the installation of floor slabs.

How to lay floor slabs correctly

The use of factory-made monolithic reinforced concrete floor slabs is considered more traditional. The most popular are PC slabs - slabs with round voids. The weight of such slabs starts from 1.5 tons, so laying floor slabs with your own hands is impossible. A crane is required. Despite the apparent simplicity of the task, there are a number of nuances and rules that must be observed when working with floor slabs.

Rules for laying floor slabs

The prefabricated floor slab is already reinforced at the factory and does not require additional reinforcement or formwork. They are simply laid in a span supported on the walls, following some rules:

• The span should not be more than 9 m. This is the length of the slabs that are the largest.
• Unloading and lifting of slabs is carried out using special equipment provided by the project. For this purpose, the slabs have mounting loops to which the mounting slings are hooked.
• Before laying floor slabs, the surface of the walls on which they will be laid must be leveled. Not allowed large differences heights and distortions.
• The slabs should rest on the walls by 90 - 150 mm.
• The slabs must not be laid dry; all cracks and technological seams must be sealed with mortar.
• The location of the slabs must be constantly monitored in relation to the walls and supporting surfaces.
• The slabs are laid only on load-bearing walls, all partitions are installed only after the installation of the floors.
• If you need to cut a hatch in the ceiling, then it must be cut at the junction of two slabs, and not in one slab.
• The plates should be located as close to each other as possible, but with a gap of 2 - 3 cm. This will ensure earthquake resistance.

If there are not enough floor slabs to cover the entire span, and there remains, for example, 500 mm, then there are different ways laying floor slabs in this case. The first is to lay the slabs end to end, leaving gaps along the edges of the room, then seal the gaps with concrete or cinder blocks. The second is laying slabs with uniform gaps, which are then sealed concrete mortar. To prevent the solution from falling down, formwork is installed under the gap (a board is tied up).

Floor slab laying technology

During the process of laying floor slabs, there must be clear coordination of actions between the crane operator and the team receiving the slab. To avoid injury on a construction site and to comply with all technological process and the rules described in SNiPs, the construction foreman must have routing installation of floor slabs. It indicates the sequence of work, the quantity and location of equipment, special equipment and tools.

It is necessary to start laying floor slabs from the flight of stairs. After laying the slabs, their position is checked. The slabs are laid well if:

• The difference between the lower surfaces of the plates does not exceed 2 mm.
• The height difference between the upper surfaces of the slabs does not exceed 4 mm.
• The height difference within the site should not exceed 10 mm.

As the installation diagram for floor slabs demonstrates, after laying the slabs, they must be connected to each other and to the walls using metal connecting parts. Work on connecting embedded parts and connecting parts is carried out by welding.

Don't forget to follow safety precautions. It is not allowed to carry out work using a crane in an open area with a wind of 15 m/s, as well as during ice, thunderstorms and fog. When moving the slab using a crane, the installation team should be away from the path along which the slab will move, on the opposite side of the feed. Despite the fact that using the services of a professional foreman and a team of installers significantly increases the cost of installing floor slabs, this is still not the case when you can save money. The foreman must provide the project.

Before ordering slabs from the factory, it is necessary to carry out preparatory work. It is better to coordinate the delivery time of the machine with slabs and the crane at the same time, so as not to overpay for downtime of special equipment. In this case, the installation of the slabs can be carried out without unloading, directly from the vehicle.

Preparatory work before laying floor slabs

First - flat supporting surface. The horizon should be almost ideal; a height difference of 4 - 5 cm is unacceptable. First of all, we check the surface of the walls, then, if necessary, level it with concrete mortar. Subsequent work can be carried out only after the concrete has acquired maximum strength.

Second - ensure the strength of the support area. If the walls are built from brick, concrete or concrete blocks, then no additional measures need to be taken. If the walls are built from foam blocks or gas blocks, then before laying the slabs it is necessary to fill in the reinforced belt. Correct styling floor slabs assumes that the supporting surface must be strong enough to support the weight of the slab and not deform along the abutment line. Neither aerated concrete nor foam concrete have the necessary strength. Therefore, formwork is installed along the entire perimeter of the building, a reinforcement frame made of 8 - 12 mm rod is installed in it, and then everything is filled with concrete with a layer of 15 - 20 mm. Further work You can continue only after the concrete has dried.

Third - install mounting towers. Telescopic supports, as described in the section on installing a monolithic floor slab, are installed in increments of 1.5 m. They are designed to take on the weight of the slab if it suddenly slips out of its place. After installation, these towers are removed.

Installation of hollow core slabs using a crane

After the freshly poured concrete has acquired sufficient strength and has dried, the installation of the floor slabs can begin. For this, a crane is used, the lifting capacity of which depends on the size and weight of the slab; cranes of 3 - 7 tons are most often useful.

Stages of work:

• Concrete mortar is applied to the supporting surface in a layer of 2 - 3 cm. The depth of application of the mortar is equal to the depth of support of the slab, i.e. 150 mm. If the slab rests on two opposite walls, then the solution is applied only to two walls. If the slab rests on three walls, then on the surface of three walls. The actual laying of the slabs can begin when the mortar reaches 50% of its strength.

• While the solution dries, the crane operator can hook the slings to the slab fasteners.
• When the crane operator is given a signal that the slab can be moved, the team of workers must move away from the place where the slab is moving. When the slab is very close, the workers hook it with hooks and turn it around, thereby dampening the oscillatory movements.

• The plate is sent to Right place, one person should stand on one wall and the other on the opposite wall. The slab is laid so that its edges rest on the wall at least 120 mm, preferably 150 mm. After installation, the slab will squeeze out excess mortar and evenly distribute the load.

• If there is a need to move the slab, you can use a crowbar. Its position can only be aligned along the laying area; the slab cannot be moved across the walls, otherwise the walls may collapse. The slings are then removed and a signal is given to the crane operator to pick them up.
• The procedure is repeated for all slabs without exception. The rules for installing floor slabs suggest that the slabs should be aligned along the bottom edge, since it is the bottom surface that will be the ceiling in the room. Therefore, the slab is laid with the wider side down and the narrower side up.

You may come across a recommendation that reinforcement must be placed in the area where the slab is supported. Proponents of this method say that it is more convenient and easier to move the stove. In fact, placing anything other than concrete mortar under the slab is prohibited by the technical map. Otherwise, the slab can easily move out of the support area, as it will slide along the reinforcement. In addition, the load will be distributed unevenly.

Laying floor slabs on a foundation is practically no different from laying interfloor ceilings. The technology is exactly the same. Only the surface of the foundation must be thoroughly waterproofed before laying the slabs. If the project provides for non-standard support of floor slabs, then special steel elements are used for this. Such work should not be carried out without a specialist.

Anchoring - tying the slabs together - can be done in two ways, depending on the project.

First - tying slabs with reinforcement. Reinforcing rods with a diameter of 12 mm are welded to the fastening embedded elements on the slab. For slabs from different manufacturers the location of these elements can be different: in the longitudinal end of the slab or on its surface. The strongest connection is considered to be a diagonal connection, when the plates are connected to each other with an offset.

The slab must also be connected to the wall. Why is reinforcement built into the wall?

Second way - ring anchor. In fact, it looks like an armored belt. Formwork is installed around the perimeter of the slab, reinforcement is installed into it and concrete is poured. This method slightly increases the cost of laying floor slabs. But it's worth it - the slabs end up clamped on all sides.

After anchoring, you can begin to seal the cracks. The gaps between the floor slabs are called rustications. They are filled with concrete grade M150. If the gaps are large, then a board is tied from below, which serves as formwork. If the gaps are small, then the floor slab will be able to withstand maximum load The next day. Otherwise you need to wait a week.

All modern slabs with round voids are produced with the ends already filled. If you purchased slabs with open holes, then they need to be filled with something 25 - 30 cm deep. Otherwise the slab will freeze. You can fill the voids mineral wool, concrete plugs or simply fill with concrete mortar. A similar procedure must be performed not only on those ends that face the street, but also on those that rest on the internal walls.

The price for laying floor slabs depends on the amount of work, the area of ​​the house and the cost of materials. For example, the cost of PC floor slabs alone is approximately 27 - 30 USD. per m2. The rest is related materials, crane rental and workers, as well as the cost of delivering the slabs. Professional teams have very different prices for installation of floor slabs, from 10 to 25 USD. per m2, maybe more depending on the region. As a result, the cost will be the same as for pouring a monolithic floor slab.

Laying floor slabs: video example

Walkthrough ventilation ducts and communications through reinforced concrete floor slabs.

GOST 9561-91. Reinforced concrete hollow-core floor slabs for buildings and structures
clause 1.2.9. In cases provided for by the working drawings of a particular building (structure), slabs may have embedded products, reinforcement outlets, local cutouts, holes and other additional structural details.
A manual for the design of residential buildings.
Vol. 3
(to SNiP 2.08.01-85)
clause 6.15. It is recommended to install channels for hidden electrical wiring in floor slabs. The diameter of channels in solid slabs is recommended to be no more than 30 mm.
It is recommended to seal through technological and communication holes in floor slabs with a mortar based on expanding cement or gypsum. Moscow 1989 .

clause 6.6. In slabs with holes or cutouts for the passage of sanitary communications, the mesh reinforcement crossing them is usually cut. To compensate for this, shortened rods or flat frames cross-section equivalent in strength to cut reinforcement.
The rods should be inserted beyond the edge of the hole or cutout to a distance equal to 50 diameters, and if the hole is located near the support, to the edge of the mesh above the support. If the position of the hole or cutout is asymmetrical relative to the center of the slab, most of the compensating rods should be located: for slabs supported along the contour, closer to the center, for slabs supported on three sides; closer to the free edge of the slab (Fig. 16).
clause 6.7. If it is necessary to replace the design reinforcement with reinforcement of a different diameter or class, it is not necessary to maintain the bar spacing specified by the project; it is only necessary to comply with the requirements regulatory documents in terms of the distance between the rods (see clause 6.4) and the sufficiency of the strength of the reinforcement being replaced. In this case, the value of the design force in the replacement (n) reinforcement per 1 m section of the slab must be no less than in the replacement (b), i.e.

Rice. 16. Layout of compensating rods along the perimeter of the cutouts (holes)

Schemes of incoming and operational quality control of construction and installation works
Part 1, issue 2
Installation of prefabricated reinforced concrete structures residential buildings, installation of light enclosing structures

Plates must have:
- steel embedded parts, reinforcement outlets and other structural elements intended for connection with adjacent building structures;
- channels for hidden electrical wiring, sockets for junction boxes and sockets, plastic boxes with anchors for fastening lamps;
- holes and openings for passage engineering communications.

Reinforcement of elements of monolithic reinforced concrete buildings
Design Guide
Moscow, 2007

Reinforcement at holes

Openings of significant sizes (more than or equal to 300 mm) in monolithic reinforced concrete walls and slabs must be bordered by additional reinforcement with a cross-section not less than the cross-section of the working reinforcement (of the same direction), which is required by the calculation of the slab as solid (Fig. 3.26,a).
Holes up to 300 mm are not edged with special rods.
The knitted working and distribution reinforcement around such holes is thickened - the two outer rods are placed with a gap of 50 mm (Fig. 3.26, b).

Figure 3.26 - Reinforcement of slabs at holes

A, b - holes, respectively, more than 300 and up to 300 mm (with working and distribution knitted fittings); 1 - slab reinforcement bars: 2 - special reinforcement bars bordering the hole

When reinforcing welded mesh It is recommended to cut holes up to 300 mm in the reinforcement locally, and it is advisable to bend the cut rods into the body of the slab.

Guidelines for the design of concrete and reinforced concrete structures made of heavy concrete
(without pre-tension)
Moscow, 1978

Holes in slabs

3.141. Large holes in reinforced concrete slabs, panels, etc. must be bordered by additional reinforcement with a cross-section no less than the cross-section of the working reinforcement (of the same direction), which is required by the calculation of the slab as continuous (Fig. 108, a).
Holes up to 300 mm in size are not framed with special rods. The knitted working and distribution reinforcement of the slab around such holes is thickened - two rods are placed with a gap of 50 mm (Fig. 108, b). When reinforcing a slab with welded mesh, it is recommended to cut such a hole in the reinforcement locally.
Holes (openings), if necessary by calculation, are framed with reinforced ribs. The dimensions and reinforcement of these ribs depend on the size, shape, location in plan relative to the floor beams, the purpose of the opening, and in each individual case are decided by the designer based on calculations.
In reinforcement drawings, special rods for reinforcing the slab within the size of the hole, with the exception of the bordering ones, are usually not given, and a note should be placed on the drawing: within the hole, the rods should be cut in place and bent into the body of the slab.
When reinforcing the floor with welded mesh, holes up to 500 x 500 mm in size are not taken into account when laying out the mesh, and a note is given on the drawing: cut the hole in place.
For larger mesh opening sizes, the mesh openings are laid out taking into account the holes, however, in the area of ​​the opening, it is recommended to reinforce the slab with separate rods without disturbing the unification of the mesh.
Additional reinforcement bordering the holes must be placed beyond the edges of the hole to a length not less than the overlap ln in accordance with clause 2.46 of this Manual.

Rice. 108. Reinforcement of slabs at holes
a - holes larger than 300 mm; b - holes up to 300 mm in size; 1 - slab reinforcement rods; 2 - border rods formed by thickening the reinforcement of the slab; 3 - rods of special reinforcement bordering the hole

4.3. The outlines of reinforced concrete structures designed for the loads specified in clause 4.1 should be taken as simple: without sudden changes in elevations, without breaks in elements and sudden changes in sections. In places where structural elements meet (for example, a crossbar with a column), as well as changes in the cross-sections of elements by more than 1.5 times, as a rule, it is necessary to install haunches, rounding of incoming corners, etc. It is recommended to make the holes round, and if it is necessary to make a rectangular hole, its corners should be rounded.

Reinforced concrete spatial structures of coverings and floors
SP 52-117-2008
Part 1
Calculation methods and design

6.5 Openings and openings

6.5.1 In thin-walled spatial structures, it is allowed to design holes and openings various shapes within the distance between the diaphragms or stiffeners, as well as a larger value, but with verification by calculation. Light openings can also be arranged using a difference in the surfaces of the coating or the sliding of shells, folds or arches.
For large openings in the slab, it is recommended to install spacers and braces, which, together with the bordering ribs, form a frame or truss capable of absorbing normal or tangential forces, or only normal forces. It is possible to use special metal structural elements that provide strength and rigidity to reinforced concrete shell elements with holes and support translucent panels.
6.5.2 Holes in the slab of shells and folds with a side size (or diameter) of no more than 15δ may be installed without special thickening of the edge of the slab, but with the installation of structural reinforcement bordering the hole with a diameter of at least 8 mm for δ > 30 mm.
It is recommended to design the holes round, oval or polygonal with rounded corners with a radius r ≥ 2δ (Fig. 6.7).

1 - fittings; 2 - joint of reinforcement with bypass at 30d or equal strength welded joint

Figure 6.7 - Bordering reinforcement of holes

6.5.3 In the area of ​​slab openings larger than 15δ, the edges of the shelves and walls must be thickened and reinforced according to calculation. The thickening must have a height ≥ 3δ, a width ≥ 2δ and an area of ​​concrete and reinforcement not less than the area of ​​concrete and reinforcement in cross section cut out part of the slab. Holes made in stretched shelves or walls must have enough reinforcement in the ribs to absorb the force exerted on the cut-out part of the shelf or wall.

Design Guide for Reinforced Concrete Structures with Beamless Floors
Moscow, 1979

1.10. When constructing holes or openings in ceilings for the passage of utilities, elevator shafts, staircases, etc. they should be placed within the slab part of the floor. The installation of holes within capitals is, as a rule, not recommended. If necessary, it is allowed to install holes within the capital with a diameter of no more than 200 mm.
Between the capitals, in the above-column strip of a monolithic beamless floor, it is recommended to place holes so that they occupy no more than 0.5 of the width of this strip, i.e., no more than 0.5 of the width of the capital.
In prefabricated beamless floors, it is advisable to provide special slabs with holes, and not to install slabs in places where openings are formed. In ceilings, in areas adjacent to openings, additional slabs and capitals can be used, and, in case of emergency, half-capitals. In some cases, when holes are formed, it is allowed to install monolithic sections of the floor.
The presence of holes and openings in the ceilings must be taken into account in the calculation.

Rice. 21. Examples of designing floor slabs at holes
a - for single holes with dimensions up to 700 mm; b and c - when the slab is weakened by holes by 50% or more or with concentrated forces applied to the edges of the slab at the hole

3.11. The horizontal reinforcement of the walls of the capital glass must be continuous, closed along the inner and outer perimeters of the glass; the vertical reinforcement of these walls should be securely anchored in the slab of the capital and the lower part of the glass.
3.12. In order to reduce the opening of cracks on the contact monolithic concrete with a prefabricated one, it is recommended to install reinforced rods in the upper zone of the interface of the capital with the column at the edge of the column (Fig. 15).
3.13. Single holes with maximum size up to 700 mm are installed in the ceiling without local thickening of the slab (Fig. 21, a). The weakening of the slab by the hole should be compensated for by additional reinforcement laid along the edges of the hole.
If concentrated forces are applied to the edge of the slab adjacent to the hole, as well as in cases where the prefabricated slab is significantly weakened by holes (by 50% or more), it is recommended to reinforce the slabs along the edges of the holes with rigid reinforcement (see Fig. 21 b) or provide thickening the slabs, or edging the holes with ribs (see Fig. 21 c).
The rigidity of the bordering ribs must be no less than the rigidity of the section of the slab section occupied by the hole.
It is recommended to thicken (strengthen) the part of the heel adjacent to the hole based on the condition that the rigidities of the section weakened by the hole are equal and without taking into account the weakening.
At rectangular holes At the corners of these holes in the slab, 2 - 4 reinforcing bars with a diameter of 10 - 14 mm should be laid, placing them in plan at an angle of 45° to the sides of the hole.
The load-bearing capacity of slabs with holes is determined by calculation.

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