Making an opening in a reinforced concrete floor for a staircase. Do-it-yourself monolithic ceiling Installation of metal beams for an opening in the ceiling under the stairs

Walkthrough ventilation ducts and communications through reinforced concrete floor slabs.

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.

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 of ≥ 3δ, a width of ≥ 2δ and an area of ​​concrete and reinforcement not less than the area of ​​concrete and reinforcement in the cross section of the 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.

Even in professional floor layout schemes, there is often a monolithic section between the slabs in buildings with complex configurations. Concreting this piece is much easier than casting a solid slab, since the lower and upper levels are set by default, there is no side formwork, the lower panel is sufficient. One option is to use a prefabricated monolithic SMP floor.

Monolithic floor section technology

IN individual construction slabs are more often used standard height 220 mm. This must be taken into account when reinforcing a homemade area, ensuring the minimum possible protective layer of 15 - 30 mm. If the monolithic section between the floors protrudes above the adjacent ones, an increase in the thickness of the screed will be required when finishing the floors.

Factory floors have voids in which it is convenient to stretch electrical cables. In a homemade slab, communications must be walled up before pouring, so as not to chisel the concrete later. This technique often used for making hatches. If openings for stairs are cut out in industrially manufactured slabs, the reinforcement pattern is disrupted, the structure loses its load-bearing capacity and becomes dangerous for use.

Formwork

The monolithic section between the slabs is poured onto a shield, which must be supported from below with racks. The simplest calculations of lumber sections are the most a budget option for an individual developer, show that boards and timber with minimal dimensions can be used for formwork:

In this case, the structure will support the weight concrete floor without sagging or geometry changes.

By default, the monolithic section between the floors has side formwork, which is the ends of the reinforced concrete products laid in place. All that remains is to place the boards under the bottom surface, placing their edges under the existing PC boards, to check the flatness and absence of deflection in any direction. To do this you need to follow these steps:

After that, the remaining pillars are mounted between the outer posts, ensuring the horizontality of the beams, purlins, and deck boards. When choosing grade 2 wood, the bending strength of the lumber is insufficient. Except bottom trim pillars with 25 mm boards, necessary to prevent shifting when pouring, additionally similar strapping is used at a level of 1.3 - 1.5 m. All pillars are stitched crosswise and lengthwise with an inch, forming a rigid spatial structure.

To facilitate stripping, extendable racks are used:

• they are manufactured smaller than the design height
• are built up in pieces in the upper part, which just needs to be unscrewed when dismantling

When stripping, first the lower bars of the racks are dismantled, then the beams with the upper pieces of the racks are removed. After which, the deck with the purlins screwed to it is dismantled. In the future, all lumber is suitable for construction rafter system. If you choose grade I wood, you can reduce the cost of inch boards for tying the posts in the middle part.

If it is necessary to fix formwork elements to existing walls, it is better to use anchors with metal sleeves. They are easily removed from the masonry after stripping, unlike dowel-nails, the plastic elements of which are almost impossible to remove from the wall.

Deck

At this stage, the monolithic section between the slabs is equipped with a deck on top of the purlins. The edges of the boards are placed under the existing floor slabs, the middle lies on the beams, which ensures the rigidity of the structure.

The gaps between the boards are foamed from the inside of the formwork (from above), the boards are covered with plastic film. This will retain water in the concrete, facilitate stripping, and prevent cracking of the floor slab. The plank design is convenient for wiring engineering systems– holes of any diameter can be drilled with crowns and drills without problems in any area.

When the width of the void section is less than 1 m, technology without racks and beams is often used:

The deck is attracted by wire twists through the timber to the lower planes of the laid slabs, reinforced, and poured using standard technology. It is not recommended to punch holes for reinforcement at the ends of the slabs, as they weaken the structure of hollow PC products. Wire clamps are cut flush with an angle grinder when stripping the formwork, part remains inside the monolithic piece.

To increase the service life of the floor, reinforcement of at least A-III periodic section (hot rolled) with a diameter of 10 - 16 mm is used. The main nuances of reinforcement are:

To knit the joints of the cells, 1 - 2 mm wire is used, the knots are created with manual, mechanical hooks, homemade equipment installed in a screwdriver or a special knitting gun.

The area between the slabs can be reinforced with a ready-made mesh or knitted on site. In the first case, the dimensions of the longitudinal and transverse rods are taken, taking into account a 4 cm protective layer on each side. The nets are knitted on flat areas and laid on the deck on top of the film on spacers of 15 - 30 mm. More often used concrete blocks 10 x 10 cm or plastic coasters with cross-shaped slots for reinforcement.

These devices are not suitable for the top layer due to small sizes. Clamps, brackets, tables are used here different forms, designs. The main task of these elements is to support the upper mesh in the design position (15 - 30 mm below the plane of the slab).

Used for bending reinforcement homemade devices. For example, a piece of 50 - 70 cm pipe with a 10 - 15 cm mandrel welded to one edge will provide the required radius (5 rod diameters) and will reduce the force.

The area between the slabs may contain input nodes for engineering systems. Embeds and void formers are installed after or before reinforcement, depending on location, configuration, and size. For example, it is better to install an 11 cm sewer cross before laying the grids; sleeves for water pipe risers can be installed at any stage.

Void formers complex shape necessary for specific communications. Therefore, they are usually made from polystyrene foam, polystyrene foam, cutting pieces of the same format to achieve the desired length from a 5 cm sheet.

For rigid fixation and absence of movement of light polymer fittings and polystyrene foam void formers when pouring the floor, the following technology is used:

• plugs are put on the fitting
• fixed with self-tapping screws from below through the deck
• or the plug is screwed on top
• then a fitting is put on it

These self-filled areas can support internal flights of stairs. For them you need:

• release the reinforcement of the lower mesh
• make a step for supporting a reinforced concrete flight structure with a counter seat
• install formwork for the staircase/hatch

To release the reinforcement, you will need to make cuts in wooden shield jumpers with a chain saw. Place the board on the reinforcement, inserting it into the cuts, and foam the remaining cracks. Steps and recesses are created by screwing narrow strips to the formwork from the inside.

Fill

Before laying concrete between floor slabs, it is recommended to prime the ends of existing slabs to improve adhesion. The main recommendations for concrete works are:

Concrete is contraindicated in solar ultraviolet radiation, hot dry weather, and frost. Covering with burlap, sawdust, and sand allows you to wet the surface without destruction. The film protects against sun rays, in winter it provides the principle of a thermos, preserving the heat generated by the hydration of cement with water.

The grade of concrete is selected in accordance with the standards SP 63.13330 for reinforced concrete structures:

• density – 1,800 – 2,500 kg/m3
• compressive strength – from B7.5

Water resistance and frost resistance are not particularly important for structures used indoors. At self-production concrete, it is necessary to take into account that the likelihood of cracking is sharply reduced if filler of different fractions with a continuous series of grains is used. Sand should not exceed 1/3 of the total volume of filler.

After pouring between the floor slabs, sagging may remain in the newly made area. They are polished with diamond equipment for an angle grinder (“grinder”) of a disc type. If the project includes a self-leveling, heated floor, screed, alignment of the joints is not necessary. For better adhesion of two adjacent reinforced concrete structures, grooves can be made in the side faces of factory slabs if the appropriate tool is available.

When laying concrete, these recesses are filled with the mixture, the two slabs are almost monolithic. The quality of the bottom edge of the slab is usually inferior to factory analogues, so finishing with suspended, level ceilings is more often used.

This technology is very convenient in the manufacture of hatches or stairwells. These technological holes can be reinforced with diagonally placed rods near them, dramatically increasing the strength of reinforced concrete. If you cut out a hatch in a factory slab, the integrity of the reinforcing mesh is compromised, which weakens the default structure. This is especially true when the opening is shifted to the middle of the slab.

Technology monolithic area homemade ceiling allows you to fill voids when laying out slabs without reducing structural strength. Even without pre-tensioning the reinforcement, the slabs have a high service life if the specified requirements are met.

The technology for reinforcing openings in monolithic reinforced concrete slabs is covered rather sparingly in domestic regulatory documentation. In the design manual “Reinforcement of elements of monolithic reinforced concrete buildings” (Moscow, 2007) in the section Reinforcement at holes it says: 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 continuous. 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. When reinforcing a slab with welded mesh, it is recommended to cut holes up to 300 mm in the reinforcement in place, and it is advisable to bend the cut rods into the body of the slab.

In the Guide to the Design of Reinforced Concrete Structures with Beamless Floors (Moscow, 1979) in paragraph 3.13. said: Single holes with a maximum size of up to 700 mm are installed in the ceiling without local thickening of the slab. 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, and also in cases where the precast 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 or provide for thickening of the slabs, or edging the holes with ribs. 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. For rectangular holes, 2-4 reinforcing bars with a diameter of 10-14 mm should be placed at the corners of these holes in the slab, placing them in plan at an angle of 45° to the sides of the hole.

The requirement for indirect reinforcement of the corners of openings to accommodate longitudinal loads in slabs and prevent the formation of cracks is contained in the guide to the design of reinforced concrete products (S. N. Sinha Handbook of Reinforced Concrete Design, 2008. Round openings in slabs are also subject to indirect reinforcement.

Foreign regulatory documentation (Swedish building code VVK 04, Polish building code PN-B-03264) provides the following requirements for the reinforcement of holes and openings in monolithic reinforced concrete slabs:
Holes and openings with a diameter (side) of 150 mm or less do not require reinforcement. Holes from 150 to 450 mm require reinforcement with U-shaped clamps (transverse reinforcement) around the perimeter of the opening, connecting two layers of reinforcement. In foreign sources, the length of the clamps is defined as three slab thicknesses, and in domestic sources as two slab thicknesses (SP 63.13330.2012 Concrete and reinforced concrete structures. Basic provisions. Updated version of SNiP 52-01-2003, paragraph 10.4.9). Holes (openings with a diameter) (side) of 450 mm to 900 mm require framing the opening with double condensed reinforcement around the perimeter and laying indirect corner double reinforcement. Holes or openings with a side of more than 90 cm require reinforcement of the slab with internal hidden beams or retaining beams.
Maximum size According to various sources, the opening can be up to 1/4 of the largest side of the slab, or no more than 1/3 of the smallest side of the slab. Minimum allowable thickness

Ladder - important element designs multi-story building. It must, of course, be as reliable and safe as possible during operation. To increase its load strength, it is imperative to reinforce the staircase opening (flight). This will increase the stability of the staircase itself, protect the structure from sagging and stretching, and prevent chips and cracks.

Before starting work, you need to pay attention to the type of structure of the future staircase and take into account the level of loads that it will receive daily. Under intense loads, the structure will begin to experience pressure from above, where the concrete will begin to compress, while tension will occur from below, which will lead to a loss of concrete strength. Therefore, reinforcement of the lower part of the march is especially important. When reinforcing a staircase opening, staple-bending products and flat reinforcing cages are used, less often - reinforcing mesh, but their effectiveness in these designs is practically zero. When assembling frames and laying reinforcement, they use additional elements– channels laid on the sides of the formwork, and reinforcing angles for reinforcing the edges of steps.

It is necessary to reinforce the staircase opening from top to bottom, because the main pressure is exerted from above, which means that the staircase needs to be reinforced from the reverse side. The dimensions of the flat frames of both the upper and lower ones must match. Simple monolithic stairs, which do not have platforms in their design, do not need reinforcement of the lower part; only the upper part will be sufficient. The reinforcement will increase the rigidity of the stairs and protect it from possible impacts and damage. Double-flight staircases must be securely fastened to the walls, since their monolithic platforms take on enormous loads from the weight of the same staircase. For this purpose, special reinforced concrete crowns are used. If the house is being built using technology monolithic casting, the construction and reinforcement of stairs should be taken up during the construction of the walls themselves.

To calculate the amount of required reinforcement, you need to compare indicators such as the length of the flight of stairs, the distance between the rods, minimum height working plates, diameter of reinforcing bars. The calculations should be entrusted to professionals, people who are knowledgeable in this matter. Even if you decide to do reinforcement yourself, you cannot do this without a well-developed reinforcement design scheme.