Floor plan is a graphic representation of horizontal structures that perform load-bearing and enclosing functions. The immediate purpose of the floors is to divide the building into floors to increase the usable area of the structure, which could be used, for example, to accommodate residential premises.
To draw up a floor plan, it is necessary to determine what load-bearing structures will be used - this is also included in the design of houses (prefabricated or monolithic reinforced concrete; reinforced concrete beams, wood or metal, etc.).
General information about precast floor slabs
Houses made from prefabricated reinforced concrete slabs have standard dimensions, but differ in type.
Prefabricated buildings have a number of advantages compared to a monolith:
- high installation speed;
- laying the slabs can be carried out regardless of the conditions: frost, heat, rain, etc. will not be a problem;
- low price, you can save up to 15% of the cost of the monolith.
Reinforced concrete slabs together with the concrete floor of the first floor lead to the main disadvantage of the structure - large mass. Due to their high weight, the slabs have a limited area of use and require the installation of a high-strength foundation. By increasing the depth of foundations for internal and load-bearing walls, the construction estimate increases. Even taking into account additional costs, reinforced concrete slabs are cheaper than a monolith.
Numerous comparisons have proven that slab floors are 50-70% cheaper than monolithic floors and hollow core slabs
The thickness of the external and internal walls of the building differs; the load-bearing slabs are 140-220 mm thick and up to 9 m long, depending on the span. The thickness of the internal walls is about 8-12 mm. When working with panels, it is important to consider the layout and type of construction.
In total there are 3 main types:
- full-bodied. Without voids, they have the greatest weight. They are distinguished by the greatest strength. They are included in the plan, drawing of the floors of exclusively multi-storey buildings. They are used to create interfloor slabs. Due to their solid structure, the slabs have reduced heat and sound insulation properties;
- empty. Inside there are longitudinal voids, usually round in shape. The addition of air tanks resulted in an increase in thickness - 220 mm. They are the most common prefabricated elements. They are distinguished by high insulating characteristics. Due to the presence of voids, in comparison with monolithic floors, hollow blocks create less load on the base and walls. An additional advantage is the ability to cover large spans and load-bearing walls, since the length of the slabs reaches 12 m;
- tent They are a tray with ribs pointing down or up. The thickness of the slabs ranges from 140 to 160 mm.
When working with roofs and external walls, monolithic floors are often used due to their advantages compared to prefabricated slabs:
- distribute the load evenly;
- construction does not require the use of special equipment;
- can be laid not only on walls, but also on columns;
- the monolith can be prepared in any size, including non-standard.
The ceiling retains its monolithic-reinforced structure.
Monolithic panels have 3 main disadvantages:
- labor intensity of construction;
- the need for a complex process of strengthening the structure, which is unlikely to be possible without the help of highly qualified builders;
- The formation of formwork is required; the process is labor-intensive and requires a lot of materials.
When drawing up a plan and considering the layout of floor slabs, it is worth taking into account the features of each type of floor.
Construction of a beamless structure for an opening in the ceiling under a staircase
There is also a more economical option for constructing a staircase opening when, instead of a welded structure, a so-called beamless structure is used. It does not include 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 is only suitable for fairly narrow stairs, 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, the options for supporting the bowstring on the lower and upper beams are the same as for stairs on stringers.
Floor slab plan
An important step in drawing up a diagram is calculating the number of slabs. The indicator is defined as the sum of the floor areas and the area of one slab. When dividing, the result may be a non-integer value; rounding is carried out upward.
When considering the plan, you can choose several types of floors for different floors. Differences are often made for rooms below grade level, but changes can be made for each floor separately.
It is better to leave the drawing of the floor plan in the hands of a professional. The work itself can be done by a beginner or an unskilled worker, but the drawing requires an understanding of the properties of reinforced concrete slabs and correct calculations. Any mistake can result in the destruction of the structure. The architect will take into account the building's features and help determine the best plan.
Floor plan - a graphic representation of horizontal structures that perform load-bearing and enclosing functions
For flooring, reinforced concrete beams with a T-section and inter-beam filling are used (lightweight concrete slabs or hollow liners). The length of the beams ranges from 2.4-6.4 m. Support on the wall - from 150 mm. The ends are anchored into the wall on both sides. The pitch is defined as the size of the aggregate, usually 60, 80 cm or 1 m.
If you plan to lay wooden floors, the situation is greatly simplified, since you will not have to operate with heavy structures, but with easily movable beams. If errors are made in terms of overlaps, they are easier to eliminate; the result of the error is not disastrous. Even a beginner can perform flooring with wood. It is important to choose impregnated beams, and their installation is a simple procedure.
Wooden beams are capable of covering a span of up to 4.8 m. The height of the beam is selected in the range of 5-10% of the span, and the width is in the range of 60-120 mm. The support for the interbeam shields are 40-50 mm cranial beams, which are attached to the sides of the beams. The pitch of the beams is taken from 600 to 1500 mm, this has a decisive effect on the width of the boards. The length of the shields is calculated based on the length of the boards.
Floors: principle and importance of calculations
Before using the program to calculate the floor, you need to decide on the material of the structure. In private construction, three main types of flooring are used:
Wooden
The load-bearing beams when constructing a wooden floor are: timber (log), metal profile (channel, I-beam, corner) or reinforced concrete elements. The beams are covered with boards, forming floor slabs. Based on calculations based on building codes, the cross-section of the load-bearing beam is determined by summing its weight and operational load. The approximate load of the interfloor wooden floor is 400 kg/m². If the active use of this area is not expected, for example, in the case of the creation and arrangement of an attic or space under the roof, the load taken into account can be reduced.
Layout of wooden floor slabs
The length of each wooden beam is at least 24 cm, which is necessary for its fastening. An important element in the calculation of wooden structures is the deflection of the beam. Correct calculations will help you choose the optimal cross-section of an element for a given length. This will prevent changes in the geometry of the room and increase the safety of the ceiling.
The number of required beams is calculated based on the installation step. Laying is carried out over a narrow span, at intervals of two and a half to four meters. In turn, the step depends on the width of the frame racks.
Reinforced concrete monolithic
When installing monolithic reinforced concrete floor structures in a house, metal profiles or reinforced concrete beams are used as load-bearing structures. Floor slabs are formed from monolithic reinforced concrete parts. This allows you to withstand heavy loads and bandage wide runs.
Calculation of a monolithic floor in a special program
When calculating the load on an I-beam, its weight without taking into account the screed is calculated based on the value of 350 kg/m², and taking into account the screed - 500 kg/m². The installation step during installation is usually set to 1 meter.
When creating a reinforced concrete floor, the rule applies: the length of the opening should be 20 times the height of the beam. This is the acceptable minimum. The height and width of the reinforced concrete element are related to each other as 7 to 5. When calculating the floor, it is also necessary to take into account the probable bending, geometry of the slabs, choice of reinforcement and characteristics of concrete. The video shows the process of calculating a monolithic floor.
Reinforced concrete prefabricated
The elements for the manufacture of such floors have standard sizes and do not require special calculations. It is necessary to determine their number and the load on the general foundation of the building.
Preliminary calculations will help you save significantly when purchasing building materials. In addition to financial benefits, load calculations will guarantee the safety of the structure.
If the strength of the floor is not taken into account, the building may collapse and lead not only to additional costs, but also to even more disastrous consequences. Correct preliminary calculation is the basis for the safety of a building.
Floor slab layout plan
After drawing up sketches regarding the approximate location of the slabs, it is important to determine the axes and overall dimensions of the panels along the axes. The dimensions of the slab will help determine the height of the building and the number of panels. Vertical dimensional values take into account relative heights from the finished floor level.
To draw up a plan, it is important to take into account the location of the load-bearing walls to which the floors will be attached.
When laying out the load-bearing elements of the floor, you will see that the selection of their width is as important as the length
Making an opening in a reinforced concrete floor for a staircase
Unlike a wooden interfloor floor, it is more difficult to create a staircase opening in a reinforced concrete floor. If you plan to install a staircase, then this should be taken into account at the stage of manufacturing the interfloor reinforced concrete floor. The opening in such a ceiling should be framed with metal corner, I-beam, and channel profiles.
For an opening in the ceiling under the stairs, even during the construction of the building, a gap is left along the width of a standard reinforced concrete slab. 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.
Plan of load-bearing floor structures
Hollow-core floors are supported on a load-bearing brick wall on the short side, at least 90 mm. If the support is cellular concrete - 120-150 mm. It is not recommended to rest the long side on self-supporting elements. For the construction of low-rise buildings, it is better to use slabs with a width of 1.8 m and a length of up to 7.2 m.
If the walls of the building are made of cellular concrete, it is better to use a ceiling made of the same material. On the short side they should be supported by load-bearing walls - 10-15 cm, and on the sides - 2-5 cm. To strengthen the structure, the plan should include a reinforced concrete belt made of a monolith that encircles the building and internal walls.
When drawing up a plan for a structure made of prefabricated reinforced concrete or cellular concrete slabs, it is important to make footnotes with the dimensions of the elements, indicate the sections of the monolith, the height of the support, the width of the reinforced concrete belt and the anchorage of the panels.
Mostly for floors, I-beams with a height of 16-27 cm are used. Floor beams should rest on the walls by 18 cm or more. To form a hard drive, you need to connect the beams together and attach them to the walls. The distance between the beams is 60, 77, 80 cm or 1, 1.1 m. The type of interbeam filler has the greatest influence on the step. It is better to fix the beams along the edges of the structure near the load-bearing walls (up to 5 cm from the edge of the beam to the wall). It is better to make elements of non-standard shape from monolithic concrete.
Upon completion of the arrangement of load-bearing elements on the walls of the building, they proceed to applying designations and dimensions
Installation of a staircase in a wooden floor
The sequence of manufacturing a staircase opening in a wooden floor is as follows.
Construction of a staircase in a wooden floor:
- a - in the middle of the ceiling;
- b - near the wall;
- c - device for connecting beams.
- First, in the place where the staircase opening is planned, it is necessary to trim the ordinary floor beam. If the dimensions of the staircase opening should be larger than the hole formed after trimming one beam, you can shorten another beam, but no more than two.
- Two paired beams are installed parallel to the row floor beams.
- Short paired beams are attached to the paired beams, which form the staircase opening.
- Short, cut ones are fixed to the already installed beams: they will provide additional rigidity to the opening.
The thickness and height of the paired beams must be equal to the dimensions of the main beams. The beams are connected to each other using metal corners and self-tapping screws or using a special fastening profile.
If the staircase opening is located near a brick wall, the beams must be secured at one end to the wall using the technology discussed above.
General installation information
Prefabricated reinforced concrete slabs are installed with a minimum gap between each other. Installation will require special lifting equipment. The seams of the floors are filled with cement mortar. Metal anchors that are mounted to the hinges of the slabs will help create a complete and extremely rigid horizontal floor. In places where the panels come into contact with the internal slabs, composite anchors are used, which are fastened by welding.
If precast slabs are based on external walls, it is recommended to attach their end parts to the masonry using L-shaped anchors. After installation, they are filled with cement, it will prevent corrosion. If gaps appear between the slabs and partitions, they can be eliminated with brickwork.
An important rule is that reinforced concrete slabs are laid exclusively on load-bearing walls; other self-supporting structures and partitions are laid after the slabs are installed.
When laying slabs, a foundation is formed under load-bearing and self-supporting walls with a thickness of over 250 mm. Additionally, the base is installed under ventilation ducts and individual supporting elements. To create a foundation sketch, you should take into account the size of the base under the walls and determine the connection of the base of the foundation to the modular alignment layers. When using columnar and prefabricated foundations, the width of the foundation slabs is determined according to the strength required to withstand the loads.
In addition to the good economic effect in terms of construction costs and speed of building construction, the use of reinforced concrete provides a number of other advantages
The thickness of the rubble concrete and rubble strips is determined 8-10 cm wider than the wall. The size of the prefabricated foundation is determined equal to the thickness of the blocks (30-60 cm), but the wall itself is sometimes 4-5 cm wider than the base. Common block lengths: 80, 120, 240 cm To reduce pressure on the soil, the foundation can be made with an expanded base with 1-2 ledges, dimensions (HxW) - 30-40x15-25 cm. In a prefabricated foundation for widening, a foundation slab-cushion with reinforcement with a width of 60 cm to 1.6 m is used , height 30 cm.
The process of laying a monolithic foundation slab
Monolithic slab slabs are chosen for laying the foundation of buildings with an unstable foundation and low load-bearing capacity, since this type of pouring allows the load to be evenly transferred from all walls of the building and exerts pressure on the ground over its entire area.
The first thing to do when laying the foundation is to dig a pit of the required depth. Preferably using a bulldozer. After the pit is ready, it must be brought to an absolutely level state with a permissible error of 5 centimeters.
Leveling the pit is carried out using two methods:
- Manual. Workers manually, using shovels, level the soil surface;
- Mechanical. For these purposes, a mini-excavator is hired, onto which a leveling bucket that has no teeth is installed, and the driver of the technical equipment cleans the bottom using a laser level.
So, the bottom of the pit has a flat surface and is ready for further work. At the first stage, it is necessary to lay the so-called tubercle or lean concrete. The first layer of low-grade concrete is poured to a thickness of no more than 10 centimeters. This layer is necessary in order to reduce any error along the base horizon and finally level the bottom.
At the next stage of installation, formwork made of laminated plywood is installed. For formwork this material is most preferable. In order to save money, you can rent these construction elements.
After installing the waterproofing and formwork, the bottom mesh, consisting of reinforcement, is knitted. The lower part of the mesh is mounted on special plate-shaped metal stands. The round plates at the bottom of the stands are needed to avoid pushing through and damaging the installed waterproofing.
To ensure the strength of the foundation, embedded outlets are used for the installation of monolithic columns. They are built directly into the concrete slab. Such reinforcement is L-shaped; it is inserted into the body of a monolithic slab with a vertical stick.
It is mandatory to vibrate the thickness of the concrete when laying the slab. With this operation, air bubbles are expelled from the wet layer of concrete, bringing the structure closer to the GOST requirements for the construction of multi-story buildings. Vibration of concrete is carried out using a deep vibrator. This mechanical device, after immersing the shaft in concrete, expels air bubbles from the latter.
Upon completion of this procedure, be sure to level the surface with a rubber vibrating screed. In fact, a vibrating screed is such a long rule with an installed gasoline engine. The principle of its operation is extremely simple: the vibration of the engine is transferred to the vibrating screed and when moving, a perfectly flat surface is obtained. You can check how well the alignment process went with a rotary laser level.
Factory-prepared concrete is mixed in a concrete mixer, after which it can be poured into the space between the workpieces. The quality of concrete must be checked in advance. For this purpose, test concrete cubes measuring 10x10 are made in the amount of two pieces. After 28 days, the concrete gains its brand strength, and the cubes are sent to a testing laboratory for quality control and compliance with construction requirements. After this, the concrete can be poured.
The finished foundation must be stable. The drying process occurs within 28-30 days, during which the base gains strength and the necessary strength. Upon completion of the work, the formwork is removed, instead of which a base is erected, which is most often made of water-repellent “turtle” brick or processed in other ways. The foundation is ready.
Sequence of installation of floor slabs
Initially, you need to complete 2 steps:
- Preparation. It is important to create the correct level between all the supporting walls of the structure. The permissible difference is 1 cm, it is not necessary to eliminate it. To check the horizontal plane, use a building level. A beam is laid between opposite walls and the evenness is checked. If there are small irregularities, they can be eliminated with cement mortar.
- Next, a distribution belt is made to level the wall. The reinforcing belt is made of cement M500 1 to 3 with sand. It is important to ensure the cleanliness of the sand, rinse and sift if necessary. A solution of medium viscosity is prepared. The mixture is poured into the formwork and pierced or tamped to remove voids. The solution takes up to 3-4 weeks to dry.
The main qualities for which reinforced concrete is valued are always called strength and good resistance to bending moment.
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 the metal profile, covering 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.
Floor slab installation technology
To install prefabricated reinforced concrete slabs, it will be necessary to rent a crane and 4 workers: a driver, a slinger and 2 installers.
Load-bearing walls should be calculated taking into account the need for a 5 cm gap on the street side. Insulation is placed in the recess; it prevents drafts through the cracks in the ceiling. Wear of thermal insulation in such houses leads to cold, dampness and drafts.
Installation procedure:
- Concrete is laid in a layer of 15-20 mm on the prepared cement mortar cushion on the supporting walls.
- The panel is lifted with a crane and placed on top of the installation site.
- Installers rotate the slab to guide it to the desired position. Crowbars will help to accurately position the slab before removing the slings. The correct location implies a contact point between the wall and the slab of at least 15 cm on each side.
- The slings are released and a final check of the installation is made.
There are no temperature restrictions for reinforced concrete
Consequences of breaking the sequence
The cake for each type of wooden floor has certain functions. Violation of the sequence of layers or their absence can lead to negative consequences.
The basement structure gives strength to the floor of the first floor , which bears the main load. If there is no insulation or it is not done properly, the floor will freeze in the winter.
Without ventilation or waterproofing, a wooden structure will dampen and rot.
Failure to comply with the characteristics of the pie leads to:
- reducing the temperature in the building;
- the appearance of dampness and fungus;
- condensation and mold formation;
- increasing the cost of heating a home;
- gradual destruction of a wooden structure from the inside.
In addition, attention should be paid to the choice of material for each layer.
Checking the correct installation of floor slabs on supporting load-bearing walls
A viewfinder and a building level will help you most accurately determine the correct installation. If the walls have a difference of more than 4 mm on opposite sides, the slab should be re-installed. It is raised, the solution is corrected and the mixture is added in large quantities from the low side. If the cement begins to harden, it is better to remove it and mix it again. Even after adding water to the old mixture, it will no longer acquire the desired strength. If there are no problems with the level, the slabs are fastened.
To fix reinforced concrete panels, anchors are welded to the mounting loops. Next, the loops are welded together. The cracks are filled with cement. To prevent the solution from spilling out from below, crushed stone (up to 2 cm) is poured into the gap.
The following tools will be useful during the fastening process:
- tap;
- compressor unit;
- scaffolding;
- building levels;
- hammers, including jackhammers;
- crowbars;
- trowels;
- hacksaws for metal;
- tank or surface for preparing the solution.
Break through the ceiling under the stairs
In most cases, this type of redevelopment is resorted to out of a desire to combine two apartments located on different floors into one. Designing such an event is quite complex, and it itself requires mandatory approval.
Floors, as well as any other load-bearing structures, should be handled by professionals. Unauthorized work can lead to the most dire consequences, including the collapse of the slab. And at the initial stage, punching an opening for the so-called vertical connection of apartments with the subsequent installation of stairs requires strict official approval. Otherwise, you cannot avoid large fines.
Features of installing prefabricated floor slabs in private construction
The procedure is similar to the previous methods, but there are differences that occur due to the reduction in size and weight of the slabs. Even with a reduction in weight, the load on the supporting elements remains high. To prevent the destruction of the structure, you will have to increase the estimate to order the calculation of the load, the construction of the foundation, and the thickening of the walls. An additional cost is the need to hire skilled workers with experience.
It is easier to perform the ceiling from a wooden beam; the technique is much easier and less expensive. Reinforced concrete slabs are clearly preferred when constructing flat roofs. Roll or sheet roofing material is simply laid on top of the panels. When using reinforced concrete slabs for roofing, a more durable and durable coating is obtained.
Calculators and free design programs
To build your own house, it is unnecessary to spend time learning complex programs for calculating floor slabs. Simple tools have been developed especially for those who build a house with their own hands.
Floor slab drawing created in a special program
Among such software there is paid and free, intended for downloading, and working on-line. Programs for calculating wooden floors. If the house to be built is wooden, then it is more convenient to use simple software to calculate the flooring.
A tool for calculating the load of beams made of glued and profiled timber. The main direction is multi-span elements.
Construction portal No. 1
04/04/2019 admin Comments No comments
To reduce material consumption, floor slabs are designed to be lightweight - hollow or ribbed (Fig. 7.2a). When removing concrete from the tension zone, only the ribs with the width necessary to accommodate the welded frames and ensure the strength of the panels along the inclined section are retained. In this case, the slab in the span between the crossbars bends like a T-section beam. The top flange of the slab also acts on local bending between the ribs. The lower shelf, forming a closed void, is created if it is necessary to install a smooth ceiling.
Rice. 7.2. Cross-sectional shapes of floor slabs
The slabs are made with voids of various shapes: oval, round, etc. In panels of considerable width, several adjacent voids are arranged (Fig. 7.2.a).
The general principle of designing floor slabs of any cross-sectional shape is to remove as much concrete as possible from the tension zone while maintaining the vertical ribs that ensure the strength of the element along the inclined section, in conjunction with the technological capabilities of the manufacturer.
According to the cross-sectional shape, slabs can have oval, round and vertical voids, ribbed with ribs up (with a clean floor along the ribs), ribbed with ribs down, solid (Fig. 7.2a - f).
In slabs with voids, the minimum thickness of shelves is 25-30 mm, ribs 30-35 mm; in ribbed slabs with ribs downwards, the thickness of the shelf (slab) is 50-60 mm.
For a given length of slabs of different types, their width is taken such as to obtain weight gradations that do not exceed the lifting capacity of assembly cranes 3...5 tons, and sometimes more. Slabs 3.2 m wide with a span of 6 m cover the entire living room; the mass of such slabs with voids is 5...6 tons. Hollow and solid slabs, which make it possible to create a smooth ceiling, are used for residential and civil buildings, ribbed panels with the ribs down are used for industrial buildings with standard loads over 5 kN/m 2.
The efficiency of the slab is assessed by the reduced thickness of concrete, which is obtained by dividing the volume of concrete of the panel by its area and by the consumption of steel reinforcement (Table 7.1).
Technical and economic indicators of floor slabs with a nominal span of 6 m and a standard load of 6-7 kN/m 2
The most economical in terms of concrete consumption are slabs with oval voids; the reduced concrete thickness in them is 9.2 cm, while in slabs with round voids the reduced concrete thickness reaches 12 cm. However, when producing panels with oval voids in factories, technological difficulties arise due to the fact that after removing the void formers (punches) the walls channels of a freshly molded product sometimes collapse.
Design span of slabs l
taken equal to the distance between the axes of its supports (Fig. 7.3. a - c);
when supported on the top of the crossbars l
=
l
-
b/2
(where
b
is the width of the crossbar);
when leaning on the shelves of the crossbars l
=
l
–
a
–
b (a
is the size of the shelf). When supported with one end on the crossbar and the other on the wall, the design span is equal to the distance from the axis of the support on the wall to the axis of the support on the crossbar.
Rice. 7.3. Design spans and sections of slabs
Slab section height h
must be selected so that, along with the strength conditions, the requirements of rigidity (maximum deflections) are satisfied. For spans of 5–7 m, the height of the slab section is determined mainly by rigidity requirements. The preliminary height of the panel section, which simultaneously satisfies the strength conditions and rigidity requirements, can be determined using the approximate formula
(7.1)
where with
- coefficient, for hollow panels it is 18 - 20, for ribbed panels with a shelf in a compressed zone - 30 - 34;
- long-term standard load per 1 m 2 of floor;
- short-term standard load per 1 m 2 of floor;
— coefficient of increase in deflections under long-term load: for hollow panels = 2, for ribbed panels with a shelf in the compressed zone = 1.5.
The cross-sectional height of prestressed slabs can be pre-set equal to:
h= l
/20 - for ribbed ones;
h= l
/30 - for hollow ones.
When calculating the bending moment strength, the width of the rib is equal to the total width of all the ribs of the slab, and the calculated width of the compressed flange is taken to be equal to the total width of the panel. With a small thickness of the compressed flange, when ,
The width of the shelf entered into the calculation should not exceed
(7.2)
where n
- the number of ribs in the cross section of the panel.
In a ribbed panel with the ribs downwards, with the thickness of the flange but in the presence of transverse ribs, the width of the flange entered into the calculation is taken to be equal to the full width of the panel.
Thus, the calculation of the strength of the slabs is reduced to the calculation of a T-section with a flange in the compressed zone.
When calculating deflections, sections of panels with voids are reduced to equivalent I-sections. For panels with round voids, the equivalent I-section is found from the condition that the area of a round hole with a diameter d
equal to the area of a square hole with a side (Fig. 7.4):
(7.3)
Rice. 7.4. Equivalent sections of slabs for calculating deflections
Section of panels with oval voids (see Fig. 7.4)
lead to an equivalent I-section, replacing the oval cross-section of the void with a rectangular one with the same area and the same moment of inertia and observing the condition that the center of gravity of the oval and the replacing rectangle coincide.
Designating b1
and
h1
- the width and height of the equivalent rectangle;
F
and
I
- area and moment of inertia of the oval:
; (7.4)
The panel flange operates under local bending as a slab partially clamped on supports with span l
, equal to the clear distance between the ribs. In ribbed panels with ribs downwards, pinching of the flange is created by pouring concrete into the seams, which prevents the ribs from rotating (Fig. 7.5, a). Bending moment
(7.5)
In a ribbed panel with transverse intermediate ribs, the bending moments of the flange can be determined as in a slab supported along the contour and working in two directions (Fig. 7.5, b).
Rice. 7.5. Calculation diagrams of slab flanges
Welded mesh and frames made of ordinary reinforcing wire and hot-rolled reinforcement of a periodic profile are used (Fig. 7.6). As prestressed longitudinal reinforcement, rods of classes S800, S1200, high-strength wire and ropes are used. Reinforcement can be done without prestressing if the panel span is less than 6 m.
Longitudinal working reinforcement is located across the entire width of the lower flange of the section of hollow-core panels and in the ribs of ribbed panels.
Transverse rods are combined with longitudinal mounting or working non-prestressing reinforcement into flat welded frames, which are placed in the ribs of the slabs. Flat welded frames in round-hollow slabs can only be placed in the support areas, through one or two ribs. Anchors from corners or plates are welded to the ends of the longitudinal non-tensioned reinforcement of ribbed slabs to secure the rods to the support.
Solid slabs of heavy and lightweight concrete are reinforced with longitudinal prestressing reinforcement and welded mesh. Mounting loops are placed at the four corners of the slabs. In places where hinges are installed, solid panels are reinforced with additional upper meshes.
An example of reinforcement of a ribbed floor panel of an industrial building is shown in Fig. 7.7. The nominal width of this panel is considered to be 1.5 m. Such slabs are also used with a width of 3 m.
Rice. 7.7. Reinforcement of a ribbed floor slab
Assembly connections of all types of panels are made by welding steel embedded parts and filling the joints between the slabs with concrete. In the longitudinal side edges of the slabs, depressions are provided, designed to form intermittent keys, ensuring the joint operation of the slabs for shear in the vertical and horizontal directions (Fig. 7.8a). With such connections of prefabricated floor elements, the floors are rigid horizontal diaphragms.
If the temporary loads on the floors are more than 10 N/m2, then it is advisable to convert the ribbed slabs into continuous ones when cementing the seams. For this purpose, the seams between the ribbed slabs on the supports are reinforced with welded saddle-shaped frames crossing the crossbar (Fig. 7.8b). For loads acting after embedding, such slabs are designed as continuous.
Building the foundation inside the house
When partitions are made of heavy materials (brick, cinder blocks), then a foundation is required.
Formwork with reinforcement cage for pouring tape
The construction process includes the following stages:
- the floor inside the building is dismantled;
- mark the location of the foundation trenches;
- dig recesses of the required depth (approximately 0.5 m) and width;
- cover the bottom with a sand cushion about 10 cm thick;
- install shields;
- lay waterproofing material;
- a reinforcement frame is installed inside, connecting it, for example, with anchors to the main foundation;
- pour concrete;
- The surface of the monolith is leveled, checking with a level.
After the supporting structure has gained strength, the construction of partitions begins. The width of the tape is determined by the dimensions of the material used. It should exceed the thickness of the interior walls by approximately 5 cm on each side.
Lightweight partitions can even be installed directly on the floor, securely fastening them to it, the ceiling and adjacent walls. This is done by creating recesses, using anchors or reinforcement.
The entire process of building a foundation for interior partitions with your own hands is shown in the video below. The construction of a foundation structure designed to support interior partitions during redevelopment is necessary if you plan to use heavy material. The simplest option is to use technology similar to the construction of a strip foundation. In addition to concrete, various blocks can be used. Correct calculation is important so that the support can withstand the load and the partition does not deform.
Increased load-bearing capacity
In budget construction, the joints between slabs are often simply filled with mortar or construction foam. However, there is a proven method for laying floor slabs while simultaneously increasing the strength of the entire floor. To do this, the gaps between the PCs need to not only be filled with mortar, but reinforced
. Lay at least one (preferably two - below and above) reinforcing rod. Place a monolithic belt around the outer perimeter, at least 5 cm wide. Tie the reinforcement cage from two rods and place it vertically. The gaps between the PCs in the internal load-bearing walls are also sealed.
Fragment of a monolithic ribbed floor (a) and a grid of breakdown into slab and beam elements (b)
1 - plate; 2, 3 - secondary and main beams; 4 - columns; 5 - slab element; b - beam element of T-section
The dimension of the created finite element mesh is determined by the overall dimension of the problem (the number of finite elements and nodes in the overall spatial diagram), the geometric dimensions of the structure and configuration (dimensions in plan, regularity of the structure of the supporting system, the presence of curvilinear elements, etc.). In regular structures, labor intensity is reduced at the stage of forming the calculation model and in the process of analyzing the results obtained. It should be remembered that the geometry of the design diagram is formed along the axes of the elements. Accordingly, the forces in the zones of nodal interfaces are determined based on actual spans and are somewhat overestimated. At the same time, in a real system, the internal forces along the lines of mating elements are significantly influenced by the dimensions of the structures, which must be taken into account when designing the reinforcement of sections.
Loads on the floors are specified according to the actual scheme of their application in the structure. Loads from the structure's own weight are taken into account by specifying the volumetric mass of the material. Loads from equipment, depending on the nature of the interaction with the floor, are taken in the form of concentrated, linear or uniformly distributed. Loads from snow cover are specified as uniformly distributed, taking into account changes in intensity at the locations of snow bags. Temperature effects are set using the temperature difference for the entire structure, its part along the length or cross-section. Wind load is most often represented as a horizontal concentrated force at the slab level.
Calculation of the strength of floor elements based on the finite element method is generally carried out as linear (beam elements) and planar elements under the action of forces in these elements, obtained from the spatial static calculation of the load-bearing structural system as a whole.
The design forces for linear elements are Nx, NY, Qz, Mx and My applied at the element boundary, for slab elements - the combined action of bending moments Mx and My in the direction of mutually perpendicular axes X and Y and torque moments Mxy applied on the lateral sides of the flat selected element, under the action of transverse forces Qx and Qy applied on the lateral sides of the flat element (Fig. below).
Anchoring
The anchoring procedure is carried out after the ceiling is installed. Anchors fasten the slabs to the walls and to each other. This technology helps enhance the rigidity and strength of the structure. Fasteners are made of metal alloys, often galvanized or stainless steel.
For slinging high-density elements, fastenings in the shape of the letter “L” are used. Their bend length ranges from 30 to 40 centimeters. Such parts are installed 3 meters from each other. Adjacent slabs are fastened transversely, the outer ones - diagonally.
The algorithm for anchoring is as follows:
- the fastener is bent on one side under the eye in the slab;
- adjacent anchors are tightened to the limit, after which they are welded to the mounting loop;
- interpanel seams are closed with mortar.
Anchoring can be done by two workers.
Reinforcement and strapping
After installing the formwork, it is lubricated with an anti-adhesive compound and the installation of reinforcement begins. On the crowns and supporting ribs, the rods are tied into a square, maintaining the minimum permissible protective layer on all sides. The main floor mass is reinforced with mesh. The bottom layer is placed on plastic “crackers” that control the preservation of the bottom protective layer. The mesh is tied at the intersection of every third rod.
After tying the bottom mesh, intermediate clamps are installed on it every 100 cm in a checkerboard pattern. To strengthen the support, end clamps are mounted on the walls. These elements help maintain the design distance between two reinforcement planes.
How are floor panels anchored?
An anchor is a fastener made of a metal alloy: galvanized or stainless steel, brass and the like. It is installed in a load-bearing base and holds a building structure, for example, a floor slab. Anchors are used in the construction of any objects: single- and multi-story buildings, industrial buildings, garages. They increase the strength, stability and durability of buildings. In seismically active areas, anchoring floor slabs is a direct necessity: during an earthquake, reinforced floors collapse more slowly, which gives people a chance to escape.
Depending on the design, place of application and base, there are 5 types of anchors:
1. A wedge bolt is a bolt with a cone-shaped head and a spacer sleeve. It is used for dense materials (solid brick, concrete). Anchoring occurs due to the friction of the sleeve against the inside of the hole in the wall. The advantages of fastening are low cost and quick installation, including end-to-end installation. The disadvantage is that it cannot be reused.
2. Sleeve fasteners work in the same way as wedge fasteners. It is used for solid materials - reinforced concrete, natural stone. A sleeve runs along the length of the part, which is pushed apart by a bolt or nut. The advantages of the anchor are simple installation (including through). The downside is the large connection holes.
3. A drive-in fastener is a sleeve with slots on one end. When hit, they burst apart with a wedge that is inside the part. The anchor is used for strong, non-elastic foundations. The connection occurs as a result of friction and internal stop. Pros: quick installation and vibration resistance. Disadvantages: high requirements for the accuracy of connecting holes.
4. Chemical fasteners hold structures together using glue that is pumped into the channel of the part. It is used for any materials. Advantages: ease of installation, minimal requirements for hole accuracy. The disadvantage is the high cost.
A separate type is special-purpose anchors. Among them:
- Frame. Used for fastening window profiles and door frames.
- Ceiling. For suspended ceilings.
- Fundamental.
- Bolt Molly. For materials with a cavity inside or low load-bearing capacity (plasterboard, hollow brick, chipboard).
Connecting floor panels
The standard interfloor structure is a reinforced concrete structure with internal voids. Anchoring is done after each floor, including the basement and attic. Interfloor slabs are fastened to each other and to the walls. The connection method depends on the base and the presence of mounting loops (eyes) on the floor panels. In a building made of dense materials (brick, natural stone, solid concrete), the anchoring of slabs to the walls is done with steel L-shaped fasteners, with a bend length of 30–40 cm. They are installed every 3 m. Adjacent slabs are connected with transverse fasteners, and the outer ones with diagonal fasteners.
Procedure for anchoring:
- the edge of the fastening is bent with a loop that clings to the eye of the ceiling;
- adjacent anchors are tightened if possible;
- weld them to each other and to the mounting loops;
- seal the seams between the slabs and the eyelets with mortar.
In buildings made of hollow materials (foam and aerated concrete blocks, effective brick, limestone), the anchoring of floor panels to each other is carried out in the same way as with dense foundations. But in addition, a concrete belt is laid around the perimeter of the house. This is a ring anchor that lies in the same plane with the floor slabs and fastens them to the walls and to each other. It consists of a reinforcement cage embedded in concrete.
An anchor can also be used to tie floor slabs without eyelets. A steel plate 50x50 or 100x100 mm is attached to the panels. A metal rod is welded to it. Its second end is placed in the belt and thus anchored. The floor disc is further strengthened by creating connections on the internal walls. If it is necessary to strengthen the anchorage of reinforced concrete products, use pins, reinforcing bars and hooks.
Construction and fastening of the ceiling
While the reinforced concrete panels are still on the ground, they are inspected and defective ones are removed. In the remaining ones, the holes are sealed: one and a half bricks are placed in the gap and covered with mortar, protecting the slabs from freezing. Then they check the readiness of the load-bearing walls. The top edge of the brickwork should be bonded. If the panels rest on block walls, a concrete reinforced belt is made, which evenly distributes the load and protects the building from deformation.
