Among the many structural elements of a private house, the ceiling is one of the most important and difficult to design and install components. This is where inexperienced builders make, perhaps, the most dangerous mistakes; it is about the arrangement of this system that the most questions are asked.
1. Why choose a tree
In any building, the ceiling is a horizontal structure that serves as the basis for creating the floor. In addition, being connected to the load-bearing walls of the house, it provides lateral stability to the structure, evenly distributing possible loads. Therefore, the highest demands are placed on the reliability of this design.
Regardless of what material is used in the construction of a house, wooden floors are most widespread in the private sector. They can often be seen in various stone cottages, and it is quite obvious that in wood construction(log, timber, frame and frame-panel technology) there is no alternative to such a decision. There are many objective reasons. Let's look at the advantages and disadvantages of wood floors.
In private low-rise construction, floors are installed in several options:
- Ready reinforced concrete slab,
- Monolithic reinforced concrete slab,
- Ready-made reinforced concrete beams,
- Beams and trusses made of rolled metal,
- Flooring made of lumber.
pros
Or why wooden floors are so popular.
- Small mass. By using boards or timber, we do not overload load-bearing walls and foundations. The weight of the ceiling is several times less than that of concrete or metal structures. Usually no technology is required.
- Minimum deadlines for completing work. Minimum labor intensity among all options.
- Versatility. Suitable for any building, in any environment.
- Possibility of installation at sub-zero and very high temperatures.
- No “wet” or dirty processes.
- Possibility of obtaining any level of thermal insulation and sound insulation characteristics.
- Possibility of using cavities for gaskets engineering communications(power grid, heating, water supply, sewerage, low current...).
- Relatively low price of prefabricated frame floor from lumber, both in terms of the cost of parts/components and the contractor’s wages.
Minuses
The disadvantages of a wooden ceiling system made of wood are quite conventional.
- Difficulty in choosing the cross-section of materials and constructive solutions to ensure settlement bearing capacity.
- The need to carry out additional fire prevention measures, as well as provide protection from moisture and pests (antiseptic treatment).
- The need to purchase soundproofing materials.
- Strict adherence to technology to avoid construction errors.
2. What material to use for assembly
Wooden flooring always consists of beams. But they can be made from a variety of lumber:
- Rounded log up to 30 cm in diameter.
- The beam is four-edged.
- Large section board (thickness from 50 mm, width up to 300 mm).
- Several boards of relatively small thickness, twisted face to face.
- I-beams, the upper and lower chords of which are made of edged planed boards/bars, and the vertical wall is made of OSB-3, plywood or profiled metal (wood-metal product).
- Closed boxes made of sheet materials(plywood, OSB).
- SIP panel. In essence, these are separate sections in which the beams are already sheathed and have an insulator inside.
- Various truss designs, allowing to cover large spans.
The easiest options for installation, as well as the cheapest and most convenient for subsequent operations, are those where the floor beams are made of edged lumber.
Due to the very high requirements for load-bearing capacity, durability and geometric deviations, first-grade lumber must be considered as blanks. It is possible to use products classified as second grade according to GOST, which do not have critical geometric deviations, defects and processing defects that can reduce the strength characteristics and service life of finished parts (through knots, twists, cross-layers, deep extended cracks...).
In these structures, the use of dead wood (dead wood, dead wood, burnt wood) is excluded due to insufficient strength and multiple damage to wood-destroying diseases and insects. Also big mistake will buy a beam or board “with air”, “with Armenian size”, “TU” - due to the reduced sections.
It must be exclusively healthy material from green spruce or pine, since needles, due to their resin content and the structure of the massif, withstand bending loads and compression much better than most hardwoods, and having a relatively low specific gravity.
In any case, edged lumber must be freed from remnants of bark and bast fibers, treated with an antiseptic and fire retardant. Dry planed lumber will perform best here, but material with natural humidity (up to 20 percent) during normal processing is also actively (and most importantly, effectively) used, especially since the price of edged timber or boards of this type is noticeably lower.
3. How to choose the size of beams and at what step to arrange them
The length of the beam is calculated in such a way that it covers the existing span and has a “margin” to provide support on load-bearing walls (read below for specific figures for permissible spans and wall penetration).
The cross-section of the board/beam is determined depending on the design loads that will be exerted on the floor during the operation of the building. These loads are divided into:
- Permanent.
- Temporary.
Temporary loads in a residential building include the weight of people and animals that can move along the floor, moving objects. Constant loads include the mass of the lumber of the structure itself (beams, joists), floor filling (insulation/noise insulation, insulating sheets), hemming (rolling), rough and finishing flooring, finishing flooring, partitions, as well as built-in communications, furniture, equipment and household items...
Also, you should not lose sight of the possibility of storing objects and materials, for example, when determining the load-bearing capacity of the floors of a non-residential cold attic, where unnecessary, rarely used things can be stored.
The sum of the dead and live loads is taken as a starting point, and a safety factor of 1.3 is usually applied to it. Exact figures (including the cross-section of lumber) must be determined by specialists in accordance with the provisions of SNiP 2.01.07-85 “Loads and Impacts”, but practice shows that the load values in private houses with wooden beams are approximately identical:
- For interfloor (including under a residential attic) and basement floors, the total load is about 350 - 400 kg/m2, where the share of the structure’s own weight is about 100 kilograms.
- For covering an unloaded attic - about 130 - 150 kg/m2.
- For covering a loaded non-residential attic up to 250 kg/m2.
It is obvious that unconditional safety is of paramount importance. Here a good margin is taken into account and the option is considered not so much of distributed loads on the entire floor (in such quantities they are practically unrealistic), but rather the possibility of a local load that can lead to deflections, which in turn caused:
- physiological discomfort of residents,
- destruction of components and materials,
- loss of aesthetic properties of the structure.
By the way, certain deflection values are allowed regulatory documents. For residential premises, they can be no more than 1/350 of the span length (that is, 10 mm at 3 meters or 20 mm at six meters), but provided that the above limiting requirements are not violated.
When choosing the cross-section of lumber to create a beam, they are usually guided by the ratio of the width and thickness of the beam or board in the range of 1/1.5 - 1/4. Specific figures will depend, first of all, on: loads and span lengths. At independent design You can use data obtained from calculations using online calculators or publicly available tables.
Optimal average cross-section of wooden floor beams, mm
As you can see, in order to increase the load-bearing capacity of the floor, it is enough to choose lumber with a larger width or greater thickness. It is also possible to assemble a beam from two boards, but in such a way that the resulting product has a cross-section no less than the calculated one. It should also be noted that the load-bearing properties and stability of a wooden floor increase if logs or various types of subfloors (sheet flooring made of plywood/OSB or edged boards) are used on top of the beams.
Another way to improve the strength properties of a wooden floor is to reduce the spacing of the beams. In their designs for private houses, engineers determine under different conditions the distance between beams from 300 mm to one and a half meters. In frame construction, the pitch of the beams is made dependent on the spacing of the posts, so that there is a post under the beam, and not just a horizontal frame run. Practice shows that the most appropriate from the point of view of practicality and cost of construction is a step of 600 or 1000 mm, since it is best suited for the subsequent installation of insulation and noise insulation by surprise (insulating materials have just such a form factor of plates and rolls). This distance also creates optimal distance between support points for mounting floor joists installed perpendicular to the beams. The dependence of the cross section on the pitch is clearly visible from the numbers in the table.
Possible cross-section of floor beams when changing the pitch (total load per square meter is about 400 kg)
4. How to properly install and secure beams
We have decided on the step - from 60 centimeters to a meter will be the golden mean. As for spans, it is best to limit yourself to 6 meters, ideally: four to five meters. Therefore, the designer always tries to “lay” the beams along the smaller side of the house/room. If the spans are too large (more than 6 meters), then they resort to installing load-bearing walls or support columns with crossbars inside the house. This approach makes it possible to use lumber of a smaller cross-section and increase the spacing, thereby reducing the weight of the floor and its cost for the customer with the same (or better) load-bearing characteristics. As an option, trusses are created from lighter lumber using metal perforated fasteners, for example, nail plates.
In any case, the beams are placed strictly horizontally, parallel to each other, maintaining the same pitch. The wooden beam must rest on load-bearing walls and purlins by at least 10 centimeters. As a rule, use 2/3 thickness outer wall from the side of the room (so that the end of the beam does not go out onto the street and remains protected from freezing). IN wooden walls they make a cut, in stone ones they leave openings during laying. Where the beams touch load-bearing structures it is necessary to lay insulating materials: damping elastic pads made of rubber/felt, several layers of roofing felt as waterproofing, etc. Sometimes they use firing of sections of the beam that are subsequently hidden or coating them with bitumen mastics/primers.
Recently, special perforated brackets “beam holders/supports” have been increasingly used to create floors, which allow the beam to be mounted end-to-end with the wall. Using this type of brackets, units with transverse crossbars and beams truncated in length are also assembled (an opening for flight of stairs, chimney passage, etc.). The advantages of this solution are obvious:
- The resulting T-shaped connection is very reliable.
- The work is done quickly (there is no need to make cuts, it is much easier to set a single plane).
- No cold bridges are formed along the body of the beams, because the end is moving away from the street.
- It is possible to buy lumber of shorter length, since there is no need to insert the timber/board inside the wall.
In any case, it is very important, after adjusting the lumber to size, to thoroughly antisepticize the end of the beam.
5. What insulating layers should be used inside wooden floors
To answer this question, first of all, it is necessary to divide the overlapping structures (in a year-round habitable house) into three separate types:
- Basement ceiling,
- Interfloor,
- Attic.
In each specific case, the set of pie will be different.
Interfloor ceilings in the vast majority of cases separate rooms in which the temperature regime is similar or close in value (if there is room/floor/zone adjustment heating system). These also include the attic floor, which separates residential attic, since this room is heated, and the insulation is located inside the roofing pie. For these reasons, thermal insulation is not needed here, but the issue of combating noise, airborne (voices, music...) and shock (steps, rearranging furniture...) becomes very relevant. As sound insulation, acoustic fibrous materials based on mineral wool, and also sheets of soundproofing membranes are laid under the sheathing.
The basement design assumes that under the ceiling there is soil or a basement, cellar, or ground floor. Even if the room below is equipped for use, this type of floor requires full insulation, characteristic of the enclosing structures of a specific climate zone and a specific building with its unique thermal balance. According to standards, the average thickness for the Moscow region modern insulation with good thermal conductivity will be about 150-200 mm.
Similar thermal insulation requirements apply to the attic floor, which does not have a heated attic above it, because it will be the main barrier to heat loss through the roof of the building. By the way, due to the greater flow of heat through the upper part of the house, the thickness of the insulation here may be required more than in other places, for example, 200 mm instead of 150 or 250 mm instead of 200.
They use polystyrene foam, EPS, mineral wool with a density of 35 kg/m3 in slabs or cut into mats from a roll (one that is allowed for use in non-load-bearing areas is suitable). horizontal structures). Thermal insulation is laid between the beams, usually in several layers, with the joints bandaged. The load from the insulation is transferred to the beam through the rough hemming (often it is attached to the beams using cranial bars).
Where wadding insulation/sound insulation is used in structures, it should be protected from moisture. In the basement, moisture can rise in the form of evaporation from the ground or from the basement/cellar. Water vapor can enter interfloor ceilings and attics, which always saturates the air in residential premises during human activities. In both cases, underneath the insulation you need to lay construction material vapor barrier film, which can be ordinary or reinforced polyethylene. But, if thermal insulation is performed using extruded polystyrene foam, which does not have any significant level of water absorption, then a vapor barrier will not be needed.
On top, insulation and fibrous soundproofing materials are protected with waterproof sheets, which can be membranes or non-perforated waterproofing.
A reliable water barrier is especially relevant in rooms with high humidity: kitchen, laundry room, bathroom... In such places it is spread on top of the beams, always with the strips overlapping by 100-150 mm and gluing the seam. The canvases along the entire perimeter of the premises must be placed on the wall - to a height of at least 50 mm above the finishing coating.
The ceiling, which will later be lined tiles, it makes sense to supplement with rough flooring made of waterproof sheet materials - various types cement-containing slabs, preferably tongue-and-groove. On such a continuous flooring you can carry out additional coating waterproofing, perform thin-layer leveling of the plane with a leveling compound or lay the tiles immediately.
You can choose another option - assemble a continuous flooring from edged boards, lay a hydraulic barrier, pour a thin-layer screed (up to 30 mm), and install tiles.
There are also modern adhesive compositions(and elastic grouts) allowing tiling wooden bases, including movable and heated ones. Therefore, tiled floors are often sold here on moisture-resistant plywood or OSB.
Important! Taking into account the increasing loads (general or local - a large bathtub, a Jacuzzi bowl, a floor-standing boiler...), the calculation of the cross-section and pitch of beams under such rooms must be performed individually.
If desired, floors in the bathroom or kitchen wooden house can be equipped with a heating cable or pipes of the water circuit of the heating system. They are mounted both in screeds and a layer of tile adhesive, and between joists in a deliberately created air gap. With any chosen option, the ceiling must be well insulated so as not to heat the ceiling of the room from below, preferably equipped with waterproofing with a reflective foil layer.
Installation of wooden beams in the floors of houses is not uncommon. Their main purpose is to evenly distribute the load on the walls and foundation of the building. In order for a beam structure to fulfill its functions, it is necessary to select the correct material for it and calculate the length and cross-section.
All wooden beams are divided among themselves according to their purpose and the type of material from which they are made. According to their purpose, they can be: interfloor, attic, basement and basement. Depending on the type of material, beams can be made of solid wood or laminated wood.
wooden floors in aerated concrete house
The interfloor span must be strong and reliable. Sound and vapor barrier fillers are placed in the internal volume between the ceiling and floor. The ceiling part is sewn up necessary material, the floor is laid on top.
The attic floor can be installed as a roof element, being part of its rafter structure. Can be installed as a separate independent element. In order to preserve heat, it must be equipped with steam and thermal insulation.
Basement ceiling and ground floor must be of great strength and withstand high loads. These spans are equipped with heat and vapor barriers to prevent the penetration of cold from the basement.
Beams differ in types, which have their own advantages and disadvantages.For the manufacture of solid beams hardwood is used. A significant disadvantage of solid wooden beams is the length limitation, which cannot exceed 5 meters.
Beams made of laminated wood combine high strength and aesthetics. Their use significantly increases the maximum length, which can be up to 20 meters. Considering that glued floors look beautiful, they are often not covered with a ceiling and serve as a design element.
They have a few more significant advantages, which include:
- ability to block large spans;
- ease of installation;
- small weight;
- long period of operation;
- high level of fire safety;
- cannot be deformed.
The wooden parts of the floor beams may have rectangular section, which is typical for timber or boards, or round, made from logs.
Requirements for wooden floor beams
Installation of wooden beam floors entails a number of requirements that must be taken into account. They are as follows:
- Beam products must be made coniferous species wood, which have a high margin of safety. At the same time, the moisture content of the wood should be no more than 14 percent, otherwise the logs under load will have a large deflection.
- It is prohibited to use wood that is susceptible to fungal diseases or damaged by insects to make beams.
- Before installation, beam elements must be treated with an antiseptic.
- To ensure that the ceiling or floor does not sag even under load, it is necessary to perform a construction lift. The ceiling of the lower floor will receive a slight rise in the center, which will become even under load.
- If the beams are planned to be laid with great frequency, then instead of them you can use boards that need to be installed on the ribs.
The procedure for calculating wooden beams
Before installing a wooden floor, it is necessary to carry out calculations in which to determine the number and dimensions of beams. To do this you need:
- determine the length of the span on which they will be installed;
- calculate the possible load they will bear after installation;
- Having the specified data, calculate the cross-section of the beams and the step with which they will be installed. For this, special tables and programs are used.
Beam length consists of the length of the span that needs to be covered and the stock of the beam that will be mounted into the wall. The span can be determined using any measuring device. The supply of beams that will be mounted in the wall depends on the material from which the wall is made.
Important!
If the building is built of brick, then the margin for beams made from boards should be at least 10 cm and at least 15 cm for beams made from timber. IN wooden buildings special grooves are made, with a depth of 7 cm or more, for laying beams. If the beams serve as the basis for the roof rafters, then they are made 4-6 cm longer than the span.
The most used span, which is covered with beams, ranges from 2.5 to 4 meters. Maximum length beams made of timber or boards cannot exceed 6 meters. If the span length exceeds this size, then it is recommended to install beams made of laminated veneer lumber. In addition, to cover spans longer than 6 meters, you can install a wooden truss.
Load , which is carried by a wooden beam, consists of a mass of span parts (beams, internal filling, ceiling and floor cladding) and a mass of temporary elements (furniture, household appliances, people present in the room).
Accurate calculations of the load-bearing capacity of beams are usually carried out by specialized organizations. At independent execution The following system is used for calculation:
- an attic floor with a lining, in which the insulation is mineral wool, carries a constant self-load of 50 kg per square meter. With such a load, according to SNiP standards, the standard load will be 70 kg per square meter with a safety factor of 1.3. Finding out the total load is not difficult: 1.3x70+50=130 kilograms per square meter;
- if a heavier material than cotton wool is used as insulation, or thick boards were used as lining, then the standard load will be 150 kg per square meter. And the total load will have a different value: 150x1.3+50=245 kg per square meter;
- if the calculation is carried out for attic room, then the weight of the material from which the floor is laid and the objects located in the attic is taken into account. The load in this case will be 350 kg per square meter;
- in the case where the beams serve as interfloor spans, the calculated load is 400 kg per square meter.
Calculation of wooden floor beams
Determination of the section and pitch of wooden beams
By calculating the load and length of the beams, you can determine their pitch and cross-sectional dimensions or diameter.
These indicators are interrelated and are calculated according to established rules:
- The width and height of the beams should be in proportion 1:1.,4. In this case, the width of the beams should be in the range from 4 to 20 cm, and the height from 10 to 30 cm, taking into account the thickness insulation material. Logs for floors should have a diameter in the range from 11 to 30 cm.
- The installation step should be in the range from 30 to 120 cm, taking into account the insulation and lining materials that will be in the space between the beams. If the structure is frame, then the step should correspond to the distance between the frames.
- The cross-section of wooden beams is determined using developed tables or using certain programs. When calculating sections, it is necessary to take into account that the maximum bending attic beams should not exceed 1/200, and between floors 1/350.
Application of wooden trusses, advantages and disadvantages
Floor trusses made of wood look like two parallel logs or bars located above each other, which are connected to each other by supports located at an angle or vertically in relation to these logs or bars. The main task that trusses solve is covering long spans, if the installation of additional support posts impossible.
For the manufacture of trusses, developed tables and programs are used, which take into account the type of connections, installation pitch, cross-section of structural parts and its overall dimensions. Often, trusses are manufactured industrially using high-precision equipment. Along with this, you can make a farm with your own hands.
By comparing wooden beams and floor trusses, you can determine the advantages and disadvantages that the trusses have. The advantages include:
- the ability to cover a span of significant size without additional support posts;
- insignificant mass, which entails a small load on the load-bearing elements of the building;
- high strength and resistance to deflection, which entails long-term operation of lining and flooring materials;
- ease of installation on any load-bearing elements of the building, regardless of the material from which they are made;
- the ability to change the width of the truss laying step;
- possibility of installing internal communication lines;
- excellent sound insulation;
- beautifully made trusses can be left unsewn and used as a decorative element.
In addition to advantages, farms have some disadvantages, which include the following:
- due to design features, the thickness of interfloor ceilings increases significantly;
- significant labor costs when making a farm with your own hands, the need for special equipment;
- high price for a finished structure.
Wood truss design
appointed after fulfilling a number of requirements. Thus, the removal of the side elements of the formwork, which do not bear the load from the weight of the structure, is allowed only after the concrete has achieved strength that ensures the safety of the surface and edges of the corners.
More stringent requirements apply to the removal of load-bearing formwork reinforced concrete structures, which can be removed only after the concrete reaches the design strength value:
- load-bearing structural elements with a span of up to 2 m – 50%;
- load-bearing structures of beams, crossbars, purlins, slabs and vaults with a span of 2-6 m – at least 70%;
- load-bearing structures with a span of more than 6 m – at least 80%;
- load-bearing structures reinforced with load-bearing welded frames - at least 25%.
Standard conditions for concrete hardening are: temperature 20±5ºC and air humidity above
90%. It should be borne in mind that in practice, as a rule, real conditions do not correspond to standard standards, and the concrete hardening process either slows down or accelerates. For example, at a temperature of 10ºC, after 7 days concrete will gain 40-50% strength, and at 5ºC - only 30-35%. If hardened at a temperature of 30-35ºC, concrete will gain 45% strength within 3 days. At negative temperatures Concrete without special additives does not gain strength at all. Therefore, the decision to strip the formwork and load the structure should be made after testing the concrete for strength.
The time frame for concrete to achieve a given strength is established by the construction laboratory based on the results of testing control samples or methods non-destructive testing. At sites with a total volume of work of less than 50 m3, receiving ready-mixed concrete mix from factories or installations located at a distance of no more than 20 km, it is allowed to assess the strength of concrete according to the laboratory of the concrete mix manufacturer without making control samples at the installation site. However, this instruction does not apply to critical paired and thin-walled structures: beams, columns, floor slabs, as well as monolithic joints of prefabricated structures.
Of course, when constructing suburban residential buildings They usually do not measure concrete for strength, since most construction companies working in the private housing construction sector simply do not have construction laboratories. Therefore in in this case you will have to rely on the laboratory data of the concrete mix manufacturer. Additionally, you can conduct your own concrete strength testing. To do this, you need to take a metal ball with a diameter of at least 20 mm and throw it from the same height onto a concrete surface: control and test. Based on the height of the ball’s rebound, it will be possible, I’ll make a reservation right away - with a big stretch, to determine whether the strength of the concrete has reached the required value.
The full design load in a stripped reinforced concrete structure can only be allowed after the concrete has acquired its design strength.
A metal floor beam in the form of an I-beam has a number of undeniable advantages. So a metal I-beam can cover large spans with a significant load. In addition, the metal steel beam is absolutely non-flammable and resistant to biological influences. However, a metal beam when exposed to aggressive environment may corrode, so a protective coating must be applied to it.
In most cases in private housing construction, a metal beam has hinged supports - its ends are not rigidly fixed, for example, since in a frame steel structure. The load on the floor with steel I-beams, taking into account its own weight, should be calculated without a screed of 350 kg/m2 and 500 kg/m2 with a screed.
It is recommended to make the step between I-beams equal to 1000 mm, however, in order to save money, you can increase the step between the metal beams to 1200 mm.
The table below shows the choice of the number of an I-beam metal beam for different pitches and lengths of purlins.
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Span3 m |
Span4 m |
Span6 m |
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I-beam number at step |
I-beam number at step |
I-beam number at step |
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As can be seen from the table, with a total load of 500 kg/m2 and a span length of 6 m, you should have chosen an I-beam of a higher number and chosen a smaller beam installation step.
Added: 05/26/2012 08:21
Discussion of the issue on the forum:
We poured the ceiling between the first and second floors along I-beam No. 12, span 6 meters with an outlet 1 meter from load-bearing wall first floor. The distance between the I-beams is 2 meters, from below between them a mesh of cell 20 is connected from reinforcement No. 12, on top of mesh No. 5, cell 10 cm. Question: after how many days can the formwork be removed and after how many days can the walls be laid, including at the outlet?
Beams in a house usually belong to rafter system or overlap, and to get reliable design, the operation of which can be carried out without any fear, must be used beam calculator.
What is the beam calculator based on?
When the walls have already been brought under the second floor or under the roof, it is necessary to make, in the second case smoothly turning into rafter legs. In this case, the materials must be selected so that the load on the brick or log walls does not exceed the permissible value, and the strength of the structure is at the proper level. Therefore, if you are going to use wood, you need to choose the right beams from it, make calculations to find out required thickness and of sufficient length.
The subsidence or partial destruction of the ceiling can be caused by various reasons, for example, too large a step between the lags, deflection of the cross members, too small area their cross sections or defects in the structure. To eliminate possible excesses, you should find out the expected load on the floor, be it basement or interfloor, and then use a beam calculator, taking into account their own weight. The latter can change in concrete lintels, the weight of which depends on the density of the reinforcement; for wood and metal, with a certain geometry, the weight is constant. The exception is damp wood, which is not used in construction work without pre-drying.
Beam systems in floors and rafter structures are loaded by forces acting on section bending, torsion, and lengthwise deflection. For rafters, it is also necessary to provide for snow and wind loads, which also create certain forces applied to the beams. You also need to accurately determine the required step between the jumpers, since too many crossbars will lead to excess weight of the floor (or roof), and too little, as mentioned above, will weaken the structure.
You may also be interested in an article about calculating the amount of unedged and edged boards in a cube:
How to calculate the load on a floor beam
The distance between the walls is called a span, and there are two of them in the room, and one span will necessarily be smaller than the other if the shape of the room is not square. Interfloor or attic floor lintels should be laid along a shorter span, the optimal length of which is from 3 to 4 meters. Larger spacing may require non-standard sized beams, which will result in some unsteadiness of the deck. The best solution in this case would be to use metal crossbars.
Regarding the section wooden beam, there is a certain standard that requires that the sides of the beam be in a ratio of 7:5, that is, the height is divided into 7 parts, and 5 of them must make up the width of the profile. In this case, deformation of the section is excluded, but if you deviate from the above indicators, then if the width exceeds the height, you will get a deflection, or, if the opposite discrepancy occurs, a bend to the side. To prevent this from happening due to the excessive length of the beam, you need to know how to calculate the load on the beam. In particular, the permissible deflection is calculated from the ratio to the length of the lintel as 1:200, that is, it should be 2 centimeters per 4 meters.
To prevent the beam from sagging under the weight of logs and flooring, as well as interior items, you can grind it from below a few centimeters, giving it the shape of an arch; in this case, its height should have an appropriate margin.
Now let's turn to the formulas. The same deflection mentioned earlier is calculated as follows: f nor = L/200, where L– span length, and 200 – permissible distance in centimeters for each unit of timber subsidence. For reinforced concrete beam, distributed load q which is usually equated to 400 kg/m 2, the calculation of the limiting bending moment is performed using the formula M max = (q · L 2)/8. In this case, the amount of reinforcement and its weight is determined according to the following table:
Cross-sectional areas and mass of reinforcing bars
Diameter, mm | Square cross section, cm 2, with the number of rods | Weight 1 linear meter, kg | Diameter, mm |
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Wire and rod reinforcement |
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Seven-wire ropes class K-7 |
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The load on any beam made of a sufficiently homogeneous material is calculated using a number of formulas. To begin with, the moment of resistance W ≥ M/R is calculated. Here M is the maximum bending moment of the applied load, and R – design resistance, which is taken from reference books depending on the material used. Since most often beams have rectangular shape, the moment of resistance can be calculated differently: W z = b h 2 /6, where b is the width of the beam, and h– height.
What else should you know about beam loads?
The ceiling, as a rule, is at the same time the floor of the next floor and the ceiling of the previous one. This means that it needs to be made in such a way that there is no risk of combining the upper and lower rooms by simply overloading the furniture. This probability especially arises when the step between the beams is too large and logs are abandoned (plank floors are laid directly on the timber laid in the spans). In this case, the distance between the crossbars directly depends on the thickness of the boards, for example, if it is 28 millimeters, then the length of the board should not be more than 50 centimeters. If there are lags, the minimum gap between the beams can reach 1 meter.
It is also necessary to take into account the mass used for the floor. For example, if mineral wool mats are laid, then a square meter of the basement floor will weigh from 90 to 120 kilograms, depending on the thickness of the thermal insulation. Sawdust concrete will double the mass of the same area. The use of expanded clay will make the flooring even heavier, since the load per square meter will be 3 times greater than when laying mineral wool. Further, we should not forget about the payload, which for interfloor floors is at least 150 kilograms per square meter. In the attic it is enough to take permissible load 75 kilograms per square.
Possibility of unsupported ceiling large areas significantly expands architectural possibilities when designing a house. A positive solution to the beam issue allows you to “play” with the volume of rooms, install panoramic windows, build large halls. But if it is not difficult to cover a distance of 3-4 meters with “wood”, then which beams to use on a span of 5 m or more is already a difficult question.
Wooden floor beams - dimensions and loads
Made a wooden floor in timber house, and the floor shakes, bends, a “trampoline” effect appears; we want to make wooden floor beams 7 meters long; you need to cover a room 6.8 meters long so as not to rest the logs on intermediate supports; what should be the floor beam for a span of 6 meters, a house made of timber; what to do if you want to make an open plan - such questions are often asked by forum users.
Maxinova User FORUMHOUSE
My house is about 10x10 meters. I “threw” wooden logs onto the ceiling, their length is 5 meters, cross-section is 200x50. The distance between the joists is 60 cm. During the operation of the floor, it turned out that when children run around in one room and you stand in another, there is quite a strong vibration along the floor.
And such a case is far from the only one.
Elena555 User FORUMHOUSE
I can’t figure out what kind of beams are needed for the interfloor floors. I have a house 12x12 meters, 2 floors. The first floor is made of aerated concrete, the second floor is an attic, wooden, covered with timber 6000x150x200mm, laid every 80 cm. The logs are laid on an I-beam, which rests on a pillar installed in the middle of the first floor. When I walk on the second floor, I feel shaking.
Beams for long spans must withstand heavy loads, therefore, in order to build a strong and reliable wooden floor with a large span, they must be carefully calculated. First of all, you need to understand what load it can withstand. wooden joist one section or another. And then think about, having determined the load for the floor beam, what roughing and finishing coat gender; what the ceiling will be hemmed with; whether the floor will be a full-fledged residential space or a non-residential attic above the garage.
Leo060147 User FORUMHOUSE
- The load from the own weight of all structural elements of the floor. This includes the weight of beams, insulation, fasteners, flooring, ceiling, etc.
- Operating load. The operating load can be permanent or temporary.
When calculating the operating load, the mass of people, furniture, household appliances, etc. is taken into account. The load temporarily increases when guests arrive, noisy celebrations, or furniture is rearranged if it is moved away from the walls to the center of the room.
Therefore, when calculating the operating load, it is necessary to think through everything - right down to what kind of furniture you plan to install, and whether there is a possibility in the future of installing a sports exercise machine, which also weighs more than one kilogram.
The following values are taken for the load acting on long wooden floor beams (for attic and interfloor floors):
- Attic floor – 150 kg/sq.m. Where (according to SNiP 2.01.07-85), taking into account the safety factor, 50 kg/sq.m is the load from the floor’s own weight, and 100 kg/sq.m is the standard load.
If you plan to store things, materials and other household items in the attic, then the load is assumed to be 250 kg/sq.m.
- For interfloor slabs and slabs attic floor the total load is taken at the rate of 350-400 kg/sq.m.
Flooring with boards 200 by 50 and other common sizes
These are the types of beams on a span of 4 meters that are allowed by the standards.
Most often, in the construction of wooden floors, boards and timber of the so-called running sizes are used: 50x150, 50x200, 100x150, etc. Such beams meet the standards ( after calculation), if you plan to cover the opening no more than four meters.
For floors 6 or more meters long, the dimensions 50x150, 50x200, 100x150 are no longer suitable.
Wooden beam over 6 meters: subtleties
A beam for a span of 6 meters or more should not be made of timber and boards of standard sizes.
You should remember the rule: the strength and rigidity of the floor depend to a greater extent on the height of the beam and to a lesser extent on its width.
A distributed and concentrated load acts on the floor beam. Therefore, wooden beams for large spans are not designed “end-to-end”, but with a margin of strength and permissible deflection. This ensures normal and safe operation of the ceiling.
50x200 - overlap for openings of 4 and 5 meters.
To calculate the load that the ceiling will withstand, you must have the appropriate knowledge. In order not to delve into the strength of strength formulas (and when building a garage this is definitely redundant), an ordinary developer just needs to use online calculators for calculating wooden single-span beams.
Leo060147 User FORUMHOUSE
A self-builder is most often not a professional designer. All he wants to know is what beams need to be mounted in the ceiling so that it meets the basic requirements for strength and reliability. This is what online calculators allow you to calculate.
These calculators are easy to use. To make calculations of the required values, it is enough to enter the dimensions of the logs and the length of the span that they must cover.
Also, to simplify the task, you can use ready-made tables presented by the guru of our forum with the nickname Roracotta.
Roracotta User FORUMHOUSE
I spent several evenings to make tables that would be understandable even to a novice builder:
Table 1. It presents data that meets the minimum load requirements for the floors of the second floor - 147 kg/sq.m.
Note: since the tables are based on American standards, and the sizes of lumber overseas are somewhat different from the sections accepted in our country, you need to use the column highlighted in yellow in the calculations.
Table 2. Here is data on the average load for the floors of the first and second floors - 293 kg/sq.m.
Table 3. Here is the data for the calculated increased load of 365 kg/sq.m.
How to calculate the distance between I-beams
If you carefully read the tables presented above, it becomes clear that with an increase in the span length, first of all, it is necessary to increase the height of the log, and not its width.
Leo060147 User FORUMHOUSE
You can change the rigidity and strength of the lag upward by increasing its height and making “shelves”. That is, a wooden I-beam is made.
Self-production of laminated wood beams
One solution for spanning long spans is to use wooden beams in the floors. Let's consider a span of 6 meters - which beams can withstand a larger load.
According to the type of cross section, a long beam can be:
- rectangular;
- I-beam;
- box-shaped
There is no consensus among self-builders as to which section is better. If you don't take into account purchased products(factory-made I-beams), then ease of manufacture comes first in “ field conditions", without the use of expensive equipment and accessories.
Just Grandfather User FORUMHOUSE
If you look at a cross section of any metal I-beam, you can see that from 85% to 90% of the metal mass is concentrated in the “shelves”. The connecting wall contains no more than 10-15% of the metal. This is done based on calculation.
Which board to use for beams
According to the strength of strength: the larger the cross-section of the “shelves” and the farther they are spaced apart in height, the greater the loads the I-beam will withstand. For a self-builder, the optimal I-beam manufacturing technology is a simple box-shaped structure, where the upper and lower “shelves” are made of boards laid flat. (50x150mm, and side walls made of plywood with a thickness of 8-12 mm and a height of 350 to 400 mm (determined by calculation), etc.).
Plywood is nailed to the shelves or screwed with self-tapping screws (not black ones, they do not work for cutting) and must be placed on glue.
If you install such an I-beam on a six-meter span with a step of 60 cm, then it will withstand a large load. Additionally, an I-beam for a 6-meter ceiling can be lined with insulation.
Also, using a similar principle, you can connect two long boards, collecting them in a “package”, and then put them on top of each other on an edge (take boards 150x50 or 200x50), as a result, the cross-section of the beam will be 300x100 or 400x100 mm. The boards are placed on glue and tied together with pins or placed on wood grouse/dowels. You can also screw or nail plywood to the side surfaces of such a beam, having previously lubricated it with glue.
Also interesting is the experience of a forum member under the nickname Taras174, who decided to make his own glued I-beam to cover a span of 8 meters.
To do this, the forum member purchased 12 mm thick OSB sheets and cut them lengthwise into five equal parts. Then I bought a board 150x50 mm, 8 meters long. Using a dovetail cutter, I used a dovetail cutter to select a groove 12 mm deep and 14 mm wide in the middle of the board, so as to create a trapezoid with a downward expansion. OSB in grooves Taras174 glued with polyester resin(epoxy), having previously “shot” a strip of fiberglass 5 mm wide to the end of the slab with a stapler. This, according to the forum member, would strengthen the structure. To speed up drying, the glued area was heated with a heater.
Taras174 User FORUMHOUSE
On the first beam I practiced “pushing my hand.” The second one was done in 1 working day. In terms of cost, taking into account all materials, I include a solid board of 8 meters, the cost of the beam is 2000 rubles. for 1 piece
Despite the positive experience, such “squatter construction” did not escape several critical remarks expressed by our experts. Namely.
