Wooden floor beams provide not only the strength of the horizontal structure. Overlapping is designed to give rigidity to the entire building. It is for this reason that the choice of load-bearing elements and their installation should be given special attention.
Pros and cons of wood flooring
To install the ceiling with your own hands, you need to prepare. The floor in the house should be based on a solid and rigid structure. Before starting work, you will have to study the requirements for the elements, the features of their calculation and the types of sections.
The following advantages of wood flooring can be distinguished:
- attractive appearance, the ability to make a wooden floor without additional measures;
- light weight, reducing the load on walls and foundations, saving on construction;
- the possibility of carrying out repairs during operation;
- speed of installation, performance of work without additional machines and mechanisms.
But it is also worth highlighting the disadvantages:
- combustibility of wood, the need for special impregnation with flame retardants;
- lower strength compared to reinforced concrete or metal elements;
- shrinkage and deformation during temperature and humidity changes;
- susceptibility to rotting, fungus and mold at high humidity, it is necessary to carry out antiseptic treatment at the construction stage and periodically during the service life.
wood flooring requirements
Wooden floor beams must meet the following requirements:
- correspondence of the cross-sectional dimensions to the load, span and step, this requires the calculation of beams;
- good strength and rigidity;
- Fire safety;
- absence of serious defects of wood and damages.
For work it is necessary to prepare high-quality material There are also certain requirements for the material from which the beams are made. It is recommended to choose softwood. It contains a lot of resin, so it better resists various microorganisms. The best material is those trees that have grown in harsh conditions. Their stem density is higher. For this reason, it is worth buying pine or spruce, which grew in the northern regions of the country.
You also need to pay attention to the preparation time. The best period is at the end of winter. At this time, the tree is in a dormant state, there is less juice in it, therefore, the moisture content of the material will be less.
What are wooden floors
Wooden floor beams are used for almost all levels of the house. The beam frame must be provided for the following types of construction:
- basement or basement floor (floor of the first floor);
- interfloor overlap;
- attic cover.
The thickness of the supporting beam for the attic is from 10 to 20 cm The normalized payload depends on the type, which is taken into account in the calculation of wooden floor beams.. Also, the difference will be in the thickness of the insulation and its need.
Between the beams above the basement, usually 5 to 15 cm of mineral wool, polystyrene foam or extruded polystyrene foam are laid. In interfloor structures, it will be enough to provide a couple of centimeters for sound insulation. A cold attic requires the most material. Here the thickness can be from 10 to 20 cm. The exact values \u200b\u200bdepend on the climatic area of \u200b\u200bconstruction.
Between the beams of the basement, mineral wool is laid Sometimes the basement ceiling is preferred not to be made of wood, but of metal and reinforced concrete. In this case, an I-beam or channel is used as load-bearing beams, and concrete is poured into the formwork from a profiled sheet. This option will be more reliable with the likelihood of flooding. It will also better resist dampness from the basement.
What are the beams
There are several signs by which the classification of wooden floor beams is carried out: by size, material, type of section. The length of the floor beams depends on the distance between the walls. To this value you need to add a margin for support on both sides. Optimally, it is necessary to provide for 200-250 mm.
According to the material, the elements are divided into the following types:
- from a solid bar or board;
- from glued timber.
Bent beams are made from glued beams The latter are significantly more expensive. But on the other hand, such material is suitable for covering large spans. A regular beam can work at 4-6 m, while a glued beam copes well with distances of 6-9 m. Glued laminated timber practically does not shrink, is fireproof and resistant to moisture. It is possible to produce not only linear elements, but also bent. A significant drawback of such a material will be the presence of non-natural components (glue).
The beam section can be of the following types:
- square;
- rectangular;
- I-beam.
The latter has broadened elements at the top and bottom. In the middle of the section, it is reduced to the maximum possible size. This option allows you to rationally use wood and reduce its consumption. But to make such an element is not easy. For this reason, the I-beam is not so often used in construction.
Most often, a rectangular bar is used. The best option would be a rectangle. In this case, the long side is located vertically, and the short side is horizontal. This is due to the fact that an increase in height has a better effect on strength than width. Installing a beam from a board flat is almost useless.
The most unfavorable of the presented can be considered a square section. It is the least fitted to the diagram of forces in the element.
You can also use logs to cover. But this option has not gained popularity. The cross section of the board is much more profitable and easier to install, so it is used much more often.
Calculations
The calculation of the section will allow you to have no doubt about the strength and rigidity of the structure. This determines the maximum length that is allowed for any section. To perform the calculation, you need the following data:
- the length of the wooden floor beam (more precisely, the distance between the bearing walls);
- the distance between the beams (their step);
For the calculation, you need to know the distance between the beams, the span width and the load on the structure The load consists of two values: permanent and temporary. The constant includes the mass of the beams themselves (so far preliminary), insulation, ceiling filing, rough and clean floor. A temporary load is a mass of people and furniture. According to regulatory documents for residential premises, it is taken equal to 150 kg / m2. For the attic, you can take less, but it is recommended - the same. This will not only provide a certain margin of safety, but will also make it possible in the future to convert your attic into an attic without reconstructing the load-bearing elements.
The beam frame should be calculated according to the following formulas:
- Mmax = (q*l2)/8;
- Wreq = Мmax/130.
In these formulas, q is the load per sq. m of overlap, which includes a lot of structures and 150 kg of useful value. In this case, these values \u200b\u200bmust be multiplied by the distance between the beams. This is due to the fact that the calculations require a load per linear meter, and initially the value is calculated per square meter. l2 - the distance between the bearing walls on which the run rests, taken in a square.
Knowing Wreq, you can choose the overlap section. W = b*h2/6. Knowing W, one can easily write an equation with one unknown. Here it is enough to specify one geometric characteristic b (width of the section) or h (its height).
Most often, a wooden beam already has a known width. It is more convenient to make it from a board 50 or 100 mm wide. You can also consider the option with a composite section. It is made from several boards 50 mm thick.
Calculation in this case find the required height of the element. But there are cases when you need to fit into a certain floor pie so as not to reduce the height of the premises. In this case, as a known value, the height of the section is added to the equation, and the width is found. But the lower the height, the more uneconomical the floor frame will be.
To tighten two or three boards together, it is convenient to use metal studs. In this case, when tightening the nuts, wider washers must be used. They prevent the metal from being pressed into the softer wood. It is imperative to provide insulation between wood and steel fasteners. To do this, you can use a material such as TECHNOELAST brand EPP.
Wooden blocks must be waterproofed before installation. Before using wooden elements, they are treated with an antiseptic composition. This is necessary to prevent mold and decay. It is also recommended to perform fire retardant treatment, which will increase fire safety. When the runs are supported on a brick or concrete wall, their ends are wrapped with technoelast, linocrom, hydroisol or roofing material.
The beams in the house usually belong to the rafter system or ceiling, and in order to obtain a reliable structure, the operation of which can be carried out without any fear, it is necessary to use beam calculator.
What is the beam calculator based on
When the walls are already brought under the second floor or under the roof, it is necessary to make, in the second case, smoothly turning into rafter legs. At the same time, the materials must be selected so that the load on the brick or log walls does not exceed the permissible level, 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 the desired thickness and sufficient length.
Sagging or partial destruction of the floor can be caused by various reasons, for example, too large a step between the lags, deflection of the crossbars, too small a cross-sectional area or defects in the structure. To exclude possible excesses, you should find out the estimated load on the floor, whether it is basement or interfloor, after which we use the beam calculator, taking into account their own mass. The latter can vary in concrete lintels, the weight of which depends on the density of reinforcement; for wood and metal, with a certain geometry, the mass is constant. An exception is damp wood, which is not used in construction work without prior drying.
Beam systems in ceilings and truss structures are loaded by forces acting on the bending of the section, on torsion, on deflection along the length. For rafters, it is also necessary to provide for snow and wind loads, which also create certain forces applied to the beams. It is also necessary to accurately determine the required step between the jumpers, since too many crossbars will lead to an extra mass of the floor (or roof), and too little, as mentioned above, will weaken the structure.
You may also be interested in the article on calculating the number of unedged and edged boards in a cube:
How to calculate the load on the floor beam
The distance between the walls is called a span, and there are two of them in a room, and one span will necessarily be smaller than the other if the shape of the room is not square. Lintels of an interfloor or attic floor should be laid along a shorter span, the optimal length of which is from 3 to 4 meters. Larger spacings may require non-standard sized beams, resulting in some swaying in the deck. The best way out in this case would be to use metal crossbars.
As for the cross section of a 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 should make up the width of the profile. In this case, the deformation of the section is excluded, but if you deviate from the above indicators, then with a width exceeding the height, you will get a deflection, or, in case of a reverse discrepancy, 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 allowable deflection is calculated from the ratio to the length of the jumper, as 1:200, that is, it should be 2 centimeters by 4 meters.
So that the timber does not sag under the weight of the lags and flooring, as well as interior items, you can carve it from below by several centimeters, giving it the shape of an arch, in which case its height should have an appropriate margin.
Now let's turn to the formulas. The same deflection, which was mentioned earlier, is calculated as follows: fnorm \u003d L / 200, where L- the span length, and 200 - the allowable distance in centimeters for each unit of subsidence of the timber. For reinforced concrete beam, distributed load q to which 400 kg / m 2 is usually equated, the calculation of the limiting bending moment is performed according to the formula M max \u003d (q · L 2) / 8. In this case, the number of reinforcement and its weight is determined according to the following table:
Cross-sectional areas and masses of reinforcing bars
Diameter, mm | Cross-sectional area, cm 2, with the number of rods | Weight 1 linear m, kg | Diameter, mm |
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Wire and bar fittings |
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Seven-wire ropes class K-7 |
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The load on any beam of 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 beams are most often rectangular in shape, the moment of resistance can be calculated differently: W z \u003d b h 2 / 6, where b is the width of the beam, and h- height.
What else you should 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. So, you need to make it so that there is no risk of combining the upper and lower rooms by simply overloading the furniture. Especially such a probability arises when the step between the beams is too large and the lags 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. In the presence of lags, the minimum gap between the beams can reach 1 meter.
You should also take into account the mass used for the floor. For example, if mineral wool mats are laid, then a square meter of the basement will weigh from 90 to 120 kilograms, depending on the thickness of the thermal insulation. Sawdust concrete will double the mass of the same section. The use of expanded clay will make the floor even harder, since the load per square meter will be 3 times more than when laying mineral wool. Further, we should not forget about the payload, which for interfloor ceilings is 150 kilograms per square meter minimum. In the attic, it is enough to accept an allowable load of 75 kilograms per square.
Floor span tableThe span table of the frame house floors helps to choose the correct section of the floor lag, which means avoiding problems with floor sagging, creaking and vibration when walking. Our homegrown approach - to take more beams - is not economically justified. The board is cheaper than a bar, especially a large section. Most often, the length of the spans of the floors is in the range of 3.5-4.5 meters and, observing the correct section and step, you can install a reliable floor.
Let me remind you that the floor joists are set with a certain step, a multiple of the long side of the rough sheathing slab, namely 305 mm, 407 mm, 488 mm and 610 mm for osb / plywood board 2240 x 1220 mm in size.
For 305mm pitch (12" OC)
For 407mm pitch (16" OC)
For 488mm pitch (19.2" OC)
For 610 mm pitch (24" OC)
Where did the data in these tables come from?
How to work with tables correctly and what are residential and non-residential loads?
Residential is everything that is located and moves around the floor space: people, objects. Non-residential load is the weight of building elements. For example, the weight of the floor lag and subfloor slabs.
Depends on what will be located on top: a double bed or a regular chair. The final floor covering can be a light laminate, or it can be a warm floor screed with tiles.
Typically, for residential premises, the total load is in the range of 200-250 kg per sq.m. If you plan to install a cast iron bath, then look at its weight and add a lot of water and yourself in it.
What type of wood are these values taken for?
Since our markets do not have a quality system and an accurate determination of the grade of lumber, the tables show the values \u200b\u200bfor ordinary spruce and grade II pine according to the North American classification.
The actual dimensions of the section of the boards in the American tables are smaller than the European ones, what should I do?
It's true. If Americans say a board is 2" x 6", it's not 50.8mm x 152.4mm. In fact, it is 38.1 mm x 139.7 mm. The reduction in the cross section of the board occurs as a result of drying and planing. Our sawmills, lumberyards and markets also do not have a furniture store. Sellers claim that the board is 50 mm x 150 mm, but in fact it can be 40-50 mm x 135-150 mm.
In order to build a reliable wooden floor, it is necessary to correctly select the dimensions of the beams, and for this it is necessary to calculate them. Wooden floor beams have the following main dimensions: length and section. Their length is determined by the width of the span to be covered, and the cross section depends both on the load that will act on them, on the length of the span and the installation step, that is, the distance between them. In this article, we will look at how to independently make such a calculation and choose the right size for the beams.
Calculation of timber floor beams
In order to determine how many wooden beams and what sizes are required for the flooring device, it is necessary:
- measure the span that they will cover;
- determine how to fix them on the walls (to what depth they will go into the walls);
- make a calculation of the load that will act on them during operation;
- using tables or a calculator program, select the appropriate step and section.
Now let's see how this can be done.
Length of wooden floor beams
The required length of the floor beams is determined by the size of the span that they will cover and the margin necessary for embedding them into the walls. The length of the span is easy to measure with a tape measure, and the depth of embedding into the walls largely depends on their material.
In houses with walls made of bricks or blocks, beams are usually embedded in "nests" to a depth of at least 100 mm (board) or 150 mm (beam). In wooden houses, they are usually laid in special notches to a depth of not less than 70 mm. When using a special metal fastener (clamps, corners, brackets), the length of the beams will be equal to the span - the distance between the opposite walls on which they are mounted. Sometimes, when mounting the roof rafters directly on wooden beams, they are released outside, outside the walls by 30-50 cm, thus forming a roof overhang.
The optimal span that can overlap wooden beams is 2.5-4 m. The maximum length of a beam made of edged boards or timber, that is, the span that it can span, is 6 m. beams made of glued beams or I-beams, and you can also rest them on intermediate supports (walls, columns). In addition, wooden trusses can be used instead of beams to cover spans longer than 6 m.
Determination of the load acting on the floor
The load acting on the ceiling on wooden beams consists of the load from the own weight of the ceiling elements (beams, inter-beam filling, lining) and permanent or temporary operational load (furniture, various household appliances, materials, people's weight). It, as a rule, depends on the type of overlap and the conditions of its operation. The exact calculation of such loads is rather cumbersome and is performed by specialists when designing the floor, but if you want to do it yourself, you can use a simplified version of it, given below.
For an attic wooden floor, which is not used for storing things or materials, with light insulation (mineral wool or others) and filing, a constant load (from its own weight - Rown.) Is usually taken within 50 kg / m2.
The operational load (Reexpl.) for such an overlap (according to SNiP 2.01.07-85) will be:
70x1.3 \u003d 90 kg / m 2, where 70 is the standard load value for this type of attic, kg / m2, 1.3 is the safety factor.
The total design load that will act on this attic floor will be:
Ptot.=Pown.+Reexpl. \u003d 50 + 90 \u003d 130 kg / m 2. Rounding up, we accept 150 kg / m 2.
In the event that a heavier insulation, material for inter-beam filling or filing will be used in the construction of the attic space, and also if it is supposed to be used for storing things or materials, that is, it will be intensively used, then the standard load value should be increased to 150 kg / m2. In this case, the total load on the floor will be:
50 + 150x1.3 \u003d 245 kg / m 2, round up to 250 kg / m 2.
When using attic space for an attic device, it is necessary to take into account the weight of floors, partitions, and furniture. In this case, the total design load must be increased to 300-350 kg/m 2 .
Due to the fact that the interfloor wooden floor, as a rule, includes floors in its construction, and the temporary operational load includes the weight of a large number of household items and the maximum presence of people, it should be designed for a total load of 350 - 400 kg / m 2.
Cross-section and step of timber floor beams
Knowing the required length of the wooden floor beams (L) and determining the total design load, you can determine their required cross section (or diameter) and the laying step, which are interconnected. It is believed that the best is a rectangular section of a wooden floor beam, with a ratio of height (h) and width (s) as 1.4: 1. The width of the beams, in this case, can be in the range of 40-200 mm, and the height is 100-300 mm. The height of the beams is often chosen such that it corresponds to the required thickness of the insulation. When used as log beams, their diameter can be in the range of 11-30 cm.
Depending on the type and section of the material used, the pitch of the wooden beams 
overlapping can be from 30 cm to 1.2 m, but most often it is selected in the range of 0.6-1.0 m. Sometimes it is chosen so that it matches the size of the insulation boards laid in the inter-beam space, or ceiling filing sheets. In addition, in frame buildings, it is desirable that the step of laying the beams correspond to the step of the frame racks - in this case, the greatest rigidity and reliability of the structure will be ensured.
You can calculate or check the already selected sizes of wooden floor beams using the reference tables (some are given below) or using the online calculator "calculation of wooden floor beams", which is easy to find on the Internet by "scoring" the corresponding query in the search engine. At the same time, it should be taken into account that their relative deflection for attic floors should not be more than 1/250, and for interfloor floors - 1/350.
Table 1
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Step,m \ span,m |
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table 2
Table 3
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Step,m/ span,m |
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Table 4
appointed after meeting a number of requirements. Thus, the removal of the side formwork elements that do not bear the load from the weight of the structures is allowed only after the concrete has reached strength, which ensures the safety of the surface and edges of the corners.
More stringent requirements are imposed on the removal of the bearing formwork of reinforced concrete structures, which can be removed only after the concrete reaches the strength value from the design one:
- load-bearing structural elements with a span of up to 2 m - 50%;
- load-bearing structures of beams, crossbars, girders, slabs and arches 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%.
The standard conditions for hardening concrete 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 strength of 40-50%, and at 5ºC - only 30-35%. In the case of hardening at a temperature of 30-35ºC, concrete will gain 45% strength after 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 applied after testing the concrete for strength.
The terms for concrete to achieve a given strength are established by the construction laboratory based on the results of testing control samples or non-destructive testing methods. At facilities with a total volume of work of less than 50 m 3, receiving ready-mixed concrete 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 manufacturer of the concrete mix without making control samples at the place of laying. However, this instruction does not apply to critical paired and thin-walled structures: beams, columns, floor slabs, as well as to monolithic joints of prefabricated structures.
Of course, during the construction of suburban residential buildings, concrete strength measurements are usually not performed, since most construction companies operating in the private housing sector simply do not have construction laboratories. Therefore, in this case, you will have to focus on the data of the laboratory of the manufacturer of the concrete mix. Additionally, you can conduct your own test of concrete for strength. 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. According to the height of the rebound of the ball, it will be possible, I will immediately make a reservation - with a big stretch, to determine whether the strength of the concrete has reached the required value.
The full design load in the stripped reinforced concrete structure can be allowed only after the concrete has acquired design strength.
The metal beam of floors in the form of an I-profile 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-combustible and resistant to biological influences. However, a metal beam can corrode when exposed to an aggressive environment, 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, as in a steel frame structure. The load on the ceiling with steel I-beams, taking into account their own weight, should be calculated without a screed of 350 kg / m 2 and 500 kg / m 2 with a screed.
It is recommended to make the step between I-beams metal beams equal to 1000 mm, however, in order to save money, you can increase the step between metal beams up to 1200 mm.
The table below shows the choice of the number of an I-beam metal beam at different pitches and lengths of runs.
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Span3 m |
span4 m |
Span6 m |
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No. I-beam at step |
No. I-beam at step |
No. I-beam at step |
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As can be seen from the table, with a total load of 500 kg / m 2 and a span of 6 m, you should have chosen an I-beam of a higher number, and choose a smaller installation step for the beams.
Added: 05/26/2012 08:21
Forum discussion:
We poured the ceiling between the first and second floors along the I-beam No. 12, a span of 6 meters with a release of 1 meter from the load-bearing wall of the first floor. The distance between the I-beams is 2 meters, from the bottom between them from the reinforcement No. 12 a mesh cell 20 is connected from above, a 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?