What load can a wooden beam withstand. Types of wooden floor beams - beam calculation for bending, strength and load

Walls and ceilings are the main elements of any construction.

The purpose of the floor is to separate the floors in the house, as well as to carry and distribute the load from the components located at the top - walls, roofs, communications, furniture, interior details.

There are several types of floors: metal, reinforced concrete and wood.

Let us dwell in more detail on wooden floors, since they are the most widely used in private construction.

Wooden beam ceiling has advantages and disadvantages

Pros:

• beautiful appearance;
• light weight of the tree;
• maintainability;
• high installation speed.

Minuses:

• without special protective impregnation combustible;
• low strength compared to reinforced concrete or metal beams;
• exposed to moisture, fungus and living organisms;
• can be deformed by temperature changes.

Material for wooden beams overlap must have certain properties and meet the requirements:

• strength. The floor material must withstand possible loads. Consideration should be given to the effects of both permanent loads and variable loads;

• rigidity. Means the ability of a material to resist bending;

• sound and heat insulation;

• Fire safety.

Types and types of wooden floors - classification

1. By appointment

The main requirement for such an overlap is high strength. Since in this case, the beams will serve as the basis for flooring and, accordingly, must withstand a significant load.

Advice. If a garage or a large basement is located under the first floor, it is better to do wooden floor over metal beams. Since wooden ones are prone to rotting and cannot always withstand a significant load. Or reduce the distance between the beams.

Principle constructive device may be independent or be a continuation of the roof, i.e. part truss system. The first option is more rational, because is repairable, plus, provides better sound insulation.

The design feature is the two-in-one effect - the floor beams between the floors on the one hand are floor joists, and on the other, they are supports for the ceiling. The space between them is filled with heat and soundproof materials, with the obligatory use of vapor barrier. The bottom of the cake is sheathed with drywall, and the top is covered with a floorboard.

2. By appearance

Wooden floor beams also differ from each other, and each type has its own advantages.

Solid (massive) wooden floor beams

For their manufacture, an array of solid wood of coniferous or deciduous trees is used.

Interfloor ceilings on wooden beams can be made solid only with a small span (up to 5 meters).

Laminated wooden floor beams

Remove the length limit because this technology manufacturing allows you to implement floor beams of great length.

Due to the increased strength, wooden glued beams are used in cases where it is required to withstand an increased load on the ceiling.

Advantages of glued beams:

• high strength;
• ability to overlap large spans;
• ease of installation;
• light weight;
• long term services;
• no deformation;
• Fire safety.

The maximum length of a wooden floor beam of this type reaches 20 linear meters.

Since glued wood beams have a smooth surface, they are often not sewn up from below, but left open, creating a room stylish design interior.

Section of wooden floor beams

As practice shows, the cross-section of timber floor beams has a significant impact on the ability of the beam to withstand the bearing load. Therefore, it is necessary to first calculate the cross section of wooden floor beams.

IN wooden houses a log can be used as interfloor beams for decorative purposes.

As a rule, they are used for the device of attic floors. The round beam is highly resistant to bending (depending on the diameter).

The maximum length of a wooden floor beam made of logs is 7.5 r.m.

They can be made from solid wood, or a combination of OSB and plywood. They are actively used in frame construction.

Advantages of wooden I-beams:

• exact dimensions;
• possibility of use on long spans;
• the possibility of deformation is excluded;
• light weight;
• reduction of cold bridges;
• the ability to consolidate communications;
• the possibility of installation by one's own hands without the involvement of special equipment;
• wide scope.

Disadvantages:

• high price;
• inconvenient for insulation with plates.

The correct selection of the section of a wooden beam must be included in the calculation plan, otherwise, the floor structure will be insufficiently or excessively rigid (an extra cost item).

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Calculation of a wooden floor

The distance between the wooden floor beams is determined by:

First, the expected loads.

The load, in turn, can be constant - the weight of the ceiling, the weight of partitions between rooms or the weight of the truss system.

As well as a variable - it is taken equal to 150 kg / sq.m. (According to SNiP 2.01.07-85 "Loads and impacts"). Variable loads include the weight of furniture, equipment, people in the house.

Advice. Since it is difficult to take into account all possible loads, the floor should be designed with a margin of safety. Professionals recommend adding 30-40%.

Secondly, rigidity or standard deflection.

For each type of material, GOST sets its own stiffness limits. But the formula for calculating is the same - the ratio of the absolute value of the deflection to the length of the beam. The stiffness value for attic floors should not exceed 1/200, for interfloor 1/250.

The amount of deflection is also influenced by the type of wood from which the beam is made.

Calculation of the floor on wooden beams

Let's assume that the distance between wooden beams is 1 m.p. The total length of the beam is 4 r.m. And the expected load will be 400 kg / sq.m.

This means that the greatest amount of deflection will be observed under load

Mmax \u003d (q x l in a square) / 8 \u003d 400x4 in a square / 8 \u003d 800 kg sq.m.

We calculate the moment of resistance of wood for deflection according to the formula:

Wreq = Mmax / R. For pine, this figure will be 800 / 142.71 = 0.56057 cubic meters. m

R - wood resistance, given in SNiP II-25-80 (SP 64.13330.2011) "Wooden structures" put into operation in 2011

The table shows the larch resistance.

If not pine is used, then the value should be adjusted for the transfer coefficient (given in SNiP II-25-80 (SP 64.13330.2011)).

If we take into account the expected service life of the building, then the resulting value must be adjusted for it.

An example of beam calculation showed that the beam resistance to deflection can be halved. Therefore, it is necessary to change its section.

The calculation of wooden floor beams can be performed using the above formula. But you can use a specially designed calculator for calculating wooden floor beams. It will allow you to take into account all the points, without bothering to search for data and calculate.

Thirdly, the parameters of the beam.

The length of solid wooden floor beams can be no more than 5 meters for floors. For attic floors, the span can be 6 r.m.

The table of wooden floor beams contains data for calculating the appropriate height of the beams.

The thickness of the wooden floor beams is calculated based on the premise that the thickness of the beam must be at least 1/25 of its length.

For example, a beam with a length of 5 m.p. should have a width of 20 cm. If it is difficult to maintain this size, you can achieve the desired width by a set of narrower beams.

You should know:
If the beams are stacked side by side, they can withstand a load twice as much, and if they are stacked on top of each other, they can withstand a load four times as much.

Using the graph shown in the figure, you can determine the possible parameters of the beam and the load that it can bear. Please note that the graph data is suitable for the calculation of a single-span beam. Those. for the case when the beam rests on two supports. By measuring one of the parameters, you can get the desired result. Usually, the pitch of the wooden floor beams acts as a variable parameter.

The result of our calculations will be the drawing up of a drawing, which will serve as a visual aid during work.

In order to qualitatively and reliably carry out overlapping on wooden beams with your own hands, the drawing must contain all the calculated data.

Wooden floor beams - GOSTs and SNiPs

State standards regulate all aspects of the use of wooden floor beams, regardless of their type or place of use.

Below is a selection of the most important papers on this topic.

Conclusion

In this article, you got acquainted with the factors that influence the choice of material for the installation of wooden floor beams. They also learned how to determine the cross section and perform the calculation of wooden floor beams.

The program for the calculation of wooden floor beams- small and handy tool, which will simplify the basic calculations for determining the cross section of the beam and the step of its installation when constructing interfloor ceilings.

Instructions for working with the program

The considered program is small and does not require additional installation.

To make it clearer, consider each item of the program:

• Material- select the required material of timber or logs.
• beam type- beam or log.
• Dimensions- length height width.
• Beam spacing- the distance between the beams. By changing this parameter (as well as the dimensions), you can achieve the optimal ratio.
. As a rule, the calculation of the load on the floors is carried out at the design stage by specialists, but you can do it yourself. First of all, the weight of the materials from which the floor is made is taken into account. For example, attic floor, insulated with lightweight material (for example, mineral wool), with a light lining, can withstand a load from its own weight within 50kg / m². The operating load is determined according to normative documents. For attic floors made of wooden base materials and with light insulation and lining, operating load in accordance with SNiP 2.01.07-85 calculated in this way: 70 * 1.3 \u003d 90 kg / m². 70 kg/m². In this calculation, the load is taken in accordance with the standards, and 1.3 is the safety factor. : 50+90=140 kg/m². For reliability, the figure is recommended to be rounded slightly up. In this case, you can take the total load as 150 kg / m². If attic space is planned to be operated intensively, then it is required to increase the standard load value in the calculation to 150. In this case, the calculation will look like in the following way: 50+150*1.3=245 kg/m². After rounding up - 250 kg/m². It is also necessary to carry out the calculation in this way if heavier materials are used: heaters, filing to fill the interbeam space. If an attic is to be built in the attic, then the weight of the floor and furniture must be taken into account. In this case, the total load can be up to 400 kg/m².
• With relative deflection. The destruction of a wooden beam usually occurs from transverse bending, at which compressive and tensile stresses occur in the beam section. At first, the wood works elastically, then plastic deformations occur, while in the compressed zone, the extreme fibers (folds) are crushed, the neutral axis falls below the center of gravity. With a further increase in the bending moment, plastic deformations increase and destruction occurs as a result of rupture of the extreme stretched fibers. The maximum relative deflection of beams and girders of roofing should not exceed 1/200.
- this is the load taken from the slab (full) plus the own weight of the crossbar.

When designing roofing system a small building (private house, garage, barn, etc.) uses load-bearing elements such as single-span wooden beams. They are designed to cover the spans and act as the basis for laying the flooring on the roof. At the stage of planning and creating a project for a future building in without fail the bearing capacity of wooden beams is calculated.

Wooden beams are designed to cover the spans and act as the basis for laying the flooring on the roof.

Basic rules for the selection and installation of single-span beams

The process of calculating, selecting and laying load-bearing elements should be approached with all responsibility, since the reliability and durability of the entire floor will depend on this. Over the many centuries of the existence of the construction industry, some rules for the design of a roofing system have been developed, among which the following are worth noting:

1. The length of single-span beams, their dimensions and number are determined after measuring the span to be covered. It is important to consider how they are attached to the walls of the building.
2. In walls built from blocks or bricks, load-bearing elements should be deepened by at least 15 cm if they are made of timber, and by at least 10 cm if boards are used. Beams should be deepened at least 7 cm into the walls from the log house.
3. The optimal span width suitable for overlapping with wooden beams is in the range of 250-400 cm. In this case, the maximum length of the beams is 6 m. If longer bearing elements are required, then it is recommended to install intermediate supports.

Calculation of loads acting on the floor

The roof transfers the load to the load-bearing elements, which consists of its own weight, including the weight of the used thermal insulation material, operational weight (objects, furniture, people who can walk on it in the process of performing certain work), as well as seasonal loads (for example, snow). You are unlikely to be able to perform an exact calculation at home. To do this, you need to contact the design organization for help. More simple calculations you can do it yourself like this:

Figure 1. Table of the minimum allowable distance between beams.

1. For attic floors, which were insulated with light materials (for example, mineral wool), which are not affected by large operational loads, we can say that on average 1 m 2 of roof has a weight of 50 kg. According to GOST, for such a case, the load will be equal to: 70 * 1.3 \u003d 90 kg / m 2, where 1.3 is the margin of safety, and 70 (kg / m 2) is the normalized value for the above example. The total load will be equal to: 50 + 90 \u003d 140 kg / m 2.
2. If a heavier material is used as a heater, then the normalized value according to GOST will be 150 kg / m 2. Then the total load: 150 * 1.3 + 50 \u003d 245 kg / m 2.
3. For the attic given value will be equal to 350 kg / m 2, and for interfloor overlapping - 400 kg / m 2.

Having learned the load, you can begin to calculate the dimensions of single-span wooden beams.

Calculation of the section of wooden beams and laying step

The bearing capacity of the beams depends on their cross section and the laying step.. These quantities are interrelated, so they are calculated simultaneously. Optimal shape for floor beams it is rectangular with an aspect ratio of 1.4: 1, that is, the height should be 1.4 times greater than the width.

The distance between adjacent elements should be at least 0.3 m and not more than 1.2 m. In the case of installing rolled insulation, they try to take a step that will be equal to its width.

If designed frame house, then the width is taken equal to the step between the racks of the frame.

To determine the minimum allowable sizes beams with a laying step of 0.5 and 1.0 m, you can use a special table (Fig. 1).

All calculations must be made in strict accordance with existing rules and regulations. If there is some doubt about the accuracy of the calculations, it is recommended that the obtained values ​​be rounded up.

To select the cross section of the beam, you must first determine the maximum bending moment in it ( M ) and on it for specific dimensions of the beam section (width and height) the maximum stress is determined (  ). The cross section is chosen so that this stress (  ) did not exceed the calculated resistance of the beam material (in this case, wood) R u . To ensure the economy of the choice of section, it is necessary that the difference between  And R u was as small as possible. This calculation refers to "calculations for bearing capacity”(otherwise “calculations for the I group of limit states”).

After selection of the section according to the bearing capacity, “calculation by deformations” is carried out (in other words, “calculation by group II of limit states”), i.e. the deflection of the beam is determined and its admissibility is evaluated. If, with a beam section selected according to the bearing capacity, the deflection is greater than the permissible one, the section is additionally increased, if less, it is left unchanged.

2.5. Bearing capacity calculation

Maximum bending moment M in the beam is determined according to the rules of mechanics (strength of materials) by the formula

where q)

l - beam span ( m).

Stress in the beam  is determined by the formula

, (2)

where M - bending moment ( kNm) determined by formula (1),

W– section modulus ( m 3 ).

, (3)

where b, h- respectively, the width and height of the beam section.

Example. Beam span l = 3.6 I = 2.56 kN/m. Check beam section 0.10.2 m(large side - height).

= 4.15 kNm

= 0.00056 m 3

= 6 200 kN/m 2 (kPa) =6.2 MPa R u =13 MPa

Thus, the cross section is 0.10.14 m satisfies the strength (load-bearing capacity) requirements, however, the maximum stress obtained  about half the design resistance of wood R u, i.e. "margin of safety" is unreasonably large. Reduce the cross section to 0.10.14 m and check the possibility of its acceptance.

= 0.000327m 3

= 12 691kPa = 12.7 MPa MPa

"Margin" at a section of 0.1 0.14 m less than 5%, which fully satisfies the requirements of economy. Thus, we accept (at this stage) the cross section 0.1 0.14 m.

2.6. Deformation calculation

beam deflection f is determined by the formula ( strength of materials)

, (4)

where) in relation to deformation calculations (see table 4);

l - beam span ( m);

E is the modulus of elasticity of the beam material, i.e. wood (kPa);

I – moment of inertia of the beam section ( m 4)

, (5)

where the designations are the same as in formula (2).

= 0.0000228 m 4 = 2.28 10 -5 m 4

= 0.0173m= 1.73 cm

Relative beam deflection, i.e. deflection ratio f to the span l, is in this case

=

The resulting relative deflection is less than the allowable one (1/200). In this regard, we accept the cross section of the beam 0.10.14 m as the final, satisfying the requirements of not only bearing capacity, but also deformability.

Obviously, any other building structure must also meet the requirements for both load-bearing capacity and deformability. Verification of the compliance of its parameters with both requirements is not carried out only in cases where it is clear without calculation that one of the requirements is certainly satisfied.

The calculation of wooden floor beams is in demand both for residential attics, second floors, and for non-exploited attics. Low fire safety, resistance to fungal attack wooden structures compensated by affordable price, low weight, manual installation. Starting the calculation of the cross section, it is necessary to take into account several parameters recommended by specialists:

• leaning on the wall from 12 cm;
• rectangular section with a ratio of 7/5 (height is always greater than width);
• span 4 - 2.5 m (placement on the short side of the rectangle);
• allowable deflection 1/200 (2 cm per recommended length).

For ease of calculation, a static load with a margin of 200 kg or 400 kg per unit area is used for attics, operated premises, respectively. This method eliminates long-term calculations of operational loads - people, furniture, household utensils. Most often, the floors of the upper level are based on logs, so there are actually concentrated loads. In practice, the number of lags exceeds 5-7, so the load is assumed to be evenly distributed.

The calculations are reduced to determining the rational section of lumber, providing a 20-30% strength margin with a minimum construction budget. At big step beams, laying a plank floor without a log, the minimum possible section of the floorboard is additionally calculated.

An example of calculating a wooden beam

Figure 1. Table with the characteristics of the design resistance of materials different humidity.

The calculation of the overlap begins with the determination of the bending moment for the operating conditions. The formula applied is:

M = N x L 2 /8, where L is the span length, N is the load per unit area.

A four-meter ceiling over a span of 4 m for an operated floor / attic in this case experiences a bending moment at a beam spacing of 1 m:

M \u003d 400 kg / m 2 x 4 2 m / 8 \u003d 800 kgm (to bring 80,000 kgcm into a single system of units)

The SNiP standards contain tables with the characteristics of the design resistance of materials of various moisture content. Rice. one.

The parameter is denoted by the letter R, is for conifers most commonly used in load-bearing structures cottages due to cheapness, 14 MPa. When translated into more convenient units, this value will be 142.7 kg / cm 2. Providing a margin of safety, the figure is rounded down to 140 units for further use. Thus, each floor element will require a moment of resistance:

In the example with the specified conditions, the overlap must have the value:

W \u003d 80,000/140 \u003d 571 cm 3

For floor beams, a beam with a rectangular section is preferable. The moment of resistance of elements of this form is determined by the formula:

Figure 2. Table for calculating resistance various breeds trees.

In this formula, two parameters are initially unknown - height h, width a. Substituting one value (width) into it, the second side of the section (height) that the floor beam has is easily calculated:

• find 6W/a;
• take the root of this value.

In our case, h \u003d 18.5 cm with a width of 10 cm. The closest standard beam section of 20 x 10 cm fully meets the requirements.

Dependence on the spacing of wooden beams

If the distance between the axes of single-span wooden beams is changed in any direction, the dimensions of the section of the beam, boards used as flooring will change. Therefore, it is recommended to perform several calculations with different parameters to achieve the minimum construction budget.

In our example, we got a wooden beam 20/10 cm, the amount of lumber for the entire room 6 x 4 m will be 7 pcs. (0.56 cube).

The calculation of wooden beams for the same conditions with a step of 0.75 m will reduce the bending moment to 60,000 kgcm, the moment of resistance to 420 cm 3, the height of the beam to 15.9 cm. In this case, 9 beams of 17.5 x 10 cm (0 .63 cubic meters of lumber).

The calculation of wooden beams with a step of 0.5 m will reduce these characteristics to 40,000 kgcm, 280 cm 3, 12.9 cm, respectively. The number of beams will increase to 13, lumber to 0.78 cubic meters.

In the first case, the floor will require a 50th or 40th board, in the latter case, an "inch" is enough, which will significantly reduce the construction budget.

The specifics of the calculations of wooden floors

Figure 3. Scheme of installation of floor beams.

The SNiP standards contain other tables necessary for calculations for tree species that differ in characteristics from pine, spruce (Fig. 2). In addition, there are coefficients for the resource of structures:

• to ensure secular reliability k = 0.8;
• operation within 50-90 years is provided at k = 0.9;
• if 50 years reliability is sufficient, k = 1 is used.

This factor is multiplied design resistance beams, the minimum allowable width / height of the sawn timber section increases.

The performed calculations are not enough to check the selected beam. It is necessary to calculate the deflection of the structure, compare it with the admissible possible. For work, the hinged support of the beams is taken, the formula is as follows:

F = 5NL 4 /IE, where E is the modulus of elasticity of the lumber, I is the moment of inertia.

The first characteristic of the beam depends on the material, for all types of wood it is the same - 100,000 kg / cm 2. However, depending on the humidity, the value varies between 110,000 - 70,000 kg / cm 2.

The moment of inertia is:

I \u003d a x h 3 / 12.

Which for the conditions considered in the example will be:

I \u003d 10 x 20 3 / 12 \u003d 6 666 cm 4.

After that, the deflection of the beams will be:

F \u003d 5 x 400 kg x 4 4 m / 384 x 100,000 \u003d 2 cm.

The norms of SNiP regulate the deflection of wooden floor beams within 1.6 cm. Therefore, the condition is not met, the next lumber value is taken.

Practice shows that with a beam spacing of 1 m, 4 cm of a floorboard is sufficient, with a step reduction of up to 0.75 m, a 35 mm board can be dispensed with.

"Inch" (25 mm board) is usually used in unused attics with a beam spacing of 0.5 m. In other cases, it is recommended to make calculations similar to those considered for flooring boards. The span length in this case is reduced to the distance from the edge of the beam to the edge of the neighboring element.

When using multilayer plywood, it is recommended to use 14 mm sheets along the beams with a step of 0.75 m, 18 mm sheets with a step of 1 m. It is not recommended to use chipboard as a subfloor, it is better to replace the material with OSB, which has a long service life. Rice. 3.

If between flooring, floor beams use logs, identical to that considered in the example. In practice, a section of 10 x 7 cm is sufficient for this.

Typically, strength analysis is applied under standard operating conditions:

• lining in the form of laminate, parquet, linoleum;
• no plaster.

If the ceiling is planned to be plastered, to tile the wooden floor, it is much more important to calculate the deflection. In this case, instead of the recommended SNiP allowable value 1/20 of the span length uses the value 1/350. Otherwise, the tile will peel off with a short-term increase in operational loads. The subfloor in this case is made of rigid wood-containing boards or plywood, and not from boards. In difficult operating conditions, wooden beams are either shifted up to 0.4-0.5 m, or replaced with rolled metal.

Fast and accurate, must use online calculator website. Reliable and competent calculation taking into account SNiP II-25-80 (SP 64.13330.2011).

What are wooden floor beams

On-for-more eco-nomic vari-an-tom for a private house is yav-la-yut-sya wooden beams of a river-ry-tia. They are dos-to-accurate, but easy to mount, - you don’t need to bring in a special tech-no-ku.

Wooden beams have a pre-im-image in comparison with iron-concrete-us and metal-li-ches-ki-mi bal-ka- we are in the plan of heat-lopro-water-ness. However, they also have a number of shortcomings: low heat-to-bone, low density and, as a result, the ability to keep vat small nag-ruzki, from-suts-tvie mustache-to-chi-vost-ti to defeat mik-ro-or-ga-niz-ma-mi and insects-mymi. In this way, wooden beams are pre-variant-but before us-ta-nov-koy ob-ra-baty-va-yut-spe-tsi-al-nym an- ti-sep-ti-kami.

When mont-the-same de-revyan-nye bal-ki per-river-ry-tia uk-ladva-yut-sya on transverse supports, which can serve as a full-full beam, or-bo ar-mo-po-yas, for- cast along the perimeter of the wall treasure. The transverse supports serve for the equal-measurement of the distribution of the load on the walls, and further on the fund-da-ment to the ma. Hours of ba-loks, laid on the walls, wrap-around with hydro-iso-lyatsi-on-ny ma-teri-al, usually used they use rub-bero-id, while the to-rts do not isolate, which allows the beam to "breathe".

Length of wooden floor beams

Not-about-ho-dimaya length-on-wood-ba-lok cross-river-ry-tia op-re-dividing-there-by times-by-measures of that pro-summer, which they will re-re-roar, up to-half-no-tel-but you need to take into account the times -me-ry zas-tu-pov on the wall. Zas-tuple beams on the wall should be at least 12 cm, for a bru-sa it should be at least 15 cm.

If, when fastening-le-nii-bal-ki, use-pol-zu-yut-spe-tsi-al-metal-li-ches-kie fastenings (ho-mute, corner-ki ), the ball can be us-ta-nav-li-vat-sya not-pos-reds-tween-but in the pro-years between the walls-us, then-yes-on-wood-noy bal-ki per-river-ry-tia will be equal to the distance between the walls where it is cre-pit-sya. But in practice, more often than not, the bal-ka of the river-ry-tia lays on the walls.

An op-ti-small span, over which there is a de-raven-naya beam, is 2.5 - 4.5 m. Max-si-mal-naya the length of the beams from the wooden beam does not exceed 6 m, thereby op-re-dividing the maximum pro-year.

When trans-r-rying spans with a length of more than 6 meters, wooden farms are used.

Wooden floor beam calculator will select the most optimal parameters of the section and beam step. Try to calculate for free right now!

Loads acting on wooden floor beams

Nag-ruzka, rendered onbal-ki per-river-ry-tiya,a warehouse from a nag-ruzka from its own-twen-no-go weight of elements of a river-ry-tia (bal-ki, for-half-ni-tel, ob-shchivka ; The ex-pl-ata-qi-on-naya nag-ruzka is the vest of various household items, furniture, people.

Usually, when arranging wooden beams for the cher-dacha-th cross-r-ry-tia, use the value - 150 kg / m2, where 50 kg / m2 is the load of its own weight, and 100 kg / m2 is the standard load for attic rooms (SNiP 2.01.07 -85) taking into account the co-ef-fi-qi-en-ta margin for strength.

If it is supposed to actively use the attic room for storing things and materials, then the total load, at- ma-mable in races, taken equal - 250 kg / m2.

When ras-che-tah is a section of a wooden beam for an inter-floor-no-th cross-river-ry-tia, or a cross-river-ry-tia of the attic floor, the total load is assumed to be equal to - 350 - 400 kg / m2.

The calculation of a wooden floor beam, which can be read in detail in the article, is carried out in the following order.

Floor loads are determined per 1 m 2. The floor loads are created by the weight of the floor parts and temporary operational load - the weight of people, materials stored on the floor, etc.

For attic floors on wooden beams with easy effective insulation, a constant load from the weight of the floor is usually taken without making calculations in the amount of 50 kgf / m 2.

Guided by SNiP 2.01.07-85 "Loads and Impacts", we determine the temporary operational design load for the attic floor: 70 kgf / m 2 x 1.3 = 91 kgf / m 2,

where 70 kgf / m 2- the normative value of the load on the attic floor;
1.3 - reliability coefficient.

In this way, the total design load on the attic floor in the house will be, rounding up, - 150 kg/m2 (50 kgf / m 2 + 91 kgf / m 2).

If the attic is planned to be used as unheated room , for example, for the storage of materials, the design load should be increased. Standard value in this case, we take the loads on the floor as for interfloor overlap 150 kgf / m 2.

Then the calculated temporary operational load will be 150 kgf / m 2 x 1.3 = 195 kgf / m 2. As a result the total design load on the attic floor will be equal to 250 kgf / m 2 (50 kgf/m 2 + 195 kgf / m 2).

If the attic is planned to be converted into attic heated rooms in the future with the device of screeds, floors, partitions, then the total design load is increased by another 50 kgf / m 2, up to 300 kgf / m 2.

According to the known load on the floor and the length of the span to be covered determine the cross section of a wooden beam and the distance between the centers of the beams - the step of the beams.

For this, tables from reference books and calculators are used.

For example, in SP 31-105-2002 "Design and construction of energy-efficient single-apartment residential buildings with wooden frame”, table B2, the dimensions of the beams from the boards are given:

In Table B-2, the length of the spans is determined for the value of the calculated uniformly distributed load on the floor no more than 2.4 kPa =240 kgf / m 2., and the maximum deflection of the beam is not more than 1/360 of the clear span.

In the same joint venture for an unused attic The following beam sizes are available:

In table B-3, the calculation is made for a live operating load of only 0.35 kPa=35 kgf / m 2., and the maximum deflection of the beam is not more than 1/360 of the clear span. Such an overlap is designed for a rare visit to the attic by people.

The step of the beams does not have to be the one indicated in the table. For plank beams it is more profitable to choose a step that is a multiple of the size of the sheets of the binder, so that the sheets are fastened directly to the beams, without crates.

It is advisable to choose the height of the beam so that thermal and sound insulation of the required height is located in the interbeam space. At the same time, it should be remembered that the price of 1m3 of wide boards is usually higher than narrow ones.

Calculator program for calculating wooden beams(Excel file) can be downloaded if, in the window that opens, in the menu at the top left, select "File" > "Download".