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 make their calculation. Wooden beams floors have the following basic dimensions: length and section. Their length is determined by the width of the span that needs 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 pitch, that is, the distance between them. In this article, we will look at how to independently make such a calculation and correctly select the dimensions of the beams.

Calculation of timber floor beams

In order to determine how many wooden beams and what dimensions will be required for the floor device, it is necessary:

• measure the span that they will overlap;
• decide on the methods of fixing 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 timber floor beams

The required length of the floor beams is determined by the dimensions of the span that they will overlap 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 (plank) or 150 mm (timber). V wooden houses they are usually placed in special notches to a depth of not less than 70 mm. When using a special metal mount(clamps, corners, brackets) the length of the beams will be equal to the span - the distance between the opposite walls on which they are attached. Sometimes, when installing the roof rafter legs 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 be covered by wooden beams is 2.5-4 m. The maximum length of a beam from edged boards or timber, that is, the span that it can overlap is 6 m.With a longer span (6-12 m), it is necessary to use modern wooden beams made of glued laminated timber or I-beams, and you can also lean 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 floor on wooden beams consists of the load from the dead weight of the floor elements (beams, interbeam filling, stitching) and a permanent or temporary operating load (furniture, various household appliances, materials, weight of people). 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 a floor, but if you want to do it yourself, you can use a simplified version of it, given below.

For an attic wooden floor that is not used for storing things or materials, with light insulation ( mineral wool or others) and a filing, a constant load (from its own weight - Psob.) is usually taken in the range of 50 kg / m2.

The operational load (Rexpl.) For such an overlap (according to SNiP 2.01.07-85) will be:

70x1.3 = 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:

Rtot. = Rsob. + Rexpl. = 50 + 90 = 130 kg \ m 2... Rounding up we take 150 kg / m 2.

In case the design attic space heavier insulation, material for inter-girder filling or filing will be used, 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 floor load will be:

50 + 150x1.3 = 245 kg / m 2, round up to 250 kg / m 2.

When using the attic space for the attic, it is necessary to take into account the weight of the floors, partitions, furniture. In this case, the total design load must be increased to 300-350 kg / m 2.

Due to the fact that interfloor wooden floors, as a rule, include floors in their structure, and the temporary operational load includes weight a large number household items and the maximum presence of people, then it should be designed for a total load of 350 - 400 kg / m 2.

Section and spacing of timber floor beams

Knowing the required length of timber floor beams (L) and determining the total design load, it is possible to determine their required section (or diameter) and laying spacing, which are interconnected. It is believed that the best is rectangular section timber joists, with a height (h) to width (s) ratio of 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 to match required thickness insulation. When used as beams of logs, 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 beams of the wooden the overlap can be from 30 cm to 1.2 m, but most often it is chosen within the range of 0.6-1.0 m. Sometimes it is chosen so that it matches the size of the insulation slabs laid in the interbeam space, or sheets of ceiling filing. In addition, in frame buildings, it is desirable that the step of laying the beams corresponds 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 dimensions of wooden floor beams using the reference tables (some are given below) or using online calculator"calculation of wooden floor beams", which is easy to find on the Internet, "hammering" the corresponding query in a search engine. It should be taken into account that their relative deflection for attic floors should not be more than 1/250, and for interfloor ones - 1/350.

Table 1

Step, m \ Span, m

table 2

, kg / m 2 \\ Span, m

Table 3

Step, m / Span, m

Table 4

Floor Spans Table

Floor Spans Table frame house helps to choose the correct cross-section of the floor lag, which means avoiding problems in the floor sagging, creaking and vibration when walking. Our home-grown approach - to take larger beams - is not economically justified. A board is cheaper than a bar, especially a large section. Most often, the length of the floor spans is within 3.5-4.5 meters and, observing the correct section and pitch, you can install a reliable overlap.

Let me remind you that the floor logs are placed with a certain step, a multiple of the long side of the slab of the rough sheathing, namely 305 mm, 407 mm, 488 mm and 610 mm for osb slabs/ plywood 2240 x 1220 mm.

For 305mm pitch (12 "OC)

For pitch 407mm (16 "OC)

For 488mm pitch (19.2 "OC)

For 610mm pitch (24 "OC)

Where did the data in these tables come from?

How to work with tables correctly and what is residential and non-residential load?

Living room is everything that is located and moves through the overlapping space: people, objects. Non-residential load is the weight of the building elements. For example, the weight of the log floor and subfloor slabs.

Depends on what will be located on top: a double bed or a regular chair. The floor finish can be a light laminate, or there can be a heated 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 cast iron bath, then look at its weight and add the mass of water and yourself loved in it.

For which wood species are these values ​​taken?

Since our markets do not have a quality system and an accurate determination of the grade of sawn timber, the tables show the values ​​for ordinary spruce and pine of the II grade 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?

This is true. If Americans say a 2 "x 6" board is not 50.8mm x 152.4mm. In fact, it is 38.1 mm x 139.7 mm. Reducing the section of the board occurs as a result of drying and planing. At our sawmills, timber yards and markets, there is also no furniture store... Sellers say that the board is 50 mm x 150 mm, but in fact it can be 40-50 mm x 135-150 mm.

01.10.2010, 11:47

payment:
1) timber 200 * 200 * 6000 through 0.5M = 22 tr (deflection 20 mm)
2) I-beam 20B b / w 1.2m = 27 tr. (deflection 20 mm)

By weight 1) -90 kg timber, 2) - 120 kg beam

In theory, the solutions are very similar. practice interests what is still better?

Green cat

01.10.2010, 11:55

Bar.
Iron is generally not worth doing any bearing structures for in a fire, wood holds on to the last, and iron is grist and ready.

01.10.2010, 15:55

The temperature at which the deformation of the I-beam will go is incompatible with life. Especially if from below it is all sheathed with plasterboard.

If you still decide to do it with a tree, then I advise 200x60x6000 with a step of 600 mm.

01.10.2010, 16:55

"hrya and ready" - but will it be all the same)))

It can deform in one place, and fly to another, where there are still conditions for life ... :) but on the whole you are right.
+ Wood itself will support combustion, but iron will not ...

Green cat

01.10.2010, 17:41

The temperature at which the deformation of the I-beam will go is incompatible with life.
Not right.
It's one thing when he's on his own, and another when he's under load.

Until recently, it was generally forbidden to use met. profile, now I'm looking at doing it with might and main.

I advise 200x60x6000 with a step of 600 mm
Malavato will be, malavato - let's look at the cuckoo.

01.10.2010, 20:32

In my room, the span turned out to be 5.7 meters, the overlap between the 1st and 2nd floors. I chose an I-beam 20B every 1.3 meters, it seems, according to the calculation, the I-beam was stronger than a tree. It is worth considering that a tree can be found 6.5 meters, and the length of the I-beam is 11.7 meters or 12 meters (to cover a span of 6 meters, at least 15 cm per side is needed). It would have been more correct to lay the plates, but I didn't succeed. The difference between wood and I-beams was somewhere around 10-12%. When laying the walls, I installed 3 cm foam plastic between the cutout in the gas block and the I-beam.
At the expense of the fire, it is necessary to protect ourselves.

02.10.2010, 00:47

And I put a 5.8 meter concrete slab on a 6 m span and I don't think about anything else. Does not burn, does not melt, does not bend ...

02.10.2010, 09:00

Thank you all, I still lean towards the I-beam, because it is stronger, I want to put the inner walls of the foam block 100 cm on the ceiling. (although it was probably possible to put 2 beams under the wall)
then wawan001 span 6M is along the axes of the walls, that is, 15 cm on each side of the support will be.
then the Cat, I suppose, if you fill in a non-combustible insulation ala expanded clay, then there will be nothing to burn there at all (a house made of foam block).

And another question if you overlap with an I-beam, is it possible to use a wooden, say 50-ku, fixed to the side walls instead of the extreme beams ??

02.10.2010, 18:30

There is another option.

02.10.2010, 19:12

There is another option.
Do load-bearing beam(albeit from an I-beam), on which you lay simple wooden floor beams. It will be much cheaper.
I-beams will need one or two, but powerful ones. The price will still come out cheaper.

I did so myself

02.10.2010, 20:01

dengt, I came up with this idea from the point of view of the manufacturability of the device in the future of floors, if the wooden floors are installed inside the I-beam, and a counter-lattice (beams by calculation) is made on top. The distance from the edge of the beam to the I-beam is 40 cm - reliable. Indeed, according to calculations on the extreme beam, the load is less than 2 times than on the neighboring one, you can put a 150x200 beam or take 2 pieces of 50x200 boards and install pieces of a board of the same size 1.5 meters long between them, and I think 50 is flimsy, although if the wall can pull in and it will be fine. If you are sure of the fasteners, then probably yes.

04.10.2010, 05:57

I covered the span with a 5m bar 150 * 150 folded in half and tightened with hairpins, i.e. it turned out a beam 150 * 300. It turned out pretty tough, but I would still make it out of concrete if I could :(

05.10.2010, 09:32

[
I did so myself
span 11 by 6, divided into three parts with two I-beams and laid wooden beams, and in order not to increase the thickness of the ceiling, laid them inside the T-bar. Pre-welded the corners to the brand and fastened the beams to the bolts.

As I understand it, were I-beams 6 meters high?
here a minimum of 25B2 is already needed, it is 5 cm thicker overlapping, it seems not fatal.

Regarding the fixing of the side beams to the walls, I am concerned that all the other beams will bend and the extreme ones will not, then the overlapping will bend "with a bubble"?

05.10.2010, 10:11

6-meter I-beam 20B1 - two pieces across the length, it turned out 3 zones, two with the support of the beams of one side on the wall, and the second on the I-beam, and one zone with the beams sandwiched between the I-beams. I did not notice the flexing, the I-beam does not walk at such a length.

06.10.2010, 13:06

06.10.2010, 13:47

depending on how to load, if, according to theory, 400 kg / m, then in your case 20B1 will bend by 77 mm

I wonder how you calculated it?

The possibility of unsupported overlap of large areas significantly expands the architectural possibilities when designing a house. A positive solution to the beam question allows you to “play” with the volume of rooms, install panoramic windows, and build large halls. But if it is not difficult to block a distance of 3-4 meters with a "tree", 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 log house, and the floor is shaking, bending, the "trampoline" effect has appeared; we want to make wooden floor beams of 7 meters; you need to overlap a room with a length of 6, 8 meters so as not to rest the logs on intermediate supports; what should be the floor beam for a span of 6 meters, a house from a bar; what if you want to make a free layout - such questions are often asked by members of the forum.

Maxinova FORUMHOUSE user

My house is about 10x10 meters. On the ceiling, I "threw" wooden logs, their length - 5 meters, section - 200x50. The distance between the lags is 60 cm. During the operation of the floor, it turned out that when children are running in one room and you are standing in another, there is a fairly strong vibration on the floor.

And this case is far from the only one.

elena555 FORUMHOUSE user

I can't figure out what kind of beams are needed for the floors. I have a house of 12x12 meters, 2-storey. The first floor is made of aerated concrete, the second floor is attic, wooden, covered with a 6000x150x200mm beam, 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 a shaking sound.

Beams on 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 kind of load can withstand wooden log of one or another section. And then think over, having determined the load for the floor beams, which rough and final floor covering will need to be done; how the ceiling will be hemmed; whether the floor will be a full-fledged living space or a non-residential attic above the garage.

Leo060147 FORUMHOUSE user

1. Dead weight of all structural elements overlap. This includes the weight of beams, insulation, fasteners, flooring, ceiling, etc.
2. Operational load. The service 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 with the arrival of guests, noisy celebrations, rearrangement of furniture, if it is moved away from the walls to the center of the room.

Therefore, when calculating the operational load, it is necessary to think over everything - down to what kind of furniture you plan to install, and whether there is a possibility in the future of installing a sports simulator, which also weighs more than one kilogram.

For the load acting on wooden floor beams of great length, the following values ​​are taken (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 it is planned to store things, materials and other household items in the attic, then the load is assumed to be 250 kg / sq.m.

• For intermediate floors and floors attic floor the total load is taken at the rate of 350-400 kg / sq.m.

Overlapping boards 200 to 50 and other running sizes

These are the beams on a span of 4 meters are allowed by the standards.

Most often during construction wooden floors boards and beams of the so-called running dimensions are used: 50x150, 50x200, 100x150, etc. Such beams meet the standards ( after checkout), if it is planned to block the opening of no more than four meters.

For an overlap with a length of 6 meters or more, the sizes 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 running dimensions.

The rule should be remembered: the strength and stiffness of the floor in to a greater extent depend 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 safety and allowable deflection. This ensures normal and safe operation overlap.

50x200 - overlap for an opening of 4 and 5 meters.

To calculate the load that the floor will withstand, you must have the appropriate knowledge. In order not to delve into the formulas of resistance (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 FORUMHOUSE user

A self-builder is most often not a professional designer. All he wants to know is what beams need to be mounted in the floor so that it meets the basic requirements for strength and reliability. This is what online calculators allow to calculate.

These calculators are easy to use. To make the calculations for the required values, it is enough to enter the dimensions of the lag and the length of the span, which they should overlap.

Also, to simplify the task, you can use ready-made tables presented by the guru of our forum with the nickname Roracotta.

Roracotta FORUMHOUSE user

I spent several evenings to make tables that even a novice builder would understand:

Table 1. It presents data that meet the minimum load requirements for the floors of the second floor - 147kg / sq.m.

Note: since the tables are based on American standards, and the sizes of lumber overseas differ somewhat from the sections adopted in our country, you need to use the column highlighted in yellow in the calculations.

Table 2. Here are the data on the average load for the floors of the first and second floors - 293 kg / sq. M.

Table 3. Here are 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 FORUMHOUSE user

You can change the stiffness and strength of the lag upward by increasing its height and making "shelves". That is, a wooden I-beam is made.

Self-made wooden glued beams

One of the solutions for bridging long spans is the use of wooden beams in the floors. Consider a span of 6 meters - which beams can withstand the heavy load.

By the type of cross-section, a long beam can be:

• rectangular;
• I-beam;
• box-shaped.

There is no consensus among self-builders which section is better. If you do not take into account purchased products (prefabricated I-beams), then the first place comes out the ease of manufacture in " field conditions", Without the use of expensive equipment and accessories.

Just grandfather FORUMHOUSE user

If you look at the 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 accounts for no more than 10-15% of the metal. This is done by calculation.

Which board to use for beams

According to the strength of materials: the larger the cross-section of the "shelves" and the further they are spaced from each other in height, the more loads the I-beam will withstand. For self-builder optimal technology making an I-beam is a simple box-shaped structure, where the upper and lower "shelves" are made of a plank laid flat. (50x150mm, and the side walls are 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 (only not black, they do not work for cutting) and must be set 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 heavy load. Additionally, an I-beam for a 6 meter ceiling can be installed 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 the edge (take boards in 150x50 or 200x50), as a result, the cross-section of the beam will be 300x100 or 400x100 mm. Boards are planted on glue and pulled together with pins or planted on wood grouses / dowels. Plywood can also be screwed or nailed to the side surfaces of such a beam, having previously greased it with glue.

Also interesting is the experience of a forum member under the nickname Taras174, who decided to independently make a glued I-beam to cover the span of 8 meters.

For this, the member of the forum purchased sheets of OSB 12 mm thick, cut them lengthwise into five equal parts. Then I bought a board 150x50 mm, 8 meters long. Milling cutter " dovetail"I chose a groove in the middle of the board, 12 mm deep and 14 mm wide, so that a trapezoid with a downward extension was obtained. OSB in grooves Taras174 pasted with polyester resin(epoxy), after "shooting" with a stapler to the end of the plate a strip of fiberglass 5 mm wide. This, according to the forum member, would strengthen the design. To speed up drying, the glued area was heated with a heater.

Taras174 FORUMHOUSE user

On the first beam, I practiced “getting my hand in”. I made the second one in 1 working day. At cost, taking into account all materials, I include solid board 8 meters, the cost of the beam is 2000 rubles. for 1 pc.

Despite the positive experience, such a "squatter" has not escaped several critical remarks expressed by our experts. Namely.

appointed after meeting a number of requirements. So 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.
Stricter requirements apply to the removal of load-bearing formwork reinforced concrete structures, which is allowed to be removed only after the concrete reaches the strength value from the design:

• load-bearing structural elements with a span of up to 2 m - 50%;


• load-bearing structures of beams, girders, girders, 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%.

Roughly, we can assume that after 3 days concrete on Portland cement will gain strength of about 30%, after 7 days - about 60% and after 14 days - about 80% in relation to the 28-day strength. However, concrete hardening continues after the onset of 28 days of age. So by 90 days of hardening, concrete can gain an additional 30-35% strength.
Standard conditions for concrete hardening are considered: 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 process of concrete hardening is either slowed down or accelerated. For example, at a temperature of 10ºC after 7 days, concrete will gain strength 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 concretes without special additives do not gain strength at all. Therefore, the decision on stripping and loading the structure should be applied after concrete strength tests have been carried out.
The timing of the concrete reaching the specified strength is established by the construction laboratory based on the test results of control samples or methods non-destructive testing... At facilities with a total volume of work 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 manufacturer's laboratory. concrete mix 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 to monolithic joints of prefabricated structures.
Of course, when building suburban residential buildings, concrete strength measurements are usually not taken, since most construction firms there are simply no construction laboratories working in the private housing sector. Therefore, in this case, you will have to focus on the data of the laboratory of the manufacturer of the concrete mixture. Additionally, you can conduct your own concrete strength test. To do this, take a metal ball with a diameter of at least 20 mm and throw it from the same height onto concrete surface: control and test. By the height of the ball's rebound, it will be possible, I will make a reservation right away - with a big stretch, to determine whether the concrete strength has reached the required value.
The full design load in a demoulding reinforced concrete structure can be allowed only after the concrete has acquired its design strength.
A metal floor beam in the form of an I-profile - has a number of undeniable advantages... So a metal I-beam can be overlapped 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 when exposed to aggressive environment can corrode and therefore requires a protective coating.
In most cases, in private housing construction, a metal beam has articulated supports - its ends are not rigidly fixed, for example, since in a frame steel structure... The load on a floor with steel I-beams, taking into account its own weight, should be calculated without a screed in the amount of 350 kg / m 2 and 500 kg / m 2 with a screed.
It is recommended to make the spacing between the I-beams equal to 1000 mm, however, in order to save money, the spacing between the metal beams can be increased to 1200 mm.
The table below shows the choice of the number of the I-beam metal beam for different spacing and length of the purlins.

Span3 m			Span4 m			Span6 m
No. of I-beam at a step			No. of I-beam at a step			No. of I-beam at a step

As can be seen from the table at total load 500 kg / m 2 and a span length of 6 m, you should have chosen a higher number of I-beams, and choose a smaller step for installing the beams.

Added: 2012-05-26 08:21

Discussion on the forum:

We have filled the overlap 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 the bottom between them from the reinforcement No. 12 mesh is connected cell 20 on top of the 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 release?