Wooden floor beams with a span of 6 meters. Calculation and design of floors on wooden beams

In this article, we will discuss how to perform a floor calculation on wooden beams. We will not consider the fastening of logs (wooden beams) in this article, but will focus on the calculation.

Let's look at the types of floor construction for lags (wooden beams).

Ceiling above the plinth

Overlapping the basement with wooden beams is as follows

Because in this case, it is not possible to carry out work under the floor, then in order to lay the subfloor to the logs on the sides, a cranial bar with a section of 40x40 or 50x50 mm is nailed.

A waterproofing vapor-permeable membrane is laid on the subfloor. It should be noted that the membrane must be vapor-permeable (vapor barrier cannot be laid on both sides of the insulation), otherwise the moisture inside the floor will not be able to ventilate.

Next, the heater is installed. As a heater glass wool or mineral wool from basalt fiber is used. The thickness of the insulation is selected according to the heat engineering calculation, depending on the region of construction. At the same time, it should not be much less than the height of the lag, so that the vapor barrier has a slight sag. Therefore, if it is required to lay insulation with a thickness of 150 mm, then the log must have a height of at least 200 mm.

A vapor barrier is laid on top of the insulation.

Next comes the flooring. The floor covering can be boards laid on logs; or carpet / linoleum laid on OSB sheets. In the case of laying tiles, it is recommended to lay another layer of DSP boards for rigidity.

Overlapping between floors

One of the options for overlapping on wooden beams between floors is presented below:

Interfloor overlap is finished on 2 sides. From below, directly on the logs or through a wooden crate, a plasterboard sheet is fixed, which is subsequently painted. The crate has a pitch of 400 mm and is made of a bar with a section of 40x40 or 50x50 mm.

A vapor barrier film is fixed between the crate and the floor beams.

The step and section of wooden beams is selected according to the calculation.

Mineral wool made of basalt or glass wool is laid between the beams, but it serves here not as thermal insulation, but as sound insulation. The thickness must be at least 100 mm.

On top of the floor beams, an OSB sheet is attached, the thickness of which is selected based on the step of the beams. To prevent floor creaking in case of small deformations, a rubber-cork substrate is laid between the OSB plate and the floor beam.

Above is the floor structure.

Ceiling between floors (soundproof)

To improve the soundproofing ability of the floor, the following floor design is used:

In this type of ceiling, the floor of the upper floor rests on its own beam, and the ceiling of the lower floor is suspended from its own. Thus it is possible to reduce noise very well.

Boarding or slab selectionOSB for floor

The thickness of the floor board is selected based on the lag step according to the following table:

The thickness of the OSB board is selected based on the lag step according to the following table:

Calculation of wooden beams

We begin the calculation of the beam structure with the collection of loads. Take, for example, the construction of an interfloor overlap. There are 2 types of loads acting on the floor: constant loads from the weight of the structure itself and useful temporary long-term load (weight of people, furniture, etc.).

Also, loads are standard and calculated. Design loads are taken into account in the calculation for the 1st limit state (strength). Normative loads are taken into account when calculating the 2nd limit state (deformations). The transfer of loads from normative to calculated ones is carried out by multiplying them by the load reliability factor. Next, we will consider these loads.

The calculation is carried out by the selection method, i.e. before starting the calculation, we assign the beam section and its step, and then check its load-bearing capacity.

I would recommend taking the step of the beams equally in such a way that the insulation clearly fits between the beams without trimming - this will save on mineral wool. there will be less waste for trimming and it will be more convenient to mount the beams. Mineral wool has a width of 500 or 600 mm. For example, let's take mineral wool 500 mm wide, and let's take the thickness of the board 50 mm, i.e. the step between the beams will be 500 + 50 = 550 mm.

The design scheme for the beams is adopted as a single-span i.e. beams rest on the walls with 2 ends, while there are no intermediate supports.

Calculation of permanent loads

Permanent loads include the weight of the floor. We collect the weight of all the components of the overlap, and then combine them in a table. We calculate the load for 1 r.m. beams with a section of 50x250 with a step of 550 mm with a span of 5 m.

1. Beam weight. To calculate the weight of the beam, first assign its cross section. For example, we take the cross section of the beam 50x250. The volume of wood per 1 m.p. beams will be V \u003d 1 * 0.25 * 0.05 \u003d 0.0125 m 3. The density of the tree is different for different species and humidity. For the calculation, let's take a pine board, the density for it at a humidity of 20% is 520 kg / m 3. Thus, the weight of the board is q=0.0125*520=6.5kg/m.p.
2. Lattice weight. lathing pitch 400 mm, section 50x50 mm. The crate gives a point load, but with an equal step, so it can be taken as evenly distributed. The lathing is transverse to the beam and the weight transferred to the beam depends on the pitch of the beams themselves. With a beam spacing of 550 mm, the volume of the lathing tree is V=0.55*0.05*0.05=0.001375 m 3 . The weight of one lath of the crate F=0.001375*520=0.715 kg. The step of the crate is 0.4m, so the uniformly distributed load from the weight of the crate is q=0.715/0.4=1.7875kg/m.p.
3. The weight of the vapor barrier is not taken into account.
4. The weight of a drywall sheet with a thickness of 9.5 mm is 9.5 kg / m 2. With a beam spacing of 550 mm, the load on the beam from the weight of the drywall: q=9.5*0.55=5.225kg/m.p.
5. Mineral wool weight. For the calculation, we take the thickness of mineral wool 150 mm. Density of mineral wool is 50 kg/m 3 . The weight of mineral wool with a beam spacing of 550 mm and a beam width of 50 mm will be equal to: q=50*0.15*(0.55-0.05)=3.75kg/m.p.
6. OSB sheet weight on the floor. To calculate the weight of OSB, we determine its thickness - for a step between beams of 550 mm, this will be a sheet with a thickness of 18 mm. Weight 1 m 2 according to the manufacturer 11.7 kg / m 2. With a step between the beams of 550 mm, the load from the OSB weight will be equal to q=11.7*0.55=6.435kg/r.m.
7. floor covering weight. Different coatings can be laid on wooden beams, even ceramic tiles, but the cake will be different, the loads will be different, and this must be taken into account at the beam calculation stage. The easiest will be carpet or laminate flooring. The heaviest of all will be ceramic tiles. Accordingly, you can change the pitch or section of the beams depending on the weight of the coating.

For carpet there is no need to arrange something additionally, so the weight of the floor covering will be equal to the weight of the carpet 0.6-1.2 kg / m 2.

Before laying the laminate, it is required to additionally lay the DSP or OSB board with a thickness of 12 mm, the weight, taking into account the laminate, will be 16.2+7=23.2 kg/m 2 .

To lay the tiles, you will need to lay a layer of waterproofing, make a reinforced screed with a thickness of at least 5 cm and lay tiles on the screed. The total weight of the cake will be about 140-150 kg/m 2 .

As you can see, the spread is too large to accept any of the options as the main one. For example, let's make a calculation when laying a floor with a laminate. With a beam spacing of 600 mm, the load on the beam will be q=23.2*0.55=12.76 kg/r.m.

Payload calculation

The payload is accepted based on the purpose of the premises according to Table 8.3 of SP 20.13330.2016:

Table 8.3 SP 20.13330.2016

With a beam spacing of 600 mm, the load on the beam from the payload will be 150 * 0.55 = 82.5 kg / r.m.

Collection of loads:

Above, we calculated the standard loads. To convert the loads into calculated ones, they must be multiplied by the load safety factor in accordance with SP 20.13330.2016. For wooden structures, the load safety factor is γ=1.1, for insulating and finishing materials, including mineral wool and slabs, γ=1.3 (Table 7.1 of SP 20.13330.2016), for a uniformly distributed (useful) load safety factor is γ =1.3 (clause 8.2.2 of SP 20.13330.2016). The collection of loads is reflected in the following table:

Calculation for the 1st limit state (for bending)

Calculation for the 1st limit state (calculation for structural strength), while ensuring against loss of stability, is carried out according to the design loads in accordance with formulas 23 and 24 of SP 64.13330.2017 Wooden structures. The stability of the beams is ensured by fixing the OSB board on top (it is imperative to fix the OSB sheet on top, which will secure the beams from transverse displacement). If the beams are not fixed, then the beam is checked according to formula 30 of SP 64.13330.2017.

Verification of bending elements (beams) is carried out according to the formula 23 SP 64.13330.2017:

where M is the maximum bending moment acting on the beam

Wcalc - the calculated moment of resistance of the cross section

W calc - the calculated moment of resistance of the cross section

R and - design resistance to bending

Calculation of the maximum bending moment:

For a single-span beam with a uniformly distributed load, the bending moment diagram will be as follows:

The maximum bending moment is:

M max \u003d ql 2 / 8 \u003d 153 * 5 2 / 8 \u003d 478 kg * m

The design modulus of the cross section for a rectangular section is calculated by the formula:

W \u003d b * h 2 / 6 \u003d 0.05 * 0.25 2 / 6 \u003d 0.0005208 m 3

where b=0.05m is the width of the beam, h=0.25m is the height of the beam in meters.

The calculated bending resistance of wood is determined by formula 1 of SP 64.13330.2017. Read more about how to determine the design resistance for wooden structures. In our case, R and \u003d 10.017 MPa

We check the beam according to the formula 23 SP 64.13330.2017:

M=478 kg*m=4.78 kN*m

W \u003d b * h 2 / 6 \u003d 0.05 * 0.25 2 / 6 \u003d 0.0005208 m 3

M / W \u003d 4.78 / 0.0005208 \u003d 9179 kPa \u003d 9.2 MPa, which is less than the maximum allowable 10.017 MPa

Thus, the beam section satisfies the conditions of bending strength.

Calculation for the 1st limit state (for shearing)

The checking of bending elements for shearing is carried out according to the formula 24 of SP 64.13330.2017:

where Q is the calculated transverse force, determined from the beam stress diagram (see below);

S' br - gross static moment of the shifted part of the cross-section of the element relative to the neutral axis, which is equal to the product of the area of ​​the shifted part and the distance from the center of gravity of the shifted part to the neutral axis;

I br - gross moment of inertia of the cross section of the element relative to the neutral axis;

b race - the calculated width of the section of the element (for our example, b race \u003d 0.05 m);

R CK is the design resistance to shearing in bending, determined by formula 1 of SP 64.13330.2017 (see the article Determination of design resistance). In our case, R CK = 1.28 MPa

For a single-span beam with a uniformly distributed load, the diagram of the transverse force is shown above. The maximum transverse force is:

Q=ql/2=153*5/2=382.5kg

where q is the calculated uniformly distributed load on the beam (see load collection);

l is the beam span length (in our example l=5m).

For a rectangular section, the gross static moment of the shifted part of the cross section of the element relative to the neutral axis is:

S’ br \u003d bh² / 8 \u003d 0.05 * 0.25² / 8 \u003d 0.00039 m 3

The moment of inertia of the gross section of the element about the neutral axis for a rectangular section is:

I br=bh 3 /12=0.05*0.253/12=0.0000651 m 4

Calculation for the 2nd limit state (by deformations)

The maximum allowable deflection for the beam according to line 2. Tables E.1 of SP 64.20.13330.2016.

Maximum vertical deflection for beams length:

In our case, at l=5 m, the maximum deflection is f=l/200=5000/200=25 mm

Deflection for a hinged beam loaded with a uniformly distributed load, the maximum vertical deflection is calculated by the formula:

l is the span length;

E is the modulus of elasticity of wood, equal to 10 GPa (for pine of the 1st grade);

I x - moment of inertia of the cross section, for a rectangular section is:

I X=bh 3 /12=0.05*0.253/12=0.0000651 m 4

In our example, the calculation will be as follows:

Wooden floors have the effect of "trampoline" i.e. the floor seems to be springy, but the deformations are still within the normal range. However, if you want to reduce deformations, then you can do this by increasing the section modulus I x . The greatest contribution to it is made by the height of the section, therefore, when selecting beams, it is necessary first of all to try to choose a beam of the greatest height.

The selection of beams is easier to perform in

For the convenience of selecting beams, I made a table for selecting floor beams from pine of the 1st grade, when installing a floor covering from a laminate:

To block a span of more than 6 meters, you need to use special beams produced by factories, for example, I-beams, which have a large sectional height.

One of the most popular solutions for the construction of interfloor floors in private houses is the use of a supporting structure made of wooden beams. It must withstand the design loads without bending and, moreover, without collapsing. Before proceeding with the construction of the ceiling, we recommend using our online calculator and calculating the main parameters of the beam structure.

Wood has always been and will remain for a long time one of the most popular materials for arranging all kinds of load-bearing and load-bearing elements, roof frames, ceilings, partitions in an ordinary low-rise building. Instead of using expensive and very heavy concrete slabs or I-beams, you can make a wooden floor between floors without the involvement of construction equipment, relatively quickly and at minimal cost.

Typical design of the ceiling on beam supports

The arrangement of wooden floors between floors usually differs from the design of the ceiling in a number of ways, primarily in the way the wooden beams are laid and in thickness. If, when arranging the ceiling, wooden load-bearing elements most often rely on walls or a specially formed concrete belt, then the ceiling between floors has to be cut into the walls of the box. Accordingly, the requirements for the strength of the beams and the thickness of the ceiling between floors are much more stringent than for the ceiling.

Structurally, a wooden floor is assembled from the following parts:

• Supporting wooden beams that take the weight of all structural elements, a lot of furniture, household appliances, people - everything that is on the floor above;
• Sheathing with plywood or OSB boards of the ceiling surface;
• Log system with floor boards of the upper floor;
• Thermal insulation mats or slabs laid on a wooden crate;
• A waterproofing film against moisture leakage from the floor on the floor above and a vapor barrier is required to prevent the penetration of water vapor into the wooden floor elements from the lower floor.

The arrangement of wooden floors between floors largely resembles the roofing pie of a conventional gable roof, but there is one feature. If the rafters have at least one attachment point on the hinge, then the wooden floor beams between the floors most often have to be laid in a free-sliding pattern, without fixing at the support points. Provided that the distance between the walls is not more than 3 m.

Such schemes are used in houses with brick and concrete walls, where the rigidity of the box allows the use of self-aligning wooden floors. What does it give? Regardless of the settlement of the building and the pressure on the floor of the upper floor, the floor plane will remain in the same position.

If the length of the wooden floor beams exceeds 4.5 m, or the walls of the house are made of weak materials, for example, aerated concrete blocks, foam concrete, wood concrete, the load-bearing floors between floors must be strengthened with additional corners, anchors, struts and pin embeds.

Varieties of structures and materials of wood flooring

The main element of the floor between the floors are load-bearing beams. The strength of the floor and the safety of the owners themselves depend on how correctly the materials for the manufacture of the wooden “pie” between the floors are selected. The thickness of the cake is always limited, so you either have to increase the number of load-bearing elements or change the material.

Traditionally, the following materials are used as load-bearing elements:

• Glued timber;
• Sawn log;
• A package of sanded and knocked down boards.

It is clear that the best option will be the most expensive. The use of glued laminated timber for overlapping between floors makes it possible to make the wooden frame as rigid as possible, therefore, they resort to timber puffing either at the request of the owners, or with very large sizes of the premises of the upper floor. Most often, glued laminated timber is laid in a wooden floor with a distance between the walls of 4 m. It turns out expensive, but reliable.

A more economical way is to use coniferous lumber, usually a barked pine log is cut with disc cutters into a two-edged or three-edged timber. Such a beam is stronger and cheaper than a conventional rectangular wooden beam.

The most budget option is a package beam. It is knocked down from a calibrated and polished forty board, two or three per beam. Before assembly, the wooden surface is treated with impregnation, dried and painted over with drying oil. Overlapping from a package bar is considered the most flexible and at the same time the most reliable.

Even if an overload occurs, the wooden elements will bend, but there will be no break and collapse between floors. It is much easier and cheaper to assemble such a wooden floor between floors with your own hands, since there is no need to purchase drill or glued beams.

To reduce the complexity of the work and the cost, taking into account the design of the house and the width of the walls, several design options are made, depending on how it is planned to lay the floor of the second floor along wooden beams:

• Lightweight covers. For frame houses, the step between the supporting elements can be reduced to 30 cm, and the logs under the wooden floor are not laid. The structure itself is assembled without insulation and film insulation;
• Middle floors on the floors. The design uses logs and sound insulation, vapor barrier film and insulation are not used;
• Warm medium wooden floors. A full-fledged package with insulation and film hydro- and vapor barrier is laid between the floors.

Light ceilings on floors are used for unheated buildings, medium systems are used for buildings with powerful external wall insulation. Warm wooden structures are used if the top floor borders on an attic or attic.

From practice it is known that for wooden structures the best sound insulation between floors is provided by sheet and fiber materials. You can use mineral wool or bulk expanded clay granulate. But both materials are highly absorbent, so you have to lay a vapor barrier film. Expanded polystyrene is not afraid of moisture, but the sound insulation on the floor is about 3-4 times worse than mineral. Therefore, XPS or foam plastic is used where the sound insulation of a wooden floor between floors is not of particular importance. For example, between the basement and first floors.

Ways to terminate load-bearing elements

In order for the wooden flooring on the floors to turn out to be reliable and stable, it is necessary to choose the right way to embed the load-bearing beam into the walls of the house. The fastening system is chosen depending on the material of the walls.

The easiest way is to fix the beam on brick walls. For each support in the wall, a niche is cut out according to the marking, at least 100 mm deep and 15-20 mm larger than the beam section. A lining of hard rubber is placed in the niche, and the ends of the timber must be covered with liquid rubber or hot resin before assembling the wooden frame. If the beam is more than 4.5 m, one end is fixed with a through metal stud. The remaining space of the niche is blown out with mounting foam so that there is no draft in the cracks on the floors.

More difficult is the fastening of supports on the walls of aerated concrete. Before you make a wooden floor between floors, you will need to build a carrier box, in which the timber is laid. For a building made of aerated concrete on two floors, with brick walls, it is allowed to lay a wooden box, in other cases, the supporting box must be cast from reinforced concrete.

If the beam is planned to be cut into wooden walls, then this is best done at the stage of laying the crowns. As in the case of brick walls, a niche in the form of a truncated dovetail wedge is cut out in the wall beam according to the marking. The end of the carrier beam is adjusted to the shape of the castle and placed in a niche. After laying the beam, the docking point is reinforced with metal plates and corners.

We assemble the ceiling on the floors with our own hands

After the required wall height has been reached to the level of the next floor, it is necessary to make an overlap. The next row of brick or block is laid out with niches for timber. To ensure the necessary strength of the wooden frame, you need to make a verification calculation or select the cross section of the beam according to the reference tables and nomograms.

Approximately for a two-meter span, it will be enough to use a beam support with a section of 75x150 mm; for a five-meter span, the beam section should be at least 150x225 mm. The standard step is 80-90 cm, but sometimes its value is deliberately reduced in order to increase the rigidity of the lower floor box.

Laying load-bearing elements of a wooden span

At the time of assembling the frame of the span on the floor, the wooden beams must be completely ready for work, but without applying resin to the supporting ends. With a beam length of 3-4 m, it is difficult to accurately guess the length of the beam, so the wooden blanks are raised to the level of the upper floor and sequentially adjusted to the linear dimensions of the landing nests.

If the measurement of the distance between the niches corresponds to the length of the workpiece, proceed to assembly:

• Both ends are cut at an angle of 60 ° to facilitate the laying of the supporting ends in niches, and treated with tar or bituminous mastic;
• Lining material is laid in niches, after which wooden floor beams are installed.

Each beam must be carefully adjusted along the horizon and along the general plane; for this, the linings are replaced with thicker dies or cut them to lower the end. The remaining space is clogged with tarred tow and blown with foam.

Note! To simplify the work, the two extreme beams of the wooden span are initially laid and exposed, and the remaining workpieces are adjusted using cords or a laser level.

Assembly of the crate

After the wooden load-bearing beams have been laid and fixed in the niches, it is necessary to perform the stuffing of the cranial bar. In fact, this is a long rail, with a section of at least 40x40 mm, the cranial rail is stuffed onto the side surfaces of the beam flush with the bottom edge. The bottom padding will be attached to the cranial bar with sheets of plywood or OSB. If the plywood is nailed directly to the beam, this can weaken the load-bearing beam. In addition, when walking on the floor of the upper floor, the nails and fasteners driven into the wooden beam of the ceiling come out of the body of the wood, so it is necessary to strengthen the fastening of the padding.

At the same time, a vapor barrier film is sewn under the plywood, each new sheet of film must be glued with construction tape, otherwise the condensate will rot the wooden floors on the second floor. If the upper floor is unheated, then it is necessary to make vents in the ceiling structure that remove part of the condensate that has got inside.

After the padding has been laid, you can proceed to the insulation and soundproofing. Often, instead of mineral wool or slab polystyrene foam, a special filler made of polystyrene granules is poured into niches. In order to create a zone of silence on the floor, it is enough to fill the floor with a layer only 40 mm thick. That is, the interfloor overlap can be reduced by almost 50-60 mm.

Final operations

This is followed by the laying of waterproofing, the film must be laid without fail if the higher floor is intended for living or there is no floor ventilation system in it. Even if the wooden floors are not flooded with water, when airing out, the colder air will collect condensation inside the wooden floor. You can lay a regular plastic film with a thickness of 0.2 mm.

All other details of the floor depend on the way the floor is arranged on the top floor. If you plan to lay laminate or parquet, it is best to lay a layer of OSB or moisture-resistant drywall. If an ordinary wooden floor is planned on the second floor, then it will be enough to fill the logs and sew up the surface with a grooved board.

Conclusion

In special cases, a cement-sand screed can be provided in the floor structure. To do this, two layers of fiberglass reinforcing mesh are laid on top of the insulation and waterproofing. The thickness of the screed should be no more than 50 mm. Under such a base on a wooden floor, you can lay self-leveling or decorative 3D coatings.

The possibility of unsupported overlapping of large areas greatly expands the 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 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

They made a wooden floor in a log house, and the floor is shaking, bending, the effect of a “trampoline” has appeared; we want to make wooden floor beams of 7 meters; you need to block the 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 made of timber; what to do 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. I “threw” wooden logs onto the ceiling, their length is 5 meters, the section is 200x50. The distance between the lags is 60 cm. During the operation of the floor, it turned out that when children run in one room and you stand in another, there is quite a strong vibration on the floor.

And this case is far from the only one.

elena555 FORUMHOUSE User

I can’t figure out which beams for interfloor ceilings are needed. My house is 12x12 meters, 2-storey. The first floor is made of aerated concrete, the second floor is attic, wooden, covered with a bar 6000x150x200mm, laid every 80 cm. 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, it is necessary to understand what kind of load a wooden log of one or another section can withstand. And then think over, having determined the load for the floor beam, what kind of rough and finish flooring will need to be done; what will the ceiling be hemmed with; whether the floor will be a full-fledged living space or a non-residential attic above the garage.

Leo060147 FORUMHOUSE User

1. The load from the own weight of all structural elements of the floor. This includes the weight of beams, insulation, fasteners, flooring, ceiling, etc.
2. 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 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 through everything - up to what kind of furniture is planned to be installed, and whether there is a possibility of installing a sports simulator in the future, which also weighs far more than one kilogram.

For the load acting on wooden beams of a long floor, the following values ​​\u200b\u200bare 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 - this is the load from the floor's own weight, and 100 kg / sq.m - 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 interfloor floors and ceilings of the attic floor, the total load is taken at the rate of 350-400 kg / sq.m.

Overlapping boards 200 by 50 and other running sizes

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

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 satisfy the standards ( after calculation), if it is planned to block the opening no more than four meters.

For overlapping with a length of 6 meters or more, 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 running sizes.

You should remember the rule: the strength and rigidity of the floor 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 strength and allowable deflection. This ensures normal and safe operation of the ceiling.

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

To calculate the load that the overlap will withstand, you must have the appropriate knowledge. In order not to delve into the strength of materials formulas (and this is definitely redundant when building a garage), it is enough for an ordinary developer 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 which beams need to be installed 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 necessary values, it is enough to enter the dimensions of the lag and the length of the span, which they must cover.

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

Roracotta FORUMHOUSE User

I spent several evenings to make tables that even a novice builder will 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 dimensions of lumber overseas are somewhat different from the sections adopted in our country, the column highlighted in yellow should be used 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 length of the span, 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 upwards by increasing its height and making “shelves”. That is, a wooden I-beam is being made.

Independent production of a wooden glued beam

One solution for long span spans is the use of timber beams in the spans. Consider a span of 6 meters - which beams can withstand a large 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 which section is better. If you do not take into account purchased products (prefabricated I-beams), then the simplicity of manufacturing in the "field conditions" comes first, without the use of expensive equipment and tooling.

Just Grandpa FORUMHOUSE User

If you look at the cross section of any metal I-beam, you can see that from 85% to 90% of the mass of the metal is concentrated in the "shelves". The bonding wall accounts for no more than 10-15% of the metal. This is done on the basis of calculation.

What board to use for beams

According to the strength of materials: the larger the section of the “shelves” and the further they are spaced from each other in height, the greater the load the I-beam will withstand. For a self-builder, the optimal technology for manufacturing an I-beam is a simple box-shaped design, where the upper and lower "shelves" are made of a board 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 cut) and must be glued.

If you install such an I-beam on a six-meter span in increments of 60 cm, then it will withstand a large load. Additionally, an I-beam for a ceiling of 6 meters can be laid with a heater.

Also, using a similar principle, you can connect two long boards, collecting them into a “package”, and then put them on top of each other on an edge (take boards at 150x50 or 200x50), as a result, the beam section will be 300x100 or 400x100 mm. The boards are planted on glue and pulled together with studs or planted on capercaillie / 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 independently make a glued I-beam to block a span of 8 meters.

For this, the forum member purchased OSB sheets 12 mm thick, cut them lengthwise into five equal parts. Then I bought a board 150x50 mm, 8 meters long. With a dovetail cutter, I chose a groove in the middle of the board with a depth of 12 mm and a width of 14 mm - so that a trapezoid with an extension downwards was obtained. OSB in grooves Taras174 glued with the help of polyester resin (epoxy), having previously “shooted” a strip of fiberglass 5 mm wide to the end of the plate with a stapler. 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 trained "filled my hand." The second one was done in 1 business day. At a cost, taking into account all materials, I include a solid board of 8 meters, the cost of a beam is 2000 rubles. for 1 piece

Despite the positive experience, such a "squatter" did not escape several criticisms made by our experts. Namely.

If the construction of a two-story or one-story house is planned, but with a basement or attic, it is necessary to correctly calculate and build interfloor ceilings. Consider the stages and nuances of the implementation of the overlap on wooden beams and calculate the sections of the beams that provide sufficient strength.

The device of interfloor ceilings needs special attention, because, made “by eye”, they may not withstand the loads that fall on them and collapse, or require unnecessary, unreasonable costs. Therefore, one or more possible options must be comprehensively considered and calculated. The final decision can be made by comparing the cost or availability of acquiring materials.

Requirements for interfloor ceilings

Interfloor ceilings must withstand constant and variable loads, that is, in addition to their own weight, withstand the weight of furniture and people. They must be sufficiently rigid and not allow the maximum deflection to be exceeded, provide sufficient noise and heat insulation.

Specific loads from furniture and people for living quarters are taken in accordance with the standards. However, if you plan to install something massive, such as a 1000 l aquarium or a natural stone fireplace, this must be taken into account.

The rigidity of the beams is determined by calculation and is expressed in the allowable bending per span. Permissible bending depends on the type of flooring and the flooring material. The main limit deflections determined by SNiP are shown in Table 1.

Table 1

Please note that cracking-prone ceramic tile or concrete screed flooring can further tighten the deflection requirements, especially for sufficiently long spans.

To reduce the loads on the beams, if possible, they should be placed parallel to the short walls, with the same pitch. The maximum span when covered with wooden beams is 6 m.

Types of floors

According to the purpose of the overlap are divided into:

• interfloor;
• attic;
• basement (basement).

The features of their design are in the permissible loads and the device of steam and heat insulation. If the attic is not intended for living or storing massive objects, variable loads can be reduced to 50-100 kg / m 2 when calculating the deflection.

Thermal insulation between two residential floors may seem redundant, but sound insulation is a desirable parameter for the majority, and this is achieved, as a rule, with the same materials. It should be taken into account that attic and basement floors need a thicker layer of thermal insulation material. Film material for vapor barrier in the attic floor should be located under the insulation layer, and in the basement - above it. To prevent the occurrence of dampness and damage to structures by a fungus, all rooms must be equipped with ventilation.

Floor options: 1 - plank shield; 2 - vapor barrier; 3 - thermal insulation; 4 - sparse flooring; 5 - boards; 6 - flooring

The design of the floors can also be different:

• with open and hidden beams;
• with various types of load-bearing beams;
• with different filling and covering materials.

Hidden beams are sewn on both sides and are not visible. Open - protrude from the ceiling and serve as decorative elements.

The figure below shows what the structure of the attic floor can be with a shield roll and with a filing of boards.

a - with a shield roll; b - with filing from boards; 1 - plank floor; 2 - polyethylene film; 3 - insulation; 4 - vapor barrier; 5 - wooden beams; 6 - cranial bars; 7 - shield reel; 8 - finishing; 9 - filing from boards

Types of fastenings and connections of wooden beams

Depending on the design and material of the load-bearing walls, wooden beams are attached:

• in the nests provided in the brick or block masonry, deepening the beam or log at least 150 mm, and the board at least 100 mm;
• on the shelves (ledges) provided in the brick or block masonry. It is used if the wall thickness of the second floor is less than the first one;
• into cut grooves in log walls to a depth of at least 70 mm;
• to the beam of the upper strapping of the frame house;
• to metal supports-brackets fixed on the walls.

1 - support on a brick wall; 2 - solution; 3 - anchor; 4 - roofing felt insulation; 5 - wooden beam; 6 - support on a wooden wall; 7 - bolt

If the length of the beam is not enough, you can lengthen it by connecting (joining) along the length using one of the known methods using wooden pins and wood glue. When choosing the type of connection, be guided by the direction of application of the load. It is desirable to strengthen the spliced ​​beams with metal plates.

a - compression; b - stretching; c - bend

About wooden beams

In construction, beams of rectangular, round or partially round section are used. The most reliable are rectangular lumber, and the rest are used in the absence of timber or for reasons of economy, if such materials are available on the farm. Glued wood materials have even greater strength. Beams made of glued beams or I-beams can be installed on spans up to 12 m.

The most inexpensive and popular type of wood is pine, but other types of conifers are also used - larch, spruce. Floors are made of spruce in summer cottages, small houses. Larch is good for building premises with high humidity (bath, swimming pool in the house).

The materials also differ in grade, which affects the bearing capacity of the beams. Grade 1, 2 and 3 (see GOST 8486-86) are suitable for floor beams, but grade 1 for such a design may be unnecessarily expensive, and grade 3 is best used on small spans.

Calculation of load-bearing beams

To determine the section and step of the beams, it is necessary to calculate the load on the ceiling. The collection of loads is carried out according to the methodology and taking into account the coefficients set forth in SNiP 2.01.07-85 (SP 20.13330.2011).

Load calculation

The total load is calculated by summing the constant and variable loads, determined taking into account the standard coefficients. In practical calculations, they are first set by a certain design, including the preliminary layout of beams of a certain section, and then corrected based on the results obtained. So the first step is to sketch all the layers of the "pie" overlap.

1. Own specific gravity of the overlap

The specific gravity of the floor is the sum of its constituent materials and is divided by the horizontal total length of the floor beams. To calculate the mass of each element, you need to calculate the volume and multiply by the density of the material. To do this, use table 2.

table 2

For wood-based materials and waste, the density depends on the moisture content. The higher the humidity, the heavier the material.

Partitions (walls) also belong to constant loads, the specific weight of which is taken approximately 50 kg / m 2.

The decor of the room, people, animals - all this is a variable load on the floor. According to Table. 8.3 SP 20.13330.2011, for residential premises, the standard distributed load is 150 kg / m 2.

The total load is not determined by simple addition, it is necessary to take the reliability factor, which, according to the same SNiP (clause 8.2.2), is:

• 1.2 - with a specific gravity of less than 200 kg / m 2;
• 1.3 - with a specific gravity of more than 200 kg / m 2.

4. Calculation example

As an example, let's take a room with a length of 5 and a width of 3 m. Every 600 mm of length we put beams (9 pcs.) Of pine with a section of 150x100 mm. We will block the beams with a board 40 mm thick and lay linoleum 5 mm thick. From the side of the first floor, we will sew the beams with plywood 10 mm thick, and inside the ceiling we will lay a layer of mineral wool 120 mm thick. Partitions are absent.

1 - beam; 2 - board; 3 - insulated linoleum 5 mm

The calculation of the constant specific load on the area of ​​​​the room (5 x 3 \u003d 15 m 2) is shown in table 3.

Table 3

Design load on the beam (qр) - 250 x 0.6 m = 150 kg / m (1.5 kg / cm).

Allowable deflection calculation

We accept the permissible deflection of the interfloor ceiling - L / 250, i.e. for a three-meter span, the maximum deflection should not exceed 330 / 250 = 1.32 cm.

Since the beam lies on the support at both ends, the calculation of the maximum deflection is carried out according to the formula:

• h = (5 x qp x L4) / (384 x E x J)

For our example:

• h \u003d (5 x 1.5 x 3304) / (384 x 100000 x 2812.5) \u003d 0.82 cm

The result obtained in comparison with the allowable deflection has a margin of 60%, which seems excessive. Therefore, the distance between the beams can be increased by reducing their number and repeat the calculation.

In conclusion, we suggest watching a video on calculating the floor on wooden beams using a special program: