Covering large spans with wooden beams: glued beams, wooden trusses. Wooden floors Which board to cover a span of 6 meters

appointed after fulfilling a number of requirements. So, removing the side elements of the formwork does not load bearing from the weight of the structures, is allowed only after the concrete has achieved strength that ensures the safety of the surface and edges of the corners.
More stringent requirements are imposed on the removal of load-bearing formwork of reinforced concrete structures, which can be removed only after the concrete reaches the design strength value:

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


• load-bearing structures beams, crossbars, purlins, slabs and vaults with a span of 2-6 m – at least 70%;


• load-bearing structures with a span of more than 6 m – at least 80%;


• load-bearing structures reinforced with load-bearing welded frames - at least 25%.

Approximately, we can assume that after 3 days, Portland cement concrete will gain strength of about 30%, after 7 days - about 60%, and after 14 days - about 80% in relation to 28-day strength. However, concrete hardening continues even after 28 days of age. So, by 90 days of hardening, concrete can gain an additional 30-35% strength.
Standard conditions for concrete hardening are: temperature 20±5ºC ​​and air humidity above
90%. It should be borne in mind that in practice, as a rule, real conditions do not correspond to standard standards, and the concrete hardening process either slows down or accelerates. For example, at a temperature of 10ºC, after 7 days concrete will gain 40-50% strength, and at 5ºC - only 30-35%. If hardened at a temperature of 30-35ºC, concrete will gain 45% strength within 3 days. At negative temperatures Concrete without special additives does not gain strength at all. Therefore, the decision to strip the formwork and load the structure should be made after testing the concrete for strength.
The time frame for concrete to achieve a given strength is established by the construction laboratory based on the results of testing control samples or methods non-destructive testing. At sites with a total volume of work less than 50 m3, receiving ready-mix concrete from factories or installations located at a distance of no more than 20 km, it is allowed to assess the strength of concrete according to the laboratory of the manufacturer concrete mixture without making test samples at the installation site. However, this instruction does not apply to responsible steam rooms and thin-walled structures: beams, columns, floor slabs, as well as monolithic joints of prefabricated structures.
Of course, when constructing suburban residential buildings, concrete strength measurements are usually not taken, since most construction companies There are simply no construction laboratories working in the private housing construction sector. Therefore, in this case, you will have to rely on the laboratory data of the concrete mix manufacturer. Additionally, you can conduct your own concrete strength testing. To do this, you need to take a metal ball with a diameter of at least 20 mm and throw it from the same height to concrete surface: control and subject. Based on the height of the ball’s rebound, it will be possible, I’ll make a reservation right away - with a big stretch, to determine whether the strength of the concrete has reached the required value.
Full design load in stripped form 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-beam has a number of undeniable advantages. So a metal I-beam can cover large spans with a significant load. In addition, the metal steel beam is absolutely non-flammable and resistant to biological influences. However, a metal beam when exposed to aggressive environment may corrode, so a protective coating must be applied to it.
In most cases in private housing construction, a metal beam has hinged supports - its ends are not rigidly fixed, for example, since in a frame steel structure. The load on the floor with steel I-beams, taking into account its own weight, should be calculated without a screed of 350 kg/m2 and 500 kg/m2 with a screed.
It is recommended to make the step between I-beams equal to 1000 mm, however, in order to save money, you can increase the step between the metal beams to 1200 mm.
The table below shows the selection of I-beam number metal beam at different steps and the length of the runs.

Span3 m			Span4 m			Span6 m
I-beam number at step			I-beam number at step			I-beam number at step

As can be seen from the table, with a total load of 500 kg/m2 and a span length of 6 m, you should have chosen an I-beam of a higher number and chosen a smaller beam installation step.

Added: 05/26/2012 08:21

Discussion of the issue on the forum:

We poured the ceiling between the first and second floors along I-beam No. 12, span 6 meters with an outlet 1 meter from the load-bearing wall of the first floor. The distance between the I-beams is 2 meters, from below between them a mesh of cell 20 is connected from reinforcement No. 12, on top of mesh No. 5, cell 10 cm. Question: after how many days can the formwork be removed and after how many days can the walls be laid, including at the outlet?

Among the many structural elements In a private house, the ceiling is one of the most important and difficult components to design and install. This is where inexperienced builders make, perhaps, the most dangerous mistakes, it is about the arrangement of this system that the most questions are asked.

1. Why choose a tree

In any building, the ceiling is a horizontal structure that serves as the basis for creating the floor. In addition, being connected to the load-bearing walls of the house, it provides lateral stability to the structure, evenly distributing possible loads. Therefore, the highest demands are placed on the reliability of this design.

Regardless of what material is used in the construction of a house, wooden floors are most widespread in the private sector. They can often be seen in various stone cottages, and it is quite obvious that in wood construction(logs, beams, frame and frame-panel technology) there is no alternative to such a solution. There are many objective reasons. Let's look at the advantages and disadvantages of wood floors.

In private low-rise construction, floors are installed in several options:

• Ready reinforced concrete slab,
• Monolithic reinforced concrete slab,
• Ready-made reinforced concrete beams,
• Beams and trusses made of rolled metal,
• Flooring made of lumber.

pros

Or why wooden floors are so popular.

• Small mass. When using a board or timber, we do not overload load-bearing walls and foundation. The weight of the ceiling is several times less than that of concrete or metal structures. Usually no technology is required.
• Minimum deadlines for completing work. Minimum labor intensity among all options.
• Versatility. Suitable for any building, in any environment.
• Possibility of installation at sub-zero and very high temperatures.
• No “wet” or dirty processes.
• Possibility of obtaining any level of thermal insulation and sound insulation characteristics.
• Possibility of using cavities for laying utilities (electrical network, heating, water supply, sewerage, low current...).
• Relatively low price of prefabricated frame floor from lumber, both in terms of the cost of parts/components and the contractor’s wages.

Minuses

The disadvantages of a wooden ceiling system made of wood are quite conventional.

• The difficulty of choosing the cross-section of materials and design solutions to ensure the calculated load-bearing capacity.
• The need to carry out additional fire prevention measures, as well as provide protection from moisture and pests (antiseptic treatment).
• The need to purchase soundproofing materials.
• Strict adherence to technology to avoid construction errors.

2. What material to use for assembly

Wooden flooring always consists of beams. But they can be made from a variety of lumber:

• Rounded log up to 30 cm in diameter.
• The beam is four-edged.
• Board large section(thickness from 50 mm, width up to 300 mm).
• Several boards of relatively small thickness, twisted face to face.
• I-beams, the upper and lower chords of which are made of edged planed boards/bars, and the vertical wall is made of OSB-3, plywood or profiled metal (wood-metal product).
• Closed boxes made of sheet materials(plywood, OSB).
• SIP panel. In essence, these are separate sections in which the beams are already sheathed and have an insulator inside.
• Various truss designs, allowing to cover large spans.

The easiest options for installation, as well as the cheapest and most convenient for subsequent operations, are those where the floor beams are made of edged lumber.

Due to the very high requirements for load-bearing capacity, durability and geometric deviations, first-grade lumber must be considered as blanks. It is possible to use products classified as second grade according to GOST, which do not have critical geometric deviations, defects and processing defects that can reduce the strength characteristics and service life of finished parts (through knots, twists, cross-layers, deep extended cracks...).

In these structures, the use of dead wood (dead wood, dead wood, burnt wood) is excluded due to insufficient strength and multiple damage to wood-destroying diseases and insects. It would also be a big mistake to buy a timber or board “with air”, “with Armenian size”, “TU” - due to the underestimated sections.

This should be exclusively healthy material from green spruce or pine, since needles, due to their resin content and solid structure, can withstand bending loads and compression much better than most hardwoods, and having a relatively low specific gravity.

Anyway edged lumber must be freed from remnants of bark and bast fibers, treated with an antiseptic and fire retardant. Dry planed lumber will perform best here, but the material natural humidity(up to 20 percent) during normal processing are also actively (and most importantly - effectively) used, especially since the price edged timber or boards of this type are noticeably lower.

3. How to choose the size of beams and at what step to arrange them

The length of the beam is calculated in such a way that it covers the existing span and has a “margin” to provide support on load-bearing walls (read below for specific figures for permissible spans and wall penetration).

The cross-section of the board/beam is determined depending on the design loads that will be exerted on the floor during the operation of the building. These loads are divided into:

• Permanent.
• Temporary.

Temporary loads in a residential building include the weight of people and animals that can move along the floor, moving objects. Constant loads include the mass of the lumber of the structure itself (beams, joists), floor filling (insulation/noise insulation, insulating sheets), hemming (rolling), rough and finishing flooring, finishing flooring, partitions, as well as built-in communications, furniture, equipment and household items...

Also, you should not lose sight of the possibility of storing objects and materials, for example, when determining the load-bearing capacity of the floors of a non-residential cold attic, where unnecessary, rarely used things can be stored.

As starting point the sum of permanent and temporary loads is taken, and a safety factor of 1.3 is usually applied to it. Exact numbers(including the cross-section of lumber) should be determined by specialists in accordance with the provisions of SNiP 2.01.07-85 “Loads and impacts”, but practice shows that the load values ​​in private houses with wooden beams are approximately identical:

• For interfloor (including under a residential attic) and basement floors, the total load is about 350 - 400 kg/m2, where the share of the structure’s own weight is about 100 kilograms.
• For covering an unloaded attic - about 130 - 150 kg/m2.
• To cover the loaded non-residential attic up to 250 kg/m2.

It is obvious that unconditional safety is of paramount importance. Here a good margin is taken into account and the option is considered not so much of distributed loads on the entire floor (in such quantities they are practically unrealistic), but rather the possibility of a local load that can lead to deflections, which in turn caused:

• physiological discomfort of residents,
• destruction of components and materials,
• loss of aesthetic properties of the structure.

By the way, certain values deflections are allowed regulatory documents. For residential premises, they can be no more than 1/350 of the span length (that is, 10 mm at 3 meters or 20 mm at six meters), but provided that the above limiting requirements are not violated.

When choosing the cross-section of lumber to create a beam, they are usually guided by the ratio of the width and thickness of the beam or board in the range of 1/1.5 - 1/4. Specific figures will depend, first of all, on: loads and span lengths. At independent design You can use data obtained from calculations using online calculators or publicly available tables.

Optimal average cross-section of wooden floor beams, mm

Span 3 mSpan 3.5 mSpan 4 mSpan 4.5 mSpan 5 mSpan 5.5 mSpan 6 m

As we can see, to enlarge load-bearing capacity ceilings - it is enough to choose lumber with a larger width or greater thickness. It is also possible to assemble a beam from two boards, but in such a way that the resulting product has a cross-section no less than the calculated one. It should also be noted that the load-bearing properties and stability of a wooden floor increase if logs or various types of subfloors (sheet flooring made of plywood/OSB or edged boards) are used on top of the beams.

Another way to improve the strength properties of a wooden floor is to reduce the spacing of the beams. Engineers in their projects of private houses determine different conditions the distance between the beams is from 300 mm to one and a half meters. IN frame construction The pitch of the beams is made dependent on the spacing of the posts, so that there is a post under the beam, and not just a horizontal frame run. Practice shows that the most appropriate from the point of view of practicality and cost of construction is a step of 600 or 1000 mm, since it is best suited for the subsequent installation of insulation and noise insulation by surprise ( insulating materials slabs and rolls have just such a form factor). This distance also creates optimal distance between support points for mounting floor joists installed perpendicular to the beams. The dependence of the cross section on the pitch is clearly visible from the numbers in the table.

Possible cross-section of floor beams when changing the pitch (total load on square meter about 400 kg)

4. How to properly install and secure beams

We have decided on the step - from 60 centimeters to a meter will be the golden mean. As for spans, it is best to limit yourself to 6 meters, ideally: four to five meters. Therefore, the designer always tries to “lay” the beams along the smaller side of the house/room. If the spans are too large (more than 6 meters), then they resort to installing load-bearing walls or support columns with crossbars inside the house. This approach makes it possible to use lumber of a smaller cross-section and increase the spacing, thereby reducing the weight of the floor and its cost for the customer with the same (or better) load-bearing characteristics. As an option, trusses are created from lighter lumber using metal perforated fasteners, for example, nail plates.

In any case, the beams are placed strictly horizontally, parallel to each other, maintaining the same pitch. The wooden beam must rest on load-bearing walls and purlins by at least 10 centimeters. As a rule, use 2/3 thickness outer wall from the side of the room (so that the end of the beam does not go out onto the street and remains protected from freezing). IN wooden walls they make a cut, in stone ones they leave openings during laying. In places where the beams of supporting structures touch, it is necessary to lay insulating materials: damping elastic pads made of rubber/felt, several layers of roofing felt as waterproofing, etc. Sometimes they use firing of sections of the beam that are subsequently hidden or coating them with bitumen mastics/primers.

IN Lately Increasingly, special perforated brackets “beam holders/supports” are being used to create floors, which allow the beam to be mounted end-to-end with the wall. With help of this type brackets are also assembled assemblies with transverse crossbars and beams truncated in length (opening for flight of stairs, chimney passage, etc.). The advantages of this solution are obvious:

• The resulting T-shaped connection is very reliable.
• The work is done quickly (there is no need to make cuts, it is much easier to set a single plane).
• No cold bridges are formed along the body of the beams, because the end is moving away from the street.
• It is possible to buy lumber of shorter length, since there is no need to insert the timber/board inside the wall.

In any case, it is very important, after adjusting the lumber to size, to thoroughly antisepticize the end of the beam.

5. What insulating layers should be used inside wooden floors

To answer this question, first of all, it is necessary to divide the overlapping structures (in a year-round habitable house) into three separate types:

• Basement ceiling,
• Interfloor,
• Attic.

In each specific case, the set of pie will be different.

Interfloor ceilings in the vast majority of cases separate rooms in which temperature regime similar or close in value (if there is room/floor/zone adjustment heating system). These also include the attic floor, which separates the residential attic, since this room is heated, and the insulation is located inside roofing pie. For these reasons, thermal insulation is not needed here, but the issue of combating noise, airborne (voices, music...) and shock (steps, rearranging furniture...) becomes very relevant. As sound insulation, acoustic panels are installed in the ceiling cavity. fibrous materials, created on the basis of mineral wool, as well as sheets of soundproofing membranes are laid under the sheathing.

The basement design assumes that under the ceiling there is soil or a basement, cellar, ground floor. Even if the room below is equipped for use, this type of floor requires full insulation, characteristic of the enclosing structures of a particular climate zone and a specific building with its unique thermal balance. According to standards, the average thickness for the Moscow region modern insulation with good thermal conductivity will be about 150-200 mm.

Similar thermal insulation requirements apply to attic floor, above which there is no heated attic, because it will be the main barrier to heat loss through the roof of the building. By the way, due to the greater heat flow through top part at home, the thickness of the insulation here may be required more than in other places, for example, 200 mm instead of 150 or 250 mm instead of 200.

They use polystyrene foam, EPS, mineral wool with a density of 35 kg/m3 in slabs or cut into mats from a roll (one that is allowed for use in non-load-bearing areas is suitable horizontal structures). Thermal insulation is laid between the beams, usually in several layers, with the joints bandaged. The load from the insulation is transferred to the beam through the rough hemming (often it is attached to the beams using cranial bars).

Where wadding insulation/sound insulation is used in structures, it should be protected from moisture. In the basement, moisture can rise in the form of evaporation from the ground or from the basement/cellar. IN interfloor ceilings and attics, water vapor can enter, which always saturates the air in residential premises during human daily activities. In both cases, underneath the insulation you need to lay construction material vapor barrier film, which can be ordinary or reinforced polyethylene. But, if thermal insulation is performed using extruded polystyrene foam, not having any significant level water absorption, then a vapor barrier is not needed.

On top, insulation and fibrous soundproofing materials are protected with waterproof sheets, which can be membranes or non-perforated waterproofing.

A reliable water barrier is especially relevant in rooms with high humidity: kitchen, laundry room, bathroom... In such places it is spread on top of the beams, always with the strips overlapping by 100-150 mm and gluing the seam. The canvases along the entire perimeter of the premises must be placed on the wall - to a height of at least 50 mm above the finishing coating.

The ceiling, which will later be lined tiles, it makes sense to supplement with rough flooring made of waterproof sheet materials - various types cement-containing slabs, preferably tongue-and-groove. On such a continuous flooring you can carry out additional coating waterproofing, perform thin-layer leveling of the plane with a leveling compound or lay the tiles immediately.

You can choose another option - collect from edged boards continuous flooring, lay a hydraulic barrier, pour a thin-layer screed (up to 30 mm), install tiles.

There are also modern adhesive compositions(and elastic grouts) allowing tiling wooden bases, including movable and heated ones. Therefore, tiled floors are often sold here on moisture-resistant plywood or OSB.

Important! Taking into account the increasing loads (general or local - a large bathtub, a Jacuzzi bowl, a floor-standing boiler...), the calculation of the cross-section and pitch of beams under such rooms must be performed individually.

If desired, floors in the bathroom or kitchen wooden house can be equipped with a heating cable or pipes of the water circuit of the heating system. They are mounted both in screeds and a layer of tile adhesive, and between joists in a deliberately created air gap. With any chosen option, the ceiling must be well insulated so as not to heat the ceiling of the room from below, preferably equipped with waterproofing with a reflective foil layer.