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An important stage in the construction of any building is the installation of interfloor ceilings. They distribute the weight of the building elements above, such as the roof and walls, as well as communications and interior details of the upper floors. To withstand a considerable load, you need strong ceilings. In the article we will tell you what types of beams are used for different parts of the building, and consider how to correctly calculate the load and length of beam ceilings.
Floor types
Ceiling is a horizontal load-bearing structure made of beams that divides the building in height into functional zones or floors and maintains the strength of the entire structure. When building a house, the following types of floors are used:
- basement or basement floor;
- interfloor overlap;
- attic floor.
Naturally, the most durable are metal beams in the form of a channel, angle or I-beam, made of high-strength steel. They are best used for the basement, as it carries the greatest load. From steel beams it is possible to arrange long spans with a large distance between the beams. They are resistant to mechanical damage and decay. However, due to their heavy weight, they are difficult to work with, and the high price of the metal increases construction costs.
Reinforced concrete floor beams withstand heavy loads and are suitable for the construction of multi-storey buildings. But for their installation, you need special equipment.
Basically, in the construction of private houses, wooden beams are used for floors. Wood is a reliable and environmentally friendly material that will not harm the residents of the house. Wooden beams are relatively inexpensive and have a small weight compared to previous types, so they are easy to install. However, the tree is flammable, susceptible to rotting and damage by bark beetles, and therefore requires pre-treatment.
Types of wooden beams
Wooden beam ceilings differ in size, cross-section, production method and the type of wood from which they are made. The reliability and strength of the structure depends on the choice of wooden beams. Depending on the distance between the walls and the expected load for the ceilings, a board or beam made of solid wood, or glued products is used.
solid beams
Beams made from solid solid wood are less durable than glued or I-beams. Therefore, their length should not exceed 6 meters. Often, on-site builders pair boards to increase strength. They are tightened with bolts and nuts with rubber or plastic gaskets that prevent moisture from entering and rusting on the fasteners.
Glued laminated timber
Glued beams are made by gluing several parts together. Beams made of this material are able to withstand high loads, so they can be used in the construction of ceilings up to 14 meters long. From such a beam, you can make curved ceilings for arches.
Such products also have disadvantages. In the manufacture, low-quality lumber can be used, so over time, shrinkage of the beam ceiling is possible. In addition, glued beams are much more expensive than solid ones. In order to use the funds allocated for construction more rationally, it is necessary to correctly calculate the load and length of the beams.
Floor beams are made from coniferous wood, but oak, acacia, maple and other trees are also often used. The main condition necessary for the strength of the structure is humidity no more than 12-14%. Types of some products are shown in the table below.
I-beams
The advantages of I-beams are versatility, ease of installation and high strength. They retain their parameters under heavy loads without auxiliary structures for reinforcement.
An I-beam is made using well-dried planed or glued timber, durable glued waterproof plywood or OSB-boards, based on refractory and moisture-resistant glue. Therefore, an I-beam wooden beam does not require impregnation with special compounds and is easy to saw. However, due to the complex manufacturing technology, they are rarely used for flooring.
For all types of manufactured products there is a range. Assortment is a selection of various products of finished products by brands, profiles or sizes. Often the table contains additional information about strength, weight, etc.
Section of beam ceilings
The cross section of the beam also affects the strength of the floor. By type of section, the following types of lumber are included:
- rectangular;
- square;
- round;
- oval;
- I-beams.
The most common are beam ceilings of rectangular section. They are easy to install and such beams will serve as lags for arranging floors. When mounting rectangular beams, they are installed vertically with a wide part, since with an increase in height, the strength of the structure increases.
For attic floors, round beams or rounded logs are often used. Such beams have good strength and resistance to deflection.
The strongest and most functional are I-beams.
Calculation of the load and dimensions of wooden beams
Before erecting a building, it is necessary to calculate the load and length of the beam ceilings. For better floor strength during construction, it is necessary to use wooden beams with a margin of safety slightly greater than the calculated one.
To correctly calculate the load on the floor beam, you need:
- Know the distance between the walls and the spacing between the beams.
- Calculate the constant load, consisting of the mass of beams, insulation and materials from which the floor and ceiling are made.
To calculate, you need to add the specific gravity per sq. meter of all building materials - temporary load. It includes a lot of furniture and people in the building. As a rule, it is considered equal to 150 kg / m2.
- Calculate the estimated load per 1 m2 overlap (the sum of temporary and permanent indicators).
Since the calculation requires knowing the load per linear meter, you need the estimated load per 1 m2 multiply by the distance between the beams. Further, the resulting figure is multiplied by the square of the distance between the bearing walls and divided by 8. This is how the load of the beam ceiling is calculated.
Mmax = (q*L2) / 8
Where:
- q – full load per sq. m;
- L2 is the square of the distance between the walls.
When designing the floor frame, attention should be paid to spatial rigidity, which largely depends on the deflection of the beam floor.
The calculation of a wooden beam for deflection is carried out according to the formula: W = Mmax / RWhere M is the maximum load, and R – wood resistance from SP 64.13330.2017 of 2017 (current version of SNiP II-25-80). For wood of the 2nd grade, it is considered to be equal to 130 kg / cm2.
From the formula W=b*h2/ 6, knowing the index W, we calculate the cross section of the overlap. It is enough to specify one geometric characteristic b (width of the section) or h (its height).
The deflection of a wooden floor under the calculated load should not exceed the ratio to the length of the beam 1:350 for basement and interfloor floors, and 1:250 for attic and attic floors.
The size of the beams depends on the distance between the bearing walls. To determine the required length of the beam, add 40 cm to this value, approximately 15–20 cm on each side. Professional builders recommend using beams with a cross section equal to 4–5% of the span length for the flooring device.
Floor installation
In order for the building to serve for a long time, beam ceilings must correspond to a high level of strength. Have good sound and heat insulation, as well as good ventilation.
When installing wooden beams, the beacon installation method is most often used. First, the extreme beams are mounted, and then the intermediate ones. In order to avoid mistakes during operation, use a level. In the event of height differences, the beams can be leveled by placing trimmings impregnated with a bitumen primer under the end ends.
Before installation, the beams are spliced or trimmed to the desired dimensions. Splicing of beams from a bar along the length is usually carried out using the “key groove” method. To do this, the ends of the bars are cut down to 12 thicknesses and one end is deepened into the thickness of the other. Then the joints are fixed.
The distance between wooden beams should not be less than 60 cm and not exceed 1 meter. In the construction of logs or glued laminated timber, the step is taken more than in plank floors. When installing the attic floor, the distance between the chimney and the beams must be at least 40 centimeters.
For the strength of the frame, the ends of the beams are deepened into the load-bearing wall by at least 15 cm. For I-beams, this value can be reduced to 7 cm. The recesses are sealed with mortar or mounting foam. It is possible to fasten the ends to the walls with steel ties. In places of supports on the beams, waterproofing is done.
Advantages and disadvantages of wooden beams
The use of wooden beams in the construction of buildings, unlike other types, is characterized by the following advantages:
- affordable price;
- ease of delivery to the construction site;
- the possibility of installation without the use of special equipment;
- environmental Safety;
- maintainability.
However, despite many advantages, such floors are less durable than metal and reinforced concrete. They require treatment with flame retardants, as well as agents against rot and mold. Installation of wooden beams is possible only after careful calculations.
In conclusion, the article should be added that the use of wood in construction significantly reduces costs. In order not to disturb the structure of the entire building and install durable floors, it is better to entrust their design and installation to professional builders.