Types of wooden beams for floors, length calculation, installation

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 the communications and interior details of the upper floors. To withstand a considerable load, strong floors are needed. 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 floors.

Interfloor overlap with wooden beams

Floor types

A slab is a horizontal supporting structure made of beams, dividing a building in height into functional zones or floors and supporting 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.

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 basement slabs, as they carry the greatest load. Long spans with a large distance between the beams can be made from steel 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 metal increases construction costs.

Reinforced concrete floor beams can withstand heavy loads and are suitable for the construction of multi-storey buildings. But for their installation you will 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 low weight compared to previous types, so they are easy to install. However, the tree is flammable, prone to decay and damage by the bark beetle, therefore, requires preliminary processing.

Types of timber beams

Timber joists 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 floors, a board or a bar made of solid wood, or glued products, is used.

Varieties of wooden beams

Solid beams

Beams made from solid wood are less durable than glued or I-beams. Therefore, their length should not exceed 6 meters. Often, to increase strength, builders will pair boards on site. They are tightened with bolts and nuts with rubber or plastic gaskets to prevent moisture and rust formation on the fasteners.

Glued laminated timber

Glued laminated timber is made by gluing several parts together. Beams made of this material are capable of withstanding high loads, so they can be used in the construction of floors up to 14 meters long. Curved ceilings for arches can be made from such a beam.

Such products also have disadvantages. In the manufacture, low-quality lumber can be used, so over time, shrinkage of the beam floor is possible. In addition, glued beams are much more expensive than solid ones. In order to more efficiently use the funds allocated for construction, it is necessary to correctly calculate the load and the length of the beams.

Glued laminated timber with a similar section with the usual one has greater strength

Floor beams are made from softwood, but oak, acacia, maple and other trees are also often used. The main condition necessary for the strength of the structure is humidity not more than 12-14%. Some types of 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.

I-beam device

An I-beam is made using well-dried planed or glued beams, durable glued waterproof plywood or OSB boards, based on refractory and moisture resistant glue. Therefore, a wooden I-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 overlapping devices.

I-beams from OSB (OSB)

Connection of I-beams to each other

All types of products have their own assortment. Assortment is a selection of various finished products by brands, profiles or sizes. Often times, the table provides additional information on strength, weight, etc.

Section of beams

The strength of the floor is also influenced by the cross-section of the beam. By the type of section, the following types of sawn timber are included:

• rectangular;
• square;
• round;
• oval;
• I-beams.

The most common are rectangular beams. They are easy to install and such beams will serve as logs for arranging floors. When installing rectangular beams, they are installed vertically with a wide part, since the strength of the structure increases with increasing height.

For attic floors, round beams or rounded logs are often used. Such beams have good strength and deflection resistance.

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 joist floors. For the best strength of the floor during construction, you need to use wooden beams with a margin of safety slightly larger than the calculated one.

Choice of width or thickness of the beam depending on the length

To correctly calculate the load on the floor beam, you need:

1. Know the distance between the walls and the step between the beams.
2. Calculate the constant load from 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 square meter. meter of all building materials

3. Temporary load. This includes the mass of furniture and people in the building. As a rule, it is considered equal to 150 kg / m².
4. Calculate the estimated load per meter² overlap (the sum of temporary and permanent indicators).

Since for the calculation you need to know the load per linear meter, you need an estimated load of 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 floor is calculated.

Mmax = (q * L²)/8

Where:

• q - full load per sq. m;
• L² - the square of the distance between the walls.

When designing a floor frame, you need to pay attention to the spatial rigidity, which largely depends on the deflection indicators 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 - resistance of wood from SP 64.13330.2017 of 2017 (current edition of SNiP II-25-80). For grade 2 wood, it is considered to be equal to 130 kg / cm2.

From the formula W = b * h²/6, knowing the W exponent, we calculate the overlap section. It is enough to specify one geometrical characteristic b (section width) or h (its height).

The deflection of a wooden floor under the calculated load should not be more than the ratio to the length of the beam 1: 350 for basement and interfloor floors, and for attic and mansard floors - 1: 250.

The size of the beams depends on the distance between the load-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 overlapping devices.

Floor installation

For a building to last for a long time, beamed floors must meet a high level of strength. Have good sound and thermal insulation and good ventilation.

When installing wooden beams, the lighthouse installation method is most often used. First, the extreme beams are mounted, and then the intermediate ones. To avoid mistakes during work, use a level. In case of height differences, the beams can be leveled by placing trims impregnated with bitumen primer under the end ends.

Before starting the installation, the beams are spliced ​​or cut to the desired size. Splicing of beams from a bar along the length is usually carried out by the "key groove" method. To do this, the ends of the beams are cut down to 1/2 of the thickness and one end is buried into the thickness of the other. Then the joints are fixed.

Splicing two beams

The distance between wooden beams should not be less than 60 cm and exceed 1 meter. In a structure made of logs or glued beams, a 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 buried into the load-bearing wall by at least 15 cm. For I-beams, this value can be reduced to 7 cm. The grooves are covered with mortar or foam. It is possible to fix the ends to the walls with steel ties. In places of supports on the beams, waterproofing is done.

Waterproofing of beams in places of supports is required

Advantages and disadvantages of wood 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 ability to install 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 processing with fire retardants, as well as anti-rot and mold agents. Installation of wooden beams is only possible after careful calculations.

In conclusion of the article, it should be added that the use of wood in construction significantly reduces costs. In order not to disrupt the structure of the entire building and install solid floors, it is better to entrust their design and installation to professional builders.