There are many types of beams. They are divided according to their purpose: foundation, for floors, supporting; by material: steel, wooden, reinforced concrete. In most cases, all the information is in the designation of the element, but it is clear only to specialists. To find out what is hidden behind the abbreviations in the names, how to find out the sizes of beams, determine the weight, the desired type, consider the main categories of building products.
General concept
A beam is a horizontal supporting element of a structural system, having from one to several support points. It can cover both one (split) and several spans (continuous). According to the material, the beams are divided into:
- Metal (steel).
- Wooden.
- Reinforced concrete.
They are used in construction as bending supporting structures, and in mechanical engineering (for example, as an element of a bridge crane).
Metal beams
The biggest group. Classification by which you can get a general idea of metal beams:
1. According to the working scheme:
1.1. Single span (split).
1.2. Multi-span (continuous).
1.3. Cantilever (with one support in the form of pinching).
Split are the most convenient for manufacturing and installation in comparison with multi-span. Continuous beams should be installed on reliable supports where there is no danger of uneven subsidence.
2. By section view :
2.1. Rolling (single-beam, double-tee, through).
2.2. Compound: welded, bolted, riveted.
I-beams are considered the most common in application - they are simple in production and are universal in use. Further, we will consider them.
I-beam parameters
Metal products are distinguished by their reliability and high technical performance. I-beams are no exception. They are classified as long products, production is carried out according to technical conditions. In turn, the technical specifications are based on the requirements that the beam must comply with: GOST 535-2005 “Long products and shapes made of carbon steel of ordinary quality” regulates them.
By the type of profile, beams can be:
1) With parallel shelves:
1.1) Normal (B).
1.2) With a wide shelf (W).
1.3) Column (K).
In the product name, the profile view is always encrypted. For example, a beam 20b1 dimensions implies the following: height 20 cm, B - normal, width of the shelf - 100 mm (10 cm).
2) With a slope of the internal faces:
2.1) Normal - 6-12% slope.
2.2) Special: M - for suspension ways of cranes and other equipment (≤12%).
2.3) C - for reinforcing mine shafts (≤16%)
I-beam: dimensions and weight
These values depend on each other, as well as on the type of steel used for production. To identify them, you need to use lookup tables. Where to get them?
There are assortments based on GOST 8239-89, 19425-74, 26020-83. By type of profile, select the appropriate table, find the necessary beam sizes in it, for each specific case the mass of the product per 1 running meter is given. This value is considered a reference, used in the calculations, but in reality it may slightly differ from the actual one (if the production is conducted according to the technical specifications).
For example: beam 20b1. Dimensions according to the assortment: height - 200 mm, width - 100 mm, wall thickness - 5.6 mm, shelf size - 8.5 mm, radius of curvature of the inner face - 12 mm.
An I-beam, the dimensions and weight of which are indicated in the table, is the standard for this type. When purchasing products, the manufacturer must provide information on the actual parameters of the elements to the client.
Wooden beams
The most commonly used in the construction of houses as elements of overlapping floors, floors, finishing layer of the ceiling, as part of the construction of trusses, rafters for roofing. The element is a rectangular beam with parameters in height - 140-250 mm, in width - 50-160 mm. The length can be from 2 to 5 meters (excluding the amount of support).
In terms of composition, the timber can be either solid or glued (multilayer). For production, coniferous trees are used, because they have good elasticity and work on bending, which is important for horizontal bearing elements.
The dimensions of wooden beams depend on the magnitude of the load on the future overlap, on the type of filling the volume of the structural element (insulation, rolls), on the span. All these parameters are regulated by GOST 4981-87 “Wooden floor beams”.
Installation Features
Before use, wooden elements must be treated with antiseptic compounds that prevent decay, damage by microorganisms and rodents, as well as increase the fire resistance of the bars.
The elements of the ceilings are installed in specially arranged nests when conducting masonry or by cutting wall structures made of various wooden materials into the upper crown. Installation is carried out from the extreme to the central bars. The supporting end must be no shorter than 15 cm.
- When laying the beam on the external walls, the free ends are cut off at 60 0 , treated with antiseptics and protected with roofing material or roofing felt.
- When embedding the beam in masonry, the end of the beam must be dried and treated with bitumen to prevent its decay.
- Fill the spatial niche in the wall with insulation. You can arrange a wooden box.
- In thick walls, it is necessary to leave a ventilation duct through which moisture will be removed from the free end.
- With thin walls (up to two bricks) it is permissible to fill the space in niches with cement mortar.
- On the inner walls of the beam, they are laid on a ruberoid layer.
The beam can be replaced with a log whose diameter corresponds to the height of the rectangular section of the element. This is economical from the point of view of purchasing material, but it is worth remembering that fixing should be done in a special way with the help of anchors with a wall seal.
Reinforced concrete beams
Widely used in large-scale construction of residential and public buildings.
Beams are classified according to several parameters, the main one can be considered the division according to purpose and type of section at the same time:
- Foundation . They are used to arrange the foundations of industrial facilities and residential buildings in areas of increased seismic activity. May have a T-shaped profile or section in the form of a trapezoid.
- Truss gable or gable systems are used for roof ceilings in production and farm complexes. They have protrusions for mounting rails.
- Rectangular beams with various configurations (mono-tee, I-beams, L- and T-shaped profiles) serve to overlap spans of facades, ceilings up to 18 meters long.
The dimensions of the beams depend on their purpose and have different parameters. For example, rafter structures have a length of up to 24 m, and ordinary elements of the floors can rely on a span of up to 18 m. The remaining parameters are determined individually for each product.
The sizes of floor beams can be found in the catalogs of Gosstandart or from specific manufacturers, since they can vary. GOST 20372-90 “Rafter and sub-reinforced concrete beams” defines the basic requirements for products, materials and structural reinforcement; on this basis, enterprises create technical specifications.
Basic calculation
All building structures in the Soviet era were divided into series. There are unified catalogs of reinforced concrete products in which all types and sizes of blocks, beams, plates produced at factories in different regions are given. The table summaries show the sizes of all parts of the elements, their estimated mass. This literature can still be used as reference in the design of buildings, but engineers must compare the concrete products with the availability of such products from modern suppliers.
There are several principles by which reinforced concrete beams are calculated . Dimensions must comply with the following parameters:
- The height is at least 5% of the length of the span to be blocked.
- The beam width is determined by a ratio of 5: 7 (width to height).
- Reinforcement of the product is carried out according to the scheme: 2 rods from the bottom and top (deflection resistance). For the framework, steel rods with a diameter of 12-14 mm are taken.
In this way, it is possible to determine the required beam dimensions for a particular section.