There are many types of beams. They are divided according to their purpose: foundation, for floors, support; by material: steel, wood, reinforced concrete. In most cases, all information is contained 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 dimensions of beams, determine the weight, the desired type, consider the main categories of building products.
General concept
Beam is a horizontal load-bearing 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 load-bearing bending structures and in mechanical engineering (for example, as an element of an overhead crane).
Metal beams
The biggest group. Classification by which you can get a general idea of \u200b\u200bmetal beams:
1. According to the working scheme:
1.1. Single-span (split).
1.2. Multi-span (continuous).
1.3. Cantilever (with one pinch support).
Split are the most convenient for manufacturing and installation in comparison with multi-span. It is advisable to install continuous beams on reliable supports, where there is no danger of their uneven subsidence.
2. By type of section:
2.1. Rolled (single-tee, double-tee, through).
2.2. Composite: welded, bolted, riveted.
I-beams are considered the most common in application - they are easy to manufacture and versatile 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 specifications. In turn, the specifications are based on the requirements that the beam must comply with: GOST 535-2005 "Rolled bars and shapes from carbon steel of ordinary quality" regulates them.
By the type of profile, the beams can be:
1) With parallel shelves:
1.1) Normal (B).
1.2) Wide front (W).
1.3) Column (K).
Bproduct name profile type is always encrypted. For example, a beam 20b1 means the following dimensions: height 20 cm, B - normal, shelf width - 100 mm (10 cm).
2) Tapered inner faces:
2.1) Regular - 6-12% slope.
2.2) Special: M - for overhead tracks 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 determine them, you must use the reference tables. Where can I get them?
There are assortments based on GOST 8239-89, 19425-74, 26020-83. According to the type of profile, select the appropriate table, find the required dimensions of the beams in it, for each specific case, the weight of the product per 1 running meter is given. This value is considered a reference value, used in calculations, but in reality it may differ slightly from the actual value (if production is carried out according to 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 edge - 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 is obliged to provide information about 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, finishingceiling layer, as part of the construction of trusses, rafters for roofing. The element is a bar of rectangular section with height parameters - 140-250 mm, width - 50-160 mm. The length can be from 2 to 5 meters (excluding the amount of support).
By composition, timber can be either solid or glued (multilayered). For production, coniferous trees are used, since they have good elasticity and bend, which is important for load-bearing horizontal elements.
The dimensions of wooden beams depend on the magnitude of the load on the future floor, 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, and also increase the fire resistance of the beams.
Floor elements are installed in specially arranged nests during masonry or by cutting into the upper crown of the wall structure made of various wooden materials. 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 outer walls, the free ends are cut off under 600, treated with antiseptics and protected with roofing material or tar paper.
- When embedding beams in stonemasonry, the end of the beam must be dried and treated with bitumen to prevent it from rotting.
- Fill a space niche in the wall with insulation. Can arrange wooden box.
- In thick walls, it is imperative 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, the beams are laid on a roofing layer.
Beam can be replaced by a log, the diameter of which corresponds to the height of the element's rectangular section. This is economical in terms of buying material, but it is worth remembering that fixing must be done in a special way using anchors embedded in the walls.
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 a division according to purpose and type of section at the same time:
- Fundamental. Are applied to the device of the bases of industrial objects and houses in zones of the increased seismic activity. May have a T-shaped profile or a trapezoid section.
- Truss gable or single-slope systems are used for the construction of roof slabs in industrial and farm complexes. They have ledges for attaching rails.
- Rectangular beams with various configurations (single-beams, I-beams, L- and T-shaped profiles) are used to cover the spans of facades, floors up to 18meters.
The dimensions of the beams depend on their purpose and have different parameters. For example, roof structures have a length of up to 24 m, and ordinary floor elements can be supported on a span of up to 18 m. The rest of the parameters are determined individually for each product.
The dimensions of the floor beams can be found in the Gosstandart catalogs or from specific manufacturers, as they may vary. GOST 20372-90 "Rafter and rafter reinforced concrete beams" defines the basic requirements for products, materials and reinforcement of the structure, on this basis, enterprises create TU.
Basic calculation
All building structures in Soviet times were divided into series. There are unified catalogs of reinforced concrete products, which list all types and sizes of blocks, beams, slabs produced at factories in different regions. The tabular summaries present the dimensions of all parts of the elements, their estimated mass. This literature can still be used as a reference when designing buildings, but engineers are sure to compare precast concrete data with the availability of such products from modern suppliers.
There are several principles by which reinforced concrete beams are calculated. Dimensions must match the following parameters:
- The height is at least 5% of the length of the overlapped span.
- The width of the beam is determined by the ratio 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 frame take steel rodsdiameter 12-14 mm.
This way you can determine the required beam dimensions for a particular section.
