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Few people today give the construction of a house completely to a team or organization. To be sure of the result, it is necessary to control the work. To do this, you have to understand the terminology, technical processes and design features. Crossbars are often found in the construction of buildings, but they are very similar to beams. And so much so that not even all professional builders can explain the difference. What is a crossbar in construction and how does it differ from a beam and we will understand. Consider also the types and types of concrete crossbars.
What is a crossbar: definition and purpose
In general, the word “rigel” itself has many meanings. This is a German surname, and a community in Germany, and the name of a star, and much more. There are crossbars in the design of the house. But many often find it difficult to answer what exactly it is. A crossbar in construction is a part of the supporting structure of a building. It is a horizontal element connecting vertical racks. The rest of the structural elements are joined to the crossbar. That is, the construction crossbar is always located horizontally between two posts (with a large length it can have retaining posts). They can be vertical or inclined.
The task of the crossbar is to mechanically connect the racks, linking them into a single system, and to give stability to the structure. Also, by linking parts of the structure, it redistributes the load from different parts of the building, evenly transferring it to the racks.
It can be found anywhere in the building. There are crossbars in some types of foundations (pile-grillage, columnar and others, where there are separate supports), wall frame, ceilings, pitched roofing system.
How is it different from a beam
We figured out what a crossbar is in construction. But there is another element found in ceilings and the roofing system, which is often confused with a crossbar – these are beams. Beams are a load-bearing element in a structure that usually compensates for bending loads. So much for the difference – the girder is part of the supporting structure. This is the frame on which the beams are supported.
Beams can be inclined and horizontal. But they almost always work in bending, so they must be calculated, as they must withstand long-term loads. Rigel – strictly horizontal elements and serve for the mechanical connection of the racks. When designing structures, standard solutions are often used, calculating with a certain margin of safety.
Another difference between the crossbar and the beam is the materials and shape. The beam is always rectangular or square in cross section. Crossbars often have a more complex shape, but can be both square and rectangular. The beam can be wooden or metal. The crossbar is also made from these materials, but it can also be reinforced concrete. So, if you see a reinforced concrete horizontal part of the structure that rests on the racks, you have a crossbar in front of you.
Horizontal wood and metal elements are a little more difficult. It is necessary to look to see if they bear a bending load. If not, this is the crossbar. Otherwise, a beam. And if the element is installed at an angle, it is exactly a beam.
Where applicable
So, a girder in construction is a horizontal part of a structure that connects the vertical or inclined parts of the system:
- Connects the struts of the building frames.
- In frames, it combines supports, columns.
- In the rafter system – rafters.
This is how you should store them.
This element is present in almost every part of the building. It can be shaped in different ways to accomplish different tasks. In the simplest cases, this is a rectangular or square bar. In rafter systems, just such crossbars are used. Rafter systems are assembled mainly from wood and the crossbars for them are also made from this material. In general, wooden crossbars are a common beam, the edges of which can be shaped into a quarter or a tenon.
What can be a concrete girder
Most often, reinforced concrete girders connect the racks of the building frame. They serve as a support for the floors. In this case, concrete is used of high grades – from B22 to B60. The choice depends on the number of storeys of the building, and also on the required structural strength. To increase reliability and strength, two reinforcement belts are made. High-strength fittings are used. All standards are spelled out in GOST 13015.3. Specifications, standard sizes are specified in GOST 18980-2015.
Forms and types
The lintels, which serve as support for the slabs, are often called the slab ledger. They come in three forms in shape: with one and two shelves or without shelves. Those with one shelf are used along the edges of the structure. Only the edge of one slab can be placed on them. With two, they are placed in the center. The overlap can be placed on two shelves from both sides.
- With one shelf (ledge) – for laying the floor slab on one side. They are also called single-shelf.
- To support one slab:
- ROP – hollow;
- ROP – ribbed.
- For stairs:
- RLP – flight of stairs;
- RLR – stairwells.
Types of reinforced concrete crossbars for supporting floor slabs and building concrete stairs
- To support one slab:
- With two shelves (double shelves), they are used for central aisles. They support two floor slabs on both sides. There are two modifications – for regular posts and for columns. The markings are the same, different base shapes:
- for posts and columns for laying slabs of different types:
- RDR – ribbed;
- RDP – hollow;
- RCP – cantilever – for supporting hollow-core slabs of balconies.
- for posts and columns for laying slabs of different types:
- Shelfless – similar in shape to two-shelf, but very small shelves. Again, there are different types of slabs:
- RBR – ribbed;
- RBP – hollow;
- Just the letter “R” – a reinforced concrete cross-section of the cross-section.
As you can see, there are crossbars for ribbed and hollow floors. They differ in concrete strength, size and reinforcement power.
Marking Interpretation
The marking contains complete information about the reinforced concrete element. It consists of numbers, Latin letters and Cyrillic. The designation is divided into blocks using a dash. There can be three blocks in total:
- The first one indicates the type of beam, its dimensions in decimeters. The transom type coding can be found in the paragraph above.
- The second block contains information about the type of reinforcement used and the bearing capacity in kilonewtons per meter of length.
- The third is information about the concrete used, if it has special properties: increased fire resistance, seismic resistance, chemical media tolerance, etc.
In general, this topic is vast, you need to have a lot of tables at hand, since it is unrealistic for a layman to remember all the encodings. Let’s consider a few examples – RDP 6.56-110АIV-Na.
- RDP – double-shelf girder for hollow core slabs. The dimensions are deciphered as follows: 6.56 – the height of the crossbar is 6 dm or 60 cm (600 mm), the length is 56 dm, this is 560 cm or 5600 mm.
- 110AIV – stands for steel reinforcement made of AIV steel, bearing capacity – 110 kN / m.
- On – the letter “N” – concrete with normal vapor permeability. Letter “a” – additional embedded elements have been added to the structure.
Reinforced concrete girders must have slinging holes or lifting eyes for lifting with machinery. It is possible to sell products with unstressed reinforcement if the concrete strength is at least 70% in warm weather and 85% in winter. Crossbars for interfloor floors must have a tempering strength of at least 90%. There should be no cracks in the concrete. Small transverse shrinkage hairline cracks with a thickness of no more than 0,1 mm are allowed.