In the article we will talk about reinforced concrete trusses of various lengths. The final moment of the construction of a building or structure is the installation of the roof. This element is the main one, it is the main one for ensuring the safety of the building. In addition, the roof has a direct impact on the comfortable stay in the building of residents or a person (if we are talking about an industrial building). Reinforced concrete and truss trusses often act as load-bearing elements of the roof. With their help, it is possible to redistribute the main and additional weight on the walls of the structure.
Why is it important to make calculations?
Given the fact that the functions of under-rafter and rafter reinforced concrete trusses 18 m long are very important in the construction of a building, then it is necessary to approach the calculation, design and installation with the utmost seriousness and care.
A slight inaccuracy can affect the strength of the entire building. And its exploitation is unlikely to be possible.
When calculatingthe following data should be taken into account:
| Snow regions | I | II | III | IV | V | VI | VII | VIII |
|
Sg, kPa (kgf/m2) |
0, 8 (80) |
1, 2 (120) |
1, 8 (180) |
2, 4 (240) |
3, 2 (320) |
4, 0 (400) |
4, 8 (480) |
5, 6 (560) |
Maximum reliability and strength for elements that are made of reinforced concrete. But there is one drawback - the installation of reinforced concrete trusses 18 m long is very difficult, and the total mass of the structure is very large. The complexity of the installation work is a moment that limits the use of rafters of this design. As a rule, farms of this type can be found in not very common cases. For example, if you need to build a one-story building with a large area.
What to rely on when calculating?
Don't think that the calculations are simple and there are no "pitfalls". You will have to acquire a considerable amount of knowledge in order to carry out the design. When working, you need to rely on GOST 20213-89, which applies to reinforced concrete trusses of 12 m and other lengths.
Pay attention to the fact that even the most insignificant moments should not be missed. Because in the end you will indirectly or directly affect what strength characteristics the finished product will have. For this reason, all design work must be carried out at the time of design. Moreover, it is recommended to entrust this to professionals, because even the smallest details should not be missed. It is important to consider not only the choice of a specific rafter option, but also small elements for connection.
What factors to consider?
When calculating truss and truss reinforced concrete trusses, you need to rely on the following factors:
- The total mass of the entire structure. This includes the mass of the rafter system and covering.
- A mass of periodic loads. These include climatic phenomena, as well as random ones (for example, the possible walking of a person).
- The mass of additional loads that may occur during the operation of the building (for example, snow, wind, etc.).
Accuracy in calculations will significantly save on construction. But you will also make the object as protected as possible, which will not be affected by various negative factors.
In order to make a farm, you need to use only high-precision equipment. It is important that it be able to perform the desired work with a minimum error. During the installation of the truss system, it is important to securely fasten all elements so as not to lose the stability of the structure.
Rafter reinforced concrete elements
There are a large number of designs of reinforced concrete trusses, they have a different appearance. You can also find differences in the materials used for the manufacture, methods of leaning on the walls. With the help of such structures, it is possible to easily build buildings in which there are sufficiently large spans - more than 24 m. The type of roof can be low-slope or pitched. Lanterns can be used on the floor. It should be noted that such reinforced concrete structures are best used in the construction of industrial premises, warehouses, hangars.
The advantages of such structures are as follows:
- Very high strength of the building as a whole and individual elements.
- The material is not affected by low temperatures.
- Fire safety.
- High hardness.
- High resistance to any type of aggressive environment.
But you can also highlight the disadvantage - it is difficult to mount, since the structure has a lot of weight. But this is a minor disadvantage, as it is overshadowed by all the benefits listed above.
How trusses are made
Heavy or light concrete (structural type) is used for manufacturing. Typically, expanded clay concrete and agglomerated concrete are used for the manufacture of trusses. Production takes place in special booths, which have several (sometimes only one) tiers. On these tiers, steel molds with a steam jacket are installed. Be sure to carry out the correct calculation of reinforced concretefarms. This will affect all building characteristics.
In order to create racks and braces that are laid directly during reinforcement, you need to use a vibrating table. It must have special cassette forms. The upper reinforcement belt is simple rods, there is nothing complicated in the design. But the lower chord is a high-strength wire with a diameter of 5 mm, assembled in special string packages.
To tension these string packs, you need to use hydraulic jacks. As soon as the bags are stretched, you can start pouring the concrete solution. After 2-3 hours, the farm can be subjected to heat treatment. Pay attention to the fact that at each stage it is necessary to control the quality of the string pack tension.
Product labeling procedure
In order to mark the finished product, use numbers and letters. They are written with a hyphen. The letters are the type and size of the workpiece, the numbers can reflect various characteristics, for example:
- The bearing capacity of the structure.
- Additional data.
- The brand of concrete used in the manufacture.
Letters can also reflect the permeability of concrete. This is a characteristic that shows the suitability of the design for operation under various aggressive conditions, for example:
- The letter "P" in the marking indicates that the product has reduced adaptability.
- The letter "H" is displayed if fitness is normal.
- At products,withstand seismic activity up to 8 points, there will be a letter "C" in the marking.
Concrete concrete design features
The farm is, in fact, the "skeleton" of the roof. It is she who allows you to complete the outlines of the future design. To give the frame rigidity, strength, stability, it is necessary to manufacture trusses using a large amount of reinforced materials and steel. As a result, the scheme of the entire product becomes much more complicated. Only such structures will be able to ensure the safety of the entire structure even when exposed to extreme weather events.
But, despite this, most manufacturers are striving to reduce the weight of the finished product. At the same time, strength, as you know, does not suffer, because concrete of light grades is used. The result is a reduction in the weight of the farm, but without losing strength.
Truss design features
The traditional component of any reinforced concrete truss is reinforcing steel. It resists corrosion quite easily. Therefore, high humidity and low temperature cannot even slightly affect the strength of the roof structure. The contour of the farm is two belts that work on bending. Lattice - these are braces and racks that are responsible for the force acting along the axis. The following types of farms can be distinguished:
- Segment reinforced concrete trusses. For them, a characteristic feature is the presence of a diagonal lattice and a delineating belt.
- Polygonal - the belts are parallel or arranged in the form of a trapezoid.
- Braceless arched - differ in the presence of rigid knots.
- Slanted arched - have a curvilinear upper belt and crate.
Quite often you can find such that reinforced concrete trusses with a polygonal type coating and even elements on the upper belt are replaced by segment ones. This option is more profitable from an economic point of view. You can also make the following classification of farms:
- Typical.
- Slanted.
- Slanted.
Where trusses are used
There are several areas of application for different types of reinforced concrete trusses 24 m and other lengths for the manufacture of the truss system of the structure:
- In the manufacture of a low-slope roof, it is best to use truss-free trusses. It is recommended to install additional racks in the upper belt. As a rule, such buildings have a large number of communication systems. The distance between two neighboring farms is 6 or 12 meters.
- When building a single-span building (in the absence of heating), it is best to use braced structures.
- Pitched roofs are best equipped with non-braced segmental or slanted frames.
If you plan to cover one-story buildings with several spans with roll material, it is better to use standard reinforced concrete products.
There are a lot of options, but let's take a closer look at how theymarked:
- FBS - bezskosny farms used for the manufacture of pitched roofs.
- FS - diagonal type products, which are also used on pitched roofs.
- FP - products that are used as a slab coating. The length of the material is the same as the span.
- FPN - for a roof structure with a small angle of inclination and prestressed posts.
- FPM - used on roofs with a low angle of inclination without prestressing.
- FBM - non-braced type products that are used on pitched roofs with a small slope.
- FT - non-braced types of triangular trusses.
- FPS - often found on pitched roofs.
What to consider when installing?
Before installing such structures, you need to accurately calculate what the bearing capacity of the building is. Fasteners must be made to embedded elements on load-bearing walls or columns. Consider the fact that installation should not begin until you are sure that the quality and dimensions of all elements are in accordance with the norm.
When working, you need to use welding - it is used to connect supports and embedded elements. Metal girders also need to be welded to the supports, with their help you will achieve the optimal value of frame rigidity. The farm can be like this:
- Arched (diagonal and diagonal).
- Segmental.
- Polygonal.
The entire manufacturing procedure must be carried out in full accordance withGOST. In this case, you need to rely on the main characteristics of the products:
- Strength of concrete used in manufacturing.
- Density of concrete.
- Reaction to low temperature.
- Steel grade and reinforcement elements.
- Reaction to corrosion.
- The diameter of the layer that envelops the rebar.
Despite the fact that the structures have high strength characteristics, they are unlikely to be found in private construction. The reason is that the installation is very complicated and the total mass is too large. Very often, reinforced concrete products can be found on structures that have a length of more than 18 meters. In this case, the step between the farms is 6..12 m.
In the event that the span is not more than 18 meters, it is more reasonable to use beams. But if it is planned to lay a large number of elements of communication systems that will be located in the frame, then it is still worth giving preference to reinforced concrete products.
If you plan to build a building with a span of more than 30 m, you need to take into account the total mass of the roof. But this parameter will be very large. It would be more rational to break the entire structure of the farm into blocks. But there is a drawback of this method - the cost of the work will increase significantly. Even construction using reinforced concrete trusses 24 m long will be less expensive.
If you look at everything from the side of the ratio of quality and price, then the best option would be the use of arched or segmental structures. On them almostthere is no change in the force on the belts. But it should be noted that the height of the support is not very large. As a result, a significant reduction in the mass of the structure can be achieved.
Truss construction
The easiest construction option is to install a bezraskosny arched truss. It is quite simple for her to reinforce the nodes. All the space that is obtained inside can be easily filled with taps for a variety of communication systems. Very often this is done in the construction of flat, low-slope and pitched structures.
For the manufacture of trusses, it is necessary to use the grade of concrete B30-B60. It has high strength, and the mass is quite low. In the lower belt, ropes from reinforcement, rods, and strong wire are used.
In the manufacture of reinforcement, it is allowed to use a frame made of light wire. It will avoid the formation of cracks during the operation of the structure. For convenient crimping of the lower belt, it is best to use frames no larger than 3 m.
In order to perform reinforcement of the components of the upper chord and lattice, it is necessary to use frames made of welded reinforcement. They must be installed in the support nodes. This will increase the strength of the entire frame in inclined sections. To reinforce the intermediate nodes on the belts, sets of rods with a thickness of 6..10 mm with a step of 100 mm are used. It is they who make up the frame of the welded type.
For the transportation of a ready-made structure, special equipment is used, for example, a farm locomotive FKP-16. As there is an increase in demand for steel structureslightweight type, the demand for reinforced concrete products inevitably falls. But, according to fire regulations, concrete farms are the best of their kind.
