Reinforced concrete trusses - size, calculation and

The end of the house building process is crowned by the installation of the roof. This element is fundamental to the safety of the building, and also directly affects the comfort of its operation. Roof trusses and reinforced concrete trusses of 18 m can be used as carrier elements of the roof, with the help of which the main and additional weight is redistributed to the building walls.

Calculation features

Учитывая важность выполняемых функций стропильных и подстропильных ферм, к процессу их расчета, проектировки и монтажа необходимо отнестись максимально серьезно. Мельчайшая неточность может погубить всю конструкцию (читайте также статью «Бетонолом: как на этом инструменте можно заработать, как его выбрать и на что обращать внимание при покупке»).

Elements made of reinforced concrete are most reliably and reliably operated. However, the complexity of installation in conjunction with a large final weight limits the use of this type of rafters. They are most often used in unusual cases when, for example, it is necessary to make a one-story building of a large area.

When calculating, not everything is as easy as it might seem at first glance. Therefore, for its implementation is necessary a certain amount of knowledge. In this case, GOST 20213 89 is used for trusses made of reinforced concrete.

Advice: it is very important not to miss a single factor that can have a direct or indirect impact on the final strength properties.

That is why such calculations should be carried out at the design stage by people well-acquainted with this area. Here every detail is important - from choosing the very version of the construction of rafters to choosing small connecting elements.

Three factors must be taken into account in the calculations:

1. The total mass of the structure, which includes the weight of the roof covering and the weight of the truss system.
2. Weight loads that may additionally occur during operation (snow, wind, etc.).
3. Weight of periodic loads (various climatic phenomena or random factors).

Extreme accuracy during calculations will help not only save the total estimate, but also make the object as protected as possible from all kinds of damage.

The instruction requires the use of high-precision equipment for the manufacture of trusses of reinforced concrete, which is capable of performing work with minimal errors. When installing rafters, it is especially important to fasten all the elements together securely so that the stability of the object is not reduced.

Ferroconcrete trusses

Such designs can vary significantly in appearance, based on their parameters, including the coating material used and the methods of their support. With their help, you can build buildings with huge spans (more than 24 m). In addition, the roof at the same time can be pitched or low-sloping, and lanterns can be used on the surface of buildings.

Tip: use similar reinforced concrete trusses when building warehouses and other industrial-type premises.

The main advantages of such structures:

• high strength properties;
• good stiffness;
• resistance to low temperatures;
• resistance to aggressive media;
• fire safety.

Manufacturing of concrete elements of supporting structures

For the production of reinforced concrete trusses, concrete of structural type (light or heavy) is used, most often agloporibeton or keramsit concrete. The manufacturing process itself is carried out in the stand-chambers with one or several tiers, on which steel forms with a steam jacket are mounted.

To create racks and braces laid during reinforcement, vibrating tables with special cassette forms are used.

As the upper belt for reinforcement, ordinary rods are most often used, but the lower belts are equipped with high-strength wire, O 5 mm, which is assembled into string packs. To tension the latter, it is necessary to use hydraulic jacks, after which the concrete mix is ​​added.

After 2-3 hours, the product is sent to the heat treatment shop. At each manufacturing process, quality control of pre-stressed products is carried out.

Marking process

For marking such material letters and numbers written with a hyphen are used.

Letters designate the size and type of the workpiece, and the numbers display, including:

• additional information;
• load bearing capacity;
• brand of used concrete.

With letters, the characteristic of concrete, such as permeability, is shown, which shows how the structure is adapted for operation under aggressive conditions:

• the letter "P" denotes reduced fitness;
• with the letter "H" displays the normal fitness;
• products that can withstand 8-ball seismological phenomena are denoted by the letters "C".

Construction features w / concrete trusses

The farm acts as a skeleton that reflects the shape the roof will have. In order to frame different rigidity, strength and stability, it must be made using a large number of steel and reinforced materials, which greatly complicates its scheme. Only such a construction will be able to ensure the safety of the building even under extreme weather conditions (find out here what is better - gas concrete or gas silicate).

But still, manufacturers are trying in every possible way to reduce the weight of such a "skeleton". This is achieved, first of all, due to the use of lightweight concrete, which has no effect on the overall strength of the structure.

A traditional component of the internal structure of reinforced concrete trusses is high-strength reinforcing steel, which easily withstands corrosive effects. Due to this, the ingress of moisture or strong frost in no way can affect the strength of the roof.

Two belts working on a bend act as its contour, but the pillars and braces responsible for the axial force are the grille.

There are such main types of similar farms:

1. Segmental, for which the belt shape and the lattice of the diagonal type are characteristic.
2. Polygonalwhen the belts are parallel or in the form of a trapezium.
3. Арочные безкраскосныеcharacterized by rigid knots.
4. Arched diagonalhaving an upper belt with curvilinear outlines, as well as a rare lattice.

Quite often, polygonal trusses with even elements of the upper belt replace segmental ones. This method is more economically feasible.

In addition, there is a classification of farms:

• slanting
• безрасковые.
• typical.

Scope of application of various types of trusses

1. If the roof is planned to be built low-inclined, the best option would be to use axial trusses, in the upper belt of which additional racks are installed. Most often, such buildings are equipped with a large number of communication systems. Step for them is 6 or 12 m.
2. When a building is single-span, and its heating is not planned, the use of dispersion-free structures would be an ideal option.
3. Pitched roofs are equipped with a segmented bead or slanting frame.

When overlapping single-storey buildings with one or more spans of roll materials, it is best to use typical concrete goods.

There are a lot of such options at the moment, let's look at their notation:

• FS - diagonal products used on sloping roofs;
• FBS - bezraskosny type of farms, used for pitched roofs;
• FP - products used as a plate coating, the length of which is similar to the length of the span;
• MTF - used on low side roofs without prestressing;
• FPN - for a roof with a small slope and prestressed racks;
• FBM - bezrakosnye products used on low-slop pitched roofs;
• FPS - found on pitched roofs;
• FT - bezraskosny type farm with a triangular outline.

Installation nuances

Before installing such structures, it is necessary to accurately calculate the bearing capacity of the building. Fastening is carried out to the mortgage details located on the bearing wall or column.

Tip: do not start the installation without making sure that the quality of the elements and their dimensions are fully consistent.

In addition, you will need the services of a welder who will have to connect embedded parts and supports. Metal girders are welded to the first ones, due to which the optimum value of the longitudinal rigidity of the frame is achieved.

Depending on the shape, the reinforced concrete truss may be:

1. Segmental.
2. Arched diagonal.
3. Арочной безразкосной.
4. Polygonal.

The whole process of manufacturing such structures is carried out in accordance with GOST on concrete structures or from reinforced concrete.

The main characteristics are:

• the strength of the concrete used;
• its density;
• low temperature response;
• diameter of the layer enveloping the reinforcement;
• steel and its brand used for reinforcement;
• reaction to corrosive effects.

Despite the high levels of strength and reliability, such constructions are rarely found in private homes. This is due to the complexity of the installation and a significant mass of the resulting roof. But most often the data of concrete goods can be seen on buildings, the span of which exceeds 18 m, and the step is in the range of 6-12 m.

If the span is less than 18 m, it will be more advantageous to use beams, however, if there are a large number of communications located inside the frame, it is best to opt for reinforced concrete. But in the development of buildings, the spans of which exceed 30 m, it is necessary to take into account the total weight of the roof, which will be significant. Therefore, it would be rational to break them into separate blocks, however, at the same time, the price of the work increases significantly.

If you look from the point of view of price / quality ratio, then the best options will be segmented or arched. On such farms, there is practically no change in the efforts on the belts, and the height of their support is small, which results in minimizing the total weight of the structure, as well as the height of the walls.

Manufacturing of cans farms

The simplest process of production is of an archless type, whose knots are reinforced very simply. All internal space obtained can be filled with branches for various communication systems. Most often used for installation of low-angle, flat or pitched roofs.

For the production of this material is taken concrete grade B30-B60, which has high strength characteristics. Its lower belt can be reinforced ropes, high-strength wire or rod reinforcement.

In addition, light wire cages are also used, which prevent the formation of cracks during operation. To make the lower belt more comfortable to crimp, it is recommended to use frame lengths of less than three meters.

But for the reinforcement of the elements of the lattice and the upper belt, welded reinforcement cages are used, which are installed in twos in the support units. As a result of this, the strength of the carcass in inclined sections increases. A set of transverse 6-10 mm rods, the pitch of which is 100 mm, constitutes a welded framework used to reinforce the intermediate nodes of both belts.

For the transportation of ready-made structures, specially equipped equipment is used, for example, the FKP-16 fermovoz. Due to the growing demand for light-weight steel structures, the demand for concrete goods is falling. However, according to the fire requirements the best are the reinforced concrete trusses.

Conclusion

Приведенные в статье конструкции относятся к массивному строительству, которое не получиться осуществить своими руками, лучше для этого использовать специальную технику. Изготовление данных изделий также следует отдать профессионалам, использующих современные материалы и технологии расчета нагрузки (см.также статью «Бетонная брусчатка или как недорого обустроить место на участке»).

Concrete goods data are indispensable for the construction of buildings that require wide spans. The video in this article will help you find additional information on this topic.