Reinforced concrete trusses are used for spans of 18, 24 and 30 m (rarely 36 l); subdivide them into segmental, arched, triangular, trapezoid and with parallel belts (Fig. 64). Depending on the manufacturing method, trusses can be solid, from semi-trusses, from blocks 6 m long and from individual elements.

Segmental, arched and polygonal trusses are designed for roofing with rolled roofing, triangular - under the roof of asbestos-cement and metal corrugated sheets. Farms with parallel belts are used in buildings with a flat coating under a rolled “dry” or water-filled roof.
To avoid a large slope of the roof in the extreme panels on the supports of the segmental trusses, small posts are provided to support the roofing panels. Truss step 6 and 12 l (rarely 18 m).

The truss lattice allows to support panels with a width of 1.5 and 3 m. When the panels are supported off-node, the upper chord is additionally reinforced to absorb forces from local bending. Most pitched trusses have support nodes 0.8 m high.
Farms are made of concrete grades 300-500. The lower belt is prestressed and reinforced with bundles of high-strength wire. To reinforce the upper belt, braces and racks, welded frames made of hot-rolled steel of a periodic profile are used. In fems, embedded elements are provided, similar to beams.

The most rational in terms of material distribution are segmental and arched trusses with a broken or curvilinear upper belt. Compared to others, they have lower forces in the lattice elements and smaller bending moments in the upper chord from out-of-nodal loading, which makes it possible to make the lattice more sparse. Segment and arch trusses have a small height on the support, which allows to reduce the height of the walls; however, the curvilinearity of the upper chord complicates the formwork and reinforcement.

Rice. 64. Reinforced concrete roof trusses:

The configuration of the top chord of the trapezoidal trusses is simple, they are interchangeable with steel trusses. The disadvantages of such trusses include: a relatively powerful lattice, a large height on the support, which requires the installation of vertical connections between the trusses in the plane of the support posts; these trusses are somewhat heavier than segment trusses.
Compared to others, trusses with parallel belts consume more materials, but the formwork used for their manufacture is simple and less labor intensive.

The trusses are fastened to the columns and to the sub-rafter structures with anchor bolts and welding of embedded supporting elements (similar to the fastening of reinforced concrete beams).

Reinforced concrete roof trusses 1FS 24

Roofing is the main element of the device of any object; the safety of the building and ease of operation directly depend on the correct device of roofing elements. Today, the construction industry suggests using reinforced concrete roof trusses - load-bearing roof structures that redistribute their mass and additional load from the snow cover on the foundation walls of the building. Trusses also make it possible to better withstand the wind load and various natural anomalies. To create pitched roofs, truss and truss beams are also often used in accordance with GOST 20372-90.

Types of truss reinforced concrete structures

The truss can be described as a complex reinforced concrete product, consisting of an external contour and a lattice. The contour of the farm is formed by two belts that work on bending. And the lattice inside the contour - braces and racks, withstand axial loads.

Depending on the design of the contour and lattice, trusses can be divided into:

• Segment reinforced concrete trusses - have an original upper belt and a diagonal lattice, they are necessary for pitched roofs;
• Polygonal - in such reinforced concrete products, the belts are either parallel or trapezoidal, inside there is a diagonal lattice. The top belt has a slight slope.
• Arched bezraskosnye - have rigid knots;
• Diagonal arched - have a rare lattice and curvilinear outlines of the upper belt.

Modern manufacturers use modified concrete and sophisticated steel reinforcement systems to achieve the most durable structures. The latest technologies make it possible to create any geometric shapes from reinforced concrete, but today trusses of the most rational design are used: segmented, with parallel belts and gable trapezoidal with a straight or broken lower belt. The truss lattice, as a rule, is formed triangular or supplemented with racks or braces. Naturally, when choosing and designing 1FS 24 trusses, extreme operating conditions are also taken into account, so these supporting structures have a certain margin of safety. Truss reinforcement is a complex system of welded frames that provide shape retention and high load absorption.

The farm is a frame that will determine the future outlines of the roof and the features of the distribution of loads. The design of this type of reinforced concrete products can vary significantly depending on engineering solutions, however, several popular types are common in Russia, the shape of which is determined by. The truss gives the roof rigidity, strength, stability and allows you to distribute heavy loads, therefore it is often used in areas with a large proportion of snow load, for example, in the Urals and Siberia.

Farms reinforced concrete 18, 12 and 24 meters are the most popular in modern construction. Today they are manufactured according to the most modern standards according to type drawings of series 1.463.1-16, 1.463.1-3/87, 1.063.1-1, PK 01-110/81, 1.463.1-4/87 and series 1.463.1 -fifteen. In the "Reinforced Concrete Products Directory" of the "Complex-S" company, you can always purchase any standard sizes of roof trusses with delivery throughout Russia and Kazakhstan. Roof reinforced concrete structures are made with prestressed reinforcement (depending on the loads on the trusses, it can be wire, rod, cable, pulled on the stops of the stand). The lower belt of the farm is reinforced in a special way. Rigid roofing panels are welded at the nodes along the upper chord of the truss, which play the role of ties. The trusses are mounted on the arms of reinforced concrete columns, they are fastened with anchor bolts and welding of embedded support products.

Construction of reinforced concrete trusses

From an engineering point of view, triangular trusses are the most irrational in terms of geometry. They have a large height and require significant material costs. The use of such structures can only be justified in the implementation of a roof with a large slope from sheet materials (metal, asbestos cement).

The most practical design is called segmented or arched reinforced concrete trusses with a broken or curved upper belt. Such trusses distribute the forces in the belts more evenly, and the forces in the lattice are reduced compared to other shaped trusses. Segment and arch trusses have an average height on the support, which makes it possible to reduce the height of the walls of a one-story building. Other designs - trapezoidal trusses and reinforced concrete trusses with parallel belts - have a more pronounced height on the support, which increases the consumption of material and, of course, the price of reinforced concrete trusses. Such products are heavier than arched and segmented ones, but less time-consuming to operate.

Reliable truss structures made of heavy concrete provide maximum strength and durability of the building, they make it easy to operate much longer. Various types of trusses make it possible to form buildings with spans up to 24 meters, with various types of roofs (low-slope or pitched). Also, the coating can be equipped with lights, these are most often used in industrial and warehouse facilities of a high degree of responsibility.

Rafter and truss trusses are primarily the bearing parts of the roof, their calculation, design and installation should be carried out by specialists. The use of reinforced concrete trusses may be limited due to their weight - the weight of the truss 1FS 24 is 9200 kg. As a rule, reinforced concrete trusses are used for the installation of one-story buildings with a solid area. Often they are necessary for construction in difficult conditions of the Russian climate.

Types of reinforced concrete trusses

Depending on the design solution, reinforced concrete trusses may differ in size and type. Key solutions include:

Reinforced concrete truss trusses:

• FS - diagonal trusses in the form of segments for covering buildings with pitched roofs;
• FBS - bezraskosny segmental farms for covering objects with a pitched roof type;
• FBM - for covering buildings with a low-slope roof.
• FT - triangular bezraskosnye for covering buildings with pitched roofs.

Under-rafter reinforced concrete trusses are divided into:

• FPS - roof truss with pitched roof;
• FPM - roof trusses with a low-slope roof;
• FPN - farms for a low-slope roof with prestressed racks;
• FP - for slab-type coatings with a length of one span.

In the catalog of the Complex-S company you will find any farms with delivery throughout Russia. You can also order individual production of reinforced concrete products from us.

Marking of reinforced concrete trusses

Traditionally, reinforced concrete trusses are marked with a code consisting of an alphanumeric combination.

The first group indicates the standard size of reinforced concrete products (truss serial number), as well as the design type and length of the product in meters (rounded to the nearest integer).

The second part indicates the serial number of reinforced concrete products in terms of bearing capacity, the class of prestressing reinforcement, the type of concrete (for lightweight concrete products).

The third group of labeling is additional, it may include factory information about the product. For example, resistance to the influence of aggressive environments, seismic activity, the presence of additional embedded parts, the permeability of concrete.

For example, consider a farm 1FPS 12-6AIVL-C(11960x550x2200 mm), where:

• 1 - truss standard size;
• FPS - truss truss for a pitched roof;
• 12 - length in meters;
• 6 - bearing capacity index;
• AIV - class of prestressing reinforcement;
• L - lightweight concrete;
• C - use is permissible with seismicity up to 8 points.

On the surface of the concrete goods, the brand, weight, date of issue of the batch and the stamp of the Quality Control Department are also indicated.

The calculation of truss structures of complex shape requires knowledge of information from typical series and. The specialists of the Complex-S company are always happy to help with the choice of a reinforced concrete truss. It is also worth considering objective indicators:

• The weight of the truss and the entire truss system with roofing;
• Mass and action of additional loads - snow and wind;
• Additional temporary and periodic loads from vibrations, seismic activity, etc.

Reinforced concrete trusses differ from other types of roof structures in high strength, rigidity and crack resistance. Also, concrete products do not burn, do not rot, do not suffer from corrosion. High frost resistance and moisture resistance allow to use in any climatic conditions.

Often, technologists try to make the farm as light as possible in order to reduce both the price of reinforced concrete products and the pressure on the base of a one-story building. Often, lightweight concretes are used for this purpose, which, without loss of quality, can reduce the weight of a reinforced concrete structure. The inner part of the truss includes high-quality reinforcing steel with anti-corrosion treatment, so the roofing parts of the building are reliably protected from the effects of precipitation, condensate and temperature extremes. For industrial buildings, special reinforced concrete products resistant to various kinds of chemical corrosion are also produced. In the company "Complex-S" you can order trusses of popular and complex designs with delivery throughout Russia and Kazakhstan. We work with leading manufacturers and always ensure the speed and care of the delivery of concrete products.

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

Calculation features

Given the importance of the functions of truss and truss trusses, the process of their calculation, design and installation must be taken as seriously as possible. The smallest inaccuracy can destroy the entire structure ().

The elements made of reinforced concrete are used for the longest and most reliably. However, the complexity of installation, combined with a large final weight, limits the use of this type of rafter. 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, a certain amount of knowledge is necessary. In this case, GOST 20213 89 is used for trusses made of reinforced concrete.

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

That is why such calculations should be carried out at the design stage by people who are well acquainted with this area. Every detail is important here - from the choice of the rafter design option itself to the choice of 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 roofing and the weight of the truss system.
2. The weight of 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 overall 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 reinforced concrete trusses, which is capable of performing work with minimal errors. When installing rafters, it is especially important to securely fasten all the elements so that the stability of the object is not reduced.

Roof trusses made of reinforced concrete

Such structures can vary significantly in appearance, based on their parameters, including the coating material used and how they are supported. With their help, you can build structures with huge spans (more than 24 m). In addition, the roof can be pitched or low-slope, and lanterns can be used to cover structures.

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

The main advantages of such structures:

• high strength qualities;
• good rigidity;
• resistance to low temperatures;
• resistance to aggressive environments;
• fire safety.

Production of concrete elements of load-bearing structures

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

Vibrating tables with special cassette molds are used to create racks and braces laid during reinforcement.

In the photo - reinforced concrete beams and reinforced concrete trusses

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

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

Labeling process

To mark such material, letters and numbers written with a hyphen are used.

The letters indicate the size and type of the workpiece, and the numbers display, including:

• additional information;
• bearing capacity;
• grade of concrete used.

With the help of letters, such a characteristic of concrete as permeability is also displayed, which shows how well the structure is adapted to operate under aggressive conditions:

• the letter "P" denotes reduced fitness;
• with the help of the letter "H" normal fitness is displayed;
• products that can withstand 8-point seismological events are designated by the letters "C".

Structural features of reinforced concrete roof trusses

The truss acts as a skeleton that represents what the shape of the roof will be. In order for the frame to be rigid, strong and stable, it must be made using a large amount of steel and reinforced materials, which greatly complicates its scheme. Only such a design can ensure the safety of the building even under extreme weather conditions ().

However, all the same, manufacturers are trying in every possible way to reduce the weight of such a “skeleton”. This is achieved, first of all, through the use of light grade concrete, which does not have any 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 resists corrosive attack. Due to this, the ingress of moisture or severe frosts in no way can affect the strength of the roof.

Two belts working on bending act as its contour, but the racks and braces responsible for the axial force are a lattice.

There are such main types of such farms:

1. Segment, for which the contour belt and the diagonal type lattice are characteristic.
2. Polygonal when the belts are parallel or in the form of a trapezoid.
3. Arched Beamless, characterized by rigid nodes.
4. Arched diagonal, having an upper belt with curvilinear outlines, as well as a rare lattice.

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

In addition, there is such a classification of farms:

• slanted.
• bezskosnye.
• typical.

Scope of various types of trusses

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

When covering one-story buildings with one or more spans with rolled materials, it is best to use standard reinforced concrete products.

There are currently many such options, let's dwell on their designations:

• FS - diagonal products used on pitched roofs;
• FBS - bezraskosny type of trusses used for pitched roofs;
• FP - products used as a slab covering, the length of which is similar to the length of the span;
• FPM - used on low-slope roofs without prestressing;
• FPN - for a roof with a small slope and prestressed racks;
• FBM - bezraskosnye products used on low-slope pitched roofs;
• FPS - found on pitched roofs;
• FT - trusses of a bezraskosny type with a triangular outline.

Nuances during installation

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

Tip: you should not start the installation without making sure that the quality of the elements, as well as their dimensions, are in full compliance.

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

Depending on the shape, a reinforced concrete truss can be:

1. Segment.
2. Arched diagonal.
3. Arched bezraskosnoy.
4. Polygonal.

The entire process of manufacturing such structures is carried out in accordance with GOST for concrete or reinforced concrete structures.

The main characteristics of this are:

• the strength of the concrete used;
• its density;
• response to low temperatures;
• diameter of the layer enveloping the reinforcement;
• steel used for reinforcement and its grade;
• response to corrosion.

Despite the high rates of strength and reliability, such structures are rarely found in private homes. This is explained by the complexity of the installation and the significant mass of the resulting roof. But most often, concrete goods data can be seen on buildings whose span exceeds 18 m, and the step is within 6-12 m.

If the span is less than 18 m, it will be more profitable 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 when developing buildings whose spans 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 the price / quality ratio, then the best options would be segment or arched. On such trusses, there is practically no change in the forces on the belts, while the height of their support is small, as a result of which the total weight of the structure is minimized, as well as the height of the walls.

Production of reinforced concrete trusses

The simplest production process is for the arched braced type, the nodes of which are reinforced very simply. All the resulting internal space can be filled with taps for various communication systems. Most often used in the installation of low-slope, flat or pitched roofs.

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

In addition, light wire frames are used, which prevent the formation of cracks during operation. To make it convenient to crimp the lower belt, it is recommended to use a frame length of less than three meters.

But to reinforce the elements of the lattice and the upper belt, welded reinforcing cages are used, which are installed in pairs in the support nodes. As a result, the strength of the frame along inclined sections increases. A set of transverse 6-10 mm rods, the pitch of which is 100 mm, makes up a welded frame used to reinforce the intermediate nodes of both chords.

For the transportation of ready-made structures, specially equipped equipment is used, for example, the FKP-16 farm locomotive. Due to the growing demand for lightweight steel structures, the demand for precast concrete products is falling. However, according to fire safety requirements, reinforced concrete farms are the best.

Conclusion

The designs given in the article refer to massive construction, which cannot be done with your own hands, it is better to use special equipment for this. The manufacture of these products should also be given to professionals using modern materials and load calculation technologies ().

These reinforced concrete products are indispensable in the construction of buildings that require wide spans. The video in this article will help you find more information on this topic.