Reinforced concrete purlins. Installation work in the construction of brick buildings

A roof girder is a horizontally placed beam between the supporting structure and the roof batten. Its key functions are the transfer of the load from the roofing, its even distribution in the rafter system, as well as ensuring the rigidity of the sheathing.

The girders are made of wood, steel and reinforced concrete and are used in the construction of roofs for industrial buildings and private houses. They are also installed as foundations for floor slabs and to reinforce openings.

Run in the rafter system

Roofing and construction beams

Before starting construction, study the types of beams to understand how the roof works. Each beam has its own purpose and occupies a certain place in the floor system.

Roof beams are made of metal, solid wood or lamellas glued together. Bent-glued beams are made according to GOST. They are easy to work with, have little exposure to the weather and are used to extend the gaps between runs. The section of the elements can be rectangular, T-shaped or I-beams. The shape of the I-beam (H) guarantees the rigidity of the beam, reduces the bending moment to almost zero.

Broken roof scheme with purlin

Types of timber construction beams in the roof support system:

• mauerlat - a square beam laid on the walls to support the rafters;
• ridge - a support bar at the top of the roof;
• rafter beam - forms the angle of the roof slope;
• tightening and crossbar - connect the rafters of opposite slopes;
• filly - lengthens the rafters, forming a roof overhang;
• brace - is located at an angle to the vertical elements and supports the rafters;
• run.

Sheathing scheme from wooden elements

The runs are fixed on supports at a distance of 4-5 meters from the ridge, and expanding supports are placed between them. If you need to lengthen the rafters, the joint is placed over the girder.

The structure and types of metal roof beams:

• lower belt
• top belt
• lattice.

The lattice is assembled from racks and braces and attached to the belts on both sides with the help of shaped elements.

Types of purlins for roofing

Girders are classified according to their location in the roof slab system, as well as shape and material.

Types of application in the truss system

There are three types of girder supports - lateral, ridge and Mauerlat.

Ridge run- this is the highest roof beam, it is mounted in the upper parts of the gable walls, and the edges are wrapped with a waterproof material. If necessary, the structure is reinforced with racks. The rafters rest on the ridge with the upper end.

The ridge fixed in the gables of the walls

Mauerlat or matitsa is a thick timber with a section of 150x150 mm, which is laid on the load-bearing walls parallel to the ridge in order to equally distribute the load from the roof. Mauerlat boards are called the foundation of the roof and are firmly fixed with anchor bolts on the walls, after having laid a waterproofing material. V brick buildings the mat is installed in a pre-prepared reinforced concrete armored belt on the reinforcement.

Mauerlat laid on a concrete wall on top waterproofing material

The side girder connects the rafters in the middle - with its help, the roof is strengthened, reducing the bending load of the rafters. To transfer the load to the floor, install under the side girders vertical posts.

Classification of beams by material

As mentioned above, girder supports are classified by material into reinforced concrete, metal and wood. Metal purlins are manufactured industrially and can be homogeneous or lattice. The first ones are made of channels and I-beams - they are easy to manufacture and install, cost 10% cheaper than lattice ones. The disadvantage of lattice girders is the high cost and a large number of complex nodal elements. The advantage is low weight.

Runs can be:

• whole;
• composite.

Composite beams are used when it is necessary to cover the roof large area to avoid distortion from bending loads.

Categories of wooden supports by construction

Structurally, purlins are classified into:

• continuous;
• split;
• with struts;
• cantilever-beam;
• with bolsters.

Split ones are rows of wooden supports fixed on the roof slopes and resting on supporting structures - pillars. Often secured with struts and struts.

Diagram of cantilever and continuous purlins

Cantilever-beam - these are enfilade rows of boards less than 6.5 m long, the joints of which are located outside the support beams. In this case, two consoles are formed in the middle intervals, and one in the outer ones. Cantilever beams are used in the construction of roofs with a step of load-bearing structures up to 4-5 m.

Continuous girders are suitable for roofs with a slope of up to 15 ° and covered with lightweight materials - roofing felt or shingles... With a greater slope, thin beams cannot withstand bending loads and break.

To strengthen the structure in construction, struts and supports are used:

• A bolster is a small block mounted on a support post. The supporting beam of the lathing rests on it.
• A brace is an inclined beam that supports horizontal beams and works in compression.

The struts contribute to an even redistribution of loads from the pavement to the supporting elements.

Grouping reinforced concrete purlins by profile

Reinforced concrete girders are marked according to the section shape and load. By cross-section, runs are:

• T-shaped;
• rectangular.

Reinforced concrete block rectangular

T-type beams are divided into two more groups:

• beams with metal perpendicularly attached to the ribs of the purlin - installed on the roof with a slope of up to 25%;
• supports that can withstand a roof slope angle of more than 25%.

T-supports are used in the construction of roofs for large unheated rooms, as well as in seismically active regions. They can withstand temperatures as low as -50 ° C. The key feature of T-shaped reinforced concrete supports is the presence of holes for hooks and other grippers, which ensure ease of installation.

Supports of rectangular cross-section - high and thin-walled, strong due to bends. They are classified into solid and lattice.

Gradation of metal components along the profile

Solid metal purlins are curved profile beams of several types:

• C-shaped;
• I-beam;
• Z-shaped;
• tavrovy;
• channel.

The T-profile in cross-section resembles the letter T, the I-profile - H, and the channel - the letter P.

Types of metal beams with a lattice profile:

• bar-truss with a bottom chord and a grating made of round steel;
• three-panel.

The three-panel girder is accepted as a typical one due to the smaller number of nodes and ease of manufacture. The upper chord of the beam is made of a double channel, and the lattice is made of curved single channels.

Labeling of industrial products

Runs in construction are critical structures, they are made in strict accordance with GOST and are marked. To select beams that correspond to the purpose of the roof, you need to navigate the product labeling.

Reinforced concrete blocks for roofing

Reinforced concrete girders are marked with letters and numbers, investing in the value information about the dimensions and support load of the products. The letters represent the series and design features girder:

• PR - a beam in the form of a brand with a side;
• P - one-piece run;
• PRG - support of rectangular section.

The numbers indicate the length, width and height of the purlin, and the latter indicates the load that it can withstand, in tons. Also, the marking can include values ​​about the reinforcement of the product. The purlins are either unstressed, reinforced with a steel frame or prestressed, with additional longitudinal reinforcement bars to increase the bearing capacity.

Product dimensions are taken into account when marking

Also in the production of reinforced concrete structures, markings are used of the type:

• 1PR - for flat roofs with reinforcement without reinforcement;
• 2ПР - for flat roofs with reinforced fittings;
• 3PR - for structures with a slope of up to 5%;
• 4PR - for roofs with a slope of up to 25%;
• 5PR - with a diagonal shelf for steep roofs.

An example of marking a reinforced concrete run with decoding: PRG 48-2-5-4tAIII-1. This is a rectangular purlin with dimensions of 4800x200x500 mm and a permissible load of 4 tons. It is pre-stressed, reinforced with additional reinforcement. Suitable for the construction of heated and unheated critical structures in areas with poor weather conditions and seismically active areas.

Metal roof elements

Metal beams mark by profile, design, material and dimensions.

Classification and marking of I-beams:

• Ш - with a wide shelf;
• K - columnar;
• B - ordinary.

The number in front of the letter indicates the nominal height of the beam in mm, the remaining dimensions are selected in accordance with GOST. For example, for support 30B1, the height is 296 mm, and the letter "B" denotes a normal beam. The dimensions of the beams are in the range of 10-100 mm.

Hot rolled purlin production

Metal beams for purlins are made of steel by welding or hot rolling - for each manufacturing method, GOST is provided, which describes the marking of products.

Advantages and disadvantages of purlins depending on the material

Going to build a roof compare positive sides and the disadvantages of each material. For example, metal does not provide sufficient energy efficiency for a building, but it is durable. And the tree is subject to decay, but retains heat.

Metal beams in construction

List of pros and cons for metal purlins.

Advantages:

• withstand a significant load;
• fireproof;
• durable;
• there is no waste during installation, thanks to the high precision of the parts.

Disadvantages:

• freeze when low temperatures Oh;
• difficulties in transportation;
• heavy weight relative to wood;
• expensive material.

Metal is susceptible to corrosion

List of positive and negative characteristics of timber beams.

Advantages:

• economical;
• easy to install;
• retain and transfer heat.

Disadvantages:

• annual treatment with antiseptics is required;
• there is a risk of fire on the roof.

Below are the pros and cons of reinforced concrete products.

Rafter system made of wood

Advantages:

• increased fire safety;
• environmental friendliness;
• strength and durability;
• not subject to corrosion and decay.

Disadvantages:

• heavy weight;
• laboriousness of installation and fastening of elements.

In private housing construction, roof systems are most often made of wood, and metal elements- girders or crossbars, additionally strengthen the structure. Reinforced concrete blocks used in the construction of roofs for industrial buildings.

The reliability of the roof does not allow for savings, so be sure to consult with a specialist to clarify all the nuances and get advice specifically on your construction site.

Reinforced concrete girders PRG are manufactured in accordance with the 1.225-2 series, are intended for overlapping openings in the walls of public buildings and buildings for administrative purposes from bricks or wall blocks and are designed for a design pressure of 4000 kgf / m, i.e. used in load-bearing walls with the ability to support both the floor slabs of the PC and the overlying masonry.

They are made of heavy concrete of the M-250 brand for compression, and for 6-meter ones - M-350. Reinforcement is possible in 2 variants: prestressed, reinforced with prestressed reinforcing bars of the ATV brand and space frames and unstressed, reinforced only with space steel frames. Most often they are produced not stressed, that is, with conventional reinforcement.

Since the load of the overlying wall is quite large, and the surface area on which the purlin presses is rather small, it is recommended to use base plates as linings during construction, which allow the load to be distributed over a larger surface.

The standard length of the product provided by the series can be 2.8; 3.2; 3.6; 4.2; 4.8; 5.4 and 6 meters. However, it is possible to order reinforced concrete girders and intermediate sizes.

Marking

Marking consists of alphanumeric groups separated by a hyphen:

• The 1st group contains the designation of the PRG type - rectangular purlin and dimensions(length, width, height in dm.).
• The 2nd group includes the design load without taking into account its own weight (in tons / m) and the class of reinforcement used.

For example, PRG 32.1.4-4АтV - a girder of rectangular cross-section with a length of 3180 mm, a width of 120 mm, a height of 400 mm under the design load without taking into account its own weight 39.2 kN / m (4 tn / m), reinforced with AtV steel, i.e. ... pre-stressed.

Dimensions and support

Reinforced concrete girders are reinforced concrete products with high level resistance to bending loads. They perform the function of beams-lintels, rest on the walls of the building and special supports - trusses or crossbars. To move and install the beams, a special lifting technique is used. On their upper face there are reinforcement loops or through holes up to 5 cm in diameter, designed for a secure grip. Installation is carried out on cement mortar with the help of embedded parts.

In the manufacture of this type of concrete goods, dense concrete of grades from M200 to M600 is chosen with high rates of resistance to cracking, fire resistance, frost resistance, water resistance.

Usage

They are a support for structural elements of administrative, agricultural, industrial buildings, residential complexes made of bricks or blocks. It is these buildings that have a large roof area, but an insufficient amount support points under it. Application of beams:

• as a base for slabs floor slabs, especially with a weak self-bearing capacity;
• strengthening the rafter system;
• like over wide doorways, window openings, especially if there is a likelihood of increased loads on them;
• in construction flat roofs(slope less than 5%);
• as connecting elements between separate parts large structure;
• creation of technological niches.

Types of buildings for which reinforced concrete beams are intended to cover:

• Unheated, in which the roof is laid directly along the lintels.
• Heated, with a roof laid on insulated slabs.
• Heated, equipped with light enclosing structures (slope up to 5%).

Terms of use for runs:

• air temperature not lower than -40 and not higher than + 50C;
• seismicity not higher than 7 points;
• the effect of the gas environment is not higher than the average aggressive one.

It is permissible to operate them at temperatures below -40 and above + 50C if the requirements for all characteristics of the building structure are met.

Views

According to the form, the runs are classified into:

• rectangular - are in the form of reinforced concrete pillars of simple rectangular section or with recesses;
• T-shaped (in the form of the letter T) - with a shelf for supporting the slab;
• with a one-sided shelf (series 1.255.1-3) - have the shape of an inverted letter G.

T-shaped reinforced concrete products are distinguished by the shape of the shelf and the reinforcement:

• 1ПР - the shelf is at right angles to the rib, non-tensioned reinforcement made of longitudinal rods, intended for use in the construction of buildings with a roof slope of up to 25%;
• 2ПР - a shelf at a right angle, prestressed reinforcement (reinforced to increase the bearing capacity), also designed for buildings with a roof slope of up to 25%;
• 3PR - shelf at right angles, prestressed frame, intended for use in the installation of buildings with a roof slope of up to 5%;
• 4PR - oblique shelf, non-tensioning reinforcement, roof slope 25%;
• 5ПР - oblique ledge, prestressed frame, roof slope 25%.

The tensioned reinforcement (frame) during the manufacture of the purlin, before the concrete is poured, is subjected to compressive stress at the points where it is expected to experience the greatest tension. Due to such processing, the strength characteristics increase, the resistance to cracking increases, and the consumption of reinforcing steel decreases.

Marking

The marking of purlins of different shapes has some differences. For rectangular ones, it looks like PRG 40.2.5-4AIII, where:

• PRG - rectangular section;
• 40 - length 4000 mm;
• 2 - width 200 mm;
• 5 - height 500 mm;
• АIII - type of fittings.

Dimensions indicate product-specific, rounded. If the length of the beam is 4180 mm, then it is called PRG 42. At the end it can be letter designation concrete - t (heavy).

For T-beams of the 1.255-2 series, the marking is as follows - 2PR-1 AtV-N, where:

• 2ПР - type;
• 1 - serial number according to the bearing capacity;
• AtV - reinforcement class;
• H is the characteristic of the permeability of concrete for aggressive substances (in the given example, normal), if at the end instead of the letter H is P, this means that concrete with reduced permeability is used, suitable for use in a moderately aggressive environment.

Specifications

The main parameter when selecting concrete purlins is their load bearing capacity(maximum permissible load). For rectangular products, it is calculated and expressed in kilograms per running meter... For this type, regardless of size, it is equal to 400 kg / r. m.

For T-units, the unit of measurement is kilonewton per meter (kN / m) or kilogram-force per meter (kgf / m). According to GOST, each type (1PR, 2PR, etc.) has a different maximum permissible load. It depends on the reinforcement and the strength class of the concrete. According to this parameter, six types are distinguished: the larger the number denoting the serial number of the run, the greater its bearing capacity.

Calculated permissible load T-bar reinforced concrete beams 1PR (fittings without prestressing):

The bearing capacity of other brands of this type of reinforced concrete products can be specified according to the tables from GOST 26992-86.

Dimensions and weight

Rectangular purlins have the following dimensions:

1. Width - 120 or 200 mm. The marking indicates 1 or 2.
2. Height - 300, 400 or 500 mm. On the product they are designated 3, 4 or 5.
3. Length - from 1000 (PRG 10) to 6380 (PRG 64) mm. If necessary, you can pick up almost any size, step - 1-20 cm. Six-meter ones are most in demand.

Weight depending on dimensions - 150-1500 kg.

In addition to marking, a series can be indicated in the characteristics; they are made according to different drawings. The dimensions of the T-section girders and their weight are standard. For grades 1PR, 2PR, 3PR (straight shelf) they are (in mm):

• length - 5970;
• width - 220;
• height - 300 mm;
• weight - 500 kg.

For grades 4PR, 5PR (oblique shelf):

• length - 5970;
• width - 160;
• height - 370;
• weight - 400 kg.

For brands P, PR:

• length - 6280, 5980, 3280, 2980;
• width - 420 or 540;
• height - 440, 520.

The running beams PR with a one-sided flange can also have a length of 4480 and 8980, a width of 380, and a height of 740 mm.

The brand PR (series 1.335):

• length - 4540, 5690;
• width - 200, 220;
• height - 350.

Some manufacturers have the ability to make a batch of products custom size under the order.

Prices

The characteristics on which the cost depends: concrete grade, size and type (series), manufacturer, batch size.

Price for reinforced concrete runs PRG (excluding delivery):

Reinforced concrete girders of the T-section of the 1.255-2 series can be purchased for an amount of 5,000 rubles or more. Products with a single-sided shelf range from:

• 448 - 9500;
• 598 - 24 000;
• 898 cm - 54,500 rubles.

The cost of T-shaped and L-shaped types depends on the same parameters as for the PRG brand.

Reinforced concrete girders of rectangular or T-section are used as supporting elements for slabs, floorings for covering buildings, for strengthening the upper part of openings, and for other purposes. They are made from durable grades of concrete, reinforced with a frame made of steel reinforcement. The size range of the running beams makes it possible to use them in the construction of any structures.