IN brick buildings interfloor ceilings stacked from reinforced concrete slabs along walls and crossbars.
Crossbars (purlins)(Fig. 1, a, b) rest on reinforced concrete pads, which are laid in brick walls during the laying process. The difference in the marks of the top of the pillows within a section of the house should be no more than 10 mm.
Figure 1. Installation of the crossbar (purlin): a - view of the support on the wall; b - on a pole; 1 - reinforced concrete pad; 2 – runs
Before installing crossbars (purlins) Use a level to check the horizontality of the support pads. The crossbars are slung using two loops, brought to the installation site and lowered onto a bed of mortar spread on the supports. The crossbars are brought to the design position using mounting crowbars. The crossbar can only be moved perpendicular to the longitudinal axis, working with the paw of a crowbar. Otherwise, the stability of the walls or pillars on which the crossbar rests may be compromised. Installers work from inventory scaffolds. After checking horizontality (by level and sighting on previously installed crossbars), verticality (by plumb line), the crossbar is attached to the previously installed installed structures(the method of fastening is indicated in the project) and then remove the slings.
Before installation floors check the position of the upper supporting parts of the masonry under the floor structure, which must be in the same plane (the difference in marks within the floor should not exceed 15 mm).
To ensure the horizontality of the ceiling formed by the ceiling, use the following techniques. Within an occupation (section) of the building along the perimeter of the top of the walls or purlins, using a level or flexible level, marks are applied (on pre-fixed slats) that correspond to the installation horizon, i.e. the mark at which the bottom of the floor structures will be located. A leveling layer of mortar (screed) is laid along the leveling marks (along the mooring cord), leveled with the rule, and after the screed has acquired 50% strength, the floor slabs (panels) are mounted, spreading a layer of fresh mortar 3-4 mm thick on the supporting surfaces .
Figure 2. Laying floor slabs: 1 - box with solution; 2 - shovel; 3 - tool box; 4 - crowbar; 5 - plate
The installation of the ceiling is carried out by a team of four people: a crane operator, two installers (4th and 3rd categories) and a rigger (3rd category). The rigger slings the slabs with a four-legged sling. Two installers are on the floor (initially on scaffolding), one at each support of the slab being mounted (Fig. 2). They receive the supplied slab, unfold it and guide it when lowering it to the design position.
After alignment, the floor slabs are secured by welding the mounting loops to the anchors embedded in the walls during laying; adjacent slabs are fastened with anchors using the mounting loops.
The connections between the floor and the walls are sealed after the installation of the floor. In hollow core floorings, when they are supported on external walls for the purpose of insulation, the voids are filled lightweight concrete or ready-made concrete plugs to a depth of at least 120 mm. Voids in slabs resting on internal load-bearing walls, sealed with heavy concrete or liners. This is necessary to protect the supporting parts of the floor slabs from destruction under the pressure of the overlying structures.
Jumpers. Load-bearing lintels in brick buildings, like purlins, are installed by lifting them by mounting loops and laying them on a prepared mortar bed, while ordinary lintels are laid manually. During installation, ensure the accuracy of their installation along vertical marks, horizontality and the size of the supporting area.
Staircases and landings. The elements are installed as the walls of the building are erected. Before installation landings and marches check their sizes. Then the installation sites for the platforms are marked, a layer of mortar is applied and the platform is installed. The intermediate platform and the first march are installed along the course of the masonry interior walls the staircase, the second (floor) landing and the second flight - upon completion of the floor laying.
The flight of stairs is slung with a four-legged sling with two shortened branches, which give the lifted element a slope slightly greater than the design one. When installing flight of stairs it is first supported on the lower platform, and then on the upper one. If the landing of the march on the support platforms is carried out in the opposite way, then it may fall off the upper platform or it may get jammed between the upper and lower platforms.
Before installing the flight, installers make a bed of mortar on the supporting places of the landings, spreading it and leveling it with trowels. When installing flights, one installer is on the lower platform, the other is on the overlying ceiling or on scaffolding next to the staircase. Accepting the march, the assembler directs it towards staircase, moving simultaneously to the upper platform. At a height of 30-40 cm from the landing site of the flight, both installers press it against the wall, give the crane driver a signal and install first the lower end of the flight, then the upper one. Installation inaccuracies are corrected with a mounting crowbar, after which the sling is unhooked and the joints between the march and the platforms are sealed. cement mortar and install inventory barriers.
Flights of stairs without mounting loops are lifted using a fork.
Balcony slabs . The installation of balcony slabs begins along the entire length of the grip after laying the floor. First, beacon slabs are installed along the edges of the grip, marked on the ceiling and the position of the balcony slab is recorded with marks. On subsequent floors, the position of the marks is additionally controlled along the balcony of the underlying floor, using a plumb line for this. After installing the lighthouse slabs, a wire mooring cord is pulled along their outer upper edge to the length of the entire grip and the remaining slabs are installed along it. The slabs are usually slung with a four-leg sling. The mortar bed is leveled with a trowel, not bringing it 2-3 cm to the edge of the wall. Balcony slabs are laid by two installers, monitoring the correct lowering of the slab along the risks and the mooring cord. The slab must be laid horizontally or with slight slope to the free end. The horizontal installation of the slab is checked by laying the rule with a level in two perpendicular directions. When sloped in the longitudinal direction, the slab is raised and lowered again, replacing the mortar bed. The slope towards the building is eliminated when installing temporary racks or rods.
Temporary fastenings are installed immediately after laying the slab. To do this, the racks are placed on the balcony of the underlying floor and, using a screw spacer, they support the mounted slab.
The slab remains suspended on the crane hook until the temporary fastening is installed, the position of the slab is adjusted and the embedded parts are welded to the anchors. Balcony slabs are secured by welding steel rods to the mounting hinges of the floor and balcony slabs.
Strength building structures help to provide reinforced concrete products. Their shapes and sizes are varied. Some produce directly on construction site, others are prepared in production. No construction is complete without reinforced concrete purlins.
Definition
The appearance and structure of the purlin are almost no different from a reinforced concrete pillar. Outwardly they look like frozen concrete mortar With metal frame inside. What is the difference between the runs? The designs are distinguished by their large mass, long length and enhanced strength. The production of structures is not on stream; their production is associated with the need for the element to withstand a certain load.
Purpose
Reinforced concrete purlins are used in construction to solve an important problem. For example, not a single opening can be made without using a purlin. Only after its installation are the floor slabs attached. And reinforced products made under the influence of heat treatment can withstand heavy loads. Used in public construction, industrial buildings with brick and reinforced concrete walls. Most often they are used in the construction of openings, supports on which floor slabs are attached.
Installation of the purlin: a) view of the support on the wall; b) on a pole; 1. reinforced concrete pad; 2. runs. Reinforced concrete purlins are prepared exclusively in an industrial manner, in accordance with state construction standards. For their production, only heavy concrete is used, most often M200 and M300, with the use of reinforcement for reinforcement. Use of structures in favorable conditions increases the service life of buildings.
Kinds
Reinforced concrete purlins are divided into types, which are formed according to the shape of the product and the grade of concrete. The purlins are assigned the following types
T-section
Channels and I-beams are used in production. This type is divided into two types:
- The first group includes products with metal located perpendicular to the rib of the purlin. They are suitable for the construction of buildings that have a roof slope of approximately 25%. 1PR rod frame, 2PR pre-stressed, 3PR is used when the roof slope is no more than 5% - varieties of the first group.
- The second group includes products that can withstand a roof slope of 25%. It includes products 4PR stressed and 5PR artificially created tension.
These designs can be used for unheated rooms. Used in temperature conditions from - 40 to 50 degrees and exposure to gas. Characteristic feature is the ability to use products in the construction of structures in hazardous, seismically active zones.
The difference is the presence of special holes, through which the gripping devices are inserted, making it easier to lift and install the elements. Elements with T-section suitable for building construction:
- unheated with a roof made of cement and asbestos fibers;
- heated with lightweight ceilings;
- heated with cement roof.
Rectangular section
This type of purlin has an I-beam division. The rectangular cross-section of the purlins can be solid or lattice. The lattice type is lighter, the spacing of products is 6 meters, so it is used in construction much more often. To produce a continuous type, bent channels are used. Products with a rectangular cross-section have thin walls, but excellent height. The strength of the products is ensured by specially created fastening bends.
Marking
Example of marking runs. The manufacture of building structures is approached in compliance with state standards and technology. You can get maximum information about products by studying the product series. An inexperienced builder will not be able to get full information on labeling without knowledge. It is worth focusing on the transcript data.
For ease of use, a special classification in letters and numbers is used. They encrypt information about length, height, width, and support load. The first letters encrypt information about the series of runs:
- P - one-piece product.
- PR - the presence of a side located parallel or at an angle to the axis of the element.
- PRG - rectangular section.
The second group of signs contains information about the load and type of reinforcement. The third signs indicate the specific purpose of the material, including the features of the use of concrete composition.
For example: PRG 28-1-3-4t. PRG - rectangular section. The following series of numbers indicates the dimensions of the structure: 2800 mm long, 100 mm wide, 300 mm high. The 4t indicator indicates the ability to withstand a load of 4 tons per meter.
A purlin is a part of the structure of prefabricated reinforced concrete or brick structures, installed in a horizontal position and supported by load-bearing beams or trusses. The elements themselves also have impressive strength and are used as support for floor slabs or decking. There is a separate GOST for reinforced concrete purlins, which regulates all the requirements that products must meet.
In the photo - the purlins rest on the beams and perform a load-bearing function during the installation of floors and roofing decks
Main features of this type of structure
All purlins manufactured at factories of reinforced concrete products must comply with the standards of GOST 26992-86 “Reinforced concrete purlins for covering buildings of industrial and agricultural enterprises.” This one normative document determines what requirements each product must meet, while regulating a number of indicators:
| Strength | The design load of the products must be at least 4,000 kgf/m, which allows the elements to be used in the construction of load-bearing walls. |
| Types of sections | There are two types of sections: rectangular and T-shaped. IN construction reference books you can also find Z-shaped and C-shaped purlins, but they represent metallic profile and as elements load-bearing structures are not used. |
| Production material | The manufacturing material is heavy concrete grade M250, and for structures 6 meters long or more it is necessary to use the even more durable grade M350. |
| Reinforcement | There are two main options for reinforcement: unstressed, consisting of a spatial steel reinforcement frame, and stressed, which consists of prestressed reinforcing bars and a spatial frame. |
| Installation features | It is important to remember that the weight of the products is very large and installation work It is unlikely that you will be able to do it yourself - you will need lifting equipment. It is for this reason that purlins are not often used in private development. |
Important! Do not confuse purlins with jumpers. Lintels are used for similar purposes, but are much smaller in size and are not designed for heavy loads and cannot be used in load-bearing systems. Purlins are suitable for any purpose: from strengthening openings (especially large ones) to creating additional strength in places where reinforced concrete slabs support.
Purlins are much larger and more massive than jumpers
Types of purlins
Products are divided according to the type of section. There are two main options, each of which we will consider in more detail.
Rectangular elements
From the name it is clear that this type of product has rectangular shape and is marked with the designation PR. The scope of their use is quite wide; such elements can be found in many structures.
Each of the parameters is indicated by a Latin symbol, so that all the main parameters can be easily determined by the markings
Let us note the main features of this group of products:
- The use of heavy grades of concrete provides high strength indicators, which allows the use of purlins at any industrial facilities.
- There are two main design options: solid and lattice. The second option is lighter due to the presence of voids and is most often used when mounted on trusses; they are located in 6-meter increments.
- Prestressed reinforcing bars are used to increase strength. In ordinary products, a conventional frame is used.
Some options are very tall
Do not forget that the dimensions of reinforced concrete purlins are written in decimeters, the letter “T” means that heavy concrete was used for production. If there are additional factors, they are also noted in the labeling. Labeling instructions are the same for all manufacturers, so it is important to know the general rules.
Example. Let's look at the version of the 44.3.5-4T run, the marking indicates that the length of the element is 44 decimeters, the thickness is 3, and the height is 5 Dm, the design load is 4 tons per meter, heavy concrete was used in the manufacture.
Elements with T-section
Such elements are especially often used in areas with increased seismic activity, as they can withstand shocks of up to 7 points
For this group of products we can say the following:
- The high resistance of the material allows the use of purlins at significant temperature changes - from -40 to +50 degrees.
- The design of the shelves may also vary; they can be straight (great for flat roof and roofs with a slight slope) and slanting (this option is suitable for roofs with a slope of 25 degrees).
- Special holes with a diameter of 50 mm make loading and installation work easier. Now you can move elements not only with cranes, but also with other mechanisms - loaders, lifts.
- If increased reliability is required, it is necessary to purchase products with prestressed reinforcement; their price is slightly higher, but their strength is also greater.
With the help of T-purlins you can create a very durable structure
- In addition, pins may extend from the element for additional welding of the structure to other elements. Their number and location are agreed upon with the customer in advance.
- Also, for additional strength, additional supporting elements can be removed from the purlin. This option is also made only by special order.
Remember! Whatever option you choose, it is important that it is manufactured in accordance with GOST standards. Since it will be subjected to significant loads, the quality must be at the highest level.
Run – required element to strengthen any industrial structure, which is why it is so important to choose the option that is optimal in size and characteristics. The video in this article will highlight the nuances and features in more detail.
Reinforced concrete purlins PRG are manufactured in accordance with series 1.225-2, intended for covering openings in walls public buildings and administrative buildings made of brick or wall blocks and designed for a design pressure of 4000 kgf/m, i.e. used in load-bearing walls with the ability to support both PC floor slabs and overlying masonry.
They are made of heavy concrete grade M-250 for compression, and for 6-meter ones - M-350. Reinforcement is possible in 2 options: prestressed, reinforced with prestressed reinforcing bars of the AtV brand and spatial frames and unstressed, reinforced only with spatial steel frames. Most often they are produced unstressed, i.e. with conventional reinforcement
Since the load of the overlying wall is quite large, and the surface area on which the purlin presses is quite small, it is recommended to use support 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 produce reinforced concrete purlins and intermediate sizes upon request.
Marking
The 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.).
- Group 2 includes the design load without taking into account its own weight (in tons/m) and the class of reinforcement used.
For example, PRG 32.1,4-4AtV – run rectangular section length 3180 mm, width 120 mm, height 400 mm under a design load excluding dead weight of 39.2 kN/m (4 tn/m), reinforced with AtV steel, i.e. pre-stressed.
Dimensions and support
| Dimensions | Max opening width | Min support | Load kgf/m | |||
|---|---|---|---|---|---|---|
| Length | Width | Height | ||||
| PRG28.1,3-4 | 2780 | 120 | 300 | 2420 | 180 | 4000 |
| PRG32.1,4-4 | 3180 | 120 | 400 | 2820 | 180 | 4000 |
| PRG36.1,4-4 | 3580 | 120 | 400 | 3220 | 180 | 4000 |
| PRG42.2,5-4 | 4180 | 200 | 500 | 3780 | 200 | 4000 |
| PRG48.2,5-4 | 4780 | 200 | 500 | 4380 | 200 | 4000 |
| PRG54.2,5-4 | 5380 | 200 | 500 | 4980 | 200 | 4000 |
| PRG60.2,5-4 | 5980 | 200 | 500 | 5580 | 200 | 4000 |
A purlin in roof construction is a horizontally placed beam between the supporting structure and the roof sheathing. Its key functions are load transfer from roofing, its uniform distribution in the rafter system, as well as ensuring the rigidity of the sheathing.
Purlins are made of wood, steel and reinforced concrete and are used in the construction of roofs of industrial buildings and private houses. They are also installed as bases for floor slabs and to strengthen openings.
Purlin in the rafter system
Roofing and construction beams
Before starting construction, study the types of beams to get an idea of how the roof works. Each beam has its own purpose and occupies a certain place in the floor system.
Roof crossbars are made from metal, solid wood or lamellas glued together. Bent-laminated beams are manufactured in accordance with GOST. They are easy to work with, are little affected by weather conditions and are used to increase the intervals between runs. The cross-section of the elements can be rectangular, T-shaped or I-beam. The I-beam shape (H) guarantees the rigidity of the beam and reduces the bending moment to almost zero.
Scheme of a broken roof with a purlin
Types of wooden construction beams in a roof support system:
- Mauerlat - a square beam laid on the walls to support the rafters;
- ridge - support beam at the top of the roof;
- rafter beam– forms the roof slope angle;
- tightening and crossbar - connect the rafters of opposite slopes;
- filly - extends the rafters, forming a roof overhang;
- brace - located at an angle to vertical elements and props up the rafters;
- run.
Lathing scheme from wooden elements
The purlins are fixed on supports at a distance of 4-5 meters from the ridge, and expansion supports are placed between them. If you need to lengthen the rafters, the joint is placed above the purlin.
Structure and types of metal beams for roofs:
- bottom belt
- upper belt
- lattice.
The lattice is assembled from racks and braces and attached to the belts on both sides using shaped elements.
Types of purlins for roofing
Purlin supports are classified by location in the roof slab system, as well as by shape and material.
Types according to the place of application in the rafter system
There are three types of purlin supports - side, ridge and mauerlat.
The ridge purlin is the highest beam of the roof; it is installed in the upper parts of the gable walls, and the edges are wrapped with waterproof material. If necessary, the structure is reinforced with racks. The rafters rest on the ridge with their upper end.
Ridge fixed in the gables of the walls
Mauerlat or matitsa - thick timber with a cross section of 150x150 mm, which is laid on load-bearing walls parallel to the ridge in order to equally distribute the load from the roof. The Mauerlat boards are called the roof foundation and are firmly secured with anchor bolts to the walls, having previously laid down waterproofing material. In brick buildings, the matrix is installed in a pre-prepared armored belt made of reinforced concrete on reinforcement.
Mauerlat laid on top of a concrete wall waterproofing material
The side purlin connects the rafters in the middle - with its help they strengthen the roof, reducing the bending load of the rafters. To transfer the load to the floor, vertical posts are installed under the side girders.
Classification of beams by material
As mentioned above, according to the material, purlin supports are classified into reinforced concrete, metal and wood. Metal purlins are manufactured industrially and can be uniform or lattice. The first ones are made from channels and I-beams - they are easy to manufacture and install, and cost 10% less than lattice ones. The disadvantage of grid purlins is their high cost and a large number of complex node elements. The advantage is light weight.
Runs can be:
- whole;
- compound.
Composite beams are used when it is necessary to cover a roof large area to avoid distortion from bending loads.
Categories of wooden supports by design
Structurally, purlins are classified into:
- continuous;
- split;
- with struts;
- cantilever-beam;
- with support beams.
Split ones are rows of wooden supports fixed to the roof slopes and supported by supporting structures - racks. Often secured with struts and struts.
Scheme of cantilever-beam and continuous purlins
Cantilever-beams 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 gaps, and one in the extreme gaps. Cantilever beams are used in the construction of roofs with a pitch of load-bearing structures of up to 4-5 m.
Continuous purlins are suitable for roofs with a slope of up to 15° and a covering made of lightweight materials - roofing felt or flexible tiles. With a greater slope, thin beams cannot withstand bending loads and break.
To strengthen the structure in construction, struts and beams are used:
- A support beam is a small block mounted on support post. Relies on her load-bearing beam battens.
- A strut is an inclined beam that supports horizontal beams and works in compression.
The struts contribute to the uniform redistribution of loads from the coating to the supporting elements.
Grouping of reinforced concrete purlins by profile
Purlins made of reinforced concrete are marked according to their cross-sectional shape and load. The cross-sections of the purlins are:
- T-bars;
- rectangular.
Rectangular reinforced concrete block
T-type beams are divided into two more groups:
- beams with metal perpendicularly attached to the ribs of the purlin - installed on roofs with a slope of up to 25%;
- supports that can withstand a roof slope of more than 25%.
T-bar supports are used in the construction of roofs of large-area unheated premises, as well as in seismically active regions. They endure subzero temperatures up to -50°C. Key Feature T-bar reinforced concrete supports - the presence of holes for hooks and other gripping devices, ensuring ease of installation.
Rectangular supports are tall and thin-walled, strong due to the bends. They are classified into solid and lattice.
Gradation of metal components by profile
Solid metal purlins are beams bent profile several types:
- C-shaped;
- I-beam;
- Z-shaped;
- T-bar;
- channel
The T-profile in cross-section resembles the letter T, the I-beam - H, and the channel - the letter P.
Types of metal beams with lattice profile:
- rod-truss with a lower chord and a round steel grille;
- three-panel.
The three-panel girder is accepted as standard due to the smaller number of components and ease of manufacture. The upper chord of the beam is made of double channels, and the lattice is made of curved single channels.
Labeling of industrial products
Purlins in construction are critical structures; they are manufactured in strict accordance with GOST and marked. To select beams that correspond to the purpose of the roof, you need to be guided by the product labeling.
Reinforced concrete blocks for roofing
Reinforced concrete purlins are marked with letters and numbers, including information about the dimensions and support load of the products. The letters indicate the series and design features purlin:
- PR – T-shaped beam with a side;
- P – one-piece purlin;
- 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. The marking may also include values about the reinforcement of the product. The runs can be relaxed or reinforced steel frame or prestressed, with additional longitudinal reinforcement bars to increase bearing capacity.
Product dimensions are taken into account when marking
Also in production reinforced concrete structures use markings like:
- 1PR – for flat roofs with reinforcement without reinforcement;
- 2PR – for flat roofs with reinforced reinforcement;
- 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.
Labeling example reinforced concrete purlin with decoding: PRG 48-2-5-4tAIII-1. This is a rectangular girder with dimensions 4800x200x500 mm and permissible load 4 tons. It is pre-stressed and reinforced with additional reinforcement. Suitable for the construction of heated and unheated critical structures in areas with poor weather conditions and seismically active zones.
Metal roof elements
Metal beams marked by profile, design, material and dimensions.
Classification and marking of I-beams:
- Ш – with a wide shelf;
- K – columnar;
- B – ordinary.
The number before the letter indicates the conditional 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.
Production of hot rolled purlins
Metal beams for purlins are made of steel by welding or hot rolling– for each manufacturing method, GOST is provided, which describes the labeling of products.
Advantages and disadvantages of purlins depending on the material
When planning 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. Wood is susceptible to rotting, but retains heat.
Metal beams in construction
List of pros and cons for metal purlins.
Advantages:
- withstand significant load;
- fireproof;
- durable;
- There is no waste during installation, thanks to high precision details.
Flaws:
- freeze when low temperatures;
- difficulties in transportation;
- heavy weight relative to wood;
- expensive material.
Metal is susceptible to corrosion
List of positive and negative characteristics wooden beams.
Advantages:
- economical;
- easy to install;
- retain and transfer heat.
Flaws:
- annual treatment with antiseptics is required;
- there is a risk of roof fire.
Below are the pros and cons of reinforced concrete products.
Wooden rafter system
Advantages:
- increased fire safety;
- environmental friendliness;
- strength and durability;
- not subject to corrosion and rotting.
Flaws:
- heavy weight;
- the complexity of installing and securing elements.
In private housing construction rafter systems Most often they are made of wood, and metal elements - purlins or crossbars - further strengthen the structure. Reinforced concrete blocks are used in the construction of roofs of 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 project.
