IN brick buildings interfloor ceilings are laid from reinforced concrete slabs along the 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, the joints between the flight and the platforms are sealed with cement mortar and inventory fences are installed.
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.
Concrete roofing coverings and lintels are the strongest and at the same time one of the most fragile structures that are used in construction. They are able to withstand enormous distributed pressure, but they collapse as soon as a point load is applied to them. As long as the reinforced concrete products have a solid support underneath, they are reliable and durable. If there is empty space underneath them, they begin to bend under their own weight. To avoid concrete destruction, it is necessary to provide it with support from below. And only powerful runs can cope with this task.
Reinforced concrete purlins are reinforced products with increased resistance to bending loads. In essence, this is a powerful long beam for horizontal gain ceilings and wide openings on which other elements are laid building structure. The entire applied load is transferred to the auxiliary system of purlins, and they already transfer it to load-bearing walls, trusses or other supports. For getting best characteristics For bending strength, the purlin profile is made high and narrow. And in order to provide it with reliable and stable support on other components, they are supplemented with shelves.
Classification
The main types are rectangular (PRG) and T-shaped (PR) reinforced concrete beams. The latter, depending on the profile features, are divided into two types:
- with a perpendicular shelf - grades from 1PR to 3 PR;
- with diagonal - 4PR and 5PR.
5 cm are left in the beams themselves through holes or are released from above metal hinges for slinging during installation work. The embedded elements (plates, anchors) are coated with an anti-corrosion compound.
Also, purlins may differ in reinforcement scheme:
- unstressed – reinforced only steel frame from AIII rods;
- pre-stressed, where in addition there are longitudinal prestressing rods that increase the load-bearing capacity of the product.
Marking features
Mass production and use began in the 60s. It was then created normative base for their manufacture - a series of working drawings, according to which concrete factories still produce their products. They were never combined into any single package of documents, so the markings of the purlins are slightly different from different manufacturers.
By brand you can determine not only the dimensions of the product, but also the shape of its section:
- P – general designation for a monolithic purlin.
- P – has supporting flanges, that is, in cross-section it looks like a T-beam.
- G – rectangular profile shape.
After the letter abbreviation, the rounded main dimensions are indicated, expressed in decimeters. Width and height are selected from a range of values - 12-40 and 30-50 cm, respectively, length starts from 2.78 m. general information comes the permissible load, that is, the main characteristic of the load-bearing element, expressed in t/m. Next is the symbol for the fittings.
The last thing in the product labeling is the permeability properties of concrete for aggressive gas environments: normal (N) or reduced (P). It may also contain information about embedded elements or the use of heavy concrete (t). The latter is not regulated by GOST, but is separately indicated in a series of working drawings 1.225-2 (issue 12).
Sometimes reinforced concrete purlins rectangular section PRGs are labeled differently. After the general abbreviation of the name “P”, the calculated load is placed in hundreds of kilograms per meter of length. That is, P40 is a girder that can withstand, in addition to its own weight, another 4000 kgf/m (series of drawings II-03-02). In later technical documentation, an addition to such markings appeared. The number following the load already indicates the length in decimeters, and after it the letter “p” is placed, indicating rectangular shape profile (1.225-2 issue 5).
Characteristics
To produce purlins, fairly heavy grades of concrete with varying strengths are used. It is selected depending on the size of the product and the characteristics of the reinforcement:
- 3.58 m – M200;
- 2.78 and 3.15 m – M250;
- 5.98 m with spatial reinforcement – M300;
- 5.98 m with prestressed reinforcement - M350.
The density of these concretes reaches 2.5 t/m3, and if we also take into account the dimensions of the reinforced concrete products and the weight of the steel rods, the mass of an individual product turns out to be rather large - from 150 to 1500 kg. The bearing capacity of each beam is 39.2 kN/m, which allows their use in the construction of large public buildings and residential buildings made of blocks or solid brick. However, it should be taken into account that the specified design load is the limit of the capabilities of a reinforced concrete structure, after which its destruction begins.
When choosing, it is better to focus on the standard indicator (without taking into account the reliability coefficient). For the PRG, these data are given in the accompanying note to a series of working drawings and amount to 28.9 kN/m for long-term exposure or 33.4 kN/m for temporary exposure.
Application and installation
GOST 26992-86, according to which reinforced concrete purlin beams are produced, assumes their use for the installation of flat roof coverings with a slope of no more than 5%. Products with shelves of the 1PR and 2PR brands, as well as 4PR and 5PR, can be mounted on sloping roofs (up to 25%).
However, in construction they are no less widely used to form window openings, strengthening garage and hangar doors, as rigid supports for slab floors with weak self-supporting ability. These are universal products that can completely replace reinforced concrete lintels or crossbars if the load on the beams is too great.
Due to the considerable weight and work at heights, the use of lifting equipment is required. Related operations are performed by four workers: two riggers below and builders in the area where concrete products are installed. The beam is laid horizontally on cement mortar with support on walls, load-bearing columns or reinforced concrete pillows, creating an additional stiffening rib. Formed on top roofing pie or ceilings made of reinforced concrete slabs are installed.
Price
Purlins are manufactured only in factories according to the series of drawings II-03-02, 1.225-2 and 1.225-1. Special requirements requirements for their reinforcement and the selection of concrete characteristics in accordance with the purpose and dimensions of the products. So, pouring them directly on site, like a floor slab, will not work - in any case, you will have to look for where to buy beams at the best cost.
The price of reinforced concrete products is influenced by the size of the purlins, that is, their material consumption. The brand of fittings and its consumption play a role. If serial reinforced concrete products are not suitable for the project, non-standard purlins of intermediate sizes can be ordered from the factory. Manufacturers have an impressive range of such products, so finding the necessary beams will not be difficult.
| Run | Weight, kg | Price, rub/unit |
| Rectangular section | ||
| PRG 17.1.3-4 | 150 | 1 730 |
| PRG 28.1.3-4t | 250 | 2 870 |
| PRG 36.1.4-4 | 430 | 3 190 |
| PRG 58.2.5-4 | 1 450 | 11 270 |
| P40-28p | 240 | 2 840 |
| P40-36p | 410 | 3 530 |
| P40-60p | 1 500 | 14 220 |
| T-section | ||
| PR 45.4.4-3 | 1 550 | 3 660 |
| PR 60.4.4-5 | 2 050 | 7 820 |
The release of beams from the factory to end users is strictly regulated by GOST. At the time of shipment, the strength of the concrete surface must be at least 70% of the declared grade. IN winter period these requirements are becoming more stringent, so reinforced concrete purlins are sold with characteristics that are 90-100% consistent with the design ones.
A purlin in roof construction is a horizontally placed beam between the supporting structure and the roof sheathing. Its key functions are transferring the load from the roofing covering, its uniform distribution in the rafter system, and also ensuring the rigidity of the sheathing.
Purlins are made of wood, steel and reinforced concrete and are used in the construction of roofs 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. The supporting beam of the sheathing rests on it.
- 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 bent profile beams of 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. Purlins can be unstressed, reinforced with a 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.
An example of marking a 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 made from 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.
Covering structures
Coating industrial buildings comprises:
Roofing structures (layers)
Load-bearing elements - purlins, trusses
Depending on the technological features
production of roofing coverings are
Warm
Cold.
Depending from constructive solution roofing coverings are divided into:
Coverings by purlins
Non-rubbed coatings
Choosing a roof design should be made on the basis of a technical and economic assessment of options, taking into account:
− cost of materials
− cost of manufacturing structures
− cost of installation of structures
− cost of transportation.
In addition, it should be taken into account
Purpose of the building;
Technological features of production
Temperature and humidity conditions of the environment
Construction area and the presence of production facilities in the area for the production of structures;
Transportation conditions;
Providing installation mechanisms.
Coating composition
| Item no. | Coating layers | Material |
| Protective layer | Bikrost, filiizol | |
| Waterproofing layer. | Uniflex, | |
| Leveling layer. | Cement-sand screed, asphalt-sand screed | |
| Insulation. | Mineral wool slabs, foam concrete, expanded polystyrene, foam silicate, gas silicate, expanded clay concrete | |
| Vapor barrier. | Folgoizol 1 layer | |
| Load-bearing roof elements | ||
| 6.1. Roofing by purlins | - continuous purlin - through purlin - profiled steel decking - flat steel sheet - corrugated steel sheets- asbestos cement corrugated sheets | |
| 6.2. Roofless roofs | - steel panel frames - expanded clay concrete slabs - reinforced concrete slabs | |
| Roof trusses and covering connections |
Roofing by purlins
Runs installed in increments of 1.5 or 3 m
on the upper chord of the trusses at their nodes
or on the top chord of beams.
Roofing by purlins is much lighter, economical in terms of metal consumption, but more labor-intensive during installation.
Usually used as purlins
At a pitch of 6 m, rolled or bent profiles.
With a pitch of 12 m, it is more advisable to use through structures.
Steel profiled flooring or small-sized reinforced cement, expanded clay concrete, and asbestos cement slabs are laid along the purlins.
Supporting the purlins on the truss
The profiled flooring is laid on purlins spaced every 3 m.
With a pitch of trusses of 4 m, the flooring can be laid between the trusses.
Profiled sheet
Profiled decking is made of thin galvanized rolled steel with a thickness of t=0.8-1 mm
Sheets like " N" Designed for floor coverings. Sheets like " WITH" designed for wall cladding.
In the designation of a profiled sheet, the first digit is the height of the corrugation - h; second – sheet width – B 1 ; the third is the thickness of the sheet. For example - N 57-750-0.7– covering flooring whose fiber height is 57 mm; sheet width excluding overlap – 750 mm; sheet thickness – 0.7 mm.
The length of the profiled sheet is up to 12 m.
Purlin designs.
The purlins take the load from the roof and transfer it to the roof trusses.
There are runs solid and lattice.
Continuous purlins are used with a truss pitch of 6 m. They are heavier than lattice ones, but easier to manufacture.
As purlins when stepping trusses 6 m use rolled beams, bent profiles (C-shaped or Z-shaped). Z-shaped sections are very convenient to transport.
Bent profiles can also be used with a truss pitch of 12 m, but in the case of small snow loads they are not permissible
I-beams with a perforated wall can be used as purlins.
At truss step 12 m use through lattice purlins (small farms overflight 12 m)
The upper belt of lattice purlins is made of two bent or rolled channels.
The cross-section of the lattice is taken from a single bent or rolled channel.
There may be other structural trusses of lattice purlins.
Calculation of continuous runs.
With small roof slopes, the work of the purlin is no different from the work of a conventional rolled beam on two supports.
On a roof with a large slope, the purlins bend in two planes.
q=q cr +q sn +q pr
Although the pitch component is small, the stresses from it in the purlin are large due to the low rigidity of the purlin relative to the Y axis.
Therefore, in order to reduce the bending moment from the pitched component, the purlins are distributed with strands, made of round steel with a diameter of 18-22 mm.
In ridge panels, the tie rods are attached to the roof truss or to the ridge purlin. In this case, the ridge girder must have greater horizontal rigidity.
Assembly of the tie rod to the girder
Depending on the technological features of production, roofing coverings are warm and cold.
As insulation -
They use slabs from mineral wool, glass insulation,
Various cellular slabs are used as thermal insulation─ cellular concrete, foam concrete, foam silicate, expanded clay concrete, cement fiberboard.
Synthetic materials- foamed polyurethane - polyurethane foam; phenol-formaldehyde foams.
Thermal insulation layer- protects interior space from external temperature influences. The thickness of the insulation is determined by thermal engineering calculations.
Leveling layer- cement strainer, asphalt screed ─ is the basis for the waterproofing carpet and creates required slope when flat roof.
Roof slope
Depending on the type of coating adopted, the required roof slope is established to ensure drainage:
For roofs with gravel protection, the slope is 1.5%;
For roofing made of rolled materials without gravel protection - 1/8-1/12;
For roofing made of asbestos-cement or reinforced-cement sheets - 1/4 -1/6.
-Vapor barrier layer -
Vapor barrier prevents the penetration of air vapors from the room into the insulation.
Vapor barrier laid on load-bearing elements before insulation.
Vapor barrier – foil insulation, 1 layer of glassine
Non-rubbed coatings
Reinforced concrete or metal panels or large slabs are laid between the trusses.
Recently, the most widely used metal panels. Panel width -1.5 – 3 m.
Panels combine functions enclosing and load-bearing structures
Panels coatings are completely manufactured at the factory.
They are easy to install, however they are heavier roofing along purlins, especially if reinforced concrete panels are used.
J.b. panels lead to increased consumption of materials for underlying supporting structures - trusses, columns, foundations.
The longitudinal ribs of the slabs rest on the upper chord at the truss nodes.
In the case when the width of the slab is 1.5 m, trusses are made of trusses to avoid off-nodal load transfer.
Weight reinforced concrete slab-2-2.5 kn/m.
The most common are reinforced concrete ribbed slabs coverings.
The length of the slabs is 6 and 12 m.
Width 1.5 and 3 m.
The slabs are laid on the upper chords of the trusses and welded to the trusses by welding embedded parts.
Support unit reinforced concrete panel to the farms
Weight reduction is achieved by prestressing reinforced concrete structures or by using vaulted roofs.
Three-layer sandwich coating panels
Comprises top facing layer:
− profiled flooring with a large profile;
− galvanized iron t=1 mm;
Middle layer
Polyurethane insulation t=50-80 mm;
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 farms. 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 are not used as elements of load-bearing structures. |
| 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 a 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 roofs and roofs with a slight slope) and oblique (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.
