Support fastenings of metal runs. Calculation and installation of wooden roof trusses Fastening girders to metal trusses

1. Cutting the roofing into tapes and laying the tapes under the Mauerlats and linings. 2. Laying mauerlats. 3. Laying corner runs. 4. Laying supporting elements. 5. Production and laying of linings. 6. Installation of support trusses. 7. Installation of the lower rafter shields. 8. Strengthening of supporting trusses, lower rafter shields and rafters with wire twists with ruffs driven into the masonry. 9. Installation of upper trusses. 10. Installation of crate shields. 11. Installation of fillies. 12. Lathing eaves overhangs at the corners. 13. Removal of diagonal liners. 14. Setting screeds. 15. Manufacture and installation of struts. 16. Manufacture and installation of racks for diagonal rafter legs. 17. Making and staging of sprigs. 18. Sheathing of rafters with bars. 19. Installation of the ridge board. 20. Device dormer windows with slotted openings in the crate. 21. The device of cuts near pipes.

Table 3

Norms of time and prices for 100 m2 of roof slope

B. Installation of trusses and installation of coatings on trusses Scope of work

1. Slinging structures. 2. Lifting of structures with a tower crane and installation in the design position. 3. Temporary fastening. 4. Slinging and final fastening.

Table 4

Table 5

Time limits and prices for 1 truss or beam

D. Laying of girders, installation of decking and frames of lanterns Scope of work

When laying runs

1. Manufacture and fitting of joint mates in beams or composite runs from boards. 2. Making joists with trusses. 3. Drilling holes for bolts. 4. Laying runs on trusses with the setting of fasteners.

When installing flooring on runs

1. Acceptance of packages with materials. 2. Layout of boards or battens along the girders with cutting at the joints and overhangs. 3. Nailing. 4. Trimming the ends of boards or slats protruding beyond the edges of the slopes.

When arranging lamp frames

1. Marking and manufacturing of elements according to templates with the manufacture of all interfaces. 2. Marking and drilling of bolt holes. 3. Assembling the frame with fitting mates to each other and to the supports. 4. Hanging, reconciliation and jointing of the installed frame. 5. Bolting and nailing.

The covering of the building consists of a roof (enclosing structures), load-bearing elements(runs, roof trusses), on which the roof rests, and ties along the coating. In addition, for lighting rooms with overhead light and their natural ventilation in the roofing system of multi-span buildings, lanterns resting on trusses are arranged. Depending on the purpose of the premises, roofs can be warm or cold. By design, coatings are distinguished with runs and without them.

The coating with purlins consists of steel girders installed in the nodes of truss trusses, along which asbestos-cement corrugated sheets are laid for cold roofs, for warm roofs - galvanized steel profiled flooring (Fig. below). The domestic industry produces floorings with a height of 40.60 and 80 mm from sheets with a thickness of 0.8-1 mm. The size of the cross-section of the profiled decking (fig. below) depends on the load on the coating, the width is 680-845 mm, the length is up to 12 m. Factories can produce decking of unlimited length, but the length is limited due to transportation and ease of installation.

Profiled steel deck in a package (a) and profiled deck cross section (b)

The profiled flooring is laid along the girders, usually located at the nodes of the truss truss after 3 m. The flooring sheets are attached to the girders with self-tapping bolts with a diameter of 6 mm, the sheets are connected to each other along the long side with special combined rivets with a diameter of 5 mm (Fig. below).

Fasteners

Both types of connections allow you to perform fastening work, being on one side of the flooring. Steel consumption per 1 m 2 of coating is 10-16 kg (only from flooring).

The main advantage of profiled steel decking is the low dead weight of the roof. This is achieved in combination with the use efficient lung insulation (phenolic foam, polyurethane foam, expanded polystyrene), having a density of up to 50 kg / m 3. On fig. The roofing assembly with profiled decking is shown below.

Roofing unit using profiled steel decking

1 - profiled flooring; 2 - vapor barrier; 3 - insulation;

4 - waterproofing carpet; 5 - combined rivets;

6 - self-tacking bolts

No-running warm roof performed, as a rule, from large-panel reinforced concrete slabs directly laid on the upper chords of truss trusses.

The size of such slabs is 3x6 or 3x12 m (rarely 1.5x6 or 1.5x12 m). It depends on the distance between trusses (truss spacing). The slabs have embedded parts that are welded to the truss belts. A vapor barrier, a heater, a leveling asphalt screed and a waterproofing carpet of several layers of roofing material on bituminous mastic are laid on reinforced concrete slabs. The main disadvantage of the coating of large-panel reinforced concrete slabs is a large load from its own weight (up to 2.5 kPa), which increases total consumption metal on the supporting structures of the building.

When laying reinforced concrete slabs on the belt corners of truss trusses, these corners, with their small thickness, are reinforced with overlays t = 12 mm. This must be done if the thickness of the girth corners is less than 10 mm with a truss pitch of 6 m and less than 14 mm with a truss pitch of 12 m. To drain water, the roof is given a slope, which depends on the roof material. For roll materials this slope is 1/8-1/12 when protected roll roofing a layer of bituminous mastic with embedded gravel, the slope can be 1.5% (almost flat roof). Cold roofs from metal sheets usually have an angle of 1/5, and from asbestos-cement sheets 1/3,5.

Roof purlins are solid (rolled and cold-formed) or lattice. Rolled purlins made of channels or I-beams are heavier than lattice ones, but much simpler and cheaper to manufacture, which explains their predominant use. The most common runs with a truss step of 6 m are made from channels that are simply attached to the truss chords (fig. below). They are better than I-beams, they work with oblique bending.

The disadvantage of the channel run is a narrower shelf than an I-beam of the same number or the same bearing capacity. Runs located on an inclined upper chord are subject to oblique bending due to vertical loads. They are calculated for the load from the weight of the roof and snow. This load q is decomposed into components along the main axes of the section of the run: q x = qcosa - perpendicular to the slope; q y =qsina along the slope (fig. below). Due to the low rigidity of the run relative to y-y axis, even a small bending moment along the slope M y causes large stresses in it and creates the need for a significant increase in the cross section of the run. To reduce the adverse effect of the slope components (load q y), strands are placed between the runs in the plane of the slope (Fig. below).

With steep roof slopes or under heavy loads, as well as with a truss pitch of 12 m, two strands are usually installed, and with gentle slopes and a truss pitch of 6 m - one. The setting of the strands turns the run in the plane of the slope from a single-span beam into a two- or three-span continuous, which significantly reduces the bending moment M y from the slope components q y . AT vertical plane the purlin works like a single-span beam.

Thus, the design bending moments in the run can be determined from the following formulas (fig. below):

with one weight:

M x = q x l 2 /8; M y = q y l 2 /32;

with two strands (in a theoretically dangerous section of the run, coinciding with the junction of the strands):

M x \u003d q x l 2 /9; M y = q y l 2 /90;

where l is the span of the run (equal to the step of the trusses).

Strands are made of round steel structurally with a diameter of 18 - 22 mm.

The deflection of the runs is checked only in the plane of its greatest rigidity (relative to axes x-x), it should not exceed 1/200 of the span.

To the calculation of runs

a - general form; b - diagram of the load action; c - calculation schemes

Rolling runs are attached to trusses on bolts of normal accuracy with the help of corner shorts welded to the truss belt (see figure above).

The truss truss includes several structural elements, represented by braces, racks and crates. The rigidity of this design determines the reliability of the roofing skeleton and allows you to transfer the total load from any type of roof to the walls of the structure. Most often, roof trusses are made of wood, and the basis of this design is based on the use wooden planks, wood-round timber or timber.

Variety of designs

Wooden roof trusses long years enjoy well-deserved popularity. Ecologically pure material differs in lightness, durability and relative cheapness, and the implementation of the construction technology allows you to get a durable and high-quality frame. In addition, it is possible to choose a design that will combine external aesthetics and functionality.

Today, there are two main types of truss wooden trusses, which have structural differences:

Farms based on layered rafters.

Wooden ones belong to the category of spacer structures, which are used in the arrangement of span ceilings and have small dimensions. The presence of an average load-bearing wall allows you to install a roof truss of this type with a span span of no more than eighteen meters.

Mounted under such conditions, the truss has the necessary margin of structural strength and stability, which makes it possible to easily withstand not only snow and wind load, but also the weight of the roof itself.

Farms based on hanging rafters

It is a system that consists of several rafters and has nodes connected with a cut or nails.

It has several options. They can be symmetrical and asymmetrical, as well as gable or single-sided.. Such trusses are based on the presence of a pair of rafter legs, united by tightening, which allows you to neutralize all the expansion forces formed during operation.

When making a roof with a length of more than eighteen meters, it is necessary to install crossbars, which increase rigidity and reduce the deflection of the rafter legs. For assembly, the cutting method or fastening with metal brackets is used.

Roof truss classification

When choosing a design and material for rafters, the material of the walls is taken into account. Supports for roof trusses can be represented by reinforced concrete or metal types of columns, as well as brick walls and truss trusses.

Design features determine the classification of such structures based on the following features:

• the outline of the belts;
• constructive design;
• static schema;
• lattice type.

The most significant criterion on the basis of which the division of farms into Various types, is represented by the outline of the belts, which is determined not only by various roof structures and the parameters of the overlapped spans, but also by the magnitude of the load.

The field of industrial construction is characterized by the arrangement of roofs flat view and the use of roof trusses with a parallel version of the belts. The best option for roofing material from asbestos cement or steel is a trapezoidal variety load-bearing structures. In the field of residential housing construction, the use of roof trusses with a triangular shape is most in demand.

Any variety requires application the best option lattice systems. Arrangement of farms with the presence of parallel belts or having a trapezoidal shape requires the implementation of a triangular lattice with reinforcement with additional racks. In addition, a split type of beam scheme or gratings equipped with sprengels are quite popular.

The device and nodes of wooden trusses

The main task for the high-quality fixing of any nodes in the truss truss is the reliable fixation of the joints of two or more beams. Under standard conditions, the following options for fastening nodes in roof trusses are used:

• knots of connections of legs with Mauerlat;

• joints of legs with elements of a wooden truss, if necessary, increase the rigidity and strength of structures;

• knots of rafter connections in order to lengthen them.

In addition, depending on the connection method, it is possible to obtain a rigid or sliding mount. It should be remembered that a rigid mount requires a careful approach. Weather conditions can provoke the expansion or contraction of wood, which is dangerous by the formation of deformation changes in load-bearing walls.

Rigid joints

• cutting on rafter leg . The depth of the cut should not exceed a third of the height of the board, and the rafters should rest against the Mauerlat and be fixed with a pair of nails at an angle and one fastener driven in vertically.

• sewing retaining beams on rafter legs. Hemming a meter bar to the rafter leg with an emphasis on the Mauerlat and lateral fastening by means of metal corners.

Sliding joints

The sliding connection of nodes is used for the construction of layered rafters. The hanging type of rafters has an emphasis on ridge run, a bearing walls do not experience thrust loads. It is for this reason that such rafter system does not require sliding knots.

How to calculate correctly

Immediately before the calculation, it is necessary to determine the operational loads:

• constant, including the total weight of the proposed roofing, roofing cake and crates;

• variables dependent on weather and other conditions;

• special, involving the installation of any equipment on the roof.

The main stages of calculations are made taking into account the following rules:

• load calculation is performed for each square meter mounted roof;

• for the calculation of wooden roof trusses, it is necessary to take into account the type and species of wood;

• section and size parameters roof structure depend on the angle roof slope and the size of the building;

• the difference in calculations for layered and hanging truss systems should be taken into account.

The simplest wooden truss truss is a construction based on a triangle connection of the side segments and the base.

For spans of more than six meters, the structure must be strengthened by means of struts and racks. Their number, as well as the parameters of the section and the place of installation should also be taken into account in the calculations.

To obtain high-quality calculations with a minimum level of error, it is recommended to use special computer programs.

DIY manufacturing

To make it right, you need to pay special attention to the marking of the rafters. Without exception, all the details of the future roof structure are made on the ground, for the convenience of forming a farm, it is advisable to use special goats.

Roof trusses are recommended to be pre-assembled "for profit". This rule primarily applies to end trusses. The finished structure must be installed parallel to the wall being installed and have a strictly vertical position. The correctness of assembly and installation is checked by temporary fastening and pulling the cord from the bottom corner of each truss to the top of the opposite structure.

Installation technology

The installation of wooden roof trusses has some features and is carried out in accordance with a certain technology:

• the ends of the legs of wooden trusses should rest on the Mauerlat, which is located on top of the load-bearing outer walls;

• if the span width is in the range from ten to twelve meters, it is required to mount one intermediate support, and if large sizes span, two such supports are installed;

• installation of trusses should be carried out from the bottom up, and the starting point is the installation of intermediate supports, beds and backing boards;

• next step self-assembly trusses is the installation of racks, which can be aligned with a plumb line, and these elements are fixed with a pair of special fastenings;

• further, the prepared wooden trusses are laid with a ledge on the support beam of thirty centimeters and fixed with bolts and brackets.

The installation of trusses is completed with the installation of supports and battens. It should be remembered that operational and specifications finished roof completely depend on the type of wooden trusses and the quality of their installation.

For more information about installation and fastening with your own hands, see the video.

The secondary truss pairs of plank roofs rest on purlins, which in turn are supported by wall gables and/or main trusses. As in timber roof structures, purlins can be installed vertically and obliquely under the rafters and under the crossbars (Fig. 83). To be held by uprights, forming vertical and inclined chairs, and by crossbars (collars) of the main trusses.

Rice. 83. Location of runs

Purlins installed vertically perform better than inclined purlins. A board placed on edge from a properly applied (vertical) load flexes and twists less than a board set flat or at an angle. Wooden beams tend to sag even under their own weight (Fig. 84). Therefore, it is recommended to install the purlins vertically - the rigidity increases and the production of cuts on the rafters is simplified to ensure their horizontal support on the purlin.

When splicing a run along the length, you can get a split and continuous beam. The split purlin support is made directly below the connection node so that it supports both parts of the purlin. Support for a continuous run is done under the long run (Fig. 85).

Rigidity of runs increases:

• an increase in the entire height of the section by one or two steps from the design value;
• reduction of spans - the introduction of racks and slopes under them;
• changing the height of the section in places of greatest deflection - the introduction of a supported sub-beam (Fig. 86);
• the introduction of cantilever beams under the supporting ends.

If the runs are designed between firewalls (fire walls) that do not allow installation wooden beams into the structure of the walls, then they are installed through steel shoes (Fig. 86).