In low-rise construction for the production of wooden roof rafters attics, as a rule, coniferous timber is used.
For various elements and parts of the rafter timber system, a certain type and grade of wood is used. When using sawn timber in a truss-beam system, the following properties and indicators of wood must be taken into account: bending strength, compression, chipping, wood density and moisture content.
Wooden truss structures must necessarily correspond to the special degree of fire resistance of the room. They must necessarily be treated with special fire retardants and impregnations.
There is a huge variety of options and elements of the device of wooden truss structures. There are the following types of rafter structures: layered or hanging rafters, combined, with a tightening, etc. The most popular rafter structures are layered and hanging.
The cheapest known type of rafters. They are used if the distance between all supports is no more than 6 meters.
They are installed in buildings and rooms with an average load-bearing wall or columnar intermediate supports, while resting the ends on the outer walls of the house, and the middle part on the inner walls or supports.
Slanted wooden truss systems are produced with a different number of racks - this allows you to significantly increase the width of the entire span of a building or room.
Consider their options:
For attics, wooden truss systems without middle supports are usually chosen, this is done so that the internal layout of the room does not depend on the location of these supports.
With the same width of the building, a roof with layered wooden rafters can be lighter when compared to other rafter systems.
They are used for roof spans 6- 12 m without additional supports. The attic floor is attached to the hanging rafters. If the span is more than 6 meters, then a vertical bar is attached between the upper ends of the rafter legs.
In order to avoid sagging of the entire structure, a horizontal tie is attached to the lower end of the timber using strip steel clamps to support the beams of the entire attic floor.
If the span is up to 12 m, then struts are introduced into the structure of the rafters, which reduce the estimated length of all rafter legs.
Hanging wooden rafters work in both compression and bending.
Below we will consider the types of rafter structures:
Not infrequently, to increase the entire area of the attic in the system of wooden hanging rafters, puffs are not used, but struts are used.
In this case the rafter legs are cut into the Mauerlat itself. The lower plane should lie on the wall, and in the upper one you need to make certain cuts for the correct connection with the rafter legs.
All struts rest against the end of the wooden beam. In this case, the loads that would be compensated by the tightening are directly transferred to all walls. As a result, this solution of a wooden rafter system is possible only if there is a special massive structure of the house wall.
Hanging rafters are parts and elements of rafter structures that are located in the same vertical plane and are connected to each other using cuttings, bolts, nails, clamps and brackets.
There is a combined rafter system - this is the installation of both a layered and a hanging rafter structure, which alternate in turn.
Where there are no intermediate supports, hanging rafter systems are used, and where they are present, layered rafter systems.
They are used for spans up to 15 m. Spans of this length require certain intermediate spacers, that is, special ties. They are mounted at the height of the building between two rafters and tied. And the longitudinal struts prevent lateral bending.
All structures with retaining wooden beams must be assembled in the form of rafter structures reinforced with special supports, which will rest on the cross beams and all load-bearing walls, as well as in the form of truss systems. The concept of a sprengel is a structural element of the type of an open triangular bar system, which is attached to the main rafter supporting structures.
Stiffness of the structure of this roof is given by a longitudinal brace or brace.The use of struts reduces the overall load on the entire structure. Vertical struts are usually attached with beams or uprights using cuts, trunnions, steel pads.
All the load from the rafter legs goes to the racks, which transmit it further to the supporting main walls. With this structure, the load will be distributed between all load-bearing walls. The uprights are attached to the heads of the main bearing walls. The lower ends of all struts are attached with suspension trunnions.
Sprengel beams are made of solid solid wood or glued board.
They are usually small in height. Good and high-quality bearing capacity of truss beams is carried out using a truss system and wooden beams supporting it.
Schrengel beams can cover huge spans. Sometimes they are equipped with steel belts.
Produced according to the type of rafter trusses.
Lattice trusses are divided into types according to the shape of their openings: triangular, trapezoidal or parallel belts. Usually, lattice trusses are made symmetrical, but other options are also possible, for example, single-pitched shapes. A common lattice girder includes top and bottom chords, struts and braces.
Reliable and high-quality connection of load-bearing wooden structures with central supports into one common system is called a frame. The racks and beams connected to the frame are necessarily fastened together or included in each other.
Today, there are two main types of frames - double-hinged and three-hinged. Double-hinged frames are equipped with a deadbolt that runs across the entire width of the finished frame. These frames are best suited for structures with a small angle of inclination. Three-hinged frames consist of two equal halves, which support each other in the area of the roof ridge. Three-hinged frames are used where a more significant angle of inclination is needed.
The calculation of roof structures and the final selection of their elements and details should be entrusted to specialists. The roof is subject to enormous loads. In addition to its own weight, it is influenced by wind loads, torrential rains, hail, snow and ice. The roof quite often undergoes various deformations: from temperature to seismic.
( 22 marks, average 4.
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Posted By: Work Style |12, Nov 2020
Posted By: Work Style |13, Nov 2020
Posted By: Work Style |03, Nov 2020
Posted By: Work Style |06, Nov 2020
Posted By: Work Style |03, Nov 2020