Overlappings, on the wooden beams applied in modern low building (where wood is a local material), have small weight, but are rotted, insufficiently fire-resistant and labour-consuming. For increase of durability of wooden overlappings wood antiseptirujut.
Select and stack beams, observing such requirements. Beams (logs), usually from a pine, a fur-tree, a larch, for interfloor and garret overlappings should be dry (admissible humidity - no more than 14%; at correct storage wood gets such humidity in a year). The drier a beam, the it is stronger and the caves in from loading less.
If sexual beams of the ground floor lean against the columns put often enough beams of interfloor and garret overlappings lean against walls only the ends and is rare when under them put support. That interfloor beams did not cave in, they should be calculated and stacked carefully on distance of 1 m from each other, and even is closer.
The strongest on a bend a beam is a bar with a parity of the parties 7:5, i.e. the beam height should equal to seven any measures, and width - only to five measures. The round log maintains the big loading, than vytesannyj from it a bar, however it is less strong on a bend.
Usually beams cave in under pressure upon them of weight zasypki, a floor, furniture, people etc. the Deflection basically depends on beam height, instead of from its width. If, for example, two identical bars to bolt and shponkami such beam will sustain cargo already in 2 times bolshy, than both these of a bar laid nearby. Therefore it is more favourable to increase beam height, than its width.
However and in reduction of width there is a limit. If the beam is too thin it can be bent aside. The deflection of beams of interfloor overlappings is admissible no more than 1/300 lengths of blocked flight, garret - no more than 1/250. If block an attic flight of 9 m (900 sm) the deflection should not be more than 3,5 sm (900:250=3,5 sm). Visually it is almost imperceptible, but the deflection nevertheless is.
Any overlapping, even under loading, will be absolutely equal, if in stacked beams preliminary vytesat so-called building lifting. In this case to the bottom party of each beam form a smooth curve with lifting in the middle.
a Fig. 27. An arrangement bruschatyh and board beams :
1 - a wearing floor; 2 - zasypka on roofing felt or greasing; 3 - filing
At first the ceiling with such beams will be slightly raised in the middle, but gradually from loading vyrovnitsja and becomes almost horizontal. With the same purpose it is possible to apply the logs bent in one party to beams, accordingly podtesyvaja them.
The Thickness of beams for interfloor and garret overlappings should equal not less than 1/24 its lengths. For example, establish a beam in length of 6 m (600 sm). Its thickness means should be: 600:24=25 see If it is necessary vytesat a rectangular bar with a parity of the parties 7:5, take a log in diameter 30 see
It is possible to replace the Bar with two boards the general section equal to a bar. Such boards usually force down nails, having them in chessboard order through 20 see
At more frequent packing instead of logs (bars) it is possible to use the ordinary thick boards put on an edge.
We Will consider such example. Of 5 m with loading in 1,26 tn are necessary for flight in length two beams of rectangular section 200x140 mm or three boards section 200x70 the m laid with step 50 see It is possible to lay and four boards section 200x50 mm with step of 33 sm (fig. 27).
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