Good afternoon friends!
In continuation of the series of articles on floor beams, this material is devoted to the correct splicing of beams in height. Mechanical loads and arising stresses in wood force people for many decades of inventing various solutions to increase the load-bearing capacity of a structure at its optimum section. One of such solutions is V.S. Derevyagin's method.
What is correct splicing?
Correct splicing involves splicing the beams in such a way as to incorporate them into the joint work and make the structure work as a single mechanism, ensuring minimal displacement of the beams relative to each other, eg:
The picture illustrates how the displacement of the beams occurs when the entire structure is loaded. The horizontal scale gives an understanding of where the displacement occurs. In this case, we observe the sliding of the beams among themselves and the presented composite beam does not work as a single structure.
Therefore, when constructing such structures, builders always try to eliminate displacement and for this they use a lot of techniques. For example, overlays made of board or plywood, which in turn are attached to a composite beam using nails with the obligatory use of wood glue. Also, metal nail plates are used (photo below), which are pressed into the structure, preventing the displacement of individual elements.
I want to note that two adjacent beams double the bearing capacity, but by placing them in height one above the other, the bearing capacity increases 4 times, and knowing this - V.S. Derevyagin in 1932. developed and proposed an efficient way of joining two and three beams into a single composite beam structure.
So, the Derevyagin beam is a composite beam on flexible ties, which consists of two or three separate beams, fastened together with lamellar dowels. Dowels are installed in cuts with a depth of 1/6 of the height of a separately used beam.
As plates, hardwood is used, like birch or oak with a moisture content of no more than 15%. They are installed starting from the edge and ending with the boundary of the central section, which is limited to a length of 0.2 of the length of the beam (figure above), since in this section the shift is insignificant.
The lower beam, which is in the tension zone, is always better selected in quality than the beam of the compressed zone. As a rule, this is the 1st or 2nd grade, for the compressed zone - the 2nd or 3rd grade.
As you can see, on the right side of the picture above, there is a cut along the top of the beam. It is performed in order to remove the resulting stresses in the sawn timber during drying and to avoid the appearance of cracks on the sides.
There are various types of composite beams, including dowels or wedges:
But, the version of V.S. Derevyagin surpasses all these types, since there are no tie bolts in it at all. The Derevyagin method is applicable even for edged logs with a natural slope. The beam easily withstands alternating and dynamic loads.
The span overlapped by such a composite beam is limited by the standard length of the lumber and splice lengthwise is strictly unacceptable.
Beam production is available at the construction site and does not require expensive special equipment; it is enough for the contractor to have a manual chain slotting machine (milling cutter).
If the spliced beam has a width greater than the depth of the chain-slotting tool, "blind" sockets are made and the lamellar pins are fixed on both sides of the beam in a checkerboard pattern.
In individual construction, plates are often replaced with round dowels, since a round hole is always easier to make. As a material for the key, you can use a high-quality birch shank from a shovel. The dowels are glued into both beams and the result is a reliable and inexpensive design that provides excellent load-bearing capacity!
I will be glad if the article is useful to you! Good luck with your construction!
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