Good afternoon, dear guests and subscribers of the "Build for myself" channel!
The construction of any house is not complete without the use of dowel joints. A dowel connection is a type of connection when a cylindrical element (dowel) is tightly installed in a pre-prepared hole in shear parts. In such joints, the dowel takes on the load both for crushing and bending, and for shear.
In other words, any rod that holds several elements together can act as a dowel: a hairpin, bolt, screw, self-tapping screw, nail, etc.
What does it mean to "work on a cut"? A shear in the fastener occurs when two oppositely directed forces act on the dowel. If two parallel boards are pulled together into one composite beam, then there is no shear, since the forces acting on both elements have the same vector. For example, if a load appears from above, then all the elements work in bending. But if two boards are knocked down with an overlap so as to lengthen the beam or trusses are assembled from the boards, in particular, rafter systems, then in these cases the shear force is always present:
The rafter leg tends to bend under various loads, and the tightening takes on this tension and opposes it, so the dowel works on a cut in the plane where both parts tend to shift to each other relative to a friend.
In the construction industry, any connection with the fastening of two or more parts must ensure reliability and high strength, the material of the nail must hold the load both in a plane parallel to its axis and perpendicular to her.
Today, threaded rods are one of the most popular products, since they are very convenient to work with: the length of the dowel is determined locally and the required size is cut. But, not everything is as rosy as it might seem at first glance. The hairpin has two major drawbacks.
Disadvantage number 1 - section
If the project provides for a bolted connection of a certain diameter, then using a hairpin, you automatically underestimate the working section of the dowel.
Below, I will give tabular data on the inner and outer diameters of the stud and if you take, for example, the stud 10 mm thick, the transition to a working diameter of 8.3 mm is automatically made, which is lower than the one set by the project magnitudes! The flexural strength of such a pin is 25% less, which is significant!
Drawback # 2 - crushing
But solid-threaded studs, as well as solid-threaded bolts, practically do not work for crushing. To work for crushing, the dowel must sit like a cast in the hole and tightly touch its entire body with the body of the hole made in the details. In practice, this is what happens:
Trusses are structures that are subjected to dynamic loads, they constantly take on wind and snow loads. coverings, in the presence of which the fasteners of even very tightly tightened parts will "play", since the thread cuts into the wood over time and appears backlash.
And in order for the pin to work normally for crushing, it should not be driven into the hole with a hammer, but cut into wood by rotation, it is then that such a dowel will ensure correct operation, but deficiency No. 1 will still remain - underestimated section.
Of course, you can buy oversized studs, but what is it all about?
All such compounds have been present in construction albums for a long time. It is in the joints of wooden elements that turning bolts or studs with an incomplete thread, as well as "wood grouse" screws in which the main working part is smooth, and the thread is only at the end.
In this case, it is important that the shear load acting from the displacement of the shear parts falls on withoutthreaded rod:
From the author
If you use a nail connection with a hairpin, then only as a safety net to tightly connect boards are like a vice and drive in 5-6 pcs of 150 or 200 nails, in which the working diameter is 4-5 mm. This is the case when the nails will take on all the loads described above instead of the stud ...
... or instead of nails a few wood grouse screws
That's all, thanks for your attention!
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