JP2008002267A - Joint structure of lumber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joint structure of lumber which is excellent in tensile proof stress, and which has an advantage for the construction of a large-scale wooden building by the use of lumber. <P>SOLUTION: The flat end surfaces 1402 of the ends of each of the two pieces of lumber 14 are confronted with each other, and a metal sheet 36 is put together on the side 1422 of the lumber 14. Then a projection 38 is inserted to a recess 1424. Because of this, the flat end surfaces 1402 of the ends of the two pieces of lumber 14 are joined to each other in a state that they are maintained by being confronted with each other. The projection 38 is constituted by a cylindrical wall having a cylindrical surface of smaller outer diameter than the inner diameter of the recess 1424, and a taper part is formed at the tip of the cylindrical wall. The outer diameter of the taper part becomes smaller toward its tip. Then the projection 38 is fixed to the metal sheet 36 with a pitch of which the dimension is smaller than that of the pitch of the recess 1424 formed in each of the lumber 14 in a state that the flat end surfaces 1402 of the ends of the two pieces of lumber 14 are confronted with each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a joining structure of lumber having excellent resistance to pulling.

In recent years, large-scale wooden buildings such as domes have been built, but many of them use laminated timber.
The laminated wood is composed of wood bonded with an adhesive, and VOC such as formaldehyde is released after the building is completed.
In recent years, VOCs contained in building materials are gradually released after the building is completed, which deteriorates the indoor air environment and affects the human body such as sick house syndrome.

Therefore, it is considered that the problem of VOC can be solved by using lumber (rawed raw wood) instead of laminated lumber.
However, replacing the laminated lumber with lumber will cause other problems.
That is, in the case of a large-scale wooden building, the ends of the lumber are abutted and joined at a number of locations, but when the lumber is abutted and joined, the following problems occur.
First, when the lumber is used, it is naturally dried and artificially dried, but it is inevitable that the wood will crack during this drying process. When viewed from the mouth, cracks often enter a direction perpendicular to the annual ring from the center of the annual ring of the wood toward the outer periphery. Therefore, when force is applied to the struck portion, the force acts in the direction of tearing the tree (the pulling direction). If cracks exist in the wood at this time, the yield strength is greatly reduced. Even if there is no crack, the strength against pulling of wood is originally smaller than the strength against compression.

Second, even if the wood is cut accurately at the abutted portion, a gap may be formed on the contact surface between the woods due to deformation such as subsequent expansion, contraction, bending, warping, etc. of the wood. Many. In general, an epoxy resin or the like is injected into the gap, but a problem remains from the viewpoint of the VOC described above.
Thirdly, conventional lumber joining techniques have excellent resistance to compression, but none have excellent resistance to tension. (See Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4).
Japanese Patent Laid-Open No. 10-025810 Japanese Patent Laid-Open No. 10-025812 JP 2002-115339 A JP 2002-038591 A

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a lumber joining structure that is excellent in pulling resistance and is advantageous when a large-scale wooden building is built using lumber. There is to do.

  In order to achieve the above object, the present invention has a structure in which the ends of two lumbers in the longitudinal direction are joined using an abutting jig, and the two lumbers are flat at the ends of the two lumbers. Each of the lumbers extending on the same surface is provided with a recess, and the pressing jig is formed on the same surface. It consists of a metal plate fitted to the side of each extending lumber, and two protrusions that are provided on the metal plate and can be inserted into the recess, and the protrusions have flat end surfaces at the ends of the two lumbers. In the state of butting, the metal plate is provided at a pitch smaller than the pitch of the recesses formed in each lumber, and the two lumbers are butted against the flat end surfaces of the two lumber ends. The metal plate is fitted to the side surface of the lumber, and the protrusion is The flat end surfaces of the end portions of the two lumbers are thereby maintained in contact with each other and joined, the concave portion is a circular concave portion having an inner peripheral surface, and the protrusion is It has a cylindrical surface having an outer diameter smaller than the inner diameter of the concave portion, and a tapered portion whose outer diameter decreases toward the tip thereof is formed at the tip of the cylindrical surface.

  ADVANTAGE OF THE INVENTION According to this invention, the joining structure of the lumber which is excellent in the yield strength with respect to a tension | pulling, and is advantageous when constructing a large-scale wooden building using lumber is obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
First, the joining structure of Reference Example 1 will be described.
1A is a plan view of the joining structure of Reference Example 1, FIG. 1B is a front view thereof, FIG. 1C is a sectional side view, and FIG. 2 is a perspective view of the joining structure of Reference Example 1.
With the joining structure 12 of Reference Example 1, the end portions in the longitudinal direction of the two lumbers 14 are joined using one metal plate 16, two main drift pins 18, and four sub drift pins 20. ing.
The two lumbers 14 have the same cross-sectional shape with a rectangular cross section, and a flat end surface 1402 is formed at the end in the longitudinal direction.
The end surfaces 1402 at the ends of the two lumbers 14 are formed so that the two lumbers 14 extend continuously, more specifically, the upper and lower end surfaces of the two lumbers 14 are continuous, and 2 Their end surfaces 1402 are abutted so that the left and right side surfaces of the book lumber are continuous.

The metal plate 16 is embedded over both the lumbers 14 through the two end surfaces 1402 that are abutted with each other.
The metal plate 16 is formed in a rectangular plate shape having a thickness, a width larger than this thickness, and a length larger than this width. Examples of the metal plate 16 include iron, stainless alloy, and aluminum. An alloy or the like is used.
The metal plate 16 is disposed so that it passes through the center of each lumber 14 in the width direction and both surfaces thereof extend in the longitudinal direction of the lumber 14 along the height direction of the lumber 14.
In addition, the metal plate 16 is arrange | positioned by inserting from the end surface 1402 in the slit-shaped groove | channel formed in each lumber 14, for example.

The main drift pin 18 extends along the width direction through the central portion in the height direction of the lumber 14 at locations near the end faces 1402 of the two lumbers 14 and passes through the metal plate 16 almost at right angles. It is installed.
The sub-drift pin 20 extends in a direction perpendicular to the main drift pin 18 on one surface side and the other surface side in the thickness direction of the metal plate 16 at locations near the end surfaces 1402 of the two lumbers 14. In other words, the metal plate 16 extends along the height direction on one surface side and the other surface side in the thickness direction, and is disposed so as to be in contact with the 18 main drift pins located near the end surface 1402. ing.
The main drift pin 18 and the sub-drift pin 20 are made of metal or synthetic resin, inserted into holes formed in the lumber 14 in advance, and the cross-sectional shape is not limited to a circle.

When a tensile force as an external force acts on the joint structure 12 of Reference Example 1, a force is transmitted from the metal plate 16 to the main drift pin 18, and a force is transmitted from the main drift pin 18 to the lumber 14 by a bearing pressure.
The force is not only transmitted from the main drift pin 18 to the lumber 14 by the bearing pressure, but also the force is transmitted from the main drift pin 18 to the sub-drift pin 20, and the force is also transmitted from the sub-drift pin 20 to the lumber 14 by the bearing pressure.
Therefore, the transmission of force is dispersed, the bearing area of the lumber 14 is increased, and the proof stress as a joint can be increased.
According to Reference Example 1, a lumber joining structure having excellent resistance to pulling can be obtained. Therefore, a large-scale wooden building such as a dome can be constructed using lumber, which is a problem of VOC. Can also be resolved.

Next, the joint structure of Reference Example 2 will be described.
3A is a plan view of the joining structure of Reference Example 2, FIG. 3B is a front view thereof, FIG. 4C is a sectional side view, FIG. 4 is a perspective view of the joining structure of Reference Example 2, and FIG. The enlarged view of is shown.
The same parts and members as in Reference Example 1 will be described with the same reference numerals, and the longitudinal ends of the two lumbers 14 using the two abutting jigs 24 by the joining structure 22 of Reference Example 2 will be described. It is joined.
A hole 1412 penetrating in the width direction of the lumber 14 is provided at a location near the end of each lumber 14 so as to open on both side surfaces of the lumber 14.
The abutting jig 24 includes a metal plate 26 that is fitted to the side surface of the lumber 14 and two protrusions 28 that are provided on the metal plate 26 and can be inserted into the holes 1412. In Reference Example 2, the protrusion 28 is formed of a cylinder having a diameter smaller than that of the hole 1412, and the diameter of the protrusion 28 gradually decreases toward the tip so that the protrusion 28 is smoothly inserted into the hole 1412. The part is formed.

The projections 28 are fixed to the metal plate 26 at a pitch smaller than the pitch of the holes 1412 formed in each lumber 14 in a state where the flat end surfaces 1402 at the ends of the two lumbers 14 are abutted. . Further, the protruding length of the protrusion 28 is formed with a dimension of about 1/4 of the width of the lumber 14.
The two lumbers 14 have flat end surfaces 1402 at the ends of the lumbers 14 abutted against each other, the metal plates 26 are mated to both side surfaces of the lumbers 14, and the protrusions 28 are inserted into the holes 1412. As shown, the protrusions 28 function so that the flat end surfaces 1402 of the two lumbers 14 are brought into contact with each other, and the ends of the two lumbers 14 are joined.
The pressing jig 24 is mounted on the side surface of the lumber 14 by pressing the side surface of the projection 28 against the hole 1412. To make this mounting more reliable, a nail is driven from the metal plate 26 toward the lumber 14. Alternatively, a belt or the like may be wound around the lumber 14 including the abutting jig 24.

When a tensile force as an external force is applied to the joint structure 22 of Reference Example 2, the force is transmitted from the protrusion 28 to the lumber 14 by a bearing pressure.
Therefore, the transmission of force is dispersed, the bearing area of the lumber 14 is increased, and the proof stress as a joint can be increased.
Further, even if the cutting accuracy varies or the wood is deformed, the flat end surface 1402 at the end of each lumber 14 is maintained in a state of being abutted by the projections 28. A gap is prevented from being generated between the flat end surfaces 1402 at the ends of the lumber 14.

FIG. 6 shows a modification of the abutting jig 24.
The jig 24 according to this modification includes a metal plate 26 fitted to the side surface of the lumber 14 and two protrusions 28 provided on the metal plate 26 and insertable into the holes 1412. The two protrusions 28 are not integrally formed like those shown in FIGS. 3 and 4 and are separate bodies.
The protrusion 28 is formed in a columnar shape having a smaller diameter than the hole 1412, and the protrusion length of the protrusion 28 is formed so as to extend over the entire length of the hole 1412, that is, approximately the same as the width of the lumber 14. .
A tapered portion that gradually decreases in diameter toward the tip is formed at the tip of the projection 28 so that the projection 28 is smoothly inserted into the hole 1412.

Holes 2602 into which the two protrusions 28 are inserted are formed in the metal plate 26, and the two holes 2602 are in contact with the flat end surfaces 1402 at the ends of the two lumbers 14. Are formed with a pitch smaller than the pitch of the holes 1412 formed in the above.
In the two lumbers 14, the flat end surfaces 1402 at the ends of the lumbers 14 are abutted, the metal plates 26 are mated to both side surfaces of the lumber 14, and the protrusions 28 are formed from the holes 2602 of the metal plate 26 to the holes 1412. Thus, the projections 28 function so that the flat end surfaces 1402 of the two lumbers 14 are kept in contact with each other, and the ends of the two lumbers 14 are joined.
Even when the abutting jig 24 according to such a modification is used, the same effects as those of the reference example 2 can be obtained.

Next, the joint structure of the first embodiment will be described.
FIG. 7 is an explanatory diagram of the bonding structure according to the first embodiment.
By the joining structure 32 of the first embodiment, the end portions in the longitudinal direction of the two lumbers 14 are joined using the abutting jig 34.
The two lumbers 14 have side surfaces 1422 that extend on the same plane in a state where the flat end surfaces 1402 at the ends of the two lumbers 14 are abutted.
And the circular recessed part 1424 which has an internal peripheral surface is provided in the side surface 1422 of each lumber 14, respectively.

The abutting jig 34 includes a metal plate 36 that is fitted to the side surface of each lumber 14, and two protrusions 38 that are provided on the metal plate 36 and can be inserted into the recess 1424.
The protrusion 38 is formed of a cylindrical wall having a cylindrical surface with an outer diameter smaller than the inner diameter of the recess 1424, and a tapered portion whose outer diameter decreases toward the tip thereof is formed at the tip of the cylindrical wall.
The projections 38 are fixed to the metal plate 36 at a pitch smaller than the pitch of the recesses 1424 formed in each lumber 14 in a state where the flat end surfaces 1402 at the ends of the two lumbers 14 are abutted. . In the present embodiment, the protrusion 38 is provided so as to stand up from the outer periphery of the circular substrate 3802, and the substrate 3802 is fixed to the metal plate 36 by bolts B and nuts N, for example.
In the two lumbers 14, the flat end surface 1402 at the end of each lumber 14 is abutted, the metal plate 36 is mated with the side surface 1422 of the lumber 14, and the protrusion 38 is inserted into the recess 1424, thereby 2 The flat end surface 1402 at the end of the book-made lumber 14 is maintained and joined in a face-to-face state.

When a tensile force as an external force is applied to the joining structure 32 of the first embodiment, the force is transmitted from the protrusion 38 to the lumber 14 by a bearing pressure.
Therefore, the transmission of force is dispersed, the bearing area of the lumber 14 is increased, and the proof stress as a joint can be increased.
In addition, even if the cutting accuracy varies or the deformation of the wood occurs, the flat end surface 1402 at the end of each lumber 14 is maintained in a state of being abutted by the protrusion 38. A gap is prevented from being generated between the flat end surfaces 1402 at the ends of the lumber 14.

FIG. 8 is an explanatory diagram of a modification of the first embodiment.
In the modification shown in FIG. 8, the end portions in the longitudinal direction of the four lumbers 14 are joined using the abutting jig 34A.
Two of the four lumbers 14 are arranged so as to extend coaxially with each other. For convenience of explanation, if one of the two lumbers 14 arranged on the same axis is 14A and the other two lumbers 14 are 14B, the two two lumbers 14A are flat at the ends of these lumbers 14A. The other two lumbers 14B also have the side surfaces 1422 extending on the same plane with the end surfaces 1402 butted, and the other two lumbers 14B are also in contact with each other with the flat end surfaces 1402 at the ends of the lumbers 14B butting each other. A side surface 1422 extending on the same surface is provided, and the side surface 1422 of the one lumber 14A and the side surface 1422 of the other lumber 14B are opposed to each other.
A circular recess 1424 having an inner peripheral surface is provided on the side surface 1422 of each lumber 14A, 14B.

The abutting jig 34 </ b> A includes a metal plate 36 whose both surfaces are aligned with the side surfaces of the lumbers 14 </ b> A and 14 </ b> B, and four protrusions 38 that are provided on both surfaces of the metal plate 36 and can be inserted into the recess 1424.
The protrusion 38 is formed of a cylindrical wall having a cylindrical surface with an outer diameter smaller than the inner diameter of the recess 1424, and a tapered portion whose outer diameter decreases toward the tip thereof is formed at the tip of the cylindrical wall.
The protrusion 38 is a recess formed in each lumber 14 (more specifically 14A, 14B) in a state where the flat end surface 1402 of the end of the lumber 14 (more specifically, 14A, 14A, 14B, 14B) is abutted. The metal plate 36 is fixed at a pitch smaller than the pitch of 1424. In the present embodiment, the protrusion 38 is provided so as to stand up from the outer periphery of the circular substrate 3802, and the substrate 3802 is fixed to both surfaces of the metal plate 36 by bolts B and nuts N, for example.
In the two lumbers 14A and 14B, the flat end surface 1402 at the end of each lumber 14 is abutted, the both sides of the metal plate 36 are mated with the side surfaces 1422 of the lumbers 14A and 14B, and the protrusion 38 is in the recess 1424. Accordingly, the flat end surfaces 1402 at the ends of the two lumbers 14A and 14B are maintained in a state of being butted and joined.
Also by such a modification, the effect similar to the joining structure 32 of 1st Embodiment is show | played.

FIG. 9 is an explanatory diagram of another modification of the first embodiment.
In the modification shown in FIG. 8, the end portions in the longitudinal direction of the four lumbers 14 are joined using one abutting jig 34 </ b> B, two main drift pins 40, and four sub drift pins 42. .
Two of the four lumbers 14 are arranged so as to extend coaxially with each other. For convenience of explanation, if one of the two lumbers 14 arranged on the same axis is 14A and the other two lumbers 14 are 14B, the two two lumbers 14A are flat at the ends of these lumbers 14A. The other two lumbers 14B also have the side surfaces 1422 extending on the same plane with the end surfaces 1402 butted, and the other two lumbers 14B are also in contact with each other with the flat end surfaces 1402 at the ends of the lumbers 14B butting each other. A side surface 1422 extending on the same surface is provided, and the side surface 1422 of the one lumber 14A and the side surface 1422 of the other lumber 14B are opposed to each other.
A circular recess 1424 having an inner peripheral surface is provided on the side surface 1422 of each lumber 14A, 14B.

The abutting jig 34 </ b> B includes a metal plate 36 whose both surfaces are aligned with the side surfaces of the lumbers 14 </ b> A and 14 </ b> B, and four protrusions 38 that are provided on both surfaces of the metal plate 36 and can be inserted into the recess 1424.
The protrusion 38 has a cylindrical surface having an outer diameter smaller than the inner diameter of the concave portion 1424, and a tapered portion having a smaller outer diameter toward the tip thereof is formed at the tip of the cylindrical surface.
The protrusion 38 is a recess formed in each lumber 14 (more specifically 14A, 14B) in a state where the flat end surface 1402 of the end of the lumber 14 (more specifically, 14A, 14A, 14B, 14B) is abutted. The metal plate 36 is fixed at a pitch smaller than the pitch of 1424. In the present embodiment, the protrusion 38 is provided so as to stand up from the outer periphery of the circular substrate 3802, and an insertion hole through which the main drift pin 40 is inserted is formed in the center of the substrate 3802 and the metal plate 36.

In the two lumbers 14A and 14B, the flat end surface 1402 at the end of each lumber 14 is abutted, the both sides of the metal plate 36 are mated with the side surfaces 1422 of the lumbers 14A and 14B, and the protrusion 38 is in the recess 1424. Further, the main drift pin 40 is inserted through the center of the substrate 3802 and the metal plate 36 and the lumbers 14A and 14B facing each other.
Further, the sub-drift pin 42 is used so as to be orthogonal to the main drift pin 40, and the sub-drift pin 42 is arranged so as to be in contact with the main drift pin 40 near the end face 1402 at the place near the end face 1402 of each lumber 14. It is installed.
The main drift pin 18 and the sub drift pin 20 are made of metal or synthetic resin, and are used by being inserted into holes formed in the lumber 14 in advance.
Also by such a modification, the same effect as the joining structure 12 of the reference example 1 and the joining structure 32 of the first embodiment is exhibited.

FIG. 10 is an explanatory diagram of Reference Example 3.
By the joining structure 42 of Reference Example 3, the end portions in the longitudinal direction of the two lumbers 14 are joined using the abutting jig 34C.
The two lumbers 14 have side surfaces 1422 that extend on the same plane in a state where the flat end surfaces 1402 at the ends of the two lumbers 14 are abutted.
The abutting jig 34 includes a metal plate 36 that is fitted over both side surfaces of the two lumbers 14, and two protrusions 44 that are respectively provided on both sides of the metal plate 36.
The protrusion 44 includes a metal circular substrate 4402 and a plurality of metal columnar protrusions 4404 protruding from a plurality of locations spaced in the circumferential direction of the outer periphery of the substrate 4402. . Each protrusion 4404 is provided so as to be inclined so that the distal end thereof is displaced in the direction away from the protrusion 44 on the opposite side with respect to the base end. The substrate 4402 is fixed to the metal plate 36 by, for example, bolts B and nuts N. Note that the shape of the protrusion 4404 is not limited to a cylindrical shape as long as it is a shape that can be inserted into (placed into) the side of the lumber, and may be, for example, a plate shape.
The two lumbers 14 have flat end surfaces 1402 at the ends of the lumbers 14 abutted against each other, the metal plate 36 is mated with the side surfaces 1422 of the two lumbers 14, and a plurality of projections 4404 of each projection 44. Is inserted into (injected into) the side surface 1422 of the lumber 14, and the flat end surfaces 1402 at the ends of the two lumbers 14 are maintained in contact with each other and joined by the plurality of protrusions 4404 inclined in this manner. Yes.

When a tensile force as an external force is applied to the joint structure 42 of Reference Example 3, the force is transmitted from the protrusion 4404 to the lumber 14 by a bearing pressure.
Therefore, the transmission of force is dispersed, the bearing area of the lumber 14 is increased, and the proof stress as a joint can be increased.
In addition, even if the cutting accuracy varies or the deformation of the wood occurs, the flat end surface 1402 at the end of each lumber 14 is maintained in a state of being abutted by the protrusion 4404. A gap is prevented from being generated between the flat end surfaces 1402 at the ends of the lumber 14.

In the modification shown in FIG. 11, the end portions in the longitudinal direction of the four lumbers 14 are joined using the abutting jig 34 </ b> D.
Two of the four lumbers 14 are arranged so as to extend coaxially with each other. For convenience of explanation, if one of the two lumbers 14 arranged on the same axis is 14A and the other two lumbers 14 are 14B, the two two lumbers 14A are flat at the ends of these lumbers 14A. The other two lumbers 14B also have the side surfaces 1422 extending on the same plane with the end surfaces 1402 butted, and the other two lumbers 14B are also in contact with each other with the flat end surfaces 1402 at the ends of the lumbers 14B butting each other. A side surface 1422 extending on the same surface is provided, and the side surface 1422 of the one lumber 14A and the side surface 1422 of the other lumber 14B are opposed to each other.

The abutting jig 34 </ b> D includes a metal plate 36 whose both surfaces are aligned with the side surfaces of the lumbers 14 </ b> A and 14 </ b> B, and four protrusions 34 provided on both sides of the metal plate 36.
The protrusion 44 includes a metal circular substrate 4402 and a plurality of metal protrusions 4404 protruding from a plurality of locations spaced in the circumferential direction of the outer periphery of the substrate 4402. The tip is inclined with respect to the base end so as to be displaced away from the protruding portion 44 on the opposite side. The substrate 4402 is fixed to the metal plate 36 by, for example, bolts B and nuts N.
The two lumbers 14A and 14B have the flat end surface 1402 at the end of each lumber 14 butted, the both sides of the metal plate 36 are mated with the side surfaces 1422 of the lumbers 14A and 14B, and the plurality of protrusions 4404 are side surfaces. The flat end surfaces 1402 at the ends of the four lumbers 14 are kept in abutted state and joined by the plurality of inclined projections 4404 inserted into (injected into) 1422.
Also by such a modification, the same effect as the joining structure 42 of the reference example 3 is show | played.

(A) is a top view of the joining structure of Reference Example 1, (B) is the same front view, and (C) is a sectional side view. It is a perspective view of the junction structure of reference example 1. (A) is a top view of the joining structure of Reference Example 2, (B) is the same front view, and (C) is a sectional side view. It is a perspective view of the junction structure of reference example 2. It is an enlarged view of a projection part. It is explanatory drawing of the modification of the butting jig | tool used in the reference example 2. FIG. It is explanatory drawing of the junction structure of 1st Embodiment. It is explanatory drawing of the modification of 1st Embodiment. It is explanatory drawing of the other modification of 1st Embodiment. It is a perspective view of the junction structure of reference example 3. It is explanatory drawing of the modification of the reference example 3. FIG.

Explanation of symbols

  14 ... Lumber, 16, 26, 36 ... Metal plate, 18, 40 ... Main drift pin, 20, 42 ... Sub drift pin, 28, 38 ... Projection, 44 ... Projection.

Claims (1)

A structure in which the longitudinal ends of the two lumbers are joined using an abutting jig,
The two lumbers have side surfaces that extend on the same plane in a state in which the flat end surfaces of the end portions of these two lumbers are abutted,
Recesses are provided on the side surfaces of each lumber extending on the same surface,
The abutting jig is composed of a metal plate that is fitted to a side surface of each lumber extending on the same surface, and two protrusions that are provided on the metal plate and can be inserted into the recesses.
The protrusions are provided on the metal plate at a pitch smaller than the pitch of the recesses formed on each lumber, with the flat end surfaces of the two lumber ends abutted against each other.
In the two lumbers, the flat end surfaces of the end portions of the two lumbers are abutted, the metal plate is mated with the side surfaces of the lumber, and the protrusions are inserted into the recesses, thereby the two lumbers. The flat end surfaces of the end portions of the end portions of the end portions of the end portions are kept in contact with each other and joined.
The concave portion is a circular concave portion having an inner peripheral surface,
The protrusion has a cylindrical surface with an outer diameter smaller than the inner diameter of the recess,
At the tip of the cylindrical surface, a tapered portion is formed whose outer diameter decreases as it reaches the tip.
A lumber joining structure characterized by that.

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