Bearing strength enhancing structure for friction joining

Abstract

 The present invention addresses the problem of providing a friction joined structure capable of expanding a compression force distribution for improving slip resistance and reducing a bolt inner force coefficient Θ. A high-strength bolt (50) is used to press-contact and frictionally join a member (10) to be joined and a splice plate (11). The high-strength bolt (50) is inserted into the member (10) to be joined and the splice plate (11) from one side to frictionally join both by the tightening force of the high-strength bolt (50). The axial force pressure distribution is widened by a cone of influence spreading from a high-strength bolt head part (51) to a contact surface with the splice, thereby improving the slip resistance. Also, the shear strength of the high-strength bolt is improved by reducing the ratio Θ (bolt inner force coefficient) between an external force Wa and a tensile inner force Ft added to the bolt when a compression spring constant Kc is enlarged and the external force Wa is applied.

Description

Strengthening structure in friction joints

[0001] The present invention relates to a load-bearing structure in a friction joint.

[0002] Steel structural connections are classified into fastener and welded connections. Fastener connections are a mechanical connection method in which holes are drilled in the components to be joined and fasteners are inserted into the holes to transmit force. There are three types of fastener connections based on the method of force transmission: riveted connections, bolted connections, and high-strength bolted connections. High-strength bolted connections are generally friction connections, which are distinct from shear connections, which are governed by the shear force of the bolt. The key factor is the slip resistance, or the amount of force a friction joint can withstand without slipping. If the repeated stress is below the slip resistance, there is no change in the bolt tension or the friction surface. If the friction coefficient of the joint plane is the same, the compressive stress distribution at the joint plane governs the slip resistance. As shown in Figure 11, if the slip resistance is exceeded, the joint material begins to slip and contacts the bolt shank, and the bolt's shear force supports the slip. Therefore, in friction joints using high-strength bolts, attempts are made to improve the strength by taking into account the yield strength of the base material. Among these, in order to improve the load transfer mechanism, first, it is necessary to take slip resistance into consideration and obtain a wider compressive stress distribution even with the same compressive force. Second, to ensure high slip resistance for safety, high-strength bolts are required to have high tensile and shear strength. Therefore, various surface treatment methods have been proposed to improve the slip coefficient of the contact surface, taking into account the relationship between the treatment state of the contact surface and the slip coefficient. Meanwhile, high-strength bolts with strength appropriate for the joint structure have been proposed, but there are limitations to improving the compressive stress distribution and the strength of the high-strength bolt. Therefore, the inventors conducted extensive research to improve the strength of friction joints from a different perspective than conventional methods.

[0003] Japanese Utility Model Application Publication No. 62-175104 Japanese Patent Application Publication No. 2006-349098 Japanese Patent Application Publication No. 2011-220032 Japanese Patent Application Publication No. 2019-19939

[0004] Theory and Calculation of Screw Fastening Akira Yamamoto Yokendo

[0005] Friction joints, as shown in Figure 1A, are joints in which stress is transmitted through the frictional resistance between the joined materials, resulting from the large inter-material compressive force generated when a high-strength bolt and nut are fastened to a pair of joining base materials. Stress is transmitted through the inter-material compressive force that is widely distributed around the bolt. Unlike rivet joints, which transmit stress through localized bearing pressure, stress concentration is minimal and the flow of stress is smooth, making them widely used. When considering the compressive stress distribution at the joint plane, which governs the slip resistance, using a conventional high-strength bolt and nut, a double-headed cone is assumed from the bolt head and nut to the joint plane (Figure 12A). However, if a splice is modified to a threaded splice by providing a female threaded hole that threads onto the tip of the high-strength bolt on one side of a splice plate covering the joint surface instead of a nut, the pressure distribution at the joint plane is thought to change to a single-headed cone (Figure 12B). As a result, it was found that when a threaded splice is used, the compressive stress distribution is more widespread around the bolt than when a nut is used (compare Figure 16 (1) (2) with (3) (4)). Furthermore, when the compression spring constant of the fastened object is calculated, the compression spring constant of the present invention (Equation I of Figure 1E) is greater than the conventional compression spring constant (Equation II of Figure 1E), and as a result, the load on the high-strength bolt is reduced (see Figure 1D). In other words, the objective of the present invention is to improve the strength of friction joints from a different perspective than conventional methods, and to provide a friction joint that further increases strength.

[0006] That is, the present invention provides a friction joining structure in which, when members to be joined (10, 10) are pressure-welded together by screwing a plurality of high-strength bolts together, a splice (11) serving as a support plate is used, and the members to be joined (10, 10) are joined by the frictional force generated at the contact surface between the splice and the members to be joined, wherein the support plate splice (11) on the lower side of the members to be joined (10) is made of flat steel material of substantially the same material and substantially the same thickness as the nuts to be screwed onto the high-strength bolts, and is configured with threaded holes (11A) to be screwed onto the tip-side threaded portions (21) of the plurality of high-strength bolts, and the high-strength bolts are inserted into the insertion holes (10A) of the members to be joined and then screwed into the threaded holes (11A) provided in the lower support plate splice (11), This joint structure widens the axial pressure distribution around the area where the high-strength bolt tip 21 and the splice threaded hole 11A are threaded together in an influence cone that extends from the head of the high-strength bolt to the abutment surface with the splice 11, improving the slip resistance, and also increases the compression spring constant Kc to reduce the ratio Θ (bolt internal force coefficient) of the tensile internal force Ft added to the bolt when an external force Wa is applied to the external force Wa, thereby improving the shear resistance of the high-strength bolt.

[0007] (Effect 1: Expanded compressive stress distribution in friction joints) Previously, a joint structure was proposed in which a high-tensile joint with multiple internal threads, equivalent to the nut diameter, was used instead of a nut to attach to a beam flange (Patent Document 1). However, this joint structure, like a nut-integrated joint, resulted in a shear joint rather than a friction joint between the joined members. In this invention, the splice plate provides a friction joint that extends across the entire joint surface, distinguishing it from the shear joint of Patent Document 1, which relies on the shear force of the high-strength bolt. The pressure distribution across the joint surface is considered to be changed from the double-headed conical shape of the bolt nut (Figure 12A) to the single-headed conical shape of the bolt splice (Figure 12B). As a result, the pressure distribution is more widespread around the bolt than with a nut (compare Figures 16 (1) (2) and (3) (4)), resulting in greater slip resistance with the same tightening force. (Effect 2: Reduced load on the high-strength bolt) Furthermore, the friction joint results in the tightening diagram shown in Figure 10D. Figure 10B is a schematic diagram showing the fastener of Figure 10A in spring form, with an internal tensile force Ff, indicated by A, acting on the high-strength bolt shank, while a compressive force Ff, indicated by B, acts on the fastened object, showing a balanced state (Figure 10C(a)). When an external force Wa is applied, an axial force Ft is applied to the high-strength bolt, while the compressive force Fc on the fastened object is lost, resulting in an extension of the fastened length by ε. Expressing this relationship in terms of spring constant and strain, an axial force Ft = Kt × ε (Kt = tensile spring constant) is added to the high-strength bolt, while a compressive force Fc = Kc × ε (Kc = compression spring constant) is removed from the fastened object. If we plot a tightening diagram with elongation on the horizontal axis and axial force on the vertical axis, it would look like the one shown in Figure 10D. In other words, if the tensile force of the high-strength bolt and the compressive force of the fastened object are balanced at equilibrium point A under no load, the tension spring constant Kt and compression spring constant Kc will form a triangle with point A as the tension spring constant line Kt (from 0 to equilibrium point A) and the compression spring constant line Kc (from point D to line A) intersect at point A. Here, when an external force Wa is applied, the high-strength bolt stretches by ε and the equilibrium point moves from A to B, an internal tensile force Ft is applied to the high-strength bolt, the tensile force increases to Ff + Ft and the compressive force decreases to Ft - Fc, as shown by the solid lines.Here, since the tension spring constant of the high-strength bolt is constant, the compression spring constant increases (Kc. １ From Kc ２ ) and elongation (ε １ →ε ２ ) is reduced, and the load on the high-strength bolt is reduced (Ft １ From Ft ２ Therefore, in the present invention, as is clear from the tightening diagram in Figure 10D, the change to a friction joint using a threaded splice increases the compression spring constant (from Kc1 to Kc2), thereby reducing the load on the high-strength bolt.

[0008] (Effect 3: Achieving one-sided joints) Furthermore, unlike conventional high-strength bolt joints that use nuts, there is no need to perform back nut welding on the Joint Box (registered trademark), resulting in a one-sided joint style that is easy to work with. Conventional one-sided bolts for this type of friction joining include those in which a sleeve is fitted onto the bolt shank, the bolt is passed through a hole in the workpiece from the front side to the back side, a nut is screwed onto the bolt shank, and the nut is rotated and tightened to deform the sleeve into a flange shape between the bolt head and the workpiece, preventing the bolt from coming out (Patent Document 2), those in which a sleeve is fitted over the screw insertion hole in the workpiece and the support plate, and this is deformed to prevent the bolt from coming out (Patent Document 3), as shown in Figure 8, and those in which the back side of the bolt head is tapered, and the tip of the sleeve is expanded by the back side of the bolt head, preventing the bolt from coming out (Patent Document 4), as shown in Figure 9. However, in the conventional bolts, the part that protrudes downward from the support plate is plastically deformed by tightening the bolt to form a stopper to prevent the bolt from coming out, and there was a problem that sufficient compressive force distribution could not be obtained due to the lack of strength on the flange side, and the friction joining strength of the F10 standard was not achieved. The present invention provides a friction joint structure with enhanced strength and durability that is greater than or equal to the tightening strength of the conventional high-strength bolt and nut structure shown in FIG. 1A, even though it is a friction joint structure.

[0009] In the present invention, it is preferable to use a splice plate having dimensions based on the Building Standards Act in place of the conventional nut on the splice plate side. However, if the splice plate is made of substantially the same material as the nut (for example, a heat-treated S45C or S33C splice plate is normally used for an F10T high-strength bolt, but EVERHARD C400LE steel (HRC30±2) may also be used, and the splice plate material may be changed depending on the high-strength bolt being used, and an appropriate material may be selected), and is formed of a plate thickness substantially the same as that of the nut (here, substantially the same thickness means a thickness that does not interfere with tightening, and is usually the same as the nut thickness, or preferably within a range of ±20%, more preferably ±10%), and a female thread is formed in the bolt insertion hole and is threaded onto the male thread at the tip of the high-strength bolt to frictionally join the joined members 10 to the splice plate 11, a slip coefficient of 0.45 or more can be ensured at the joining surface, resulting in a slip resistance greater than conventional values. (Relationship between increasing compression spring constant and reducing high-strength bolt load) As a result of increasing the inter-material compression spring constant Kc of the fastened objects (see paragraph

[0030] for the calculation results using Equations I and II in Figure 1E), the ratio Θ (bolt internal force coefficient) of the tensile force added to the bolt when subjected to an external force to the external force acting on the threaded fastener decreases, reducing the load on the bolt (see the dashed-dotted line in Figure 1D). More specifically, when the conventional bolt and nut tightening structure shown in Figure 1A is simulated, it becomes as shown in Figure 1B. In other words, the elasticity of the bolt is a tension spring represented by spring A, while the elasticity of the joining members is a compression spring represented by spring B. Let Kt be the tensile spring constant (load per unit elongation) of A and Kc be the compressive spring constant (load per unit elongation) of B. As shown in the transition from (a) to (b) in Figure 1C, when an external force Wa acts on this threaded fastener, causing elongation ε in the fastened object, a tensile force of Ft = Kt ε is added to the balanced tensile force Ff in the bolt shank, resulting in Ff + Ft. Meanwhile, a compressive force of Fc = Kc ε is lost from the balanced compressive force Ff in the connecting member, resulting in Ff - Fc. As a result, the high-strength bolt shank exhibits the effect shown in Figure 1D. In other words, if the horizontal axis represents the elongation of the threaded fastener and the vertical axis represents the axial force, the gradient from the origin 0 to point A represents the tensile spring constant Kt, while the gradient from point D to point A represents the compressive spring constant Kc, with the balance being reached at point A.Here, when an external force Wa is applied, the elongation (ε １ ) moves the equilibrium position from point A to point B. On the other hand, since the tension spring constant Kt of the high-strength bolt does not change, the compression spring constant Kc is D1-A(Kc １ ) to D2-A (Kc ２ ), when the same external force Wa is applied, the elongation becomes (ε １ ) to (ε ２ ) and the balance point moves from point A to point E. As a result, the influence on the axial force from point A is (Ft １ ) to (Ft ２ In other words, in the strength design of a threaded fastener, if the axial force (load) on the bolt when an external force Wa is applied increases the compression spring constant Kc, and the ratio of the tensile force Fc added to the bolt when the external force Wa acts on the threaded fastener to the external force acting on the threaded fastener (bolt inward coefficient) is Θ, then in Figure 1D, Θ = Ft / Wa = Kt / Kt + Kc, and as Kc (compression spring constant on the joining member side) increases, Θ decreases, and the compression force Ft decreases (Ft １ ) to (Ft ２), the load on the bolt is reduced, which is advantageous for the strength of the threaded fastener (see Non-Patent Document 1, pages 52-53). This is also evident from calculation formulas. The compression spring constant Kc of a flat plate when fastened with a conventional high-strength bolt and nut is shown in Figure 1E (Formula II), while the compression spring constant Kt of a flat plate when fastened with a threaded splice of the present invention is shown in Figure 1E (Formula I) (where Ec is the elastic modulus of the joining members (objects to be fastened), Lf is the fastening length, B is the diameter of the bearing surface, and Di is the hole diameter in the object to be fastened). As a result, the compression spring constant Kc when two plates are fastened with the threaded splice of the present invention is greater than the compression spring constant Kc when three plates are fastened with a conventional high-strength bolt and nut, and the load on the bolt is reduced. (Application of the effects of the present invention) The effects described above can be achieved in the same way with a normal bolt having one-way threads formed in the screw hole 11A of the splice plate 11, and with a torque-shear bolt having reverse threads formed on the tip side and the base side where the pin tail is provided. Furthermore, with the friction joint structure of the present invention, the load on the bolt is limited, so that the tightening axial force specified in JIS S B1186 is not limited to F8T equivalent, and it is possible to provide a friction joint structure having slip resistance equal to or greater than that of a friction joint using a high-strength bolt and nut equivalent to F10T.

[0010] This is a functional explanatory diagram of the friction joint structure of a conventional high-strength bolt and nut fastener, showing a pair of base materials fastened by a high-strength bolt and nut, frictionally joined by inter-material compressive force. This is a schematic diagram showing the fastener of Figure 1A in spring form, showing a balanced state in which an internal tensile force Ff, indicated by A, is applied to the high-strength bolt shank, while a compressive force Ff, indicated by B, is applied to the fastened object. This is an explanatory diagram showing the transition from the state (a) in which the tensile force Ff of the bolt shank of the fastener of Figure 1A is balanced with the compressive force Ff of the fastened object, to the state (b) in which the fastened object elongates by ε when an external force Wa is applied. This is a tightening diagram showing the elongation (reduced contraction of the fastened object) on the horizontal axis and the axial force on the vertical axis. Formula I (Formula I) for calculating the compression spring constant of a conventional bolt fastener and Formula II (Formula II) for calculating the spring constant of the bolt fastener of the present invention are shown. 1A is a plan view of a preferred embodiment of a friction welding structure according to the present invention, (b) is a front view of the embodiment, and (c) is a bottom view of the embodiment. FIG. 1B is a view showing a one-sided Torxia-type high-strength bolt for friction welding in the embodiment. FIG. 2A is a perspective view showing the workpieces and a splice plate to be friction-welded in the embodiment. FIG. 3A is a perspective view showing a state during the welding process in the embodiment. FIG. 4A is a cross-sectional view showing a state during the welding process in the embodiment. FIG. 5A is a view showing a first example of a conventional one-sided friction welding structure. FIG. 6A is a view showing a second example of a conventional one-sided friction welding structure. FIG. 7A is a view showing a third example of a conventional one-sided friction welding structure. FIG. 8A is a view showing a plan view, a partially cross-sectional side view, and a bottom view, respectively, of the friction welding structure in the second embodiment. FIG. 9A is a graph showing the load change leading to fracture of a conventional friction welding structure. FIG. 10A is a cross-sectional explanatory view of a friction welding in which a compression force distribution test for a conventional friction welding was conducted. FIG. 11A is a cross-sectional explanatory view of a friction welding in which a compression force distribution test for a friction welding of the present invention was conducted. FIG. 12D is a process diagram showing friction welding processes (a) to (d) using a Torxia-type high-strength bolt of the present invention. 1A is a side view showing the structure of a test specimen of a conventional friction welding structure, and the friction welding structures of the present invention, (b) and (c), in which (a) is a cross-sectional view of a conventional torque shear type high strength bolt during welding, and (b) is a cross-sectional view showing the state after fastening.12B shows experimental results of the compression force distribution of the friction joint of the present invention at positions (1) between the upper splice and the workpieces to be joined and (2) between the lower splice and the workpieces to be joined, and FIG. 12A shows experimental results of the compression force distribution of the conventional friction joint at positions (3) between the upper splice and the workpieces to be joined and (4) between the lower splice and the workpieces to be joined.

[0011] The strength-enhanced structure of the present invention will be described in detail below with reference to specific examples shown in the drawings. Figures 2 to 6 show preferred embodiments of the friction joint structure of the present invention. The torque shear type high-strength bolt used in the present invention is shown in Figure 3. That is, the friction joint bolt 20 is a bolt having a torque shear stud-type fracture groove 23 and a pin tail 24 formed on a stud bolt. One half of the bolt has a left-handed thread 21a, and the other half on the pin tail 24 side has a right-handed thread 21b, with a nut 22 threaded onto the right-handed thread 21b. In other words, the bolt has a left-handed thread of the same nominal dimensions as the right-handed thread, cut into the portion of the countersunk retaining head of a structural torque shear type high-strength bolt (Figure 15(a)) with a pin tail and right-handed thread. Normally, as shown in Figures 15(a), (b) and (c), a Torxear bolt 44 has a bolt shank 44 formed with a male thread that is inserted from the support plate 41 side to the joined member 40 side through an insertion hole and is prevented from coming out, so it has a round retaining head 44a on the head and is tightened with a nut 42. However, the one-sided high-strength bolt 20 used in the present invention is inserted from the joined member 10 side and is screwed into the female thread 11A of the support plate 11, so it has a new design that does not have a retaining portion on the head.

[0012] A plurality of insertion holes 10A for the friction-joint bolts 20 are formed at intervals in the workpieces 10 to be joined by the friction-joint bolts 20, and a plurality of left-handed screw holes 11A are formed at equal intervals as the insertion holes 10A of the workpieces 10 in the support plate 11 that is placed on the friction-joint bolts 20. When a support plate 11 is formed on the front side of the workpieces 10 in the same way as on the back side, no screw holes are provided in the front side support plate, but insertion holes similar to the insertion holes 10A are provided (FIGS. 14(b) and (c)).

[0013] Generally, for friction joining of steel structures with high-strength bolts, a structural torsion-type high-capacity bolt 44, a hexagonal nut 42, and a set of washers 45 are used, and installation using a torsion wrench is often used due to its excellent characteristics such as ease of installation and stability of tightening axial force, and this installation is shown in Figures 15(a), (b), and (c).

[0014] In the present invention, when performing friction welding, a hexagonal nut 22 for a high-strength bolt is set on the pin tail 24 side of the friction welding bolt 20 as shown in FIG.

[0015] Next, as shown in FIG. 4 , a support plate 11 is placed on the underside of the workpiece 10, and the workpiece 10 is inserted from the top side of the workpiece 10 through a washer 25. The left-hand screw 21 of the friction-welding bolt 20 is then screwed into the left-hand threaded bolt hole (left-hand screw hole) 11A of the support plate 11.

[0016] Finally, the tightening portion of the torque wrench is placed over the pin tail 24 and nut 22 of the friction joint bolt 20 (see Figure 6), and the pin tail 24 is broken. This causes the workpieces 10 to be tightened between the spliced ​​left-hand screw 21 and the hexagonal nut 22 in place of the torque bolt head, completing the friction joint.

[0017] More specifically, tightening to ensure the tightening axial force on the friction-joint bolt 20 using a torque wrench proceeds through the following steps, as shown in Figure 13: 1) When the pin tail 24 of the friction-joint bolt 20 is gripped with the pin tail gripping jig A at the core of the torque wrench and rotated counterclockwise with the nut 22 stopped, the tip 21 of the bolt threads into the screw hole 11A of the support plate 11 (see Figure 13(a)). 2) Next, as the friction-joint bolt 20 rotates counterclockwise, the bearing surfaces of the support plate 11 and the nut 22 clamp the fastened members 10 (see Figure 13(b)). 3) The frictional resistance of the bearing surface of the support plate 11 stops the counterclockwise rotation of the pin tail 24. 4) The pin tail gripping jig A, which has stopped rotating, functions as a counterforce receiver for the rotation of the nut 22 (see Figure 13(c)). 5) When the pin tail gripping jig A stops, the nut gripping jig B rotates clockwise and the nut 22 tightens the workpieces 10, and when a predetermined tightening axial force is generated in the friction welding bolt 20, the pin tail 24 breaks in the groove 23 and tightening is completed (see Figure 13(d)). Note that although the splice plate 11 is provided only on the back surface of the workpieces 10 here, the same applies when a splice plate is provided on the front surface as well, so explanation will be omitted.

[0018] 10(a), (b), and (c) show the second embodiment, which differs from the first embodiment in that a normal bolt is used instead of a torsion bolt. That is, the friction-joint bolt 50 comprises a bolt head 51 and a bolt shank 52, and the bolt shank 52 is formed with a right-handed male thread 53.

[0019] Insertion holes 10A for the friction welding bolts 50 are formed at intervals in the workpieces 10, and a support plate 11 placed on the back side of the friction welding bolts 50 has multiple left-handed female screw holes 11A formed at equal intervals as the insertion holes 10A in the workpieces 10.

[0020] When performing friction welding, as shown in Figure 10 (b), a support plate 11 is placed on the back side of the workpiece 10, and the bolt 50 is inserted into the insertion hole 10A of the workpiece 10 from the front side of the workpiece 10 through a washer 54, and the male thread 53 of the friction welding bolt 50 is screwed into the right-hand threaded bolt hole (splice) 11A of the support plate 11.

[0021] The friction joining bolt 50 is threaded using a tool, and when a predetermined tightening force is reached, the workpieces 10 are tightened between the right-hand thread 11A, which is spliced ​​instead of a nut, and the head 51 of the hex bolt 50, completing the friction joining.

[0022] In the first embodiment, the bolt has a shape formed with a torque stud-type fracture groove and a pin tail, and a left-handed thread is formed in the tip half and a right-handed thread is formed in the pin tail half. However, the present invention also includes a friction-joint bolt in which a right-handed thread is formed in the tip half of the torque stud-type bolt and a left-handed thread is formed in the pin tail half.

[0023] In addition, in the second embodiment, a right-handed thread is formed on the bolt shank, but the present invention also includes a friction-joint bolt having a left-handed thread formed on the bolt shank. Embodiment

[0024] One of the friction joining structures according to the present invention is a friction joining structure in which a workpiece (10) and a splice (11) are joined by a bolt (20), in which a left-handed male thread (21) is formed in the tip half of the bolt shank, a right-handed male thread (21a) is formed in the base half of the bolt shank, and a nut (22) is screwed onto the right-handed male thread (21b) in the base half, while an insertion hole (10A) for the bolt is formed in the workpiece and a left-handed female thread (11A) is formed in the splice, and at least The splice plate 11 is placed on the back side of the workpieces 10, the left-handed male thread 21 of the bolt shank is inserted into the insertion hole 10A from the front side of the workpieces to be joined and threaded into the left-handed female thread 11A of the splice plate 11, the workpieces are clamped between the splice plate and the nut as the nut is threaded, and the breakage of the pin tail 24 of the bolt makes it possible to fasten the workpieces between the splice plate and the nut with a predetermined fastening axial force. If a splice plate is also provided on the front side of the workpieces 10, the splice plate is provided with an insertion hole similar to the insertion hole 10A instead of a female threaded hole.

[0025] Another feature of the present invention is that a stud bolt having a Torxear-type fracture groove 23 and a pin tail 24 is used, a left-handed male thread 21a is formed in the tip half of the bolt, and a right-handed male thread 21b is formed in the pin tail half, a nut 22 is screwed onto the right-handed male thread 21b, an insertion hole 10A is formed in the workpieces 10, and a screw insertion hole 11A is formed in the support plate 11, the support plate 11 is placed on the underside of the workpieces 10, the left-handed male thread 21a is inserted into the insertion hole 10A from the top of the workpieces 10 and screwed into the screw hole 11A in the support plate 11, the bolt is rotated counterclockwise so that the nut 22 comes into contact with the workpieces 10, and then the nut 22 is rotated clockwise to clamp the workpieces 10, and the pin tail 24 is broken when a predetermined tightening axial force is applied.

[0026] This allows for a friction joint structure with strength classification F10T to be achieved using commercially available tools such as a torque wrench, without the need for very expensive bolts such as one-way (one-sided) bolts. Also, because the play screws can be inserted into the interior of the column base, etc., there is a large degree of freedom in the length of each joining member. Furthermore, a lightweight and highly reliable friction joint structure can be achieved.

[0027] Here, when using a commercially available tool, for example, a torsion wrench, it is preferable to use a stud bolt having a shape in which a torsion stud-type breaking groove 23 and a pin tail 24 are formed, and to form a left-handed male thread 21a on one half of the bolt and a right-handed male thread 21b on the pin tail half, and to screw a nut 22 onto the right-handed male thread 21b.

[0028] In the above, a right-handed male thread 21b is formed on the pintail half of the bolt, and a left-handed male thread 21a is formed on the tip half, but it is also possible to form a left-handed male thread on the pintail half of the bolt, and a right-handed male thread on the tip half.

[0029] Furthermore, although a torque shear type bolt is used in the above, a normal hexagon bolt 50 defined in JIS B1186, which is made up of a head and a shaft, can also be used. That is, according to the present invention, in the friction welding structure in which the workpieces 10 and the splice plate 11 of Figure 9 are joined by a bolt 22, a right-handed male thread 52 is formed on the shank of the bolt 50, an insertion hole 10A is formed in the bolt shank in the workpieces 10, a right-handed female thread 11A is formed in the splice plate 11, the splice plate 11 is placed on the back side of the workpieces 10, the right-handed male thread 52 of the bolt 50 is inserted into the insertion hole 10A from the front side of the workpieces 10 and threadedly engages with the female thread 11A of the splice plate 11, the workpieces 11 are clamped between the splice plate 11 and the bolt head 51 as the bolt head 51 of the bolt 50 threads forward, and the workpieces 10 can be fastened between the splice plate 11 and the bolt head 51 with a predetermined fastening axial force. When a splice plate is also provided on the front side of the workpiece 10, the splice plate is provided with an insertion hole similar to the insertion hole 10A, instead of a female screw hole.

[0030] The friction joining method described above is also novel. That is, in the friction joining method according to the present invention, when overlapping the workpieces 10 and the splice plate 11 and friction-joining them with a bolt, a stud bolt 20 having a torque stud-type fracture groove 23 and a pin tail 24 is used as the bolt, a left-handed or right-handed male thread 21a is formed in the tip half of the bolt shank, and a right-handed or left-handed male thread 21b is formed in the pin tail half, and a nut 22 is screwed onto the right-handed or left-handed male thread 21b, while an insertion hole 10A of the bolt is formed in the workpieces 10, and the splice plate 11 is friction-joined with the bolt. A left-handed female thread 11A is formed in the plate 11, the support plate 11 is placed on the back side of the workpiece 10, the left-handed male thread 21a of the bolt 20 is inserted into the insertion hole 10A from the front side of the workpiece 10 and screwed into the female thread 11A of the support plate 11, the pin tail 24 is gripped and the bolt 22 is rotated until the nut 22 abuts against the workpiece 10 to be joined, and the nut 22 is rotated, causing the pin tail 24 to break due to the reaction force of the tightening, making it possible to tighten the support plate 11 and the nut 22 together with a predetermined tightening axial force.

[0031] (Comparison of Compression Spring Constants) Furthermore, the compression spring constant of the plates connected by the one-sided bolt of the present invention was compared with that of the plates connected by a conventional bolt and nut. The compression spring constant when two plates are fastened together using the threaded splice of the present invention is shown in Equation 1 in Figure 10E, and is Kc = 3,387,772 N / mm. 2　 It became. Here On the other hand, when three plates are fastened together using a conventional high-strength bolt and nut structure, the compression spring constant is Kc = 2,010,055 N / mm, as shown in Equation II in Figure 10E. 2　 It became. Here Experimental Example 1

[0032] Furthermore, threaded splices are also innovative. We investigate the shortest length of engagement that will prevent shear failure of the threads in the threaded connection between a steel bolt and a threaded splice. We consider shear failure of steel female threads. If the minimum shear load of the female thread is greater than the maximum tensile breaking load of the female thread, the female thread will not shear. Calculations using this inequality with general conditions show that for bolts larger than M12, the minimum engagement length Lmin should be 60% of the nominal diameter. Experimental Example 2

[0033] Consideration of shear failure of steel female threads: If the minimum shear load of a female thread is greater than the maximum tensile failure load of the female thread, the female thread will not fail in shear. Calculations of this inequality using general conditions showed that when the ratio of the tensile strength of the female thread material to the tensile strength of the female thread material is 1.5, the minimum engagement length Lmin for bolts larger than M12 is 80% of the nominal diameter. Furthermore, when the ratio of the tensile strength of the female thread material to the tensile strength of the female thread material is 1.0, the minimum engagement length Lmin for bolts larger than M4 is 60% of the nominal diameter. In conclusion, if the thickness of a threaded splice heat-treated to a hardness standard of 20 HRC to 35 HRC is at least 80% of the nominal diameter, shear failure of the splice thread will not occur and tensile failure of the bolt will be achieved. Experimental Example 3

[0034] A slip resistance test using a standard specimen from the High Strength Bolted Joint Design and Construction Guidebook was compared between the conventional method using hexagonal bolts and hexagonal nuts and the method of this invention, and it was confirmed that the slip coefficient met the standard of 0.45 or more. Reference) Formula for calculating slip coefficient: Slip coefficient = Slip load (KN) / (Number of sliding surfaces * Sum of axial forces (KN)) The slip coefficient was measured for various combinations. 1) Conventional method: Slip test of F10 bolt and nut set specified in JIS B1186 The test specimen shown in Figure 14 (a) was 18 mm thick for the joined member 40 and 12 mm thick for the splice plate 41. Four bolts from the F10TM16x75 bolt set were used. Tightening method: First tighten with the specified torque, mark, and tighten the nuts using the 120-degree rotation angle method to obtain the specified axial force. (Nut tightening)

[0035] 2) Invention 1: Slip test of JIS B1186-specified F10 bolt and threaded backing plate (S45C) As shown in Figure 14 (b), the test specimens used were the joined member 10 (SS400, 18 mm thick) and backing plate 11 (S45C, 12 mm thick), as shown in Figure 14 (b). Tightening procedure Primary tightening: A hexagonal bolt with a washer is inserted into the bolt hole of the threaded backing plate, and the bolt thread is screwed into the screw hole of the threaded backing plate installed on the back of the member. The bolt head is then tightened primarily with a preset torque wrench specified for each nominal diameter. (Tightening with the bolt head) Marking: Mark the bolt head, washer, and member. The bolt head is finally tightened with a rotation angle controlled power tightening device to an accuracy of 120 degrees ±30 degrees.

[0036] 3) Invention 2: Slip test of double-threaded pintail bolt set As shown in Figure 14(c), the test specimens used were the joined members (SS400, 18 mm thick) 10 and a splice plate (S45C, 12 mm thick). Tightening procedure: A double-threaded pintail bolt with a nut for final tightening threaded onto it was passed through the left-hand threaded bolt hole of the threaded splice plate, and the bolt thread was threaded into the left-hand threaded hole of a threaded splice plate installed on the back of the member to be tightened. The pintail and nut were grasped with a commercially available torque wrench and rotated counterclockwise; when the nut abutted against the member, the pintail rotation stopped, and the pintail and nut rotated clockwise; when a predetermined axial force was applied to the member to be tightened between the threaded splice plate and the nut, the pintail broke and tightening was completed.

[0037] Results of measuring the slip coefficient for various combinations: 1) The slip coefficient for the JIS B1186 F10 bolt and nut set is 0.73. 2) The slip coefficient for the JIS B1186 F10 bolt and threaded backing plate is 0.71. 3) The slip coefficient for the left-right thread pintail type bolt set is 0.48.

[0038] What was confirmed by the experiment: By obtaining a tightening axial force using a 12mm thick, HRC33 threaded splice plate, it is possible to obtain a friction joint structure with a slip coefficient of 0.45 or more in a slip resistance test using a standard test specimen, as described in the High Strength Bolted Joint Design and Construction Guidebook.

[0039] (Comparison of compressive force distribution affecting slip resistance) In order to compare the effect on the compressive force distribution at the joint surface of the friction welding structure of the present invention (Fig. 12B) and the conventional friction welding structure (Fig. 12A), Fujifilm's ultra-high pressure HHS (mono-sheet: the red color changes depending on the pressure, the stronger the pressure, the darker the red color, and the lighter the red color, the weaker the pressure) was sandwiched between joint surfaces (1) and (2) in Fig. 12B and joint surfaces (3) and (4) in Fig. 12A to examine the compressive force distribution. As shown in Fig. 16, even with the same pressure, the pressure distribution at bolt hole 11A was in the order of (1) > (2) > (3) > (4), and it was confirmed that the slip resistance was approximately 1.2 to 1.5 times higher for (1) and (2) of the present invention compared to the conventional (3) and (4).

[0040] REFERENCE SIGNS LIST 10 Workpiece to be joined 10A Insertion hole 11 Splice plate 11A Left-handed screw hole 20 Friction joint bolt 21 Left-handed screw 22 Right-handed threaded nut 23 Right-handed screw 24 Pin tail 25 Washer 50 Friction joint bolt 51 Bolt head 52 Bolt shaft 53 Right-handed screw

Claims

1. A friction joining structure in which a splice 11 is used as a support plate when multiple high-strength bolts are screwed together to press the members 10, 10 together, and the members 10, 10 are joined by the frictional force generated at the contact surface between the splice and the members 10, 10; the lower support plate splice 11 of the members 1 to be joined is made of flat steel material of substantially the same material and thickness as the nuts screwed into the high-strength bolts, and is provided with screw holes 11A into which the tip screw portions 21 of the multiple high-strength bolts are screwed; the high-strength bolts are inserted into the insertion holes 10A of the members 10 to be joined, and then screwed into the screw holes 11A provided in the lower support plate splice 11; This joint structure expands the axial pressure distribution around where the high-strength bolt tip 21 and the splice screw hole 11A screw together with an influence cone that spreads from the head of the high-strength bolt to the contact surface with the splice 11, improving the slip resistance, and increasing the compression spring constant Kc to reduce the ratio Θ (bolt internal force coefficient) of the tensile internal force Ft added to the bolt when an external force Wa is applied to the external force Wa, thereby improving the shear resistance of the high-strength bolt. This is a friction joint structure using high-strength bolts.

2. A friction joint structure as described in claim 1, wherein the splice 11, which is the support plate, consists of a pair of upper and lower splices that extend over the entire joining surface of the joined members 10, and the lower splice 11 is provided with a screw hole 11A that screws into the tip screw portion 21 of the high-strength bolt.

3. A splice with a screw base 11 extending over the entire joining surface of the joined members 10 to be applied to the friction joining structure described in claim 1, characterized in that it is made of a material substantially the same as the nut used for the high strength bolt 20, is formed to have a thickness substantially the same as the nut used for the high strength bolt, and has a screw hole 11A that screws into the tip of the high strength bolt in a position overlapping with the insertion hole 10A of the joined members.

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