Buckling restraint brace

Abstract

To provide a buckling restrained brace capable of preventing bolted joints from being broken even when the core buckles.SOLUTION: A disclosed buckling restrained brace 1 is a buckling restrained brace 1 including: a steel core 3; and a wooden restraint 5 around the core 3. The core 3 includes: a plasticized part 7 in the center portion in the longitudinal direction; and an elastic part 9 at the longitudinal end having higher brace axial strength than the plasticized part 7. The restraint 5 is formed by bolting two or more wooden pieces arranged to sandwich the core 3. The bolted joint 14 is constituted of at least a bolt 18, a nut 19, and a washer 21. Multiple bolts 18 are arranged in two or more rows along the entire axial length of the brace material at both sides of the core 3. At the bolted joint 14 in the restraint 5, a bolt insertion hole and a countersink 17 are provided. The bolt axial stiffness and strength of the bolted joint 14 are adjusted to a specified value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a buckling restraining brace comprising a steel core material and a wooden restraining material arranged around the core material.

Background Art

[0002] In a building, a brace may be provided as a member that resists shear force during an earthquake. The brace is provided obliquely in the plane of the frame of columns and beams and is a member that mainly resists the shear deformation of the story caused by earthquake loads. During an earthquake, since axial tensile and compressive loads act repeatedly, the brace is required to have sufficient strength and energy absorption capacity against both loads.

[0003] Generally, when an axial compressive load acts, there is a risk of buckling in the member, and the buckling causes a decrease in the strength and deformation capacity of the member. In the brace, a decrease in strength and energy absorption capacity due to buckling may also occur. Therefore, there is a buckling restraining brace comprising a core material that resists earthquake loads and a restraining material arranged to cover the periphery of the core material to suppress the buckling deformation of the core material. Figs. 10 and 11 show such a buckling restraining brace 31 arranged in the plane of a frame composed of columns 33 and beams 35.

[0004] The restraining material is required to have sufficient strength against the bending deformation due to the buckling of the core material, and the restraining material or the joint of the restraining material is required to have sufficient strength against the local compressive force due to the buckling deformation of the core material. Fig. 12 is a cross-sectional view of a buckling restraining brace 31 composed of a core material 37 and a restraining material 39. As the cross-sectional shape of the conventional core material 37, there are a plate (see Fig. 12(a)), a circle (see Fig. 12(b)), a cross (see Fig. 12(c)), an H shape (see Fig. 12(d)), etc. Also, the restraining material 39 covering the core material 37 is often box-shaped (see Figs. 12(a), (c), (d)) or circular (see Fig. 12(b)).

[0005] Since the local compressive force due to the buckling deformation of the core material 37 is proportional to the compressive load acting on the core material and the amount of buckling deformation of the core material 37, the higher the gap between the restraint material 39 and the core material 37, the higher the yield strength required for the restraint material 39. Therefore, there are some that provide a filling material 41 such as mortar in the gap between the restraint material 39 and the core material 37 (see Fig. 12(a)). Also, there are some that apply or attach an unbonded material 43 so that the axial force of the core material 37 does not flow into the restraint material 39 (see Fig. 12(a)).

[0006] Regarding the joints between both ends of the buckling restraint brace 31 and the structure, there are a type with a bolt joint 45 joined by bolts shown in Fig. 10 and a type with a pin joint 47 joined by pins shown in Fig. 11. In either case, the width of the core material 37 near the joint is increased, high-strength steel is used, reinforcing ribs are provided, etc., to increase the yield strength of the core material and prevent plasticization, and the joint is designed not to fail first. Also, since the restraint material 39 is made of steel, local failure due to contact with the core material 37 is less likely to occur. Furthermore, since the restraint material 39 is made of steel and consists of a single member, there is no concern about failure at the joint.

[0007] On the other hand, recently, due to CO 2 emission problems, the use of wood is being promoted. Since wood burns away during a fire, it may be used for building columns and beams by imparting fire resistance through non-combustible treatment, etc. In addition, there are cases where wood is used in part such as floor slabs in steel structures, and recently, the use of wood as a restraint material for braces is being studied.

[0008] In Patent Document 1, a buckling restraint brace is proposed that consists of a steel plate-shaped core material and a pair of wooden restraint materials arranged on both sides of the wide surface of the core material, and the two are bolted together at both axial ends. Also, Patent Document 1 proposes a buckling restraint brace in which a pair of wooden restraint materials are arranged so as to sandwich both sides of the web of an H-shaped cross-section core material.

[0009] In Patent Document 2, a buckling restraint brace is proposed, which consists of a steel plate-shaped core material, a pair of wooden restraint materials arranged on both sides of the wide surface of the core material, and a pair of wooden side plates arranged on both sides of the narrow surface of the core material and joined to the restraint plates.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0011] In the buckling restraint braces disclosed in Patent Documents 1 and 2, both use bolts to join the wooden restraint materials. When the core material buckles, the restraint material is pushed by the core material, and a tensile force acts on the bolt joint. At this time, there is a risk that the bolt joint (the wood or bolt around the bolt joint) will break, and the predetermined buckling restraint effect may not be obtained. In particular, since wood has a low elastic modulus, the wood at the bolt joint may be locally deformed, and as a result, the buckling deformation of the core material may increase and the local compressive force may also increase.

[0012] Therefore, when using bolts to join the restraint materials, the bolt joint is required to have predetermined performance. However, in Cited Documents 1 and 2, the required performance is not mentioned, and there is a risk of breakage at the bolt joint when the core material buckles.

[0013] The present invention has been made to solve such problems, and an object thereof is to obtain a buckling restraint brace that does not break at the bolt joint even when the core material buckles.

Means for Solving the Problems

[0014] (1) The buckling restraint brace according to the present invention includes a steel core material and a wooden restraint material disposed around the core material, and the core material includes a plasticized portion at the central portion in the longitudinal direction and an elastic portion at the longitudinal end portion having a higher axial compressive strength than the plasticized portion in the brace axis direction, the restraint material is formed by bolt-joining two or more wooden materials arranged so as to sandwich the core material, the bolt-joining portion is composed of at least a bolt, a nut, and a washer, and two or more rows of bolts are arranged over the entire length in the brace material axis direction at both side surface positions of the core material, bolt insertion holes and counterbores are provided at the positions of the bolt-joining portion in the restraint material, the rigidity in the bolt axis direction and the axial compressive strength of the bolt-joining portion satisfy the following formula.

Equation

[0015] (2) Further, in the one described in (1) above, the flexural strength of the restraint material satisfies the following formula.

Equation

[0016] (3) Further, in the one described in (1) or (2) above, the core material is in the shape of a rectangular plate, and reinforcing ribs are welded to both surfaces of the plate at the longitudinal ends of the core material, the restraint material is composed of at least two laminated timbers, the laminated timbers are arranged such that the width direction of the veneer is orthogonal to the width direction of the core material, and a groove conforming to the shape of the core material is provided at a portion corresponding to the plasticized portion of the core material in the restraint material.

[0017] (4) Further, in the one described in (3) above, among the laminated woods constituting the restraint material, the two members provided with the grooves are joined so as to prevent displacement in the axial direction of the brace material.

[0018] (5) Further, in the one described in (3) or (4) above, the restraint material is composed of two laminated woods, and the groove is formed by forming stepped portions respectively and arranging the stepped portions of the two laminated woods to face each other.

Advantages of the Invention

[0019] In the present invention, since the rigidity and the ultimate strength in the axial direction of the bolt material of the bolt joint portion are adjusted to satisfy a predetermined value in consideration of the deformation of the bolt joint portion, it is possible to prevent breakage from the bolt joint portion during core material compression and achieve a high buckling restraint force.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0021] The buckling restraint brace 1 according to the present embodiment will be described with reference to FIGS. 1 to 3. FIG. 1(a) is an explanatory drawing for explaining the internal structure of the buckling restraint brace 1, and shows the inside by perspective viewing the state seen from the arrow A-A direction in FIG. 2. Further, FIG. 1(b) is a figure showing the state seen from the arrow B-B direction in FIG. 1(a). Furthermore, FIG. 2 is a figure corresponding to the cross section taken along the arrow C-C in FIG. 1(a). Also, FIG. 3 is a figure corresponding to the cross section taken along the arrow D-D in FIG. 1(a).

[0022] As shown in FIGS. 1 to 3, the buckling restraint brace 1 according to the present embodiment is composed of a steel core material 3 and a wooden restraint material 5 arranged around the core material 3. Hereinafter, each configuration will be described in detail.

[0023] <Core material> The core material 3 is composed of a plate-like body made of steel with a rectangular long cross section, and includes a plasticized portion 7 at the central portion in the longitudinal direction and an elastic portion 9 at the longitudinal end portion having a higher axial compressive strength in the brace axis direction than the plasticized portion 7. In order not to plasticize the elastic portion 9, the axial compressive strength in the brace axis direction is higher than that of the plasticized portion 7. For this reason, the member strength of the elastic portion 9 is determined by the size and strength of the plasticized portion 7. In the present embodiment, by welding reinforcing ribs 10 to both surfaces of the plate of the elastic portion 9, the axial compressive strength in the brace axis direction is increased. The reinforcing rib 10 is joined to the wide surface of the core material 3 by fillet welding or partial penetration welding so as to be orthogonal thereto. Therefore, a cross section is formed by the core material 3 and the reinforcing rib 10 in the joining range of the reinforcing rib 10.

[0024] In the present embodiment, since both ends of the core material 3 are bolted to the frame structure with high-strength bolts, a joint portion 13 having bolt holes 11 is provided at the end of the elastic portion 9. However, in the case of a pin joint type, a clevis is provided at the end of the elastic portion 9.

[0025] <Restraining material> The restraining material 5 is formed by bolt-joining two wooden materials arranged so as to sandwich the core material 3. The restraining material 5 sandwiches the core material 3 from both sides. Therefore, a groove 15 having a rectangular cross section corresponding to the shape of the core material 3 is provided in a portion of the restraining material 5 corresponding to the plasticized portion 7 of the core material 3. As shown in FIG. 4, this groove 15 may be provided in both of the wooden members constituting the restraining material 5, or may be provided in one of the wooden materials. It is preferable to adjust the shape of the groove so that the gap with the core material 3 becomes as small as possible. The restraining material 5 is provided with bolt holes 16 and countersinks 17 for inserting bolts 18 (see FIGS. 4 and 5).

[0026] Further, as a method that eliminates the need for grooving, as shown in FIG. 5, a pair of restraining materials 5 having a length corresponding to the groove length may be provided in a portion corresponding to the groove wall, that is, a portion facing the narrow surface of the core material 3. In addition, the restraining material 5 needs to be provided with a groove 15 having a size larger than the shape of the reinforcing rib 10 so as not to interfere with the reinforcing rib 10. When the restraining material 5 may interfere with the welded portion of the reinforcing rib 10 and the core material 3, the restraining material 5 may be notched according to the welding shape.

[0027] The wood used for the restraint member 5 may be a wood-based material such as glued laminated timber, LVL, or CLT. In consideration of the initial shape irregularity of the core material 3, it is preferable that the size of the groove 15 is slightly larger than the cross-sectional shape of the core material 3.

[0028] <Bolt joint> The bolt joint 14 consists of at least a bolt 18 inserted through the bolt counterbore 16, a nut 19, and a washer 21. However, a washer, a disc spring, or a locking mechanism may be provided as necessary. The bolts 18 are provided in at least one row on each of the two side surfaces of the core material 3, for a total of two or more rows, so as not to interfere with the core material 3. Since buckling of the core material 3 can occur over the entire length, the bolt joints 14 are provided over the entire length of the brace material in the axial direction. Note that the example shown in FIG. 1 is an example where there are two rows of bolts 18, but the present invention is not limited to this, and there may be three or more rows.

[0029] The restraint member 5 is provided with a counterbore for passing the bolt 18 and a countersink 17 at the tightening portion for arranging the nut 19 and the washer 21. Generally, the diameter of the bolt counterbore 16 is about 1 to 2 mm larger than the bolt diameter. It is necessary to adjust the number of bolts, bolt size, washer size, tree species and strength of the wood, etc. so that the bolt joint 14 satisfies a predetermined rigidity and load-bearing capacity. Also, it is necessary to adjust the tree species of the wood, the strength, and the size of the restraint member 5 so that the flexural strength of the restraint member 5 satisfies the required strength considering the elongation of the bolt joint 14.

[0030] In the present embodiment, since the restraint member 5 arranged so as to sandwich the core material 3 is formed of a wooden material, it is conceivable that the wooden material sinks into the bolt joint 14 when the core material 3 buckles. Therefore, considering such sinking, it is necessary that the rigidity in the bolt axial direction and the load-bearing capacity in the bolt axial direction of the bolt joint 14 satisfy the following formula.

Equation

[0031] Hereinafter, the derivation of the above formula will be described. When using a single flat-section restraint member 5 like the conventional structure, the gap s between the core member 3 and the restraint member 5 can be regarded as constant. However, since the restraint member 5 of the present embodiment is formed by bolt-joining a pair of wooden members, when the core member 3 is compressed, the restraint member 5 is pushed, and the gap s between the core member 3 and the restraint member 5 increases by the amount of bolt elongation and the indentation deformation of the wooden material. Therefore, in the conventional design method that assumes a constant gap s, there is a risk of underestimating the gap s and resulting in a design on the dangerous side.

[0032] When assuming buckling as shown in Fig. 9, the local load per location is from the balance of moments within one buckling wavelength enclosed by the dotted line, which is 4·dN max ·s / l n and this local load occurs at L / l n locations. Therefore, the total value P of the local load that pushes the restraint member 5 due to the buckling of the core member 3 B is obtained as follows.

Equation

[0033] The above P B represents the total local load value when the gap dimension between the core member 3 and the restraint member 5 is the initial dimension s before buckling. When the total local load value based on this initial dimension s before buckling is defined as P B1 , the elongation δ B1 of the bolt joint 14 of the restraint member 5 when P B1 acts is shown as follows.

Equation

[0034] When the bolt joint 14 elongates by δ B1 , the gap dimension between the core member 3 and the restraint member 5 increases from s to s + δ B1 . The total local load value P B2 and the elongation δ B2 of the bolt joint 14 of the restraint member 5 when P B2 acts are shown as follows.

Number

[0035] Similarly, the calculation is repeated by the amount that the bolt joint 14 extends, and the cumulative local load value P B is updated as shown below, and the following equation becomes the required proof strength of the bolt joint 14, that is, the right side of Equation (2).

Number

[0036] Here, x represents an arbitrary integer. As can be seen from the above equation, the cumulative local load value P B diverges and becomes infinitely large unless K B is sufficiently large. That is, the bolt joint 14 will break if K B is not sufficiently large. The condition for P B not to diverge is as follows.

Number

[0037] By arranging the above equation with respect to K B , Equation (1) showing the required rigidity of the bolt joint 14 described above is derived. As described above, by satisfying the elongation rigidity and proof strength of the bolt joint 14 shown in Equation (1) and Equation (2), it is possible to prevent the bolt joint 14 from being broken by the load acting on the restraint member 5 due to the buckling of the core material 3, and a sufficient buckling restraint effect can be expected.

[0038] Note that the elongation rigidity and proof strength of the bolt joint 14 can be calculated as follows as three series springs of the central bolt 18 and the woods (washer-inserted parts) at both ends in terms of structure.

Number

[0039] Next, the bending buckling restraint condition will be described. According to a non-patent document (Steel Structure Vibration Control Design Guide of the Architectural Institute of Japan, November 2014), a bending buckling restraint condition for restraining the bending deformation due to the buckling of the core material 3 is required for the buckling restraint brace. When arranging the bending buckling restraint condition shown in the non-patent document in terms of the bending strength M of the restraining material 5 yB it becomes as follows.

Equation

[0040] However, the above formula is based on the assumption that the restraining material 5 is a steel member that does not dent like a wooden material. On the other hand, when a wooden material is used as the restraining material 5 as in the present invention, since the gap dimension between the core material 3 and the restraining material 5 increases as described above, sufficient strength may not be obtained by the above formula. Therefore, it is necessary to consider the elongation δ of the bolt joint 14 B and the formula in that case becomes the following formula.

Equation

[0041] As described above, according to the present embodiment, since the structure takes into account the increase in the gap s, even when the gap s becomes large due to buckling, it is possible to obtain the buckling restraint brace 1 that does not break at the bolt joint 14 even when the core material 3 buckles.

[0042] Note that, as shown in FIG. 6, a glued laminated timber composed of a plurality of veneers 23 can be used as the restraining material 5. By using the glued laminated timber, it is possible to prevent the deflection depending on the fiber direction of the wood.

[0043] In addition, since two glued laminated timbers are used as the restraining material 5, it is preferable to provide a displacement prevention mechanism for preventing the displacement in the axial direction of the brace material of the two glued laminated timbers. As a displacement prevention mechanism, as shown in FIG. 7, a wooden side plate 25 may be provided on the side surfaces of the two laminated timbers so as to span both laminated timbers, and this may be dowel-jointed to the laminated board with wooden dowels 27. Other displacement prevention mechanisms include adhesive bonding between the laminated timbers and the combined use of dowel jointing and adhesive bonding. In any of the joining methods, a shear strength sufficient to resist displacement between the two laminated timbers is required.

[0044] By preventing displacement in the axial direction of the brace members of the two laminated timbers, the two laminated timbers will act as one and resist bending during bending deformation, thereby exhibiting high rigidity and strength. As a result, a high buckling restraint effect can be obtained with a smaller cross-sectional size.

[0045] In the example shown in FIG. 4, the restraint member 5 was grooved. However, in order to facilitate processing, for example, as shown in FIG. 8, a stepped portion 29 may be formed on the opposing surfaces of the pair of restraint members 5, and the groove 15 may be formed when the surfaces on which the stepped portion 29 is formed are joined facing each other. In this case, separate restraint members 5 will be located at positions facing the two narrow and thick surfaces of the plate-shaped core material 3.

[0046] The stepped portion 29 in the restraint member 5 will be in the form of a protruding wood. By making the stepped portion 29 of each restraint member 5 have the same shape, the two restraint members 5 will have the same shape. This eliminates the need for production differentiation. Also, by making the protruding dimension of the stepped portion 29 equal to the width of the narrow and thick surface of the core material 3, the gap between the core material 3 and the restraint member 5 can be adjusted to be minimized.

Example

[0047] According to a non-patent document (Japan Institute of Architects, Steel Structure Vibration Control Design Guide, November 2014), the buckling restraint brace 31 is required to have bending buckling restraint conditions for restraining the bending deformation caused by the buckling of the core material 37, and these bending buckling restraint conditions are as follows.

[0048]

Number

[0049] The structure to be considered is shown in FIGS. 1 and 2. The core material 3 is a plate-shaped cross-sectional member made of grade 490 N / mm 2 steel, with a width of 120 mm, a plate thickness of 25 mm, and a shaft length of 4000 mm. The buckling restraint material is a pair of wooden members with grooves 15 provided in accordance with the shape of the core material 3 as shown in FIG. 9. Each has a width of 300 mm, a depth of 150 mm, a total cross-sectional width of 300 mm, a depth of 300 mm, and a length of 4600 mm. The wood has a flexural Young's modulus of 8000 N / mm 2 , a flexural strength of 31.5 N / mm 2 , and an indentation strength of 8.1 N / mm 2 . Also, the tangent modulus E t of the core material 3 is set to 0.05 times the Young's modulus.

[0050] The results of examining the flexural buckling restraint conditions are shown in Table 1.

Table 1

[0051] When the existing design method of the buckling restraint brace is used as it is, as shown in Table 1, this structure is considered to satisfy the design conditions and have sufficient flexural performance as a buckling restraint material. However, the above is based on the premise that the gap s is constant. Therefore, for the case of using wooden materials as in the present invention, regarding the above structure, it was examined whether it satisfies the requirements of the present invention for the case where the gap s is 1 mm (Case a) and the case where it is 0.2 mm (Case b).

[0052] K B =594 (kN / mm), T B =636 (kN), and when the specifications of the bolt joint 14 and the wooden member are adjusted so that n = 40, it is as shown in Table 2.

Table 2

[0053] As shown in Case a, when the gap s is 1 mm, the result does not satisfy Equation (2). This indicates that although the conventional design method is supposed to meet the requirements, it is actually a dangerous design in reality. On the other hand, in Case b where the gap s is 0.2 mm, both Equation (1) and Equation (2) are satisfied, indicating that it can be safely designed even under the conditions of the present invention.

Explanation of Reference Numerals

[0054] 1 Buckling Restraint Brace 3 Core Material 5 Restraint Material 7 Plasticization Portion 9 Elastic Portion 10 Reinforcing Rib 11 Bolt Hole 13 Joint Portion 14 Bolt Joint Portion 15 Groove 16 Under-Bolt Hole 17 Counterbore 18 Bolt 19 Nut 21 Washer 23 Pulling Plate 25 Wooden Side Plate 27 Wooden Dowel 29 Step Shape Portion 31 Buckling Restraint Brace (Conventional) 33 Column 35 Beam 37 Core Material 39 Restraint Material 41 Filling Material 43 Unbonded Material 45 Bolt Joint Portion 47 Pin Joint Portion

Claims

1. A buckling-restrained brace comprising a steel core material and a wooden restraint material arranged around the core material, wherein the core material comprises a plasticized portion at the central portion in the longitudinal direction and an elastic portion at the longitudinal end portion having a higher axial compressive strength than the plasticized portion in the brace axis direction, the restraint material is formed by bolt-joining two or more wooden materials arranged so as to sandwich the core material, the bolt-joining portion is composed of at least a bolt, a nut, and a washer, and two or more rows of the bolts are arranged over the entire length in the brace material axis direction at both side surface positions of the core material, a bolt insertion hole and a counterbore are provided at the position of the bolt-joining portion in the restraint material, a buckling-restrained brace, characterized in that the rigidity in the bolt axis direction and the axial compressive strength of the bolt-joining portion satisfy the following formula. 【Number 1】

2. The buckling-restrained brace according to Claim 1, characterized in that the flexural strength of the restraint material satisfies the following formula. 【Number 2】

3. the core material is in the form of a plate with a rectangular cross-section, and reinforcing ribs are welded to both surfaces of the plate at the longitudinal ends of the core material, the restraint material is composed of at least two laminated timbers, the laminated timbers are arranged such that the width direction of the veneer is orthogonal to the width direction of the core material, and a groove conforming to the shape of the core material is provided at a portion corresponding to the plasticized portion of the core material in the restraint material. The buckling-restrained brace according to Claim 1 or 2, characterized in that.

4. The buckling-restrained brace according to Claim 3, characterized in that the two members provided with the grooves among the laminated timbers constituting the restraint material are joined so as to prevent displacement in the brace material axis direction.

5. The buckling-restrained brace according to Claim 3, characterized in that the restraint material consists of two laminated timbers, and the groove is formed by forming stepped portions respectively and arranging the stepped portions of the two laminated timbers to face each other.

6. The buckling-restrained brace according to Claim 4, characterized in that the restraint material consists of two laminated timbers, and the groove is formed by forming stepped portions respectively and arranging the stepped portions of the two laminated timbers to face each other.

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