JP7613342B2 - Buckling restraint brace and structure equipped with said buckling restraint brace - Google Patents

Description

The present invention relates to a buckling restraint brace consisting of a steel core and a pair of wooden buckling restraint members, and to a structure equipped with the buckling restraint brace.

In buildings, braces are sometimes installed as components to resist shear forces during earthquakes. Braces are installed diagonally within the plane of the frame and are primarily used to resist shear deformation of a story caused by earthquake loads.
During an earthquake, axial tensile and compressive loads are repeatedly applied, so the braces are required to have sufficient strength and energy absorption capacity against both loads.

Generally, when an axial compressive load is applied, there is a risk of buckling occurring in a member, and the occurrence of buckling reduces the member's strength and energy absorption capacity.
Since braces can also experience a decrease in strength and energy absorption capacity due to buckling, there are buckling-restrained braces that consist of a core material that resists earthquake loads and a buckling restraint material that is arranged to cover the core material to suppress buckling deformation of the core material.
6 and 7 show such a buckling restraint brace 41 disposed within the plane of a frame formed by columns 43 and beams 45.

The buckling restraint material is required to have sufficient strength to resist bending deformation due to buckling of the core material, and the buckling restraint material or its joints are required to have sufficient strength to resist local compressive forces due to buckling deformation of the core material.
FIG. 8 is a cross-sectional view of a buckling restraint brace 41 consisting of a core material 47 and a buckling restraint material 49. Cross-sectional shapes of conventional core material 47 include a plate (see FIG. 8(a)), a circle (see FIG. 8(b)), a cross (see FIG. 8(c)), an H-shape (see FIG. 8(d)), etc., and the buckling restraint material 49 covering the core material 47 is often box-shaped (see FIG. 8(a), (c), (d)) or circular (see FIG. 8(b)).

The larger the gap between the buckling restraint material 49 and the core material 47, the higher the strength required of the buckling restraint material 49. Therefore, in some cases, a filler 51 such as mortar is provided in the gap between the buckling restraint material 49 and the core material 47 (see FIG. 8(a)).
In addition, in order to prevent the axial force of the core material 47 from flowing to the buckling restraint material 49, an unbond material 53 may be applied or attached (see FIG. 8(a)).

The joints between both ends of the buckling restraint brace 41 and the frame include a bolt joint 55 shown in FIG. 6, which is joined by a bolt, and a pin joint 57 shown in FIG.
In either case, the core material 47 is made wider near the joint, high-strength steel is used, reinforcing ribs are provided, etc. to increase the strength of the core material 47 and prevent plasticity, so that the joint does not break first. In addition, because the buckling restraint material 49 is made of steel, localized breakage due to contact with the core material 47 is unlikely to occur.

Recently, the use of wood has been promoted due to the issue of _CO2 emissions. Since wood burns up in the event of a fire, it is sometimes used for building columns and beams after being made fireproof by fireproofing. In addition, wood is sometimes used in some parts of steel structures, such as floor slabs, and the use of wood as a buckling restraint material for braces is being considered in recent years.

For example, Patent Document 1 proposes a buckling restraint brace 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, with the two being bolted together at both axial ends.
Patent Document 1 also proposes forming both ends of a plate-like structure with an H-shaped cross section and disposing a pair of wooden restraining members that sandwich both sides of the web.

Furthermore, Patent Document 2 proposes a buckling restraint brace consisting of a steel plate-shaped core material, a pair of wooden restraint plates 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.
In addition, an insert plate is provided between the broad surface of the core material and the restraining plate to prevent the restraining plate from being damaged by localized compressive forces of the core material.

JP 2019-214881 A JP 2020-51186 A

The techniques disclosed in Patent Documents 1 and 2 basically use a plate-shaped core material and propose a scheme to restrain the deformation in the out-of-plane direction about the weak axis (the direction in which the wide surface of the plate deforms out-of-plane).
However, since the core material is made of steel, the tangential rigidity of the material becomes very small when it is plasticized, and out-of-plane deformation also occurs in the out-of-plane deformation direction around the strong axis (the direction in which the narrow surface of the plate deforms out-of-plane). The localized compressive force caused by the out-of-plane deformation around the strong axis is likely to damage the restraining material because the contact surface is small, but Patent Documents 1 and 2 do not fully consider damage to the restraining material caused by the out-of-plane deformation around the strong axis.
Furthermore, this problem is not limited to plate cross sections; in the case of core materials for open cross sections such as cross-sections or H-sections made of steel plate, the thickness surface of the steel plate, which forms the narrow width surface, may come into contact with the wooden buckling restraint material and be damaged, which may weaken the restraint against buckling deformation.

The present invention was made to solve these problems, and aims to provide a buckling restraint brace that can prevent the core material from damaging the wooden buckling restraint material when deformed and can maintain restraining force even when deformed, and a structure equipped with the buckling restraint brace.

(1) A buckling restrained brace according to the present invention comprises a steel core material, a wooden buckling restrained material arranged to cover the periphery of the core material, and a sinking prevention plate interposed between the buckling restrained material and the core material to prevent the core material from sinking into the buckling restrained material,
The core material is an open cross-section member formed by combining one steel plate or a plurality of steel plates,
the buckling restraint member is composed of a pair of members arranged and joined to sandwich the core material, and the joining surfaces of the members have grooves shaped to accommodate the core material and the indentation prevention plate,
The width of the sinking prevention plate is set to be larger than the width of the contact surface of the core material that contacts the sinking prevention plate.

(2) Furthermore, in the above-mentioned (1), the width of the anti-sinking plate satisfies the following formula.
Br≧Bs+2×tr
Where, Br: Width of the plate to prevent embedding
Bs: Width of the core material at the part in contact with the anti-slip plate
tr: Thickness of the plate to prevent embedding

(3) Also, in the above (1) or (2), the pair of buckling restraint members are joined at multiple points in the longitudinal direction by a group of bolt parts having washers and a loosening prevention mechanism.

(4) In addition, in any of the above (1) to (3), the indentation prevention plate is made of steel and is arranged so as to span between a pair of members constituting the buckling restraint material, rod holes are provided at positions corresponding to the pair of members constituting the buckling restraint material and the indentation prevention plate, and a rod is inserted into the rod holes of the pair of members and the indentation prevention plate, joining the pair of members via the indentation prevention plate by the rod.

(5) Furthermore, in any of the above (1) to (4), the gap between the anti-sinking plate and the buckling restraint material is filled with adhesive.

(6) The frame of the present invention has a pair of columns and a pair of beams, and is characterized in that it further comprises a buckling restraint brace described in any one of (1) to (5) above within the structural surface.

In the present invention, a sinking prevention plate is provided between the buckling restraint material and the core material to prevent the core material from sinking into the buckling restraint material. By setting the width of the sinking prevention plate to be larger than the width of the abutment surface of the core material that abuts against the sinking prevention plate, the stress caused by contact with the narrow surface of the core material's thickness surface is reduced by the width of the sinking prevention plate and transmitted to the buckling restraint material, preventing destruction of the buckling restraint material and realizing a buckling restraint brace with excellent buckling restraint properties.

FIG. 1(a) is an explanatory diagram of a buckling restraint brace according to embodiment 1, and FIG. 1(b) is a cross section taken along the line AA in FIG. 1(b) (part 1). FIG. 2(a) is an explanatory diagram of a buckling restraint brace according to embodiment 1, and FIG. 2(b) is a cross section taken along the line AA in FIG. 2(b) (part 2). 1A to 1C are explanatory diagrams illustrating the assembly process of the buckling restraint brace according to embodiment 1. 4A is an explanatory diagram of another aspect of the buckling restraint brace according to embodiment 1, and FIG. 4A is a cross-section taken along the line AA in FIG. 4B. 5A and 5B are explanatory diagrams of a buckling restraint brace according to an embodiment, in which FIG. 5A is a detailed diagram of the core material, FIG. 5B is an explanatory diagram of the deformation direction of the core material, and FIGS. 5C and 5D are explanatory diagrams of the arrangement and detailed dimensions of the indentation prevention plates. This is an explanatory diagram of a typical buckling restraint brace installed within the frame plane (part 1). This is an explanatory diagram of a typical buckling restraint brace installed within the frame plane (part 2). FIG. 1 is an explanatory diagram of the core material and buckling restraint material of a typical buckling restraint brace.

[First embodiment]
The buckling restrained brace 1 according to this embodiment will be described with reference to Figures 1 to 3. Figure 1 shows a state in which the core material 3 and the buckling restrained material 5 are separated, and Figure 2 shows a state in which the core material 3 and the buckling restrained material 5 are integrated together.
1(a) shows a cross section taken along line A--A in FIG. 1(b), and FIG. 2(a) shows a cross section taken along line A--A in FIG. 2(b).

The buckling restraint brace 1 in this embodiment comprises a steel core material 3, a wooden buckling restraint material 5 arranged to cover the periphery of the core material 3, and a sinkhole prevention plate 6 interposed between the buckling restraint material 5 and the core material 3 to prevent the core material 3 from sinking into the buckling restraint material 5.
Each component will be described in detail below.

<Core material>
The core material 3 consists of an open cross-section member formed from a single steel plate or a combination of multiple steel plates, and is intended for steel plates whose narrow surface, the thickness surface of the steel plate, may come into contact with the buckling restraint material 5 due to buckling deformation, for example, plate-shaped, cross-shaped, or H-shaped cross sections.
In order to prevent damage to the joints at the longitudinal ends of the core material 3, the longitudinal ends generally have elastic portions 7 that are stronger than the plasticized portion 9 at the longitudinal center. Examples of ways to increase the strength include widening the width, providing reinforcing ribs, and using high-strength steel.
In this embodiment, both ends of the core material 3 are bolted to the frame with high strength bolts, so that the ends of the elastic portion 7 are provided with bolt holes 11 as bolted joints 13. However, in the case of a pin joint type, a clevis is provided at the end of the elastic portion 7.

<Buckling restraint material>
The buckling restraint material 5 consists of a pair of members joined together so as to sandwich the core material 3 from the wide side, and the joint surfaces of each member have a groove portion 15 shaped to accommodate the core material 3 and a sink-in prevention plate 6 (see Figure 1 (a)).
The wooden buckling restraint members 5 are a pair intended to sandwich the core material 3 and the indentation prevention plate 6, and are provided with grooves that match the shapes of each. The wood used for the core material 3 may be wood materials such as laminated lumber, LVL, and CLT. Note that, taking into consideration the initial irregularities in the shapes of the core material 3 and the indentation prevention plate 6, it is advisable to make the size of the groove slightly larger than the cross-sectional shape of the core material 3.
In this embodiment, the buckling restraint members 5 are disposed so as to sandwich the core material 3 from the wide side thereof, but the direction in which the core material 3 is sandwiched is not particularly limited.

The pair of buckling restraint materials 5 are joined with the core material 3 and the anti-sinking plate 6 sandwiched between them. Joining methods include mechanical joining using bolts, screws, lag screw bolts, drift pins, etc., joining with adhesives, or joining with a combination of these. When joined, the buckling restraint materials 5 have sufficient resistance to the extrusion force in the out-of-plane direction due to contact with the core material 3, preventing the buckling restraint materials 5 from separating from each other, resulting in excellent buckling restraint properties.

<Anti-sinking plate>
The embedment prevention plate 6 is a component for preventing destruction of the buckling restrained material 5 due to contact with the narrow surface of the thickness of the steel plate, and in order to achieve this purpose, the width of the embedment prevention plate 6 is set to be larger than the width of the contact surface of the core material 3 that contacts the embedment prevention plate 6. As a result, the stress due to contact with the core material 3 is dispersed and transmitted to the buckling restrained material 5, thereby preventing destruction of the buckling restrained material 5.

As mentioned above, the purpose of installing the sinking prevention plate 6 is to disperse the stress caused by contact with the core material 3 and flow it to the buckling restraint material 5. Therefore, if the width of the sinking prevention plate 6 is not large enough, its effect will be weakened. In this regard, since it is thought that stress spreads and disperses in a 45-degree direction, the width of the stress that flows through the sinking prevention plate 6 and acts on the buckling restraint material 5 is the width of the contact surface with the core material 3 plus twice the thickness of the sinking prevention plate 6. Therefore, in this case, making the width of the sinking prevention plate 6 wider than this will provide a sufficient stress dispersion effect.

The anti-sinking plate 6 is preferably harder than wood, and examples of materials include steel and mortar. The thicker the anti-sinking plate 6, the more the stress is dispersed, and the more the buckling restraint material 5 can be prevented from breaking. It is also desirable for the anti-sinking plate 6 to be installed over the entire length of the range in which the core material 3 can be plasticized, but short anti-sinking plates 6 may be installed intermittently in the longitudinal direction.

As described above, the buckling restraint brace 1 of this embodiment can prevent damage to the buckling restraint material 5 due to contact with the plate thickness surface of the core material 3, which is a narrow surface, and can realize a buckling restraint brace 1 with excellent buckling restraint properties.

Although there is no particular limitation on the method for joining a pair of buckling restraint members 5 together, it is preferable to join them using a washer 17 and a bolt part group 23 having an anti-loosening mechanism (nut 19, washer 21), as shown in Figure 3.
This allows the buckling restraint members 5 to be mechanically joined to each other by the bolt parts group 23, and prevents the buckling restraint members 5 from coming apart due to contact with the core material 3.

In this case, the wooden buckling restraint member 5 is provided with a bolt hole 27 into which the bolt 25 is inserted. It may also be provided with a counterbore 29. The size and shape of the counterbore 29 are set to match the shape of a washer for bolt connection and to be larger than the washer.
By covering the countersunk portion with wood after the bolts are fastened, 13 minutes of the bolted joint can be hidden, resulting in a brace with excellent design.

The washer 17 is necessary to ensure the strength of the bolted joint by widening the contact area and preventing the wood from being crushed by the bolt. To prevent the nut 19 from loosening, a spring washer, an idling, or a double nut can be used. Figure 5 shows the double nut type.
The bolt connections are provided at positions outside the width of the core material 3 (see FIG. 4(a)) and in the axial direction of the core material 3. The spacing between the bolts 25 and the sizes of the bolts 25 and washers 17 are determined according to the buckling wavelength of the buckling restraint material 5 and the calculated value of the required buckling stiffening force.

[Embodiment 2]
In embodiment 1, the material of the sink-in prevention plate 6 was not particularly limited, but in this embodiment, the sink-in prevention plate 6 is made of steel and has the function of preventing the buckling restraint material 5 from separating.
As shown in FIG. 4 , in the buckling restraint brace 1 of this embodiment, the indentation prevention plate 6 is made of steel and is arranged so as to span between a pair of members that make up the buckling restraint material 5, and rod holes 30 are provided at positions where the pair of members that make up the buckling restraint material 5 and the indentation prevention plate 6 correspond, and a rod 31 is inserted into the rod hole 30 of the pair of members and the indentation prevention plate 6, so that the pair of members are joined via the indentation prevention plate 6 by the rod 31.

In this way, by giving the indentation prevention plate 6 the function of preventing the buckling restraint material 5 from separating, a stable strength can be obtained at the joint between the indentation prevention plate 6 and the buckling restraint material 5.
In order to exert the separation prevention function of the buckling restraint material 5, it is desirable to join the members mechanically, and therefore the joining is performed by using rods 31. The types of rods 31 include lag screw bolts and drift pins.

As another embodiment for providing the indentation prevention plate 6 with the function of preventing the buckling restrained material 5 from separating, an adhesive may be filled into the gap between the indentation prevention plate 6 and the buckling restrained material 5. By bonding the indentation prevention plate 6 and the buckling restrained material 5, the indentation prevention plate 6 can be used as a member that prevents the buckling restrained material 5 from separating, similar to the mechanical joining by the rod 31.
The adhesive may be used in combination with the bonding by the rod 31 .

In the above first and second embodiments, the buckling restraint brace 1 has been described, but the present invention is not limited to a single buckling restraint brace, but includes a frame having a pair of columns and a pair of beams, and further including a buckling restraint brace 1 within the structural plane. Such a frame is expected to have a higher strength than one equipped with a conventional buckling restraint brace.

The stress on the buckling restraint member 5 caused by contact with the plate thickness surface of the core material 3 was examined and is explained below. According to the conventional design guidelines for buckling restrained braces (non-patent document: Architectural Institute of Japan, Steel Structure Vibration Control Design Guidelines, November 2014), the stiffening force B due to buckling of the core material and contact between the core material and the buckling stiffener for a buckling restrained brace can be calculated as follows:

The structure under consideration is shown in Figure 5. The core member 3 is a steel material with a yield strength of 235N/mm2, and as shown in Figure 5(a), it is a cross-sectional member with a width of 140mm, a depth of 86mm, and a plate thickness of 16mm.
As shown in Figures 5(c) and 5(d), the buckling restraint material 5 is a pair of wooden members each having a groove formed to match the shape of the core material 3, and each of the pair of members is 300 mm wide and 150 mm high.
The one shown in Figure 5 (c) has a sink-in prevention plate 6 (plate thickness: 16 mm, width 48 mm) arranged in the out-of-plane deformation direction around the strong axis of the core material 3, and the one shown in Figure 5 (d) has a sink-in prevention plate 6 (plate thickness: 32 mm, width 80 mm) arranged in the out-of-plane deformation direction around the weak axis of the core material 3.
The results of the study are shown in Table 1.

As shown in Table 1, although the stiffening force B is greater for out-of-plane deformation about the weak axis, the stress at the contact surface is relatively high at 8.2 N/ ^mm2 , even when the thick plate surface (narrow surface) comes into contact with the out-of-plane deformation about the strong axis. Since the compressive strength of larch, which has high strength in general, is approximately 8 N/ ^mm2 , this shows that when the thick plate surface (narrow surface) buckles and comes into contact with the wooden buckling restraint material 5, regardless of the buckling direction, there is a high possibility that compressive failure will occur.

On the other hand, by installing the anti-sinking plate 6, the contact stress of the thick surface (narrow width) around the weak axis is reduced from 33.9 N/mm ² to 6.78 N/mm ² , and the contact stress of the thick surface (narrow width) around the strong axis is reduced from 8.20 N/mm ² to 2.73 N/mm ² .
These results show that when a embedment prevention plate 6 is provided, the width of the contact surface increases, and the stress transmitted to the buckling restraint material 5 through contact with the core material 3 is kept low; and that if the embedment prevention plate 6 is provided with sufficient thickness and width, the stress can be reduced to a level that prevents embedment failure of the wood.

REFERENCE SIGNS LIST 1 buckling restrained brace 3 core material 5 buckling restrained material 6 anti-sinking plate 7 elastic portion 9 plasticized portion 11 bolt hole 13 bolt joint portion 15 groove portion 17 washer 19 nut 21 washer 23 bolt component group 25 bolt 27 bolt hole 29 counterbore 30 rod hole 31 rod 41 buckling restrained brace (conventional)
43 Column 45 Beam 47 Core material 49 Buckling restraint material 51 Filler material 53 Unbonded material 55 Bolted joint 57 Pin joint

Claims (5)

A buckling restrained brace comprising a steel core material, a wooden buckling restraint material arranged to cover the periphery of the core material, and a compression prevention plate made of steel or mortar that is interposed between the buckling restraint material and the core material to prevent the core material from compressing into the buckling restraint material,
The core material is an open cross-section member formed by combining one steel plate or a plurality of steel plates,
the buckling restraint material is composed of a pair of members arranged and joined to sandwich the core material, and the joining surfaces of the members have grooves shaped to accommodate the core material and the indentation prevention plate,
The thickness surface of the steel plate constituting the core material abuts against the approximate center of the width surface of the indentation prevention plate to form an abutment surface, and the width of the indentation prevention plate is set larger than the width of the abutment surface of the core material,
A buckling restraint brace characterized in that the width of the anti-slip plate satisfies the following formula.
Br≧Bs+2×tr
Where, Br: Width of the plate to prevent embedding
Bs: Width of the contact surface of the core material that contacts the anti-sink plate
tr: Thickness of the plate to prevent embedding The buckling restraint brace described in claim 1, characterized in that the pair of buckling restraint members are joined at multiple points in the longitudinal direction by a group of bolt parts having washers and a loosening prevention mechanism. The buckling restraint brace described in claim 1 or 2, characterized in that the indentation prevention plate is made of the steel material and is arranged to span each of a pair of components that constitute the buckling restraint material, rod holes are provided at positions corresponding to each of the pair of components that constitute the buckling restraint material and the indentation prevention plate, and rods are inserted into each of the pair of components and the rod holes of the indentation prevention plate, joining the pair of components via the indentation prevention plate by the rod, and the indentation prevention plate has the function of preventing the pair of components from separating. The buckling restraint brace according to any one of claims 1 to 3, characterized in that the gap between the anti-sinking plate and the buckling restraint material is filled with adhesive. A frame having a pair of columns and a pair of beams, further comprising a buckling restraint brace according to any one of claims 1 to 4 within the structural plane.