JP7508755B2 - Reinforcement structure for steel joints - Google Patents

Description

The present invention relates to a reinforcement structure for steel joints, and in particular to a structure that reinforces joints between steel members of different widths by bonding with FRP (fiber reinforced plastic).

For example, in steel-framed buildings, braces are often used to connect columns to provide sufficient strength and plastic deformation capacity against horizontal deformation during earthquakes. Flat plates called gussets are welded to the columns and beams, and braces are generally friction-connected to these gussets with bolts. However, in existing buildings, the joints, i.e., gussets, do not have the joint strength to resist earthquake forces due to cross-sectional loss caused by bolt holes, and it is known that braces and gussets can break early.

To improve the earthquake resistance of existing buildings, methods are being used to weld backing plates to make the existing braces thicker, or to replace them with gussets. Welding backing plates or replacing or reinstalling them requires cutting, welding, and other work that generates high heat. However, this method is not often used in buildings or places where handling fire is not easy, such as factories.

In recent years, adhesive reinforcement and repair methods using lightweight, high-rigidity, high-strength fiber-reinforced plastics (FRP), especially carbon fiber-reinforced plastics (CFRP), as reinforcing materials have been developed and have been adopted for seismic reinforcement of existing buildings. CFRP is integrated with the structure by adhesion, which is easy to carry out and does not require open flames, so it is also applied to existing buildings where welding is not easily possible.

Carbon fiber (CF) sheets used in CFRP reinforcement materials are usually unidirectional materials with carbon fibers oriented in one direction. Because CF is an anisotropic material, unidirectional CF sheets have a strong reinforcing effect in the direction of the reinforcing fibers, but no reinforcing effect perpendicular to the fibers. Therefore, when reinforcing with CFRP, the fibers are oriented in the direction where reinforcement is required. The range in which the reinforcing effect can be efficiently exerted is limited to the reinforcing width of the CF sheet. In addition, in order to reinforce with CFRP, it is important to ensure the necessary fixing length to fully transmit the reinforcing force borne by the CFRP to the fixed member to which the CFRP is fixed.

However, when it is difficult to ensure the required anchorage length, such as in the case of gussets where space is limited, the CFRP can only bear the force equivalent to the secured anchorage length, and the expected reinforcing effect may not be obtained. Therefore, the method described in Patent Document 1 has been proposed as a means to secure the anchorage length, and the method described in Patent Document 2 has been proposed as a means to disperse the force flowing through the CFRP.

JP 2007-254953 A JP 2014-227743 A

However, when using FRP to reinforce joints between steel materials of different widths, such as the joints between a brace and a gusset, the methods described in Patent Documents 1 and 2 cannot be applied as is, especially when it is difficult to ensure the required anchorage length.

The objective of the present invention is to provide a structure for reinforcing joints between steel materials of different widths with FRP, which can realize a favorable FRP fixing structure even in cases where there are locations where the required fixing length cannot be secured using conventional methods, and which can provide a reinforcing structure for steel joints that can appropriately transmit the force generated in the FRP to the fixed member.

In order to solve the above problems, the present invention employs the following configuration.
(1) A structure in which a joint between steel materials of different widths is reinforced by bonding FRP, characterized in that a sheet-like FRP 1 is provided on the surface of a narrow steel material 1 so as to extend from said surface onto the surface of a wider steel material 2, and a sheet-like FRP 2 in which reinforcing fibers are oriented at ±(30° to 60°) relative to the extension direction of the FRP 1 is provided on at least a portion of the portion extending onto the surface of the steel material 2.
(2) A reinforcement structure for a steel joint described in (1), in which the width of FRP2 is greater than the width of FRP1.
(3) A reinforcement structure for a steel joint described in (2), in which the FRP 2 is adhered to the steel material 2 at least in a portion exceeding the width of the FRP 1 in the width direction of the steel material 2.
(4) A reinforcement structure for a steel joint described in any one of (1) to (3), in which FRP2 has a portion arranged on the outer surface of the sheet constituting FRP1.
(5) A reinforcement structure for a steel joint described in any one of (1) to (4), in which the FRP 2 has a portion disposed between the sheet constituting the FRP 1 and the surface of the steel material 2.
(6) A reinforcement structure for a steel joint described in any one of (1) to (5), in which FRP2 has a portion disposed between at least two sheets constituting FRP1.
(7) A reinforcement structure for a steel joint described in any one of (1) to (6), in which the FRP 1 is composed of a sheet with reinforcing fibers in the same direction as the longitudinal direction of the steel 1.
(8) A reinforcement structure for a steel joint described in any one of (1) to (7), wherein FRP2 is composed of a sheet in which reinforcing fibers are oriented at ±45° to the longitudinal direction of FRP1.
(9) A reinforcement structure for a steel joint described in any one of (1) to (8), in which the tip of the portion of the FRP 1 extending onto the surface of the steel 2 is formed into a tapered portion whose thickness gradually decreases.
(10) A reinforcement structure for a steel joint described in any one of (1) to (9), in which the joint between the steel materials is formed by overlapping an end of steel material 1 and an end of steel material 2.
(11) A reinforcement structure for a steel joint described in any one of (1) to (9), in which the joint between the steel materials is formed by butting an end face of a steel material 1 against an end face of a steel material 2.
(12) A reinforcement structure for a steel joint described in any one of (1) to (11), in which the reinforcing fibers of FRP1 and FRP2 contain carbon fibers.
(13) A reinforcement structure for a steel joint according to any one of (1) to (12), wherein the matrix resin of FRP1 and FRP2 is made of a thermosetting resin.
(14) A reinforcement structure for a steel joint described in any one of (1) to (13), in which an epoxy-based adhesive is used to bond FRP1 and FRP2 to the steel.

According to the present invention, by adding a specific FRP2 to FRP1 as a reinforcing FRP for joints between steel materials of different widths, it is possible to realize an excellent FRP fixing structure, and it is possible to appropriately transmit the force generated in the FRP to the fixed member, thereby providing a preferable reinforcing structure for steel joints.

For example, when reinforcing an existing joint between a brace and a gusset as a joint between steel materials of different widths with FRP, the gusset cross section that is missing at the bolt hole can be reinforced with at least FRP1, and FRP2 can reduce the adhesive stress connecting the gusset and brace from FRP1, improving the peel strength of FRP1 and improving the joint strength between the existing gusset and brace.

FIG. 1 shows a reinforcement structure for a steel joint according to one embodiment of the present invention, in which FIG. 1(A) is a schematic plan view and FIG. 1(B) is a schematic vertical sectional view. 2A and 2B show a reinforcement structure for a steel joint according to another embodiment of the present invention, in which FIG. 2A is a schematic plan view and FIG. 2B is a schematic vertical sectional view. FIG. 3 shows a reinforcement structure for a steel joint according to still another embodiment of the present invention, in which (A) is a schematic plan view and (B) is a schematic vertical sectional view. FIG. 4 shows a reinforcement structure for a steel joint according to still another embodiment of the present invention, in which (A) is a schematic plan view and (B) is a schematic vertical sectional view.

Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments.
The reinforcement structure for steel joints according to the present invention is a structure in which a joint between steel materials of different widths is reinforced by bonding FRP, and is characterized in that a sheet-like FRP 1 is provided on the surface of a narrow steel material 1 so as to extend from that surface onto the surface of a wide steel material 2, and at least a portion of the portion of the FRP 1 extending onto the surface of the steel material 2 is provided with a sheet-like FRP 2 whose reinforcing fibers are oriented at ±(30° to 60°) relative to the extension direction of the FRP 1 itself, in other words, the sheet-like FRP 2 has a cross in which the reinforcing fibers are oriented at ±(30° to 60°).

Figure 1 shows a reinforcement structure 100 for a steel joint according to one embodiment of the present invention. In the reinforcement structure 100 for a steel joint shown in Figure 1, the joint 1 between steel materials is formed by overlapping the end of a narrow steel material 1 (2) and the end of a wide steel material 2 (3). For this joint 1, a sheet-like FRP 1 (4) is provided on the surface of the narrow steel material 1 (2) so as to extend from the surface to the surface of the wide steel material 2 (3), and in this embodiment, the FRP 1 (4) is directly bonded to the surface of the steel material 1 (2) and the surface of the steel material 2 (3). In this embodiment, the FRP 1 (4) is formed of a sheet with the reinforcing fiber direction being the same as the longitudinal direction of the steel material 1 (2). In this embodiment, the FRP 1 (4) is provided on both sides of the steel material 1 (2) and the steel material 2 (3), but the present invention also includes the case where the FRP 1 (4) is provided on one side. Furthermore, the tip of the portion of FRP1 (4) that extends onto the surface of steel material 2 (3) is formed into a tapered section 5 whose thickness gradually decreases (however, in this embodiment, tapered sections are formed at both tips of FRP1 (4)).

In this embodiment, a sheet-like FRP2 (6) having a cloth with reinforcing fibers oriented at ±(30° to 60°) with respect to the extension direction of the FRP1 (4) is provided for at least a portion of the portion of the FRP1 (4) that extends on the surface of the steel material 2 (3), and in this embodiment, for almost the entire portion of the FRP1 (4) that extends on the surface of the steel material 2 (3). In this embodiment, the orientation direction of the reinforcing fibers in the FRP2 (6) is set at ±45° with respect to the extension direction of the FRP1 (4), and in this embodiment, the orientation direction of the reinforcing fibers is also ±45° with respect to the reinforcing fiber direction of the FRP1 (4) (in this embodiment, the longitudinal direction of the FRP1 (4) and the longitudinal direction of the steel material 1 (2)).

The width of FRP2 (6) is set to be larger than the width of FRP1 (4). This FRP2 (6) is directly bonded to steel material 2 (3) at least in a portion that exceeds the width of FRP1 (4) in the width direction of steel material 2 (3). In this way, FRP2 (6) has a portion that is disposed on the outer surface of the sheet that constitutes FRP1 (4), and is directly bonded to FRP1 (4) in that portion, and is also directly bonded to steel material 2 (3) in a portion that exceeds the width of FRP1 (4).

The reinforcing fibers in the above FRP1 (4) and FRP2 (6) are not particularly limited and may be carbon fiber, glass fiber, aramid fiber, etc., but from the perspective of reinforcing the steel joints, it is preferable that they contain carbon fiber, which has a large reinforcing effect.

The matrix resin for FRP1 (4) and FRP2 (6) is not particularly limited either, and either thermosetting or thermoplastic resins can be used, but from the viewpoint of easily completing a reinforcement structure by heating the resin on-site, for example, at existing steel joints, it is preferable to use a thermosetting resin. There is no particular limit to the type of thermosetting resin, and a commonly used one, such as an epoxy resin, can be used.

The adhesive used to bond FRP1 (4) and FRP2 (6) to the steel material is not particularly limited, and any commonly used adhesive, such as an epoxy adhesive, may be used. A similar adhesive may be used to bond FRP1 (4) and FRP2 (6), and when performing on-site heating, bonding between the matrix resins of FRP1 (4) and FRP2 (6) may be used.

In the reinforcement structure 100 for steel joints as shown in FIG. 1, in addition to the conventional FRP 1 (4) as a reinforcing FRP for the joint 1 between steel materials 2 and 3 of different widths, FRP 2 (6) is provided, particularly in the upper part of the steel material 2 (3), from the outer surface of FRP 1 (4) to the surface of the steel material 2 (3), which is wider than FRP 1 (4) and has a reinforcing fiber orientation direction of ±45°. This allows the structure to be fixed to the steel material 2 (3) by the definition of FRP 1 (4) itself. In addition to the attachment portion, a fixing portion is added to the portion of FRP2 (6) joined to FRP1 (4) that is wider than FRP1 (4). Even when it is difficult to obtain the fixing length in the extension direction of FRP1 (4), it is possible to realize an excellent FRP fixing structure with a high reinforcing effect, and it is possible to appropriately transmit the force generated in the FRP, especially the force generated in FRP1 (4), to the fixed member, steel material 2 (3), and a preferable reinforcing structure for the steel joint can be realized.

As shown in the lower part of Figure 1 (B), FRP1 (4) is bonded to the outer surface of steel material 2 (3). FRP2 (6) is wider than FRP1 (4) and has a reinforcing fiber orientation direction of ±45°. By providing FRP2 (6) extending from the outer surface of FRP1 (4) to the surface of steel material 2 (3), even if there is a cross-sectional defect due to a bolt hole in the existing joint 1, FRP2 (6) can reinforce the bond of FRP1 (4) to steel material 2 (3). As a result, the adhesive stress in the direction connecting the steel materials from FRP1 (4) can be reduced, improving the peel strength of FRP1 (4) from steel material 2 (3), and improving the joint strength between the steel materials.

Furthermore, because the tip of the portion of FRP1 (4) that extends onto the surface of steel material 2 (3) is formed into a tapered section 5 with a gradually decreasing thickness, the landing point of wide FRP2 (6) that is provided on and covering this tapered section 5 on the surface of steel material 2 (3) approaches the widthwise end face of FRP1 (4) the closer it is to the tip of tapered section 5, resulting in stable adhesion of FRP2 (6) to steel material 2 (3) and improved adhesive strength. As a result, the reinforcing effect of the fixation of FRP1 (4) to steel material 2 (3) by adding FRP2 (6) is increased, and an even more preferable reinforcement structure for the steel joint can be realized.

Figure 2 shows a reinforcement structure 200 for a steel joint according to another embodiment of the present invention. In the reinforcement structure 200 for a steel joint shown in Figure 2, the joint 11 between the steel members is formed by butting the end face of a narrow steel member 1 (2) against the end face of a wide steel member 2 (3). For this joint 11, a sheet-like FRP 1 (4) is provided on the surface of the narrow steel member 1 (2) so as to extend from that surface onto the surface of the wide steel member 2 (3), and in this embodiment, the FRP 1 (4) is directly bonded to the surface of the steel member 1 (2) and the surface of the steel member 2 (3).

In this embodiment, a sheet-like FRP2 (6) having a cloth with reinforcing fibers oriented at ±(30° to 60°) with respect to the extension direction is provided for at least a part of the portion of FRP1 (4) extending on the surface of steel material 2 (3), and in this embodiment, for almost the entire portion of FRP1 (4) extending on the surface of steel material 2 (3). In this embodiment, the orientation direction of the reinforcing fibers in FRP2 (6) is set at ±45° with respect to the extension direction, and in this embodiment, the orientation direction of the reinforcing fibers is also ±45° with respect to the reinforcing fiber direction of FRP1 (4) (in this embodiment, the longitudinal direction of FRP1 (4) and the longitudinal direction of steel material 1 (2)). The other configurations are similar to the embodiment shown in FIG. 1. In this embodiment, the same action and effect as in the embodiment shown in FIG. 1 can be obtained.

Figure 3 shows a reinforcement structure 300 for a steel joint according to yet another embodiment of the present invention. In the reinforcement structure 300 for a steel joint shown in Figure 3, compared to the embodiment shown in Figure 1, the wide sheet-like FRP2 (6) having a cross in which the reinforcing fibers are oriented at ±(30° to 60°) with respect to the extension direction of the FRP2 (6) is not provided on the outer surface side of at least a part of the portion of the FRP1 (4) that extends on the surface of the steel material 2 (3) (in this embodiment, for almost the entire portion of the FRP1 (4) that extends on the surface of the steel material 2 (3)), but is provided on the inner side of the FRP1 (4) between the sheet constituting the FRP1 (4) and the surface of the steel material 2 (3), and is directly bonded to the surface of the steel material 2 (3) over almost the entire surface of the FRP2 (6).

In this way, even when FRP2 (6) is provided on the inner surface of FRP1 (4), that is, between the inner surface of FRP1 (4) and the surface of steel material 2 (3), adding FRP2 (6) wider than FRP1 (4) increases the reinforcing effect of the attachment of FRP1 (4) to steel material 2 (3), and a preferable reinforcement structure for the steel joint can be realized. However, in this case, since the tip of FRP1 (4) is formed into a tapered portion 5, it is not possible to stabilize the adhesion of FRP2 (6) to steel material 2 (3) or improve its adhesive strength, but it is possible to alleviate stress concentration at the tip of FRP1 (4).

Figure 4 shows a reinforcement structure 400 for a steel joint according to yet another embodiment of the present invention. In the reinforcement structure 400 for a steel joint shown in Figure 4, the sheets constituting FRP1 (4) are divided into at least two sets, and FRP2 (6) has a portion disposed between at least two sheets constituting FRP1 (4). In the embodiment shown in Figure 4, FRP2 (6) is further provided on at least a portion of the portion of FRP1 (4) extending on the surface of steel material 2 (3), and in this embodiment, on almost the entire portion of FRP1 (4) extending on the surface of steel material 2 (3), on the outermost side, i.e., between the outer surface of the sheet constituting the outermost layer FRP1 (4), and on the innermost side, i.e., between the sheet constituting the innermost layer FRP1 (4) and the surface of steel material 2 (3).

In this embodiment, by having FRP2 (6) sandwiched between the sheets that make up the divided FRP1 (4), stress transfer between FRP1 (4) and FRP2 (6) is smoother, and the joining strength of the steel materials by FRP1 (4) in the direction in which the steel materials are joined (the direction in which the steel materials extend) can be further improved. Other actions and effects are the same as those of the embodiment shown in Figures 1 and 3.

The reinforcing structure for steel joints according to the present invention is particularly effective when reinforcing existing joints between steel materials of different widths, and more specifically, is suitable for joints between existing braces and gussets.

・ 11 Joint between steel materials 2 Steel material 1
3 Steel 2
4 FRP1
5 Tapered portion 6 FRP2
100, 200, 300, 400 Reinforcement structure for steel joints

Claims (12)

This is a reinforcement structure for steel joints in which a joint between steel materials of different widths is reinforced by bonding FRP, the reinforcement structure for steel joints being characterized in that a sheet-like FRP 1 is provided on the surface of a narrow steel material 1 so as to extend from said surface onto the surface of a wider steel material 2, and a sheet-like FRP 2 in which reinforcing fibers are oriented at ±(30° to 60°) relative to the extension direction of the FRP 1 is provided on at least a portion of the portion extending onto the surface of the steel material 2, and the joint between the steel materials is formed by overlapping an end of the steel material 1 with an end of the steel material 2 . The reinforcement structure for a steel joint as described in claim 1, wherein the width of FRP2 is greater than the width of FRP1. The reinforcement structure for a steel joint according to claim 2, wherein FRP2 is bonded to steel material 2 at least in a portion that exceeds the width of FRP1 in the width direction of steel material 2. The reinforcement structure for a steel joint according to any one of claims 1 to 3, wherein FRP2 has a portion disposed on the outer surface of the sheet constituting FRP1. A reinforcement structure for a steel joint according to any one of claims 1 to 4, in which FRP2 has a portion disposed between the sheet constituting FRP1 and the surface of steel 2. A reinforcement structure for a steel joint according to any one of claims 1 to 5, in which FRP2 has a portion disposed between at least two sheets constituting FRP1. A reinforcement structure for a steel joint as described in any one of claims 1 to 6, in which FRP1 is composed of a sheet with reinforcing fibers in the same direction as the longitudinal direction of steel 1. The reinforcement structure for a steel joint described in any one of claims 1 to 7, wherein FRP2 is composed of a sheet in which reinforcing fibers are oriented at ±45° to the longitudinal direction of FRP1. A reinforcement structure for a steel joint according to any one of claims 1 to 8, in which the tip of the portion of FRP 1 that extends onto the surface of steel 2 is formed into a tapered portion whose thickness gradually decreases. The reinforcement structure for a joint of steel materials according to any one of claims 1 to 9 , wherein the reinforcing fibers of FRP1 and FRP2 contain carbon fibers. 11. The reinforcement structure for a steel joint according to claim 1, wherein the matrix resin of FRP1 and FRP2 is made of a thermosetting resin. 12. The reinforcement structure for a joint of steel materials according to claim 1, wherein an epoxy adhesive is used to bond FRP1 and FRP2 to the steel material.

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