JP7629352B2 - Joint Structure - Google Patents

Description

The present invention relates to a joint structure.

RC (reinforced concrete), SRC (steel reinforced concrete), and SC (steel reinforced concrete) structures are structures that use reinforcing bars and steel materials as concrete reinforcement. When an external force is applied to a component, reinforcing bars and steel materials bear the tensile stress, reinforcing concrete, which is weak in tension, and giving the component strength against bending and shear.

When constructing these structures, it is necessary to form joints between rebars and steel materials from a construction perspective. In RC structures, the joints between rebars are often mechanical joints, but when using large diameter or high strength rebars, the joints become long, posing challenges in design and construction. In SC structures, just like RC structures, work is required to join steel materials, but these joints are generally welded or bolted, posing challenges in terms of construction and cost.

On the other hand, there are also examples of lap joints in which a pair of reinforcing bars or steel materials are placed in parallel and overlapped, and stress is transmitted between these reinforcing bars or steel materials via concrete (see, for example, Patent Document 1), which are considered to be rational in terms of construction, etc., and effective in absorbing construction errors.

Patent No. 6375079

In lap joints, the unevenness of the surface of the rebar or steel increases the adhesion of the concrete and improves stress transmission performance. However, when the tensile force (pulling force) acting on the rebar or steel increases, bond cracks occur from the surface, and the degree of restraint of the uneven rebar or steel plate decreases, reducing the bond stress of the concrete.

The bond strength of concrete in lap joints is determined through experiments etc. according to conditions such as the surface shape of the rebar or steel material and the strength of the concrete, but due to the bond splitting mentioned above, the potential of the bond strength cannot be fully utilized, which has been an issue in realizing a compact joint with a short joint length.

The present invention was made in consideration of the above-mentioned problems, and its purpose is to provide a joint structure etc. that can realize a compact joint.

In order to solve the above-mentioned problems, the present invention provides a joint structure in which a pair of reinforcing materials having uneven surfaces are stacked and arranged so that their axial directions are parallel, and a filler is filled between the reinforcing materials, and a cover material is arranged on the cover side of the reinforcing materials, the cover material having a bottom plate arranged on the cover side of the reinforcing material, and a plate-shaped protrusion protruding from the bottom plate toward the reinforcing material and arranged on the side of the reinforcing material with the plate surface parallel to the axial direction of the reinforcing material .
The protrusion may be disposed between the pair of stiffeners.

In the present invention, in a lap joint in which stress is transmitted between reinforcing materials via a filler, by providing a cover material on the cover side of the reinforcing material, adhesion cracking of the filler generated from the reinforcing material can be prevented from progressing to the surface of the component, and by providing a protrusion placed on the side of the reinforcing material as a cover material, adhesion cracking of the filler generated from the reinforcing material can be prevented from progressing laterally. By controlling adhesion cracking in this way, it is possible to make the most of the adhesion strength of the materials in the joint structure and realize a compact joint with a short joint length.

It is also desirable that the bottom plate be provided with a joint portion at a position in the axial direction of the reinforcing material that corresponds to the range of the lap joint of the pair of reinforcing materials, dividing the bottom plate into multiple locations in the axial direction of the reinforcing material .
This allows cracks to occur in the filler due to openings in the joints, optimizes the adhesion stress distribution of the filler, and improves the stress transmission performance of the joint structure.

It is also preferable that a plurality of the reinforcing members are arranged on one of the bottom plates.
By providing the cover material over multiple reinforcing materials, construction of the joint structure becomes easier.

It is also preferred that the covering material be formed from a fiber reinforced cementitious material.
This allows the cover material to reliably prevent the adhesion cracking from progressing.

The present invention can provide a joint structure that can realize a compact joint.

A diagram showing a joint structure 10. FIG. FIG. 4 is another example of the cover material 3. 4A to 4C are diagrams for explaining the construction of the joint structure 10. FIG. 2 shows the cover materials 3', 3''. A diagram showing a joint structure 10a. 4A to 4C are diagrams for explaining the effect of a joint portion 311. A diagram showing the cover material 3a'.

The following describes in detail a preferred embodiment of the present invention with reference to the drawings.

[First embodiment]
Fig. 1 is a diagram showing a joint structure 10 according to a first embodiment of the present invention. The joint structure 10 is provided in a member made of concrete C. Fig. 1 shows a part of the member including the joint structure 10.

The joint structure 10 of this embodiment is a lap joint, in which a pair of main steel materials 1 are overlapped and arranged so that their axial directions are parallel, and concrete C of the member is filled between the main steel materials 1 as a filler. In the joint structure 10, when an axial pull-out force A acts on the main steel materials 1, stress is transmitted between the pair of main steel materials 1 via the concrete C.

Figure 2 shows a cross section of the joint structure 10. Figure 2(a) is a cross section in the thickness direction of the member along the main steel material 1, and Figure 2(b) is a horizontal cross section at the height of the main steel material 1.

The main steel material 1 is a reinforcing material that reinforces the concrete C of the member by bearing tensile forces, and the parts other than the lap joint are also embedded in the concrete C of the member. The surface of the main steel material 1 is uneven, as shown in FIG. 3. In this embodiment, distribution steel material 4 is also provided in a direction perpendicular to the axial direction of the main steel material 1 in a plane. The main steel material 1 and distribution steel material 4 are made of shaped steel such as flat steel or H-shaped steel, but are not limited to this and other steel materials can also be used. Also, deformed bars (main bars or distribution bars) with uneven surfaces can be used as reinforcing materials within the member instead of the main steel material 1 and distribution steel material 4.

In the joint structure 10, a cover material 3 is placed on the cover side (component surface side) of the main steel material 1 to control bond splitting of the concrete C. The cover side of the main steel material 1 is the side perpendicular to the axial direction of the main steel material 1 (corresponding to the left-right direction in Figures 2(a) and (b)) and the overlapping direction of the main steel material 1 (corresponding to the normal direction to the paper surface in Figure 2(a) and the up-down direction in Figure 2(b)).

The cover material 3 has high tensile strength and is formed using a fiber-reinforced cement-based material (fiber-reinforced cement-based composite material) such as fiber-reinforced mortar or fiber-reinforced concrete, and has a base plate 31 and a protruding portion 32.

The bottom plate 31 is a flat rectangular plate material that is arranged along the axial direction of the main steel material 1 on the cover side of the main steel material 1. The bottom plate 31 is arranged with the plate surface facing the main steel material 1.

The protruding portion 32 is a plate material that protrudes from the plate surface of the bottom plate 31 toward the main steel material 1. The plate surface of the protruding portion 32 is arranged parallel to the axial direction of the main steel material 1. The height of the protruding portion 32 is determined so that the upper end of the protruding portion 32 is at or higher than the upper end of the main steel material 1.

The protrusions 32 are provided on both sides of the main steel material 1 on the plate surface of the bottom plate 31, and the protrusions 32 on the sides of the main steel material 1 are arranged between the main steel material 1 and the adjacent main steel material 1. Furthermore, multiple protrusions 32 are provided at intervals in the axial direction of the main steel material 1. The distribution steel material 4 is passed between the protrusions 32 adjacent in the axial direction. Note that in this embodiment, an example is described in which protrusions 32 are installed on both sides of each main steel material 1 to be lap-jointed, but as shown in Figure 4, the protrusions 32 between a pair of main steel materials 1 to be lap-jointed may be omitted, and the protrusions 32 may be provided only on both sides of the pair of main steel materials 1 as a unit.

The cover material 3 is placed on a formwork F as shown in FIG. 5, for example, and used to arrange the main steel material 1 and the distribution steel material 4, and then concrete C for the components is poured onto the formwork F. At this time, concrete C is also filled around the main steel material 1 that constitutes the lap joint, and the cover material 3 is embedded in the concrete C. In this way, the joint structure 10 is constructed.

In this embodiment, by providing the cover material 3 as described above, when a pull-out force A (tensile force) acts on the main steel material 1 due to bending of the member, etc., the bottom plate 31 prevents the adhesion cracking of the concrete C from progressing to the surface of the member, and the protrusion 32 prevents the adhesion cracking of the concrete C from progressing to the side of the main steel material 1, thereby preventing the adhesion cracking from penetrating into adjacent main steel materials 1, etc.

In this way, by controlling bond splitting using the cover material 3, it is possible to suppress the decrease in bond stress caused by bond splitting and to make maximum use of the bond strength of the material of the joint structure 10. As a result, it is possible to shorten the joint length of the main steel material 1 in the joint structure 10, and a compact joint structure 10 can be realized.

However, the present invention is not limited to the above embodiment. For example, the joint structure 10 is not limited to joining main steel materials 1 together within a member, but can also be applied to joining main steel materials 1 protruding from a pair of precast members, and the main steel materials 1 can be placed between the precast members using the cover material 3 in the same manner as above, and filled with filler. The filler is also not limited to the above-mentioned concrete C, and cement-based materials other than concrete C, such as mortar, can be used, and filler materials other than cement-based materials can also be used.

In addition, the cover material 3 of this embodiment has a bottom plate 31 and the like formed of fiber-reinforced mortar or the like that has high tensile strength and can reliably prevent the progression of adhesion cracking, but the material of the bottom plate 31 is not particularly limited as long as it has a predetermined tensile strength, for example, a tensile strength higher than that of concrete C. For example, the bottom plate 31 may be made of mortar with reinforcing members arranged inside, or a carbon fiber plate material may be used. Alternatively, a sheet material such as a steel mesh sheet may be used as the bottom plate 31, and the surface of the bottom plate 31 on the main steel material 1 side may be provided with irregularities to enhance the unity with the concrete C.

The protrusion 32 may be made of the same material as the bottom plate 31, or may be made of a different material, such as steel or reinforcing bars. The shape of the protrusion 32 is also not limited to a plate shape, and for example, as shown in the cover material 3' in FIG. 6(a), a truss bar made by combining reinforcing bars in a truss shape may be used as the protrusion 32. Furthermore, in some cases, the protrusion 32 may be omitted.

The bottom plate 31 is not limited to being provided for each main steel material 1, but can also be provided so that it is continuous across multiple main steel materials 1, and these multiple main steel materials 1 are arranged on one bottom plate 31, as shown in the cover material 3" in Figure 6 (b). In this case, too, by arranging a protrusion 32 between adjacent main steel materials 1, it is possible to prevent adhesion cracks from penetrating between the main steel materials 1. Furthermore, by providing a bottom plate 31 across multiple main steel materials 1, it is possible to simplify the positioning of the main steel materials 1, making it easier to construct the joint structure 10 and shortening the construction period. Figure 6 (c) is an example in which, like Figure 4, the protrusion 32 between a pair of main steel materials 1 to be lap-spliced is omitted, and the pair of main steel materials 1 is treated as a unit and protrusions 32 are provided only on both sides of it. In this case, too, the bottom plate 31 can be provided so that it is continuous across multiple pairs of main steel materials 1.

In addition, for the main steel material 1, it is possible to provide protrusions such as studs or perforated plates at the ends of the main steel material 1 located in the lap joint area to create unevenness and increase the adhesion of the concrete C, and it is also possible to improve the adhesion to the concrete C by providing an end plate at the tip of the main steel material 1.

In place of the main steel material 1, high-strength materials such as high-strength rebar (e.g. USD980) and fiber-reinforced polymers (e.g. CFRP) may be used as reinforcing materials. Even when using high-strength materials as reinforcing materials, there are many cases where the potential of high-strength materials is not fully utilized due to bond splitting. By using the cover material 3 of this embodiment, it becomes possible to control bond splitting and achieve a rational design that utilizes the potential of high-strength materials.

Second Embodiment
FIG. 7(a) is a diagram showing a joint structure 10a relating to a second embodiment of the present invention, and FIG. 7(b) is a diagram showing a cross section in the member thickness direction along the main steel material 1, similar to FIG. 2(a).

The joint structure 10a of the second embodiment differs from the first embodiment in that a joint portion 311 is provided in the bottom plate 31 of the cover material 3a at a predetermined position in the axial direction of the main steel material 1, and the bottom plate 31 is divided by the joint portion 311.

The joints 311 are made of a material with a lower tensile strength than the base plate 31 (parts excluding the joints 311), such as non-shrink mortar. The joints 311 are crack-inducing joints that open early due to bending of the member, etc., and induce cracks in the concrete C at that position, and are provided to optimize the bond stress of the concrete C within the lap joint area.

In other words, when a pull-out force A acts on the main steel material 1 due to bending of the member, as shown in Figure 8 (a), the displacement between the main steel material 1 and the concrete C is usually concentrated at position P1, which corresponds to the base of the main steel material 1 in the lap joint range B, and cracks in the concrete C expand at position P1, while the displacement is often smaller on the tip side of position P1.

As shown in Figure 8 (b), the adhesion of concrete C increases with increasing shear displacement until the shear displacement reaches a certain value x, but when the shear displacement exceeds this value x due to the expansion of cracks, the adhesion tends to decrease.

As mentioned above, when the pull-out force A is applied, cracks in the concrete C expand at position P1, which hits the base of the main steel material 1, and the slippage exceeds the above-mentioned value x, making it difficult to maintain adhesion. On the other hand, the slippage does not increase at a position closer to the tip of the main steel material 1 than position P1 (shown by the symbol P2 in Figures 8(a) and (b)), which results in limiting the stress transmission performance of the lap joint.

In this embodiment, therefore, a joint 311 is provided on the bottom plate 31 of the cover material 3a to induce cracks in the concrete C by early opening. This causes cracks in the concrete C to occur at the position of the joint 311, and the cracks in the concrete C caused by the pull-out force A are dispersed from position P1, which corresponds to the base of the main steel material 1, to other positions.

As a result, the slippage displacement at position P1, which corresponds to the base of the main steel material 1, becomes smaller as shown by arrow a1 in Figure 8(b), approaching the aforementioned value x that maximizes the adhesion force. On the other hand, the slippage displacement becomes larger at the position of the joint 311 due to the concentration of cracks, and a certain amount of slippage displacement occurs between the main steel material 1 and the concrete C even at the position next to the joint 311. Therefore, the slippage displacement at position P2 on the tip side of the main steel material 1 can also be increased as shown by arrow a2, and can be brought closer to the aforementioned value x that maximizes the adhesion force.

As a result, the bond stress of concrete C generated in the lap joint range B, as shown in bond stress distribution b in Figure 8 (c), is higher on average than bond stress distribution c when joint 311 is not provided. Since the force that can be transmitted by a lap joint is the integral value of the bond stress distribution in lap joint range B, increasing this distribution on average leads to improved stress transmission performance and a reduction in the required joint length. Note that the bond stress value is smaller at the position of joint 311 in bond stress distribution b because cracks in concrete C are concentrated at that position, causing the slip displacement to be maximized beyond the aforementioned value x.

Here, it is desirable to set the bottom plate 31 and the joint 311 so that the sum of the tensile forces borne by the bottom plate 31 and the main steel material 1 at the position P1 of the base of the main steel material 1 in the lap joint range B is the sum of the tensile forces borne by the main steel material 1 at the position corresponding to the joint 311, thereby optimally averaging the deviation between the concrete C and the main steel material 1 in the lap joint range B. Also, in FIG. 8(a), the joints 311 are provided at intervals in the axial direction of the main steel material 1, and it is desirable that the intervals be equal to or less than the calculated value of the bending crack interval of the concrete C in the lap joint range B. In particular, it is preferable to use a material with high tensile strength for the bottom plate 31 to prevent the development of bond cracking as described above, but in that case, bending cracks are unlikely to occur in the lap joint range B where the bottom plate 31 is installed, so it is expected that bending cracks will concentrate at the boundary of the installation location of the bottom plate 31, i.e., the boundary of the lap joint. Even in such a case, by providing a joint 311 in the bottom plate 31, it is possible to control and disperse bending cracks in the lap joint range B.

In the second embodiment, the materials and shapes of the bottom plate 31 and the protruding portion 32 are not limited. For example, by using truss reinforcement as shown in FIG. 6(a) as the protruding portion 32, it is possible to integrate the bottom plate 31 divided by the joint portion 311, and the construction of the cover material 3a is simplified. Also, when a bottom plate 31 is provided across multiple main steel materials 1 as shown in FIG. 6(b), these joint portions 311 can be constructed at the same time by aligning the positions of the joint portions 311 in the axial direction of the main steel materials 1 as shown in FIG. 9. This is also true when a bottom plate 31 is provided across multiple pairs of main steel materials 1 as shown in FIG. 6(c).

The joints 311 may also be made of concrete C. In this case, the individual divided parts of the bottom plate 31 are arranged with gaps between them, so that the concrete C fills the gaps when poured. In addition, it is also possible to use the high-strength material described above as a reinforcing material instead of the main steel material 1, and by arranging appropriate joints 311 in the bottom plate 31, the same effect as above can be obtained.

The above describes preferred embodiments of the present invention with reference to the attached drawings, but the present invention is not limited to these examples. It is clear that a person skilled in the art can come up with various modified or revised examples within the scope of the technical ideas disclosed in this application, and it is understood that these also naturally fall within the technical scope of the present invention.

1: Main steel material 3, 3', 3", 3a, 3a': Cover material 4: Strength distribution steel material 10, 10a: Joint structure 31: Bottom plate 32: Protruding portion 311: Joint portion

Claims (4)

A joint structure in which a pair of reinforcing materials having uneven surfaces are overlapped and arranged so that their axial directions are parallel, and a filler is filled between the reinforcing materials,
A cover material is disposed on the covering side of the reinforcing material,
The cover material is
A bottom plate arranged on the cover side of the reinforcing material;
a plate-shaped protruding portion protruding from the bottom plate toward the reinforcing material and disposed to the side of the reinforcing material with a plate surface parallel to an axial direction of the reinforcing material ;
A joint structure comprising: The joint structure according to claim 1, characterized in that a joint portion is provided in the bottom plate at a position corresponding to the range of the lap joint of the pair of reinforcing members in the axial direction of the reinforcing member , dividing the bottom plate into multiple locations in the axial direction of the reinforcing member. The joint structure according to claim 1 or 2, characterized in that multiple reinforcing members are arranged on one of the bottom plates. 4. The joint structure according to claim 1, wherein the protrusion is disposed between the pair of reinforcing members.

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