Connection between concrete-filled steel pipe column and steel beam

Abstract

To provide a junction between a concrete-filled steel pipe column and a steel beam capable of improving the overall strength and durability of a structure in a column-beam junction of a CFT structure by compensating for the lack of strength without comprising a diaphragm.SOLUTION: There is provided a junction between a concrete-filled steel pipe column and a steel beam 2. In the junction between the concrete-filled steel pipe column, in which an interior of a steel pipe column 1b is filled with concrete, and the steel beam 2: a junction steel pipe 3 with a wall thicker than that of the column steel pipes 1b respectively arranged above and below the junction steel pipe is interposed in a section where an end of the steel beam 2 is joined to the concrete-filled steel pipe column; and protrusions 4 are provided in a designated upper section of an inner surface of the column steel pipe 1b connected to a lower end of the junction steel pipe 3. By using the junction steel pipe 3 with wall thicker-than that of the column steel pipe 1b for the section where the end of the steel beam 2 is joined to the concrete-filled steel pipe column, the diaphragm 7 becomes no longer necessary, and concrete can be easily poured thereinto. Furthermore, a force can be transmitted to the column concrete via protrusions 4 located on the inner surface of the steel pipe 1b.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a column-beam joint in a concrete-filled steel pipe structure (hereinafter referred to as a CFT structure), and particularly to the structure of a joint between a concrete-filled steel pipe column and a steel beam. [Background technology]

[0002] In CFT structures, when through diaphragms or internal diaphragms are installed in the steel column pipes, voids tend to form on the underside of the through diaphragms or internal diaphragms when concrete is filled in. To prevent this, it is common to install air vent holes in the diaphragms to prevent voids from forming.

[0003] Furthermore, installing three or more diaphragms at one beam-column joint is not desirable in terms of concrete filling. Furthermore, when multiple diaphragms are installed, the minimum spacing between them exceeds the dimensions required for welding. Previously, these problems were addressed by tapering the beam ends to unify the beam depth at the beam-column joint, but this approach had the disadvantage of increasing manufacturing costs.

[0004] On the other hand, there is a construction method that can reduce the thickness of the steel pipe columns by inserting rebar cages into the columns of a CFT structure. With this construction method, the larger the cross-sectional dimensions (width and diameter) of the inserted rebar cage, the more effective it is to reduce the thickness of the steel pipe columns. Therefore, with the through diaphragm type and internal diaphragm type, the effect of reducing the steel pipe thickness cannot be expected compared to the external diaphragm type. However, with the external diaphragm type, the diaphragm tends to be large, which can lead to poor manufacturing costs and poor design, so the through diaphragm type is often adopted.

[0005] If the steel pipe columns of a CFT structure are made thinner, local buckling may occur in the steel pipe columns during a major earthquake, raising concerns about a decrease in column strength. One solution to this problem is to insert a reinforcing bar cage into the CFT structure to suppress local buckling of the steel pipe columns. In this case, too, the larger the cross-sectional dimensions of the reinforcing bar cage, the greater the effect of suppressing local buckling of the steel pipe columns, but there is a problem in that the size of the reinforcing bar cage is limited depending on the type of diaphragm.

[0006] In response to this, for example, Patent Documents 1 and 2 propose a structure in which no diaphragm is provided at the column-beam joint of the CFT structure.

[0007] Patent Document 1 discloses a joint structure between a steel concrete-filled column and a beam, which consists of a thick-walled steel pipe with internal ribs interposed by welding between an upper steel pipe column and a lower steel pipe column, concrete filled inside the steel pipe with internal ribs, and a beam butt-fixed to the outer surface of the steel pipe with internal ribs.

[0008] Patent Document 2 discloses a joint structure between a steel pipe concrete column and a beam, which consists of a connecting cylinder interposed between upper and lower steel pipe columns, an outer surface of the connecting cylinder that is aligned with the outer surface of the steel pipe columns, an inner surface of the connecting cylinder that is positioned inward from the inner surface of the steel pipe column, and concrete filled into the steel pipe column and the connecting cylinder. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 02-080729 [Patent Document 2] Japanese Patent Application Publication No. 04-106240 Summary of the Invention [Problem to be solved by the invention]

[0010] The invention described in Patent Document 1 uses a steel pipe with internal ribs at the column-beam joint to ensure adhesion between the steel pipe column and concrete at the column-beam joint, but there is a problem in that the adhesion strength in areas other than the column-beam joint is relatively low.

[0011] The invention described in Patent Document 2 eliminates the need for a diaphragm by thickening only the connecting tube that is interposed in the column-beam joint. However, even in this case, the adhesive strength of parts other than the column-beam joint is relatively low, and there is a risk that the transmission of force from the column steel pipe to the concrete will be insufficient compared to when a diaphragm is provided.

[0012] The present invention aims to provide a joint between a concrete-filled steel pipe column and a steel beam that compensates for the load-bearing capacity of the column-beam joint in a CFT structure without providing a diaphragm, thereby improving the strength and durability of the entire structure. [Means for solving the problem]

[0013] The joint between a concrete-filled steel pipe column and a steel beam according to the present invention is characterized in that, at the joint between a concrete-filled steel pipe column and a steel beam, where concrete is filled inside the column steel pipe, a joint steel pipe that is thicker than the column steel pipes above and below is interposed in the section where the end of the steel beam is joined to the concrete-filled steel pipe column.

[0014] This invention is based on the premise of a CFT structure in which steel beams are joined to steel pipe columns and filled with concrete. At the joints between the steel pipe columns and steel beams in a CFT structure, by using thicker steel pipes at the joints where the ends of the steel beams are joined to the concrete-filled steel pipe columns, the need for diaphragms can be eliminated, making it easier to fill with concrete. Furthermore, there is no need to provide haunches at the beam-column joints, and restrictions such as adding diaphragms are eliminated. Beams can be attached to any beam depth and at any position (height) within the range of the thick steel pipe joints.

[0015] In addition, in the joint between a concrete-filled steel pipe column and a steel beam of the present invention, the joint steel pipe may be thicker on the inside, and the outer surfaces of the joint steel pipe and the upper and lower column steel pipes may be flush.

[0016] Previously, force (column axial force) was transmitted from the steel column pipe to the column concrete via a diaphragm, but by eliminating the diaphragm, it became necessary to consider a method of transmitting force from the steel column pipe to the column concrete. When a steel column pipe and a thick-walled joint steel pipe are joined together on their outer surfaces, the joint steel pipe becomes thicker on the inside, creating an internal step at the joint between the steel column pipe and the joint steel pipe. It is thought that this internal step allows the vertical force from the steel beam to be transmitted to the concrete filled in the steel column pipe.

[0017] Furthermore, in the joint between the concrete-filled steel pipe column and the steel beam according to the present invention, a protrusion may be provided on the inner surface of the steel column pipe connected to the lower side of the joint steel pipe in a predetermined upper section. By providing a protrusion on the inner surface of the steel column pipe connected to the lower side of the joint steel pipe, force can be transmitted to the column concrete via the protrusion.

[0018] In addition, at the joint between a concrete-filled steel pipe column and a steel beam, a protrusion may also be provided in a predetermined lower section of the inner surface of the column steel pipe connected to the upper side of the joint steel pipe.

[0019] In the joint between a concrete-filled steel pipe column and a steel beam of the present invention, the joint steel pipe may be thicker on the outside, and the inner surfaces of the joint steel pipe and the upper and lower steel column pipes may be flush with each other. In this case, no step is created on the inner surface of the joint between the thick-walled joint steel pipe and the steel column pipe, but the protrusions on the steel column pipe can transmit the vertical force from the beam to the concrete filled in the steel column pipe.

[0020] Furthermore, at the joint between a concrete-filled steel pipe column and a steel beam, the protrusions may be protrusions formed by weld beads or rebar welding, or protrusions on the inner surface of a checkered steel plate. The protrusions on the inner surface of the steel pipe column need not pose any problems in strength or durability, and may be formed on the steel pipe column by, for example, weld beads or welding rebar. Furthermore, irregularities on the inner surface of a checkered steel plate can also be treated as protrusions.

[0021] Furthermore, in the joint between the concrete-filled steel pipe column and the steel beam of the present invention, a reinforcing bar cage consisting of main reinforcement and hoops may be inserted inside the concrete-filled steel pipe column. When a reinforcing bar cage is installed in a conventional CFT structure, only a small reinforcing bar cage that matches the size of the concrete pouring hole in the diaphragm can be used. However, since the present invention does not use a diaphragm, a larger reinforcing bar cage can be used, allowing the thickness of the steel pipe column to be thinner and suppressing local buckling. [Effects of the Invention]

[0022] Since the present invention is a joint between a concrete-filled steel pipe column and a steel beam as described above, it has the following effects. (1) In conventional CFT structures using diaphragms, voids tend to form on the underside of the diaphragm, raising concerns about the ability to fill the concrete. However, in the present invention, by eliminating the diaphragm, the ability to fill the concrete is improved.

[0023] (2) There are no longer any restrictions such as providing haunches at the beam ends or adding diaphragms, and beams can be attached to any beam depth and position (height) within the range of the thick-walled joint steel pipes.

[0024] (3) In columns of CFT structures in which reinforcing bar cages are inserted, the cross-sectional dimensions of the reinforcing bar cages can be maximized by not installing a diaphragm, which allows the thickness of the column steel pipe to be thinner and also improves the effect of suppressing local buckling.

[0025] (4) There is no diaphragm, improving the design. [Brief explanation of the drawings]

[0026] [Figure 1] 1A and 1B show an embodiment of a joint between a concrete-filled steel pipe column and a steel beam according to the present invention, where (a) is an elevation view and (b) is a cross-sectional view taken along the line AA of (a). [Figure 2]Regarding the joint between a concrete-filled steel pipe column and a steel beam according to the present invention, (a) is an explanatory diagram showing the transmission of vertical force from the step when the outer surfaces of the joint steel pipe and the upper and lower column steel pipes are flush, (b) is the transmission of vertical force from the step and the inner protrusion when the outer surfaces of the joint steel pipe and the upper and lower column steel pipes are flush, and (c) is the transmission of vertical force from the inner protrusion. [Figure 3] The figure shows the structure of a typical joint between a concrete-filled steel pipe column and a steel beam using a diaphragm, where (a) is a plan view and (b) is a cross-sectional view. [Figure 4] The figure shows the joint between a typical concrete-filled steel pipe column with a diaphragm and a reinforcing cage and a steel beam, (a) is a cross-sectional view, and (b) is a plan view. [Figure 5] 1A and 1B show a case where a reinforcing bar cage is provided at the joint between a concrete-filled steel pipe column and a steel beam of the present invention, where (a) is a cross-sectional view and (b) is a plan view. [Figure 6] The figures show the performance of reinforcing steel CFT structures, where (a) is a normal reinforcing steel CFT structure and (b) is the reinforcing steel CFT structure of the present invention. [Figure 7] This is a graph comparing the results of calculations for a CFT structure with a normal diaphragm, a CFT structure with a normal diaphragm and conventional reinforcing bars, and a CFT structure of the present invention with no diaphragm and reinforcing bars. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the joint between a concrete-filled steel pipe column 1 and a steel beam 2 of the present invention, with (a) being an elevation view and (b) being an AA cross-sectional view of (a). The present invention assumes a CFT structure in which concrete 1a is filled in a steel column pipe 1b. FIG. 1 shows a steel column pipe 1b with a square cross section joined to a steel beam 2 with a different web height. The steel pipe where the steel beam 2 is joined is a thick-walled joint steel pipe 3. By using a thick-walled joint steel pipe 3 at the joint between the concrete-filled steel pipe column 1 and the steel beam 2 and not providing a diaphragm, it becomes easier to fill the interior of the steel column pipe 1b. Furthermore, the joint steel pipe 3 shown in FIG. 1 is joined to the steel column pipe 1b so that their outer surfaces are flush with each other, and is thicker on the inside. As a result, an internal step 5 occurs at the joint between the steel column pipe 1b and the joint steel pipe 3.

[0028] In addition, inner protrusions 4 are provided on the upper part of the inner surface of steel column pipe 1b connected to the lower side of joint steel pipe 3, and on the lower part of the inner surface of steel column pipe 1b connected to the upper side of joint steel pipe 3. By providing protrusions on the inner surface of steel column pipe 1b near joint steel pipe 3, it is possible to transmit force to the column concrete via the protrusions. Note that inner protrusions 4 may be provided only on the upper part of the inner surface of steel column pipe 1b connected to the lower side of joint steel pipe 3, without providing them on the lower part of the inner surface of steel column pipe 1b connected to the upper side of joint steel pipe 3.

[0029] FIG. 2(a) shows the transmission of vertical force from a step in a joint between a concrete-filled steel pipe column 1 and a steel beam 2 according to the present invention, when the outer surfaces of the joint steel pipe 3 and the upper and lower steel column pipes 1b are flush with each other. The steel column pipe 1b and the thick-walled joint steel pipe 3 are joined with their outer surfaces facing each other, and a steel beam 2 is joined to the joint steel pipe 3. Because the steel column pipe 1b and the joint steel pipe 3 are joined with their outer surfaces facing each other, the joint steel pipe 3 is thicker on the inside, creating an inner step 5 at the joint between the steel column pipe 1b and the joint steel pipe 3. It is believed that this inner step 5 allows the vertical force from the steel beam 2 to be transmitted to the inside of the steel column pipe 1b.

[0030] Also, Figure 2(b) shows the transmission of vertical force from the step and inner protrusion 4 when the outer surfaces of the joint steel pipe 3 and the upper and lower steel column pipes 1b are flush. The inner step 5 transmits the vertical force from the steel beam 2 to the inside of the steel column pipe 1b, and the inner protrusion 4 on the inner surface of the steel column pipe 1b also transmits the vertical force from the steel beam 2 to the inside of the steel column pipe 1b.

[0031] Figure 2(c) is an explanatory diagram showing the transmission of vertical force from the inner protrusion when the inner surfaces of the joint steel pipe 3 and the upper and lower steel column pipes 1b are flush. The joint steel pipe 3 is thicker on the outside, and the inner surfaces of the joint steel pipe 3 and the steel column pipe 1b are flush. As shown in (a) and (b), there is no inner step 5 at the joint between the joint steel pipe 3 and the steel column pipe 1b, and the inner protrusion 4 on the inner surface of the steel column pipe 1b transmits the vertical force from the steel beam 2 to the inside of the steel column pipe 1b. Furthermore, the inner protrusion 4 on the inner surface of the steel column pipe 1b need not pose any problems in terms of strength or durability; it can be formed on the steel column pipe 1b by, for example, welding a weld bead or rebar.

[0032] Figure 3 shows the structure of a typical joint between a concrete-filled steel pipe column 1 and a steel beam 2 using a diaphragm 7, and Figure 4 shows a typical joint between a concrete-filled steel pipe column 1 and a steel beam 2 equipped with a diaphragm 7 and a reinforcing bar cage 6. The column steel pipe 1b is equipped with a diaphragm 7, which has a concrete pouring hole 7a and an air vent hole 7b. As shown in Figure 4, the reinforcing bar cage 6 is fitted to the size of the concrete pouring hole 7a in the center of the diaphragm 7. In conventional CFT structures, the cross-sectional size of the reinforcing bar cage 6 is determined to match the size of the concrete pouring hole 7a in the diaphragm 7, as shown in Figure 4, which results in a small diameter of the reinforcing bar cage 6.

[0033] Figure 5 shows a case in which a reinforcing bar cage 6 is provided at the joint between a concrete-filled steel pipe column 1 of the present invention and a steel beam 2. In the CFT structure of the present invention, a diaphragm is not required by using a thick-walled joint steel pipe 3 for the column steel pipe 1b at the joint with the steel beam 2. This allows the cross section of the reinforcing bar cage 6 to be rectangular along the inner surface of the joint steel pipe 3, thereby increasing the cross-sectional dimensions of the reinforcing bar cage 6. In addition, the column steel pipe 1b is provided with an inner protrusion 4, which allows force to be transmitted to the column concrete via the inner protrusion 4. The inner protrusion 4 may be provided only on the upper part of the inner surface of the column steel pipe 1b connected to the lower side of the joint steel pipe 3.

[0034] Figure 6 shows the performance of a reinforcing steel CFT structure, where (a) is a conventional reinforcing steel CFT structure and (b) is the reinforcing steel CFT structure of the present invention. Compared to a conventional reinforcing steel CFT structure, the reinforcing steel CFT structure of the present invention allows for larger cross-sectional dimensions (width and diameter) of the reinforcing steel cage, and also allows for a larger amount of main reinforcement in the reinforcing steel cage, thereby increasing the burden of reinforcing steel. Therefore, the reinforcing steel CFT structure of the present invention can achieve higher performance than a conventional reinforcing steel CFT structure. Conversely, the increased burden of reinforcing steel can also reduce the burden of column steel pipes and concrete, resulting in cost savings due to the reduced steel pipes and concrete.

[0035] Figure 7 shows a bar graph comparing the estimated steel amounts for a CFT structure with a normal diaphragm (Figure 3), a CFT structure with a normal diaphragm and conventional reinforcing bars (Figure 4), and a CFT structure of the present invention with no diaphragm and reinforcing bars (Figure 5).

[0036] In the case of steel pipe columns with cross-sectional dimensions of approximately 800mm x 800mm, the comparison was made by calculating the amount of steel = steel pipe weight + rebar weight. If the amount of steel in a CFT structure with a normal diaphragm and no rebars, as shown in Figure 3, is set to 100, then the amount of steel in a CFT structure with a diaphragm and rebars, as shown in Figure 4, is 101. Furthermore, the amount of steel in the CFT structure of the present invention, which has no diaphragm and rebars, is 97. It can be seen that the amount of steel in the present invention is roughly the same as that in a normal CFT structure and a conventional CFT structure with rebars.

[0037] In addition, if the amount of steel used in a CFT structure with a normal diaphragm and no reinforcing bars is taken as 100, the weight of the steel pipe in the case of a CFT structure with a diaphragm and reinforcing bars inserted is 92.3 and the weight of the reinforcing bars is 8.3, while the weight of the steel pipe in the case of the CFT structure of the present invention with no diaphragm and reinforcing bars inserted is 86.2 and the weight of the reinforcing bars is 11.1.

[0038] Since the construction cost per unit weight (= material cost + construction cost) is cheaper for rebar than for steel pipe, if the amount of steel is the same, the higher the proportion of rebar weight, the cheaper the construction cost. The CFT structure of the present invention can increase the proportion of rebar weight while using the same amount of steel as a regular CFT structure or a conventional rebar-reinforced CFT structure, and a significant cost-cutting effect can be expected. [Explanation of symbols]

[0039] 1...Concrete-filled steel pipe column 1a...Filled concrete 1b…Column steel pipe 2...Steel beam 3…Joint steel pipe 4...Inner protrusion 5...Inner surface step (step between the joint steel pipe and the column steel pipe) 6...Reinforced concrete cage 6a…Main reinforcement 6b...Stitching 7...Diaphragm 7a...Concrete pouring hole 7b...Air vent hole

Claims

1. A joint between a concrete-filled steel pipe column and a steel beam, in which concrete is filled inside the column steel pipe, characterized in that a thicker-walled joint steel pipe than the upper and lower column steel pipes is interposed in the section where the end of the steel beam is joined to the concrete-filled steel pipe column, and a protrusion is provided in an upper specified section of the inner surface of the column steel pipe connected to the lower side of the thick-walled joint steel pipe, and no protrusion is provided on the inner surface of the thick-walled joint steel pipe.

2. 2. The joint between a concrete-filled steel pipe column and a steel beam according to claim 1, wherein the joint steel pipe is thicker on the inside, and the outer surfaces of the joint steel pipe and the upper and lower column steel pipes are flush with each other.

3. 2. The joint between a concrete-filled steel pipe column and a steel beam according to claim 1, characterized in that a protrusion is also provided in a predetermined lower section of the inner surface of the column steel pipe connected to the upper side of the joint steel pipe.

4. 4. A joint between a concrete-filled steel pipe column and a steel beam according to claim 1 or 3, characterized in that the joint steel pipe is thicker on the outside, and the inner surfaces of the joint steel pipe and the upper and lower column steel pipes are flush with each other.

5. 4. The joint between a concrete-filled steel pipe column and a steel beam according to claim 1, wherein the protrusion is a weld bead or a protrusion formed by rebar welding, or an inner protrusion of a checkered steel plate.

6. 4. The joint between a concrete-filled steel pipe column and a steel beam according to claim 1, wherein a reinforcing bar cage consisting of main reinforcement and hoop reinforcement is inserted inside the concrete-filled steel pipe column.

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