JP6152809B2 - Beam-column joint structure - Google Patents

Description

  The present invention relates to a column beam joint structure and a column used therefor, and particularly relates to a column having a high plastic deformation ability using a square steel pipe.

At present, the “column-H structure” in which a cold-formed square steel pipe is a column and an H-shaped steel beam is widely used in medium and small-sized steel frames (Non-patent Document 1). In many cases, the column beam joint in this structure is a through-diaphragm type in order to use a CO ₂ welding robot capable of performing a good welding operation.

  A through-diaphragm column beam joint will be described below with reference to FIG. FIG. 1 shows a through-diaphragm column beam joint 10, where FIG. 1A is a sectional view and FIG. 1B is a perspective view. 1 is a column made of cold-formed square steel pipe, 2 is a beam made of H-shaped steel, and 3 is a through diaphragm made of steel plate. In the through-diaphragm-type column beam joint, the column 1 is divided at two positions in the height direction, and the two through diaphragms 3 and 3 are welded to the column skin plate 4 of the column 1 to form a column-through diaphragm weld 6. And After that, the beam-to-diaphragm welded portion 7 is formed by welding the upper and lower flanges 5 of the beam 2 to the upper and lower two through-diaphragms 3 and 3 to form the beam-to-diaphragm welded portion 10.

  In the joint 10 described above, the width-thickness ratio B / t of the cold-formed square steel pipe as the column (B is the outer dimension (mm) of the opposite side, and is also referred to as the diameter below. T is the thickness of the skin plate (mm) ).)) Is small, there is an advantage that local deformation of the column is difficult to occur due to large deformation during a large earthquake, and high plastic deformation ability can be obtained. On the other hand, since the stress greatly increases in the cross section of the column due to a large deformation at the time of a large earthquake, the risk of fracture for the column-through diaphragm weld 6 increases. Since the fracture phenomenon of such a column-through diaphragm weld is affected by the toughness of the material and the shape of the weld, the variation is greater than local buckling, making it difficult to predict the deformation of the column at the time of fracture. Become. And when a fracture | rupture arises in a column-through diaphragm welding part early, the fracture | rupture in a welding part will advance first, and as a result, the plastic deformation capability of a column beam junction will become remarkably small.

  Until now, in order to avoid the early breakage of the column-through diaphragm welded portion, means such as devising the laminated shape of the welded portion as in Patent Document 1 and Patent Document 2 have been adopted.

  Note that Non-Patent Document 2 and Non-Patent Document 3 are cited in the [Description of Embodiments] section, which will be described later, and are also described here.

Japanese Patent No. 3817669 Japanese Patent No. 3937389

“2008 Cold Forming Square Steel Pipe Design and Construction Manual” 2008 pp1-2, p162-165 “2007 edition of the structural technical reference manual for buildings” 2007 p.329 Architectural Institute of Japan “Steel Structure Limit State Design Guidelines and Explanation” 1998 pp126-127

  As shown in the background art, conventionally, means such as devising the laminated shape of the welded part are used to avoid early breakage of the column-through diaphragm welded part.

However, even if the shape of the welded portion is devised, for example, when a high-strength cold-formed square steel pipe such as a tensile strength of 780 MPa class (tensile strength of 780 N / mm class ² ) is used as a column material, It is difficult to secure a tensile strength higher than that of the column base material at the weld due to restrictions on the welding material such as it is difficult to obtain a welding material that can obtain a tensile strength equal to or higher than the same level. Due to the difference in strength of the parts, it is difficult to prevent breakage of the column-through diaphragm welded part during a large earthquake.

  The present invention has been made in view of the above problems, and provides a column-beam joint structure having a high plastic deformation capability that is difficult to break and is not easily buckled at a column-through diaphragm welded portion, and a column used therefor. For the purpose.

In order to solve the above problems, the present invention has the following features.
[1] A column beam joint structure in which a square steel pipe is used as a column and a diaphragm type is formed through a column beam joint. The square steel pipe has a generalized width-thickness ratio r expressed by the following formula (1). One or a plurality of stiffeners are provided in a column having a cross section of 1.12 or more and 1.63 or less and a distance from the through diaphragm of (0.2 to 3.0) × square steel pipe diameter. Column beam joint structure characterized by installation.

r = (B / t) · (σy / E) ^1/2 ··· (1)
Here, r: generalized width-thickness ratio (−), B: square steel pipe diameter (outside dimension of opposite sides) (mm), t: plate thickness (mm) of square steel pipe skin plate, σy: square steel pipe Yield strength (MPa) of skin plate, E: Young's modulus (MPa) of skin plate of square steel pipe.
[2] The beam-column joint structure according to [1], wherein the stiffener is a built-in diaphragm.
[3] The column beam joint structure according to [1], wherein the stiffener is a buckling stiffening rib.
[4] In the column beam joint structure according to any one of [1] to [3], the column and the through diaphragm are welded using a brittle fracture prevention welding method. Beam-column joint structure.
[5] The ratio of the tensile strength of the weld metal between the column and the through diaphragm to the tensile strength of the base metal portion of the column is 1.0 or more. [1] to [4] The beam-column joint structure according to any one of the above.
[6] A column made of a square steel pipe, and one or a plurality of stiffeners are located inside the column within a range of (0.2 to 3.0) × square steel pipe diameter from a planned position where the through diaphragm is joined. A column installed and used for the column beam joint structure according to [1].
[7] The column according to [6], wherein the stiffener is a built-in diaphragm.
[8] The column according to [6], wherein the stiffener is a buckling stiffening rib.
[9] The column according to any one of [6] to [8], wherein the column and the through diaphragm are welded using a brittle fracture prevention welding method.

  In addition, as a square steel pipe used for the column, a cold-formed square steel pipe such as a cold press-formed square steel pipe and a cold roll-formed square steel, or a square steel pipe such as a welded four-sided box can be used.

  By adopting the above-described configuration, the column-through diaphragm welded portion is less likely to be broken, and a decrease in the proof stress due to the occurrence / progress of local buckling of the column material is delayed, and a column-beam joint structure having a high plastic deformation capability is obtained. be able to.

  In particular, even in a column-beam joint structure using a square steel pipe with a tensile strength of 780 MPa or more, which is difficult to secure a tensile strength higher than that of the column base material at the welded portion, the column-through diaphragm welded portion is broken. Therefore, it is possible to obtain a column beam joint structure having a high plastic deformation capability.

It is a figure which shows the column beam junction part of a through diaphragm form, (a) is sectional drawing, (b) is a perspective view. It is a figure which shows the outline | summary of a column bending experiment. It is a figure which shows the structure of embodiment of this invention, (a) is sectional drawing, (b) is a perspective view. It is a figure which shows the structure of other embodiment of this invention, (a) is sectional drawing, (b) is a perspective view. 6 is a diagram showing an analysis model of Comparative Example 1. FIG. 10 is a diagram showing an analysis model of Comparative Example 2. FIG. It is a figure which shows the analysis model of the example 1 of an invention. It is a figure which shows the analysis model of the example 2 of an invention. It is a figure which shows the relationship between the plasticity rate (micro | micron | mu) in each analysis model, and yield strength increase rate (tau).

  In the present invention, a rectangular steel pipe having a cross section with a generalized width-thickness ratio of 1.12 or more and 1.63 or less is used as a column material. The generalized width-thickness ratio is a generalization of the width-thickness ratio B / t, and is expressed by the following equation.

r = (B / t) · (σy / E) ^1/2 ··· (1)
Here, r: generalized width-thickness ratio (−), B: square steel pipe diameter (outside dimension of opposite sides) (mm), t: plate thickness (mm) of square steel pipe skin plate, σy: square steel pipe Yield strength (MPa) of skin plate, E: Young's modulus (MPa) of skin plate of square steel pipe.

  In Non-Patent Document 3, when a square steel tube column having a cross section with a generalized width-thickness ratio r of 1.12 or more and 1.63 or less is locally buckled by bending, the proof stress is from the start of plasticization of the cross section to full plasticity. It has been shown to be proof. In addition, the square steel pipe column having a cross section in which the generalized width-thickness ratio r is less than 1.12 has a yield strength higher than the total plastic yield strength due to strain hardening and an increased deformation capability. Further, it is shown that the proof stress of the square steel pipe column having a cross section in which the generalized width-thickness ratio r exceeds 1.63 is lower than the yield moment.

  Therefore, in the present invention, the generalized width-thickness ratio r of the square steel pipe column cross section is limited to 1.12 or more and 1.63 or less. In this way, when plasticizing by bending deformation, the upper limit of the yield strength is controlled to the total plasticity of the cross section, and an excessive tensile stress that causes breakage is prevented from occurring in the column-through diaphragm weld.

  As described above, it is possible to prevent breakage of the column-through diaphragm welded portion and selectively set the failure mode of the column or the column-beam joint to the local buckling of the column.

  On the other hand, when the generalized width-thickness ratio r of the column cross section is 1.12 or more, local buckling occurs with a smaller bending deformation than in the case of the column cross-section where the generalized width-thickness ratio r is less than 1.12. Since the progress becomes faster, it becomes difficult to obtain a higher plastic deformation capacity than a column having a cross section in which the generalized width-thickness ratio r is less than 1.12.

  Therefore, an experiment as shown in FIG. 2 was conducted in order to investigate the influence of the through diaphragm on the plastic deformation ability. The test body has a length of 4000 mm, a generalized width-thickness ratio r of 1.11, 1.13, 1.39, 1.60, and 1.73, and a square steel pipe column 1 having a thickness of 32 mm. A steel through diaphragm 3 was prepared, and the diaphragm 3 was welded through the column skin plate 4 at a half position in the longitudinal direction of the square steel pipe column 1. And it loaded in the center of this test body, and the 3-point bending experiment was implemented. The loading load was a monotonic loading in the vertical direction. As a result, the following knowledge was obtained.

  That is, when the generalized width-thickness ratio r is 1.12 or more and 1.63 or less when the cross section of the rectangular steel pipe column 1 is plasticized in the vicinity of the through diaphragm 3, the distance from the position of the through diaphragm 3 is 3.0. X The range up to the column diameter (square steel pipe diameter) is greatly plasticized, and further, the distance from the through diaphragm 3 is (0.2 to 3.0) x Local buckling occurs and develops within the range of the column diameter. Was found to decrease.

  Based on the above findings, in the present invention, one or more stiffeners are provided inside the column of the plasticized portion.

  That is, as shown in FIGS. 3A and 3B, one or a plurality of built-in diaphragms 8 have a distance from each of the through diaphragms 3 and 3 within the range of 0.2 × column diameter to 3.0 × column diameter. Join. Alternatively, as shown in FIG. 4, a plurality of buckling stiffening ribs 9 are equally spaced from each of the through diaphragms 3 and 3 within a range of 0.2 × column diameter to 3.0 × column diameter. Bonding is performed so that the longitudinal direction is the column axis direction.

  By using these built-in diaphragms 8 or buckling stiffening ribs 9 to buckle and stiffen, the generalized width-to-thickness ratio r is a column having a cross section of 1.12 to 1.63. A plastic deformation ability equivalent to that of a column having a cross section where r is below 1.12 can be obtained.

  Note that the stiffener need not be limited to the configuration described above. For example, a combination of a built-in diaphragm and a buckling stiffening rib, a type in which plates are combined in a cross shape, and four tip portions are joined to the inner surface of a column, and the like.

  In the column-through diaphragm welded portion, a brittle fracture preventing welding method (a welding method for welding) that defines the laminating position of beads by gas shielded arc welding shown in Non-Patent Document 1, Patent Document 1, and Patent Document 2 By forming the first welding heat-affected zone along the groove surface of the member and the second welding heat-affected zone almost parallel to the member surface, surface cracks generated in the vicinity of the weld on the member surface are It is preferable to apply a welding method that can propagate from the welding heat-affected zone to the healthy part of the base material of the member, and as a result, suppress early brittle fracture along the first welding heat-affected zone. Since this brittle fracture prevention welding method has an effect of preventing the fracture of the column-through diaphragm welded portion, the fracture mode can be further selectively made to be the local buckling of the column.

  Moreover, it is preferable that the tensile strength of the welding material is equal to or higher than the tensile strength of the column base material so that the fracture does not occur first in the column-through diaphragm weld. That is, it is preferable that (tensile strength of weld metal between the column and through diaphragm) / (tensile strength of column base material) is 1.0 or more.

  Here, in general, when the square steel pipe is a cold-formed square steel pipe, the tensile strength of the column cross-section corner (the corner where the skin plates form a right angle) is reduced by the effect of strain hardening by cold working. There is a tendency to increase by 10 to 20% from the tensile strength of the flat plate section (skin plate section). Therefore, the tensile strength of the welding material is preferably equal to or greater than the tensile strength of the base material at the corners of the column cross section.

  Although the generalized width-thickness ratio r of the rectangular steel pipe used in the present invention is specified to be 1.12 or more and 1.63 or less, this corresponds to the type FB and FC square steel pipes shown in Non-Patent Document 2. In Non-Patent Document 3, the types FB and FC correspond to PI-2 and P-II, respectively. Note that the generalized width-thickness ratio r less than 1.12 corresponds to the types FA and PI-1.

  In addition, in order to obtain high column rigidity without changing the plate thickness of the column steel pipe skin plate, when it is necessary to increase the diameter of the steel tube, the width-thickness ratio is increased, and the plastic deformation capacity is reduced. It is possible to maintain a high plastic deformation capacity by installing it inside the column in a section separated by (0.2 to 3.0) × column diameter from the diaphragm through the stiffener.

  FEM analysis was performed using the models shown in FIGS. These models were modeled as cantilever beams in the column bending experiment shown in Fig. 2 in consideration of the symmetry of the specimen and the center through-diaphragm position was considered to be a fixed end. 1, Comparative Example 2, Invention Example 1 and Invention Example 2 are shown. In each model, a load was applied in the direction of the arrow at the tip of a cantilever of 2000 mm from the fixed end, and the analysis conditions are shown in Table 1. In Comparative Example 1 shown in FIG. 5, the steel pipe diameter is 500 mm, the thickness of the skin plate of the steel pipe is 28 mm, the outer radius of curvature of the cross section of the steel pipe is 98 mm, and the generalized width-thickness ratio r is less than 1.12. This is a model for evaluating the bending deformation behavior of a column having a cross section. In Comparative Example 2 shown in FIG. 6, the steel pipe diameter is 500 mm, the plate thickness of the steel pipe skin plate is 22 mm, the outer radius of curvature of the cross section of the steel pipe is 77 mm, and the generalized width-thickness ratio r is 1.12 or more 1 This is a model for evaluating the bending deformation behavior of a column having a cross section of .63 or less. The invention example 1 shown in FIG. 7 is a model in which a built-in diaphragm having a plate thickness of 12 mm is joined to the model of FIG. 6 at a position 250 mm (= 0.5 × column diameter) from the fixed end. The invention example 2 shown in FIG. 8 is a model in which a buckling stiffening rib extending from a position 100 mm away from the fixed end to a position 500 mm is joined to the model of FIG.

  FIG. 9 shows the “bending moment-member angle relationship” at the fixed end obtained by FEM analysis of each model. The ordinate indicates the yield rate τ calculated by (moment M / total plastic moment Mp), and the abscissa indicates the plasticity ratio μ calculated by (member angle θ / member angle θp at the total plastic moment). showed that. This result means the “bending moment-member angle relationship” in the vicinity of the column-through diaphragm weld in the column bending experiment.

  In Comparative Example 1, since the generalized width-thickness ratio r is small, the proof stress continues to increase after the cross section of the fixed end reaches full plasticity, that is, after τ = 1 (region of τ> 1). ), It can be seen that it has a high plastic deformation capability against local buckling. However, due to this increase in yield strength, high tensile stress is generated at the fixed end (through diaphragm position in the column bending experiment), and the risk of breakage increases. The tensile strength of the fixed end (column-through diaphragm weld material in the column bending experiment) is equivalent to the tensile strength of the cross-section corner of the steel pipe. If the yield strength is 1.40, it is considered that fracture occurs when the 40% yield strength is increased from the total plastic moment Mp. That is, the ultimate deformation of Comparative Example 1 is as shown by the crosses in Table 1 and FIG.

  In Comparative Example 2, the generalized width-thickness ratio r is larger than that in Comparative Example 1, and local buckling occurs immediately after the cross-section of the fixed end starts to be plasticized, and the yield strength decreases rapidly with the progress. Thus, in the cross section of Comparative Example 2, there is no risk of fracture at the welded portion, but it is difficult to obtain a high plastic deformation capability as in Comparative Example 1. In Comparative Example 2, local buckling occurs as shown by the circles in Table 1 and FIG. 9 when the plasticity ratio μ = 3.25 and the yield rate increase τ = 1.26.

  In Invention Example 1, the generalized width-thickness ratio r is the same as that in Comparative Example 2, and a built-in diaphragm is installed at a position of 0.5 × column diameter from the through diaphragm. This stiffens the local buckling of the column and suppresses the rate of increase in yield strength in plasticization to be lower than that in Comparative Example 1, thereby avoiding breakage, and the plasticity ratio higher than Comparative Examples 1 and 2 μ = 4. 55 (see Table 1 and ○ in FIG. 9).

  Inventive example 2 is provided with buckling stiffening ribs in the axial direction inside the column instead of the built-in diaphragm of inventive example 1, thereby producing the same effect as in inventive example 1, and high plasticity The rate is realized.

1 Column (square steel pipe)
2 Beam 3 Through Diaphragm 4 Column Skin Plate 5 Beam Flange 6 Column-Through Diaphragm Welding Portion 7 Beam-Through Diaphragm Welding Portion 8 Built-in Diaphragm 9 Buckling Stiffening Rib 10 Column-Beam Joint Portion

Claims (5)

It is a column beam joint structure using a square steel pipe as a column and having a diaphragm type through a beam-to-column joint , wherein the square steel pipe and the through diaphragm are joined by a column-through diaphragm weld, The generalized width-thickness ratio r represented by the formula (1) has a cross section of 1.12 or more and 1.63 or less, and the distance from the through diaphragm is (0.2 to 3.0) × square steel pipe diameter A column beam joint structure characterized in that one or a plurality of stiffeners are installed inside a column in the range.
r = (B / t) · (σy / E) ^1/2 ··· (1)
Here, r: generalized width-thickness ratio (−), B: square steel pipe diameter (outside dimension of opposite sides) (mm), t: plate thickness (mm) of square steel pipe skin plate, σy: square steel pipe Yield strength (MPa) of skin plate, E: Young's modulus (MPa) of skin plate of square steel pipe.   The column beam joint structure according to claim 1, wherein the stiffener is a built-in diaphragm.   The beam-column joint structure according to claim 1, wherein the stiffener is a buckling stiffening rib.   The beam-column joint structure according to any one of claims 1 to 3, wherein the column and the through diaphragm are welded using a brittle fracture prevention welding method. . The ratio between the tensile strength of the weld metal of the welded portion between the column and the through diaphragm and the tensile strength of the base metal portion of the column is 1.0 or more. Column beam joint structure described in 1 .

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