WO2022065220A1

WO2022065220A1 - Steel frame beam, column-beam joining structure, and structure having same

Info

Publication number: WO2022065220A1
Application number: PCT/JP2021/034260
Authority: WO
Inventors: 隆行難波; 椋太荒木田
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2020-09-23
Filing date: 2021-09-17
Publication date: 2022-03-31
Also published as: JP7226590B2; JPWO2022065220A1

Abstract

Provided are a steel frame beam, a column-beam joining structure, and a structure having the same which, even when used in a low temperature environment, can suppress a welded part at an end in a material axial direction from brittle fracturing during a short-term load action such as seismic force, and can exhibit high fatigue resistance and plastic deformation capability.　The steel frame beam has an upper flange, a lower flange, and a web connecting the upper flange and the lower flange, wherein: the upper flange, the lower flange, and the web are formed from a steel material having a Charpy impact value of at least 27 J at -40°C; and the steel frame beam has a shape such that, when a gradually increasing reverse symmetric bending moment is exerted on both ends in the material axial direction of the steel frame beam, and one or both of the upper flange and the lower flange yields, the position at which said one or both of the yielded upper flange and lower flange initially yields is a position other than the distal end in the material axial direction.

Description

Steel beam, column-beam joint structure and structure having this

The present invention relates to a steel beam, a column-beam joint structure, and a structure having the same.

In a structure having a column-beam joint structure in which the tip in the material axis direction of a steel beam having a cross section such as H-shaped, I-shaped, or groove-shaped is welded to the steel column, the steel beam may be made due to restrictions such as construction conditions. The cross-sectional performance at the end in the direction of the material axis, which is the region including the tip in the direction of the material axis, tends to be low. For example, as shown in the plan view of FIG. 13 (a) and the side view of FIG. 13 (b), the tip of the steel beam 8A made of H-shaped steel in the material axial direction is joined to the side surface of the column 2 by welding. In the structure having the beam-column joint structure 9A, in order to secure the strength of the beam-column joint structure 9A, it is necessary to weld the upper flange 81 and the lower flange 82 of the steel beam 8A to the side surface of the column 2 all around. Therefore, at the material axial end of the steel beam 8A, it is necessary to provide scallops 83s on the web 83 of the steel beam 8A, and the cross-sectional performance of the material axial end of the steel beam 8A is reduced.

When a short-term load such as a seismic force that is repeatedly input in the positive and negative directions acts on such a structure and the steel beam 8A receives a bending moment, scallops are formed at the axial end of the steel beam 8A. By providing the 83s, the load bearing load ratio of the web 83 is reduced, and the strain is concentrated in the vicinity of the welded portion between the upper flange 81 or the lower flange 82 and the side surface of the column 2 by that amount. If this welded portion breaks, the plastic deformation capacity of the steel frame beam 8A may not be sufficiently exerted, and unexpected damage may occur to the structure.

In particular, when the steel beam, the column-beam joint structure and the structure having the above are used in a low temperature environment, the toughness of the steel material and the welded part (Charpy impact value: Japanese Industrial Standard JIS Z2242 "Metallic material". Since the absorbed energy specified in the Charpy Impact Test Method) is reduced, brittle fracture occurs near the welded portion between the upper flange 81 or the lower flange 82 and the side surface of the column 2 at the material axial end of the steel beam. The risk of occurrence increases.

For example, in Non-Patent Document 1, when the toughness of the base material (web 83) of the welded portion and the scalloped 83s portion is less than 70 J in Charpy impact value, the upper flange 81 or the lower flange 82 and the side surface of the column 2 It is judged that there is a high possibility that the welded part with and will break brittlely. Then, in order to prevent this brittle fracture, the joint fracture resistance of the welded portion between the upper flange 81 or the lower flange 82 and the side surface of the column 2 should be evaluated by reducing the tensile strength of the upper flange 81 or the lower flange 82. There is.

Here, as shown in the plan view of FIG. 14A and the side view of FIG. 14B, reinforcing members are provided on both sides of the upper flange 81 and the lower flange 82 at the material axial end portion of the steel frame beam 8B. By welding 84 to stiffen between both sides of the upper flange 81 and the lower flange 82 and the side surface of the column 2, when the steel beam 8B receives a bending moment, the end portion of the steel beam 8B in the material axial direction. However, it is possible to avoid yielding ahead of other positions in the material axial direction, and to improve the plastic deformation ability of the end portion of the steel frame beam 8B in the material axial direction.

However, in Non-Patent Document 2, brittle fracture occurs at the material axial end portion of the steel frame beam 8B even in the steel frame beam 8B as shown in the plan view of FIG. 14 (a) and the side view of FIG. 14 (b). It is stated that it is possible. Specifically, stress is concentrated at the boundary position between the region where the upper flange 81 and the lower flange 82 are stiffened by the reinforcing material 84 and the region where the lower flange 82 is not stiffened by the reinforcing material 84, and the upper flange 81 or the lower flange It is described that the welded portion between the 82 and the reinforcing material 84 can be brittlely broken.

Then, when such a structure having a column-beam joint structure in which the steel beam 8B is connected to the column 2 is used particularly in a low temperature environment, the toughness of each welded portion is lowered, and the steel beam There is a problem that the possibility of brittle fracture at the end in the axial direction of the material is further increased.

The present invention has been made in view of the above circumstances, and even when used in a low temperature environment, it suppresses brittle fracture of the welded portion at the end in the axial direction of the material when a short-term load such as seismic force is applied. It is an object of the present invention to provide a steel beam, a column-beam welded structure, and a structure having the same, which can exhibit high fatigue resistance and plastic deformation ability.

In order to solve the above problems, the present invention has the following features.

[1] A steel beam having an upper flange, a lower flange, and a web connecting the upper flange and the lower flange, and the upper flange, the lower flange, and the web are charpees at −40 ° C. When a steel material having an impact value of 27 J or more and one or both of the upper flange and the lower flange yield due to an gradually increasing inversely symmetric bending moment acting on both ends of the steel beam in the material axis direction. In addition, a steel beam having a shape such that the position where the first yield is made in either or both of the upper flange and the lower flange is other than the tip in the material axial direction.

Here, the tip of the steel beam in the material axis direction means the position of the end face where the steel beam is joined to the column.

[2] The cross-sectional area of the upper flange and the lower flange in the cross section perpendicular to the material axial direction is a region including the tip in the material axial direction, and the end portion in the material axial direction is other than the end portion in the material axial direction. The steel beam according to [1], which is set larger than the area.

[3] When an inversely symmetric bending moment that gradually increases at both ends of the steel beam in the material axis direction acts and any position of the steel beam in the material axis direction reaches the maximum bearing capacity, it acts on both ends. The steel beam according to [1] or [2], wherein the magnitude of the bending moment is equal to or less than the total plastic bending moment of the steel beam at both ends.

[4] When an inversely symmetric bending moment gradually increases at both ends of the steel beam in the material axial direction and any position of the steel beam in the material axial direction reaches the maximum yield strength, it acts on both ends. The steel beam according to any one of [1] to [3], wherein the magnitude of the bending moment is equal to or less than the bending yield strength of the steel beam at both ends.

[5] A beam-column joint structure characterized in that the tip of the steel frame beam according to any one of [1] to [4] in the material axial direction is welded to the column.

[6] A structure characterized by having the beam-column joint structure according to [5].

According to the steel beam, the column-beam joint structure of the present invention, and the structure having the same, the steel beam is made of a steel material having a charmy impact value of 27 J or more at −40 ° C. When the moment acts, the position where the upper flange first yields and the position where the lower flange first yields are other than the tip in the material axial direction.

Here, in the vicinity of the welded portion between the tip of the steel beam in the material axis direction and the column, cross-sectional defects due to the provision of scallops on the steel beam and out-of-plane deformation of the side surface of the column to which the web of the steel beam is joined occur. As a result, stress and strain tend to concentrate. Since the upper flange and the lower flange yield first at positions other than the tip in the material axis direction, it is possible to prevent the welded portion between the tip in the material axis direction of the steel beam and the column from being brittlely broken at an early stage. .. Therefore, the steel beam has high fatigue resistance and plastic deformation ability.

The steel beam, the column-beam joint structure of the present invention, and the structure having the same, give special consideration to the welding conditions such as the welding material and the amount of heat input when welding the steel beam and the column exposed to a low temperature environment. Even if the low temperature toughness of the welded part of the lever is not ensured, brittle fracture occurs in the vicinity of the welded part between the upper flange or lower flange of the steel beam and the side surface of the steel column when a short-term load such as seismic force is applied. It can be suppressed.

In particular, when the tip of the steel beam in the material axial direction is joined to the column by on-site welding, it is difficult to suppress brittle fracture of the welded portion by increasing the toughness of the welded portion itself, so that the above effect is obtained. Is effectively demonstrated.

As a shape so that the position where the upper flange first yields and the position where the lower flange first yields are other than both ends in the material axial direction when an increasing inversely symmetrical bending moment acts on both ends of the steel beam. For example, in the material axial end portion where the cross-sectional area of the upper flange and the lower flange in the cross section perpendicular to the material axial direction includes both ends in the material axial direction, is larger than the region other than the material axial end portion. Make it large.

As described above, even if the steel beam, the column-beam joint structure of the present invention and the structure having the same are used in a low temperature environment, the welded portion at the end in the material axial direction is brittle when a short-term load such as seismic force is applied. Destruction is suppressed, and high fatigue resistance and plastic deformation ability can be exhibited.

FIG. 1 (a) is a plan view showing a steel frame beam and a column-beam joint structure according to an embodiment of the present invention, and FIG. 1 (b) is a side view thereof. FIG. 2A is a plan view showing a steel beam and column-beam joint structure according to another embodiment of the present invention, and FIG. 2B is a side view thereof. FIG. 3 shows the distribution of the total plastic bending strength and the maximum bending strength of the steel beam of the present invention. FIG. 4 is a graph showing the distribution of the total plastic bending strength and the maximum bending strength of the conventional steel beam. FIG. 5A is a plan view showing a test piece used in a force test for verifying the plastic deformation ability of the steel beam and column-beam joint structure of the present invention, and FIG. 5B is a vertical cross section thereof. It is a figure. FIG. 6 is a side view showing a force state of a force test for verifying the plastic deformation ability of the steel beam and column-beam joint structure of the present invention. 7 (a) and 7 (b) are side views and plan views showing the main parts of the test body used in the force test for verifying the plastic deformation ability of the steel beam of the present invention, respectively. c) is a graph showing the distribution of the design value of the bending strength of the steel beam portion of the test piece. FIG. 8 is a diagram showing a force cycle of a force test for verifying the plastic deformation ability of the steel beam and column-beam joint structure of the present invention. FIG. 9 is a graph showing the relationship between the bending moment acting on the steel beam and the deformation angle obtained in the force test for verifying the plastic deformation ability of the steel beam and column-beam joint structure of the present invention. FIG. 10 is a graph showing the relationship between the bending moment acting on the steel beam and the deformation angle obtained by the force test for verifying the plastic deformation ability of the steel beam and column-beam joint structure of the present invention in a dimensionless manner. be. FIG. 11 is an extended skeleton curve of the relationship between the bending moment acting on the steel beam and the deformation angle obtained in the force test for verifying the plastic deformation ability of the steel beam and column-beam joint structure of the present invention. 12 (a) and 12 (b) show the positions of the starting points of cracks generated in the steel beam during the ultimate strength in the force test for verifying the plastic deformation ability of the steel beam and column-beam joint structure of the present invention. It is a figure which shows. FIG. 13 (a) is a plan view showing a steel frame beam and a column-beam joint structure of a conventional embodiment, and FIG. 13 (b) is a side view thereof. FIG. 14 (a) is a plan view showing a steel frame beam and a column-beam joint structure of a conventional embodiment, and FIG. 14 (b) is a side view thereof.

Hereinafter, embodiments of the steel beam, column-beam joint structure, and the structure having the same will be described in detail with reference to the drawings.

[Embodiment 1]
1 (a) and 1 (b) show the steel beam 1A of the first embodiment of the present invention and the steel beam 1A joined to the side surface of a column 2 made of a four-sided welded box-shaped cross-section column by welding. The plan view and the side view of the column-beam joint structure 3A are shown respectively. The steel beam 1A of the present embodiment is provided in a steel-framed building (structure) such as a freezer warehouse, which is used under the condition that the structure is exposed to a low temperature environment. The steel beam 1A has an upper flange 11A, a lower flange 12A, and a web 13 connecting the upper flange 11A and the lower flange 12A. The upper flange 11A, the lower flange 12A, and the web 13 are combined in an H-shaped cross section and welded to each other to form a steel beam 1A.

Inside the column 2, an inner diaphragm 4 is provided at a height at which each of the upper flange 11A and the lower flange 12A of the steel beam 1A is joined.

The upper flange 11A, lower flange 12A and web 13 of the steel beam 1A, each skin plate of the column (four-sided welded box-shaped cross-section column) 2, and each of the inner diaphragm 4 are steel plates having a Charpy impact value of 27J or more at -40 ° C. It is composed of and has high toughness in a low temperature environment.

As shown in FIGS. 1 (a) and 1 (b), in the material axial end portion E which is a region including the tip in the material axial direction of the steel frame beam 1A, the beam widths of the upper flange 11A and the lower flange 12A are respectively. Widening portions 11w and 12w are provided by enlarging the dimensions in the direction. As a result, the cross-sectional area of the upper flange 11A and the lower flange 12A in the cross section perpendicular to the material axis direction is set to be larger than the region other than the end portion E in the material axis direction.

In this way, at the material axial end E of the steel beam 1A, the stress in the material axial direction generated in the upper flange 11A and the lower flange 12A when the bending moment acts on the steel beam 1A is increased in the widening portions 11w and 12w. Is provided to reduce the amount.

Then, when a gradually increasing inversely symmetric bending moment such as a seismic force that is repeatedly input in the positive and negative directions acts on both ends of the steel beam 1A in the material axial direction, the upper flange 11A receives a tensile force or a compressive force first. A position to surrender occurs. Further, a position where the lower flange 12A first yields due to a tensile force or a compressive force is generated. The preceding yield position Y is a boundary position between the material axial end portion E provided with the widening portions 11w and 12w and the region other than the material axial direction end portion E. Therefore, it is possible to prevent brittle fracture of the welded portion of the steel frame beam 1A with the column 2 at the tip in the material axial direction when a short-term load such as a seismic force is applied. Therefore, it is not necessary to give special consideration to the welding conditions such as the welding material and the amount of heat input when welding the steel beam 1A and the column 2 exposed to a low temperature environment to ensure the low temperature toughness of the welded portion. .. In this way, the steel beam 1A and the column-beam joint structure 3A capable of exhibiting high fatigue resistance and plastic deformation ability are obtained.

It is more preferable that the dimensions of the widening portions 11w and 12w in the beam width direction are further expanded. That is, a gradually increasing inversely symmetric bending moment acts on both ends of the steel beam 1A in the material axial direction, and when this increases, any position of the steel beam 1A in the material axial direction reaches the maximum yield strength. The magnitude of the bending moment applied to the tip of the steel beam 1A in the material axial direction at the ultimate strength of the steel beam 1A is less than or equal to the total plastic bending strength of the steel beam 1A at the tip of the steel beam 1A, and further less than or equal to the bending yield strength. It becomes. In this way, the fatigue resistance and the plastic deformation ability of the steel beam 1A, the column-beam joint structure 3A, and the building (structure) having the same are further enhanced.

The cross-sectional yield strength of the cross section perpendicular to the material axial direction of the steel beam 1A in the region where the scallop 13s is provided in the end portion E in the material axial direction of the steel frame beam 1A is set to be larger than the cross-sectional yield strength of the preceding yield position Y. It is preferable that it is. When an increasing inversely symmetric bending moment acts on both ends of the steel beam 1A in the material axial direction, the preceding yield position Y first yields and is strain-hardened, and the yield strength of the preceding yield position Y increases. Then, after the yield strength of the preceding yield position Y increases, the strain of the scallop bottom of the scallop 13s provided at the material axial end portion E increases, a crack occurs starting from the scallop bottom, and the material axial end portion E becomes. Brittle may break. Therefore, as described above, such a phenomenon can be prevented by setting the cross-sectional proof stress of the region where the scallop 13s is provided to be larger than the cross-sectional proof stress of the preceding yield position Y. The same effect can be obtained even if the scallop 13s is not provided at the material axial end portion E of the steel frame beam 1A.

[Embodiment 2]
The column-beam joint structure 3A in which the steel beam 1B and the steel beam 1B of the second embodiment of the present invention are joined to the column 2 is shown in the plan view of FIG. 2A and the side view of FIG. 2B.

As shown in FIGS. 2A and 2B, in the steel beam 1B and the column-beam joint structure 3B of the second embodiment, unlike the steel beam 1A of the first embodiment, the main body portion of the steel beam 1B is It is made of H-shaped steel having the same cross-sectional shape over the entire length in the material axis direction.

Then, at the end portion E in the material axial direction of the steel frame beam 1B, the reinforcing material 14 is joined to both sides of the upper flange 11 and the lower flange 12 of the H-shaped steel in the beam width direction by welding. The shape of the reinforcing material 14 is the same as the widening portions 11w and 12w of the upper flange 11A and the lower flange 12A of the first embodiment.

Each of the H-shaped steel, the reinforcing material 14, the skin plate of the column (four-sided welded box-shaped cross-section column) 2 and the inner diaphragm 4 constituting the main body of the steel beam 1B has a Charpy impact value of 27 J or more at −40 ° C. It is made of steel plate and has high toughness in a low temperature environment.

The welded portion between the upper flange 11 or the lower flange 12 and the reinforcing material 14 of the H-shaped steel has excellent low temperature toughness by considering the welding conditions such as the welding material and the amount of heat input when forming this welded portion. And. By doing so, the leading yield position which is the boundary position between the material axial end portion E in which the upper flange 81 and the lower flange 82 are stiffened by the reinforcing material 84 and the region other than the material axial end portion E. In Y, it is possible to prevent the welded portion between the upper flange 11 or the lower flange 12 and the reinforcing member 14 from being brittlely broken at an early stage.

Regarding points other than the above, the steel beam 1B and the column-beam joint structure 3B of the second embodiment are configured in the same manner as the steel beam 1A and the column-beam joint structure 3A of the first embodiment.

By configuring the steel beam 1B and the column-beam joint structure 3B of the second embodiment as described above, the same effects as those of the steel-frame beam 1A and the column-beam joint structure 3A of the first embodiment can be obtained.

In the column-beam

joint structures

3A and 3B of the first and second embodiments, the inner diaphragm 4 is provided inside the column 2, but instead of this, a through diaphragm or an outer diaphragm is provided. The same effect can be obtained.

Further, in the column-beam joint structure 3A of the first embodiment, the widening portion 11w of the upper flange 11A and the widening portion 12w of the lower flange 12A are formed in the same shape. Instead of this, the shape of the widened portion 11w of the upper flange 11A and the shape of the widening portion 12w of the lower flange 12A may be different from each other. Similarly, in the beam-column joining structure 3B of the second embodiment, the reinforcing material 14 joined to both sides of the upper flange 11 in the beam width direction and the reinforcing material 14 joined to both sides of the lower flange 12 in the beam width direction have the same shape. It is formed. Instead, the shape of the reinforcing material joined to the upper flange 11 and the shape of the reinforcing material joined to the lower flange 12 may be different from each other. In this case, the position where the upper flange first yields and the position where the lower flange first yields do not always match, but both the position where the upper flange first yields and the position where the lower flange first yields are The shape may be such that it is not the tip in the material axis direction.

Further, the column 2 is not limited to the four-sided welded box-shaped cross-section column, and the same effect can be obtained when the column is composed of a square steel pipe, a concrete-filled steel pipe, a reinforced concrete, a steel-framed reinforced concrete, or the like.

A steel beam (example of the present invention) in which a widening portion or a reinforcing material is provided on each of the upper flange and the lower flange at the material axial end portion of the steel frame beam, and a conventional steel frame in which neither the widening portion nor the reinforcing material is provided. The strength and plastic deformation capacity of each steel beam were calculated for the beam (conventional example).

As a conventional example, as shown in FIGS. 13 (a) and 13 (b), a steel beam having no widening portion or reinforcing material is set on each of the upper flange and the lower flange. Specifically, an analysis model in which both ends of a steel beam made of H-shaped steel having a size of H-400 (H) × 175 (B) × 16 × 28 and a total length of L = 4000 mm in the material axial direction are welded to the side surface of the column. It was set. In this analysis model, it is assumed that scallops having a height of 35 mm in the beam direction are provided on each of the upper flange side and the lower flange side of the web of the steel frame beam at the end portion in the material axial direction of the steel frame beam.

Further, as an example of the present invention, as in the first and second embodiments, a steel frame beam in which a widening portion or a reinforcing material is provided on each of the upper flange and the lower flange is set at the material axial end portion of the steel frame beam. did. Specifically, at the material axial end portion of the steel frame beam of the conventional example, a widening portion is provided on each of the upper flange and the lower flange, as in the first embodiment shown in FIGS. 1 (a) and 1 (b). The provided analysis model was set. Specifically, in the region from 0 mm to 125 mm in the material axis direction from the tip in the material axis direction, the dimensions of the upper flange 11 and the lower flange 12 in the beam width direction are expanded to 350 mm. Further, in the region from the tip in the material axis direction to 125 mm to 200 mm in the material axis direction, the dimensions of the upper flange 11 and the lower flange 12 in the beam width direction are linearly reduced from 350 mm to 175 mm. In this way, it is assumed that the widening portions 11w and 12w are formed on the upper flange 11 and the lower flange 12, respectively, at the material axial end portion of the steel frame beam 1A.

Then, assuming that the steel beams of the present invention and the conventional example are subjected to antisymmetric bending, in consideration of symmetry, up to half L / 2 of the total length L of the steel beam was analyzed and modeled. Then, the tip in the material axis direction of the steel beam, that is, the side joined to the column is set as the fixed end, and a concentrated load acts on the central position in the material axis direction of the steel beam to form a triangular shape in the material axis direction of the steel beam. It is assumed that the distributed bending moment is applied.

The tensile strength of the steel beam of the analysis model of the present invention and the conventional example was 490 N / mm ² , the yield strength was 325 N / mm ² , and the Young's coefficient was 205,000 N / mm ² .

Under the above conditions, for each of the analysis models of the steel beam of the present invention and the conventional example, the total plastic bending strength distribution and the maximum bending strength distribution at each position in the material axial direction, and the bending moment distribution at the ultimate strength of the steel frame beam. Was calculated. The calculation of the shear force at the ultimate proof stress of the steel beam of the present invention was performed according to the contents described in Non-Patent Document 1 and Non-Patent Document 3. Specifically, the calculation was performed on the assumption that the flange of the steel beam has reached the tensile strength at the preceding yield position Y of the steel beam and the yield stress is generated in the effective cross-sectional portion of the web. Further, in the conventional steel beam, it is assumed that the welded portion between the flange and the column breaks early at the tip in the material axial direction and the steel beam reaches the ultimate strength, and the maximum at the tip in the material axial direction. It was assumed that the bending strength was 0.84 times the position in the other material axial direction.

The results of the above calculation are shown in the graphs of FIGS. 3 and 4, respectively. Further, for each of the steel beams of the present invention and the conventional example, the total plastic bending strength and the shearing force at that time at each of the tip in the material axial direction and the preceding yield position Y, and the ultimate strength of the steel beam are generated in the steel beam. The calculated values of the shear force are shown in Table 1.

In the graphs of FIGS. 3 and 4, the range in which the bending moment distribution at the ultimate strength exceeds the total plastic bending strength at each position in the material axial direction is mainly plasticized. Therefore, the wider this range, the more the plastic deformation of the steel beam. It is judged that the ability is great.

In the conventional steel beam, the total plastic bending strength at the tip in the material axial direction is less than the bending moment at the ultimate strength of the steel beam, and the strain is concentrated at the tip in the material axial direction of the steel beam.

On the other hand, in the example of the present invention, the bending moment acting on the tip of the steel beam in the material axial direction when the preceding yield position Y reaches the maximum bending strength, that is, the ultimate strength of the steel beam, determines the total plastic bending strength. It is below. That is, the welded portion where the tip of the steel beam in the material axial direction is joined to the column does not fall within the range where the steel beam is plasticized. Therefore, it was confirmed that the steel beam of the example of the present invention can obtain high plastic deformation ability by using a steel material having excellent low temperature toughness such as a steel material having a Charpy impact value of 27 J or more at −40 ° C.

A test piece of the steel beam and column-beam joint structure of the present invention was prepared, and a force test was performed on this test piece to verify the performance of the steel-framed beam and column-beam joint structure of the present invention. Will be described below.

FIGS. 5 (a) and 5 (b) show a plan view and a vertical cross-sectional view of the test body S as the test object of this force test, respectively.

As shown in FIGS. 5 (a) and 5 (b), in the present loading test, the steel frame beam 1B in which the reinforcing material 14 is provided on each of the upper flange 11 and the lower flange 12 as in the second embodiment. Prepared a cruciform test piece S configured by being joined to both sides of the pillar 2. However, in the test body S, instead of the inner diaphragm 4 provided in the column 2 of the second embodiment, the column 2 has a height at which each of the upper flange 11 and the lower flange 12 of the steel frame beam 1B is joined. A through diaphragm 5 was provided so as to penetrate the cross section.

Of the test pieces S, the main body portion of the two steel beam 1B is composed of a steel plate having a plate thickness of 28 mm as the upper flange 11 and the lower flange 12 and a steel plate having a plate thickness of 16 mm as the web 13. Built-in H steel with a beam width of 400 mm and a beam width of 175 mm was used. Then, at the timber axial end E of the steel beam 1B, the reinforcing material 14 having a plate thickness of 28 mm is completely welded into the K-shaped groove on both sides of the upper flange 11 and the lower flange 12 of the built-in H steel in the beam width direction. It was joined by welding.

The planar shape of the reinforcing material 14 was 200 mm in the material axis direction of the steel frame beam 1B and 87.5 mm in the beam width direction of the steel frame beam 1B. Specifically, in the range from the joint with the column 2 to 100 mm in the timber axial direction of the steel beam 1B, the width of the reinforcing member 14 is kept constant at 87.5 mm and joined to both sides of the steel beam 1B in the beam width direction. The pair of reinforcing members 14 to be provided increases the dimensions in the beam width direction by a total of 175 mm. Further, in the range from 100 mm to 200 mm in the material axial direction of the steel beam 1B from the joint with the column 2, the width of the reinforcing material 14 is linearly gradually reduced, and 200 mm in the material axial direction from the joint with the column 2. The width of the reinforcing material 14 was set to 0 at the position.

Further, in the test body S, the pillar 2 portion was a four-sided welded box-shaped cross-section pillar having a cross-sectional size of 400 × 400 mm, which was formed by combining steel plates having a plate thickness of 40 mm. A through diaphragm 5 having a plate thickness of 40 mm was provided in each of the columns 2 to which the upper flange 11 and the lower flange 12 of the steel beam 1B are attached. Then, the upper flange 11, the lower flange 12 and the reinforcing material 14 of the steel beam 1B are passed through and joined to the diaphragm 5 by complete penetration welding of the re-shaped groove, and the web 13 of the steel beam 1B is attached to the side surface of the column 2 by K. It was joined by full penetration welding of the groove. Each of these welds is performed by performing CO ₂ welding using a welding wire equivalent to the symbol YGW18 specified in Japanese Industrial Standard JIS Z3312 "Mag welding and MIG welding solid wire for mild steel, high tension steel and low temperature steel". rice field.

The above-mentioned steel plates constituting the main body portion (upper flange 11, lower flange 12 and web 13) of the steel beam 1B of the test body S, the reinforcing material 14, and the pillar 2 have Japanese Industrial Standards JIS G3106 “rolled steel plate for welded structure”. The SM490B material specified in the above was used. Furthermore, consideration was given to ensuring a Charpy impact value of 27 J or more at -40 ° C for each of these steel sheets.

In this force test, the material test of the upper flange 11, the lower flange 12 and the web 13 of the steel frame beam 1B was performed. For the upper flange 11 and the lower flange 12, the yield strength is 432.2 N / mm ² , the tensile strength is 530.4 N / mm ² , the yield ratio is 79.8%, the uniform elongation is 28.2%, and the Charpy impact value at -60 ° C. It was 321J. For the web 13, the yield strength was 436.9 N / mm ² , the tensile strength was 538.0 N / mm ² , the yield ratio was 81.2%, the uniform elongation was 21.4%, and the Charpy impact value at -60 ° C was 333 J. rice field.

Then, as shown in FIG. 6, the cruciform test piece S was installed in the test frame. Specifically, the upper end and the lower end of the pillar 2 were supported by pin bearings and roller bearings, respectively. The distance between the pin bearing and the roller bearing was 2700 mm. Then, the test piece S was cooled until the welded portion between the steel frame beam 1B and the column 2 became stable at −60 ° C.

Then, in order to simulate the behavior of the column-beam joint of the building that receives the horizontal load, positive and negative alternating gradual increments were repeatedly applied in inverse symmetry with respect to the tips of the two steel beams 1B on both sides of the column 2. The distance between both force points of the steel beam 1B was set to 4400 mm.

7 (a) and 7 (b) show a side view and a plan view of a main part of the test body S in a state of being installed on the test frame, respectively. Further, in FIG. 7 (c), it is calculated based on the lower limit values of the yield strength and the tensile strength (325 N / mm ² and 490 N / mm ² respectively) of the steel plate constituting the steel beam 1B portion of the test body S according to the material standard. The total plastic bending strength distribution and the maximum bending strength distribution of the steel beam 1B are shown. As shown in FIG. 7 (c), at the boundary position between the stiffened portion by the reinforcing material 14 and the rest in the material axial direction of the steel beam 1B (shown by a black circle in FIG. 7 (c)), the steel beam 1B The steel beam 1B portion of the test piece S is designed so that the bending moment (broken line in FIG. 7 (c)) acting on the test piece S first reaches the maximum bending strength.

In this force test, when the entire cross section of the steel beam 1B is plasticized at the tip position in the material axial direction of the steel beam 1B or at the boundary position between the region E where the reinforcing material 14 is provided and the other regions. The member deformation angle θ was controlled based on the member deformation angle θ _p of the steel frame beam 1B. Specifically, as shown in FIG. 8, first, a force is applied for one cycle in the positive and negative directions at a deformation angle of ± 1/3 θ _p within the elastic range, and then ± 2 θ _p , ± 4 θ _p , ± 6 θ _p , Two cycles were applied in the positive and negative directions at each deformation angle.

In addition, this force test was carried out under the condition that an axial force of 300 kN (axial force ratio 0.015) was applied to the column 2 in order to stabilize the behavior of the force device.

In this force test, after applying force by one positive and negative cycle at the deformation angle ± 1/3 θ p and two positive and negative cycles at the deformation angles ± 2θ _p and ± 4θ _p , the negative side of the second cycle of the deformation angle + _{6θ p} _. Immediately after shifting to the force, a destructive sound was generated in the Bausinger part. Then, when the force was further continued, the second huge sound was generated, and the force test was completed.

FIG. 9 shows the relationship between the bending moment M at the tip of the steel frame beam 1B in the material axial direction and the member deformation angle θ obtained by performing this force test. Further, in FIG. 10, the bending moment and the member deformation angle θ in FIG. 9 are dimensionless as relative values M / M _p with respect to the total plastic proof stress M _p and relative values θ / θ _p with respect to the total plastic deformation angle θ _p , respectively. The graph expressed in the above is shown. Further, FIG. 11 shows an extended skeleton curve created based on FIG. 10. The maximum value of the member deformation angle θ was 27.65 θ / θ _p in the positive direction and 25.38 θ / θ _p in the negative direction.

As shown in FIGS. 9 to 11, in the test piece S satisfying the requirements of the steel frame beam and the column-beam joint structure of the present invention, the load-deformation relationship draws a stable curve, and the load-deformation relationship draws a stable curve under an extremely low temperature environment of -60 ° C. It was also confirmed that brittle fracture did not occur at the axial end of the steel beam and sufficient plastic deformation ability was exhibited.

Further, FIGS. 12 (a) and 12 (b) show the positions of the starting points of cracks generated in the vicinity of the material axial end portion of the steel frame beam 1B during the ultimate strength of the steel frame beam 1B in this load test. .. As shown in FIG. 12, it was confirmed that the crack generation position in the steel frame beam 1B can be set to a position different from the welded portion between the tip of the steel frame beam 1B in the material axial direction and the column. Therefore, it was confirmed that the welded portion between the tip of the steel beam in the material axis direction and the column is suppressed from brittle fracture at an early stage, and the steel beam has high fatigue resistance and plastic deformation ability.

1A, 1B Steel beam 2

Column

3A, 3A Column-beam joint structure 4 Inner diaphragm 5 Through

diaphragm

11,

11A Upper flange

12, 12A Lower flange 11w, 12w Widening part 13 Web 13s Scallop 14 Reinforcing material E Material Axial end

Claims

A steel beam having an upper flange, a lower flange, and a web connecting the upper flange and the lower flange.
The upper flange, the lower flange, and the web are steel materials having a Charpy impact value of 27 J or more at −40 ° C.
When an increasing inversely symmetric bending moment acts on both ends of the steel beam in the material axial direction and one or both of the upper flange and the lower flange yield, the upper flange and the lower flange yield. A steel beam having a shape such that the position where it first yields in one or both of the flanges is other than the tip in the material axial direction.
The cross-sectional area of the upper flange and the lower flange in the cross section perpendicular to the material axial direction is a region including the tip in the material axial direction at the end portion in the material axial direction than the region other than the end portion in the material axial direction. The steel beam according to claim 1, wherein the steel beam is set to be large.
The bending moment acting on both ends when an inversely symmetric bending moment that gradually increases at both ends of the steel beam in the material axis direction reaches the maximum bearing capacity at any position of the steel beam in the material axis direction. The steel beam according to claim 1 or 2, wherein the size of the beam is equal to or less than the total plastic bending moment of the steel beam at both ends.
The bending moment acting on both ends when an inversely symmetric bending moment that gradually increases at both ends of the steel beam in the material axis direction reaches the maximum yield strength at any position of the steel beam in the material axis direction. The steel beam according to any one of claims 1 to 3, wherein the size of the beam is equal to or less than the bending yield strength of the steel beam at both ends.
A column-beam joint structure characterized in that the tip of the steel frame beam according to any one of claims 1 to 4 in the material axial direction is welded to the column.
A structure characterized by having the column-beam joint structure according to claim 5.