Beam construction

Abstract

To provide a beam structure that can effectively suppress lateral buckling. [Solution] The beam structure 10 comprises a beam body 21 of a steel beam having an upper flange 21t and a lower flange 21d, a beam end member 16 that connects the beam body 21 to a column 15, and a joining member J1 that joins the beam body 21 and the beam end member 16. Both ends of the beam body 21 each constitute a joint 30 joined using the joining member J1. The beam structure 10 is provided with a side reinforcing plate 25 only on the beam body 21. The side reinforcing plate 25 connects the upper flange 21t and the lower flange 21d.

Description

[Technical Field]

[0001] This disclosure relates to a beam structure comprising a beam end member connected to a column and a beam body portion joined to the beam end member. [Background technology]

[0002] In a column-beam connection structure of steel columns and steel beams, a larger bending moment acts at the beam end connection than at the longitudinal center of the beam during an earthquake. Therefore, in order to suppress fracture at the beam end connection, Patent Document 1 proposes a column-beam connection structure in which a rectangular steel plate is welded to the flange side of the beam that connects to the diaphragm of the beam. The column-beam connection structure described in Patent Document 1 has a steel beam having a standard cross-sectional portion that forms the standard cross-sectional shape of the steel beam, and an increased cross-sectional area portion that is located on the end side of the steel beam than the standard cross-sectional portion and has a larger cross-sectional area than the standard cross-sectional portion. A reinforcing member is joined to the standard cross-sectional portion and the increased cross-sectional area portion, straddling the boundary between the standard cross-sectional portion and the increased cross-sectional area portion.

[0003] Furthermore, to suppress lateral buckling of steel beams, it is common practice to use slabs or to use secondary beams or braces as lateral stiffeners. For example, as described in Patent Document 2, it was common practice to prevent lateral buckling with slabs, secondary beams, and braces. However, there are cases where the above-mentioned members cannot be used, such as in open spaces. In such cases, reinforcement with side reinforcement plates can be considered. However, when using side reinforcement plates divided into multiple sections, the side reinforcement plates must be attached by on-site welding or other means after joining the beam end members and the beam body members, which is time-consuming. Furthermore, according to the inventors' studies, it has become clear that with side reinforcement plates divided into multiple sections, lateral buckling cannot be effectively suppressed because the side reinforcement plates are not continuous. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2013-181292 [Patent Document 2] Japanese Patent Publication No. 2019-056220 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, when certain configurations such as open spaces are adopted, it may not be possible to use the slabs, joists, or braces mentioned above. In such cases, as an alternative method to suppress lateral buckling of steel beams, it is conceivable to install side reinforcing plates on both sides of the steel beam and weld the upper and lower ends of each side reinforcing plate to the ends of the upper and lower flanges of the steel beam, respectively. However, attempting to install side reinforcing plates along the entire side of a steel beam was difficult because the connecting members (splice plates, bolts, etc.) used to join the beam end members and the beam body members got in the way. Therefore, a structure in which the side reinforcing plates are divided at the points where the connecting members are located could be considered. However, in order to make the multiple divided side reinforcing plates continuous, it is necessary to attach the side plates at the connecting member points by on-site welding or other means after joining the beam end members and the beam body, which is time-consuming. Consequently, there was a need to develop new technologies to effectively suppress lateral buckling in column-beam joint structures of steel columns and steel beams. [Means for solving the problem]

[0006] A beam structure that solves the above problems comprises a beam body of a steel beam having an upper flange and a lower flange, a beam end member connecting the beam body to a column, and a joining member joining the beam body and the beam end member, wherein both ends of the beam body each constitute a joint joined to the beam end member using the joining member, the beam structure is provided with a lateral buckling stiffener only in the beam body, and the lateral buckling stiffener connects the upper flange and the lower flange. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a beam structure that can efficiently suppress lateral buckling. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic front view showing a beam structure in the first embodiment of the present invention. [Figure 2] This is a cross-sectional view in the direction of line II-II in Figure 1. [Figure 3] This is a schematic top view showing a beam structure in a second embodiment of the present invention. [Figure 4] This is a schematic front view showing the beam structure in the second embodiment. [Figure 5] This is a schematic perspective view showing the main parts of the beam structure in the second embodiment. [Figure 6] This is a schematic top view showing a beam structure in a third embodiment of the present invention. [Figure 7] This is a schematic front view showing the beam structure in the third embodiment. [Figure 8] This is a schematic perspective view showing the main parts of the beam structure in the third embodiment. [Figure 9] This is a schematic front view showing a beam structure in the fourth embodiment of the present invention. [Figure 10] Figure 9 is a perspective view showing the central beam and the area surrounding the gusset plate that follows it. [Figure 11] This is a table listing descriptions of each example. [Figure 12] This is a front view illustrating the intermittent welding of Example 2, which embodies the first embodiment. [Figure 13] The following are schematic front views showing the beam structures of Comparative Examples 1 to 4 for comparison with the embodiment: (a) shows the configuration of Comparative Example 1, in which side reinforcing plates are provided along the entire length of the beam except for the 100 mm range from the column; (b) shows the configuration of Comparative Example 2, in which side reinforcing plates are provided along the entire length of the beam except for the 100 mm range from the column and the joint area; (c) shows the configuration of Comparative Example 3, in which no side reinforcing plates are provided; and (d) shows the configuration of Comparative Example 4, in which no side reinforcing plates are provided but three small beams are provided at equal intervals. [Figure 14]It is a perspective view schematically showing an analysis model of an example corresponding to each embodiment. [Figure 15] It is a perspective view enlarging the periphery of a joint part in the analysis model of FIG. 14. [Figure 16] It is a diagram schematically showing the periphery of a trabecula of the analysis model of FIG. 14. [Figure 17] It is a graph explaining the relationship between the moment and the plastic strain in the analysis result, and the analysis values of the yield strength, the maximum strength, and the plastic strain at the end. [Figure 18] It is a graph summarizing the analysis results of Example 1, 8 and Comparative Examples 1 - 4, where (a) shows the yield strength, (b) shows the maximum strength, and (c) shows the plastic strain. [Figure 19] It is a deformation diagram of a beam structure in an analysis according to the installation position of a side reinforcing plate, where (a) shows Example 1, (b) shows Comparative Example 1, (c) shows Comparative Example 2, and (d) shows Comparative Example 3. [Figure 20] It is a graph summarizing the analysis results of Examples 1, 2 corresponding to the first embodiment, where (a) shows the yield strength, (b) shows the maximum strength, and (c) shows the plastic strain. [Figure 21] It is a graph summarizing the analysis results of Examples 3 - 5 corresponding to the second embodiment and Example 1, where (a) shows the yield strength, (b) shows the maximum strength, and (c) shows the plastic strain. [Figure 22] It is a graph summarizing the analysis results of Examples 6, 7 corresponding to the third embodiment and Example 1, where (a) shows the yield strength, (b) shows the maximum strength, and (c) shows the plastic strain.

Mode for Carrying Out the Invention

[0009] (First Embodiment) Hereinafter, with reference to FIGS. 1 and 2, the first embodiment of the beam structure of the present invention will be described. The beam structure of this embodiment is composed of a steel beam.

[0010] <Beam Structure> FIG. 1 is a front view schematically showing the beam structure in the first embodiment of the present invention. FIG. 2 is a sectional view taken along the line II - II in FIG. 1.

[0011] As shown in Figures 1 and 2, the beam structure 10 in this embodiment has a symmetrical configuration with respect to the beam center C1, which is the midpoint (center) of the beam's total length. This beam structure 10 comprises beam end members 16 fixed to each of two spaced-apart columns 15, a beam member 20 of a steel beam connected to the pair of beam end members 16, and a joining member J1 for joining the beam end members 16 and the beam member 20. The beam end members 16 and the beam member 20 are joined at a joint section 30 equipped with the joining member J1. Each joining member J1 comprises two splice plates 31, two splice plates 32, and four splice plates 33. These joining members J1 are arranged to span the beam end members 16 and the beam member 20. The joint section 30 indicates the range spanned by the splice plates (31-33) of the joining member J1. Multiple spaced holes are formed in the beam end member 16 and beam member 20 at the joint 30. The splice plates 31 to 33 will be described in detail later.

[0012] The column 15 is made of a square steel pipe. A beam end member 16 is fixed to this column 15 by welding. The beam end member 16 has the same beam depth and beam width as the H-shaped steel beam body 21 of the beam member 20 of the steel beam, but is shorter in length than the beam body 21. In this embodiment, the length L1 of the beam end member 16 is 900 mm. A hole is formed at the end of the beam end member 16 on the beam body 21 side, at a position that aligns with the holes in the splice plates 31 to 33.

[0013] The beam member 20 has a beam body portion 21 and two side reinforcing plates (lateral buckling stiffening members) 25. The beam body 21 of this embodiment is made of H-shaped steel with a beam depth of 600 mm and a flange width of 250 mm. Holes are formed at both axial ends of the beam body 21 at positions that align with the holes in the splice plates 31 to 33.

[0014] One side reinforcing plate 25 is provided on each side of the web 21w of the beam member 20. The ends of each side reinforcing plate 25 are welded to the side surfaces of the upper flange 21t and lower flange 21d of the beam body 21, respectively. Continuous welding and intermittent welding are examples of welding methods, and either can be used in this embodiment. In this embodiment, both longitudinal ends of the side reinforcing plate 25 extend to the inner end 30Ea of the joint portion 30. In this embodiment, the inner end 30Ea is the end of the beam body portion 21 of the splice plate 31-33, which serves as the joining member J1, on the beam center C1 side. The thickness of each side reinforcing plate 25 is 9 mm.

[0015] As shown in Figure 1, the beam body portion 21 of the beam member 20 is joined at the joint portion 30 such that the upper flange 21t and lower flange 21d are flush with the upper flange 16t and lower flange 16d of the beam end member 16 fixed to the column 15.

[0016] The splice plate 31 is a rectangular plate-shaped member. Each splice plate 31 is positioned in contact with one side of the web 21w of the beam body 21 and one side of the web 16w of the beam end member 16, which is flush with the web 21w. The splice plate 31 is joined to the beam body 21 and the beam end member 16 by a plurality of bolts B1 and nuts (not shown) that are inserted through a plurality of holes formed therein.

[0017] The splice plate 32 is a rectangular plate-shaped member having the same width as the upper flange 21t and lower flange 21d of the beam body 21, respectively. One splice plate 32 is positioned in contact with the upper surface of the upper flange 21t of the beam body 21 and the upper surface of the upper flange 16t of the beam end member 16. The other splice plate 32 is positioned in contact with the lower surface of the lower flange 21d of the beam body 21 and the lower surface of the lower flange 16d of the beam end member 16.

[0018] The splice plate 33 is a rectangular plate-shaped member with a width that allows it to contact the lower surfaces of the upper flanges 21t and 16t and the upper surfaces of the lower flanges 21d and 16d of the beam body 21 and beam end member 16, respectively. One splice plate 33 is positioned to straddle the lower surface of the upper flange 21t of the beam body 21 and the lower surface of the upper flange 16t of the beam end member 16. The other splice plate 33 is positioned to straddle the upper surface of the lower flange 21d of the beam body 21 and the upper surface of the lower flange 16d of the beam end member 16.

[0019] Then, the bolt is inserted with the holes in splice plate 32 and splice plate 33 aligned with the holes in beam end member 16 and beam body 21. This bolt is not shown in Figures 1 and 2, but corresponds to bolt B2 in Figure 3 and beyond. In this state, the beam end member 16 and beam body 21 are joined by the splice plates 32 and 33 by screwing the bolt (B2) and nut (not shown) together and tightening them.

[0020] (Construction method for beam structures) Next, the construction method for the beam structure 10 described above will be explained. In the construction method of the beam structure 10 of this embodiment, the beam end members 16 are fixed to the columns 15 by welding in advance at the factory. In addition, side reinforcing plates 25 are welded to both sides of the beam body portion 21 of the beam member 20. Furthermore, multiple holes are formed at the ends of the beam end members 16 and the ends of the beam member 20 for passing through bolts to which splice plates 31 to 33 are attached.

[0021] Then, the column 15 and beam member 20 are transported to the site. At the construction site, after erecting a pair of columns 15, the beam member 20 is positioned between the beam end members 16 fixed to the columns 15. In this case, the upper flange 16t and lower flange 16d of the beam end members 16 and the upper flange 21t and lower flange 21d of the beam body 21 of the beam member 20 are positioned flush. Then, the splice plates 31 to 33 are positioned so as to span both the beam end members 16 of the columns 15 and the beam body 21 of the beam member 20. The beam end members 16 of the columns 15 and the beam member 20 are then joined by fixing the splice plates 31 to 33 using bolts B1 (B2) and nuts (not shown). The analysis results of the beam structure 10 of this embodiment will be described later together with the analysis results of other embodiments and conventional structures (comparative examples) described later, in an example that embodies this beam structure 10.

[0022] (Effect of the embodiment) In a beam structure 10 having a beam end member 16 fixed to a column 15 and a beam body portion 21 of a steel beam, a side reinforcing plate 25 is provided in addition to the joint portion 30, thereby increasing the rigidity of the steel beam and distributing local forces.

[0023] According to this embodiment, the following effects can be obtained. (1) The beam structure 10 of this embodiment is equipped with side reinforcing plates 25 as lateral buckling stiffening members, which are fixed only to both sides of the beam body 21 in the range from the inner end 30Ea of one joint 30 to the inner end 30Ea of the other joint 30. This makes it possible to suppress lateral buckling without installing a separate lateral buckling stiffening member in the range from the joint 30 to the column 15. Therefore, a beam structure with suppressed lateral buckling can be constructed efficiently.

[0024] Other embodiments of the present invention will be described below. In the following embodiments, components similar to those in the first embodiment will be denoted by the same reference numerals, and their detailed descriptions will be omitted.

[0025] (Second Embodiment) Next, a second embodiment of the beam structure of the present invention will be described using Figures 3 to 5. The beam structure in the second embodiment is the same as the beam structure of the first embodiment, except that it further comprises a joint reinforcing member 26a as a joint stiffening member.

[0026] The beam structure 40 of this embodiment, like the beam structure 10 of the first embodiment, comprises beam end members 16 fixed to each of two spaced-apart (a pair) columns 15, a beam member 20 of a steel beam connected to the pair of columns 15, and a joining member J1 for joining the beam end members 16 and the beam member 20 (the beam body portion 21 of the beam member).

[0027] The beam structure 40 has a symmetrical configuration with respect to the center of the beam (not shown), which is located at the halfway point of the beam's total length. For the sake of explanation, Figures 3 to 5 show only one end of the steel beam of the beam structure 40. As shown in these figures, side reinforcing plates 26 are provided on both sides in the beam width direction opposite to the web 21w of the beam body 21. The upper and lower ends of each side reinforcing plate 26 are welded to the ends of the upper flange 21t and lower flange 21d of the beam body 21, respectively. In this embodiment, a joint reinforcing portion 26a (joint reinforcing member) is formed on the side reinforcing plate 26. The joint reinforcing portion 26a is formed by extending both ends of the side reinforcing plate 26 by a length L5 from the inner end 30Ea of the joint portion 30 to the side opposite the center of the beam body 21 (towards the beam end member 16).

[0028] In this embodiment, the splice plates 32 and 33 of the joint portion 30 are fixed to the beam body portion 21 and the beam end member 16 by bolts B2 and nuts (not shown).

[0029] (Construction method for beam structures) In the construction method of the beam structure 40 of this embodiment, the side reinforcing plates 26 are welded in the factory. Specifically, similar to the first embodiment described above, first, in the factory, the beam end member 16 is welded and fixed to the column 15, and then the side reinforcing plates 26 are welded to both sides of the beam body 21 in the beam width direction. Then, after transporting the column 15 with the beam end members 16 welded to it and the beam body 21, the column 15 is erected.

[0030] Then, similar to the first embodiment, the beam body portion 21 is placed between the beam end members 16 of the pair of columns 15, the splice plates 31 to 33 are placed, and the beam end members 16 of the columns 15 and the beam body portion 21 are joined using bolts B1, B2 and nuts (not shown).

[0031] As a result, the side reinforcing plate 26 is provided to extend for a length L5 minutes further than the inner end 30Ea of the joint portions 30 at both ends of the steel beam in the axial direction, to a position on the side of the column 15 (first mounting position and second mounting position). In this case, the joint reinforcing portion 26a is already welded to the upper and lower ends of the beam body portion 21, but is not welded to the splice plates 32 and 33. The analysis results of the beam structure 40 in this embodiment will also be discussed later in the following example.

[0032] According to this embodiment, in addition to the effect of (1) above, the following effects can be obtained. (2) The beam structure 40 of this embodiment further has a joint reinforcement portion 26a formed by the side reinforcing plate 26 extending for a length L5 from the inner end 30Ea toward the beam end member 16. As a result, the side reinforcing plate 26 can further suppress lateral buckling by reinforcing the area around the inner end 30Ea with the joint reinforcement portion 26a.

[0033] (Third embodiment) Next, a third embodiment of the beam structure of the present invention will be described using Figures 6 to 8. The beam structure in the third embodiment is the same as the beam structure 40 of the second embodiment, except that it is equipped with a joint reinforcing plate 36 instead of a joint reinforcing part 26a as a joint reinforcing member.

[0034] The beam structure 50 of this embodiment, like the embodiments described above, comprises a beam end member 16 fixed to two spaced-apart (a pair) of columns 15, a beam member 20 of a steel beam connected to the pair of columns 15, and a joining member J1 for joining the beam end member 16 and the beam member 20 (the beam body portion 21). In this embodiment, as with the first embodiment described above, each side reinforcing plate 25 of the beam member 20 extends to the inner end portion 30Ea of the joint portion 30.

[0035] As shown in Figures 6 to 8, in this embodiment, a rectangular plate-shaped joint reinforcement plate 36 is welded to the upper flange 21t and lower flange 21d of the side reinforcement plate 25, respectively. This joint reinforcement plate 36 is provided so as to protrude from the beam body 21 by a length L6 in the beam width direction of the beam body 21. Furthermore, this joint reinforcement plate 36 is provided so as to extend by a length L7 (i.e., half of the total length L8 of the joint reinforcement plate 36) on the column 15 side and the beam body 21 side, respectively, with the inner end 30Ea as the center.

[0036] (Construction method for beam structure 50) In the construction method of the beam structure 50 of this embodiment, similar to the first embodiment described above, the beam end member 16 is fixed to the column 15 in advance at the factory, and the joint reinforcement plate 36 and the side reinforcement plate 25 are welded in order to both sides in the beam width direction of the beam body portion 21 of the beam member 20. Note that the area of ​​the side reinforcement plate 25 that interferes with the joint reinforcement plate 36 is cut out in advance before welding. In this case, the joint reinforcement plate 36 is welded to the ends of the upper flange 21t and lower flange 21d of the beam body 21 such that the center of the joint reinforcement plate 36 is located therein.

[0037] Subsequently, at the site, columns 15 with beam end members 16 fixed to them are erected, and beam members 20 with joint reinforcement plates 36 fixed to them are placed between the beam end members 16 of the pair of columns 15. Then, the splice plates 31 to 33 are placed, and the beam end members 16 of the columns 15 and the beam members 20 are joined using bolts B1 and B2. The analysis results of the beam structure 50 in this embodiment will also be described later in the following example.

[0038] According to this embodiment, in addition to the effect of (1) above, the following effects can be obtained. (3) In the beam structure 50 of this embodiment, a joint reinforcing plate 36 is further provided. As a result, the area around the inner end 30Ea is reinforced by the joint reinforcing plate 36, which further suppresses lateral buckling.

[0039] (Fourth Embodiment) Next, a fourth embodiment of the beam structure of the present invention will be described using Figures 9 and 10. As shown in Figure 9, the beam structure 60 in the fourth embodiment is the same as the beam structure 10 in the first embodiment, except that it includes a side reinforcing plate 75 that extends from the inner end 30Ea to the center C1 of the beam, instead of the side reinforcing plate 25 (see Figure 1) of the first embodiment, and also includes a secondary beam 73 and a gusset plate GP1.

[0040] The beam structure 60 of this embodiment, like the beam structure 10 of the first embodiment, comprises a beam end member 16 fixed to each of the columns 15, a beam member 70 of a steel beam made of H-shaped steel connected to a pair of columns 15, and a connecting member J1 for joining the beam end member 16 and the beam member 70 (the beam body portion 21 of the beam member). The beam member 70 comprises a beam body portion 21 and a side reinforcing plate 75, and has a length (total beam length) L0. In this embodiment, the side reinforcement plate 75 is provided from the inner end 30Ea of the joint portion 30 on the right side of Figure 9 to the center C1 of the beam. In other words, the side reinforcement plate 75 in this embodiment is half the length of the side reinforcement plate 25 in the first embodiment. Also, the end of the side reinforcement plate 25 opposite to the inner end 30Ea is located at a position that is half the total length L0 of the beam (L0 / 2).

[0041] Furthermore, in the beam structure 60 of this embodiment, in the area of ​​the main beam portion 21 where the side reinforcing plate 75 is not provided, secondary beams 72 and 73 are provided at a position that is 1 / 4 of the total length of the beam structure 60 (L0 / 4) and at the center C1 of the beam, respectively. Furthermore, as shown in Figure 10, the end of the side reinforcing plate 75 is joined to the gusset plate GP1 of the secondary beam 73. The secondary beams 72 and 73 are made of H-shaped steel of the same size as the main beam portion 21, and the gusset plate GP1 is positioned flush with the web 73w of the secondary beam 73. However, the shape of the secondary beams 72 and 73 and the arrangement of the gusset plate GP1 are not limited to this embodiment.

[0042] As shown in Figure 9, the secondary beam 72 is joined to the gusset plate GP1 (see Figure 16) provided on the main beam portion 21 with bolts or the like. The analysis results of the beam structure 60 in this embodiment will also be described later in the following example.

[0043] According to this embodiment, the following effects can be obtained. (4) The beam structure 60 of this embodiment has a beam member 70 to which a side reinforcing plate 75 is welded, extending from the inner end 30Ea of one joint portion 30 to the center C1 of the beam. Furthermore, in this beam structure 60, secondary beams 72 and 73 are provided in the area of ​​the beam body portion 21 where the side reinforcing plate 75 is not provided. As a result, lateral buckling can be efficiently suppressed by the side reinforcing plate 75 and the secondary beams 72 and 73. In addition, since the side reinforcing plate is not installed in the area from the joint portion 30 to the column 15, the construction time can be reduced. (5) In this embodiment, the end of the side reinforcing plate 75 is connected to the gusset plate GP1 of the secondary beam 73. As a result, the effect of suppressing lateral buckling by the side reinforcing plate 75 and the secondary beam 73 is continuous, so a high lateral buckling suppression effect can be obtained. [Examples]

[0044] Next, we will describe in detail the embodiments that embody the first to fourth embodiments described above, using Figure 11. First, let me explain the beam that was actually analyzed. The beam material of the subject beam was 490N class steel, with a beam length (total beam length L0) of 9300 mm and a slenderness ratio of 168 (calculated using the total beam length as the central cross-section). The beam cross-section of the subject beam differed between the ends and the center, with the ends being BH-600×250×12×22 and the center being BH-600×250×12×19. Furthermore, the joint portion 30 between the beam end member 16 and the beam body 21 was located 900 mm from the beam end.

[0045] Two PL-9mm x 290mm x 440mm splice plates were used as splice plates 31 (web splice plates) in the joint section 30. Furthermore, two PL-16mm x 250mm x 650mm splice plates were used as splice plates 32 (external flange splice plates) in the joint section 30, and four PL-16mm x 100mm x 650mm splice plates were used as splice plates 33 (internal flange splice plates).

[0046] (Examples 1 and 2) Examples 1 and 2 correspond to the first embodiment described above. Example 1 is a configuration in which the side reinforcing plates 25 are continuously welded. Furthermore, Example 2 is a configuration in which intermittent welding is performed at a 180 mm pitch. In Example 2, as shown in Figure 12, welded sections W1 with a length of 180 mm and unwelded sections NW1 with a length of 180 mm were arranged in a repeating manner. Furthermore, in Examples 1 and 2, the end of the side reinforcement plate 25 was positioned 10 mm away from the inner end 30Ea. By providing this 10 mm gap, interference between the welding excess between the side reinforcement plate 25 and the flanges (21d, 21t) of the beam member 20 and the splice plates 32, 33 can be prevented.

[0047] (Examples 3-5) Examples 3 to 5 correspond to the second embodiment described above. In Example 3, the length L5 of the joint reinforcement 26a is set to 60 mm, which is the midpoint between the first bolt B2 closest to the inner end 30Ea and the next closest second bolt B2. In Example 4, the length L5 of the joint reinforcement 26a is set to 100 mm, which is the midpoint between the second bolt B2. In Example 5, the length is set to 130 mm, which is the midpoint between the second bolt B2 and the third bolt B2. Note that the bolts B2 are arranged in two rows of 10 each.

[0048] (Examples 6, 7) Examples 6 and 7 correspond to the third embodiment described above. In Example 6, the length L6 of the joint reinforcement plate 36 is 125 mm, which is half the flange width, and the length L7 of the joint reinforcement plate 36 is 250 mm, which is the same as the flange width (total length L8 is 500 mm). In Example 7, the length L6 of the joint reinforcement plate 36 is 62.5 mm, which is one-quarter of the flange width, and the length L7 of the joint reinforcement plate 36 is 150 mm (total length L8 is 300 mm). Also in Examples 6 and 7, as in Examples 1 and 2, the end of the side reinforcement plate 25 is provided at a position 10 mm away from the inner end 30Ea.

[0049] (Example 8) Example 8 corresponds to the fourth embodiment described above. Here, the axial stiffness per joist is set to 5.86 kN / mm, which is the required stiffening stiffness K given by the following equation (1) (Reference: Architectural Institute of Japan, "Guidelines for Plastic Design of Steel Structures 2017"). Required stiffening stiffness K=5.0×C / Lb…(1) In equation (1), Lb is the length between the lateral buckling braces, and C is the compressive force acting in the lateral buckling area. This compressive force C is given by the following equation (2). C = σy·A / 2 …(2) In equation (2), σy is the yield stress and A is the total cross-sectional area of ​​the beam. In this embodiment 8, as in embodiments 1, 2, 6, and 7, the end of the side reinforcement plate 25 was positioned 10 mm away from the inner end 30Ea.

[0050] Next, we will explain the comparative examples. Here, we used four comparative examples. Figure 13 shows the structures of Comparative Examples 1 to 4. As shown in Figures 13(a) and 13(b), Comparative Examples 1 and 2 are configured in which side reinforcing plates are provided on both sides of the H-shaped steel beam.

[0051] (Comparative Example 1) Comparative Example 1, shown in Figure 13(a), is a configuration in which side reinforcing plates are provided along the entire length of the beam from adjacent columns (across the main beam body and the beam end members of the columns). In this configuration of Comparative Example 1, side reinforcing plates are provided up to a position 100 mm away from the main body of the column.

[0052] (Comparative Example 2) Comparative Example 2, shown in Figure 13(b), is a configuration in which side reinforcing plates are provided over almost the entire length from column to column, except at the joint. The connection point between the beam end and the beam body at the joint is 900 mm away from the column. In Comparative Example 2, as in Comparative Example 1, side reinforcing plates are provided up to a position 100 mm away from the main body of the column. In Comparative Example 2 as well, the end of the side reinforcing plate 25 is provided 10 mm away from the inner end 30Ea.

[0053] (Comparative Examples 3, 4) As shown in Figures 13(c) and 13(d), Comparative Examples 3 and 4 were configured without side reinforcing plates. Comparative Example 3, shown in Figure 13(c), has a configuration in which neither side reinforcing plates nor secondary beams are provided. Comparative Example 4, shown in Figure 13(d), does not have side reinforcing plates, but has a configuration in which three small beams 74 are provided at equal intervals (every L0 / 4 of length) along the entire length L0 of the beam.

[0054] Then, we performed the analysis using an analytical model. This analysis model is shown in Figures 14 to 16. Fig. 14 is a perspective view of the entire analysis model. Fig. 15 is a perspective view of the analysis model with the joint part 30 enlarged. Fig. 16 is a perspective view of the analysis model with the area around the part where the trabeculae 72 are attached enlarged.

[0055] As the analysis model, simple beams were used. As analysis elements, the beams, splice plates (attaching plates), and side reinforcement plates were regarded as first-order quadrilateral shell elements, and the size of each element was about 20 mm × 20 mm. The bolts B2 used for joining the splice plate - beam flange and splice plate - beam web were high-strength bolts and were regarded as connector elements. The trabeculae 72, 73 were regarded as 18 one-axis spring elements arranged on the outer periphery of the gusset plate GP1.

[0056] Furthermore, as boundary conditions, one end of the beam was pin-supported, and the other end of the beam was pin-roller supported. In this case, the rotation around the material axis (around the z-axis) was restrained at both ends of the beam. Also, as the loading method, a repeated loading with positive and negative gradual increase that gives the same forced rotation angle around the y-axis at both ends of the beam was used. The interlayer deformation angle R was repeated twice with the same amplitude in the order of ±0.005, ±0.01, ±0.015, ±0.02, ±0.03, ±0.04, ±0.05 rad ···

[0057] Fig. 17 shows a skeleton curve indicating the relationship between the beam-end moment M and the plastic strain rate μ. Here, the beam-end moment M and the plastic strain rate μ were taken as the average values at both ends of the beam. The circles on the skeleton curve shown in Fig. 17 are the yield strength analysis values c , c , p , a , y , a , max , a , y , p M y at the time of reaching, the squares are the maximum strength a M max at the time of reaching, the triangles represent the end state. Here, the yield strength analysis values a M y are the strengths at 1 / 3 tangent stiffness, and at the end state are the calculated values of the full plastic strength after reaching the maximum strength c M p when the load has decreased until, or the calculated value of the full plastic strength c M pIf the load did not decrease to a certain point and the analysis ended, it was considered to be the time of maximum deformation. Furthermore, the plasticity ratio μ was calculated by setting the beam member angle θ to the elastic limit member angle θ. bp The value obtained by dividing by, the elastic limit member angle θ bp This is the calculated value for the full plastic strength of the steel beam. c M p Initial stiffness analysis value a The value was obtained by dividing by K. The results of the buckling behavior analysis obtained by finite element method (FEM) analysis using the above analysis models and conditions are shown in Table 1 below.

[0058] [Table 1]

[0059] Figures 18(a) to 18(c) show the analysis results, displayed as bar graphs, the yield strength, maximum strength, and plasticity ratio for Examples 1 and 8 and Comparative Examples 1 to 4, respectively. From the comparison results between Example 1 and Comparative Examples 1 and 2, the yield strength and maximum strength increased as the area of ​​the side reinforcement plate increased. In addition, the plasticity ratio was similar between Comparative Example 2, in which a side reinforcement plate was provided on the column 15 side of the joint 30, and Example 1, in which no side reinforcement plate was provided. Furthermore, although the size of the side reinforcement plate in Example 8 was half that of Example 1, the yield strength and maximum strength were almost the same as in Example 1.

[0060] Figures 19(a) to (d) show the deformation diagrams of Example 1 and Comparative Examples 1 to 3, respectively. Comparative Example 3, which has no side reinforcing plates, clearly shows lateral buckling, but the larger the side reinforcing plate, the less it deformed. Also, Example 1, which does not have side reinforcing plates on the beam side of the joint 30, and Comparative Example 2, which does have them, showed almost the same deformation state. Therefore, it can be seen that the configuration of Example 1 can suppress lateral buckling to the same extent as Comparative Example 2.

[0061] Figures 20(a) to (c) show the yield strength, maximum yield strength, and plasticity ratio in Examples 1 and 2. The yield strength, maximum yield strength, and plasticity ratio were almost the same for both continuous and intermittent welding. Therefore, no differences in yield strength, maximum yield strength, and plasticity ratio were observed depending on the type of welding.

[0062] Figure 21 shows the yield strength, maximum yield strength, and plasticity ratio for Example 1 and Examples 3 to 5, which correspond to the second embodiment described above. As shown in Figures 21(a) and 21(b), the yield strength and maximum strength were almost the same as those of the configuration in Example 1, which does not have a joint reinforcement 26a, regardless of the size of the joint reinforcement 26a. Furthermore, as shown in Figure 21(c), the plasticity ratio increased as the size of the joint reinforcement 26a increased.

[0063] Figures 22(a) to (c) show the yield strength, maximum yield strength, and plasticity ratio for Example 1 and Examples 6 and 7, which correspond to the third embodiment described above. As shown in Figure 22, the yield strength and maximum strength were almost the same as those in Example 1, which lacked the joint reinforcement plate 36, regardless of the size of the joint reinforcement plate 36. Furthermore, the plasticity ratio was higher when the joint reinforcement plate 36 was provided, and it was higher the larger the joint reinforcement plate 36 was.

[0064] Each of the above embodiments and examples can be implemented with the following modifications. Each of the above embodiments, examples, and the following modifications can be combined with each other to the extent that they do not contradict each other technically. In the second embodiment described above, the side reinforcing plate 26 further has a joint reinforcing portion 26a formed by extending from the inner end 30Ea to the beam end member 16 side. The longer the length L5 of the joint reinforcing portion 26a of the side reinforcing plate 26, the greater the plasticity ratio of the beam structure 40. However, considering the construction effort of the beam structure, it is preferable that the length of the joint reinforcing portion 26a be such that it does not interfere with the fixing of the bolts B1 and nuts of the splice plate 31.

[0065] In the third embodiment described above, a joint reinforcing plate 36 is provided on the upper flange 21t and lower flange 21d of the beam body portion 21 of the beam member 20, with the inner end portion 30Ea as the center, projecting in the beam width direction. However, the configuration is not limited to this, and the joint reinforcing plate 36 may be provided in an arrangement where the inner end portion 30Ea is not the center, as long as it can straddle the inner end portion 30Ea.

[0066] In the second and third embodiments described above, the joint reinforcement portion 26a of the side reinforcement plate 26 and the joint reinforcement plate 36 were used as reinforcing members to reinforce the area around the inner end portion 30Ea, respectively. However, the joint reinforcement members that reinforce the area around the inner end portion 30Ea are not limited to the configurations shown in each embodiment. For example, the shape of the upper flange 21t and lower flange 21d of the beam body portion 21 may be made to be integrated with the joint reinforcement plate 36. Alternatively, the shape of the splice plates 32 and 33 on the beam body portion 21 side may be made to protrude outward in the beam width direction of the beam body portion 21, thereby forming the joint reinforcement plate 36.

[0067] In the fourth embodiment described above, the side reinforcing plate 75 is provided from the inner end 30Ea of the joint 30 to the center C1 of the beam. A secondary beam 73 is provided at the center C1 of the beam, and a secondary beam 72 is provided at a distance L0 / 4 from the column 15 in the area where the side reinforcing plate 75 is not provided. Furthermore, the end of the side reinforcing plate 75 is connected to the gusset plate GP1 of the secondary beam 73. In this configuration, the secondary beam 73 may be omitted, and the side reinforcing plate 75 may be extended to the secondary beam 72, and the end of the side reinforcing plate 75 may be connected to the gusset plate GP1 of the secondary beam 72. Furthermore, the length of the side reinforcing plate is not limited to distances L0 / 2 or L0 / 4 from the column 15. The length of the side reinforcing plate may be within the range from one inner end 30Ea to the other inner end 30Ea, and the gusset plate GP1 of the secondary beam may be joined (welded) to the end opposite to the inner end 30Ea. In this case, since the secondary beam and the gusset plate GP1 are in a continuous state and lateral buckling is suppressed, the side reinforcing plate 75 can be limited to the minimum extent that would create an open space, while obtaining a high level of lateral buckling restraint effect equivalent to that of the conventional technology (structure of Comparative Example 4) in which only secondary beams are arranged. Furthermore, additional secondary beams (not shown) other than the secondary beams 72 may be provided in areas where the side reinforcing plates 75 are not provided. In the fourth embodiment described above, the end of the side reinforcement plate 75 is joined to the gusset plate GP1 which is joined to the beam 73. The side reinforcement plate does not necessarily have to be joined to the gusset plate or beam.

[0068] In each of the above embodiments, the upper and lower ends of the side reinforcing plates 25, 26, and 75 are welded to the side surfaces in the beam width direction of the upper flange 21t and lower flange 21d of the beam body 21. Alternatively, the upper and lower ends of the side reinforcing plates may be welded to the lower surface of the upper flange and the upper surface of the lower flange of the beam body, respectively. In this case, the joint reinforcing plate 36 in the third embodiment is welded to the beam end member 16, the side surfaces of the upper flange 21t and lower flange 21d of the beam body 21, and the side reinforcing plate. In each of the above embodiments, side reinforcing plates 25, 26, and 75 connected to the upper flange 21t and lower flange 21d of the beam body 21 were used as lateral buckling stiffening members. The lateral buckling stiffening members are not limited to the side reinforcing plates of the above shape and arrangement, as long as they are connected to the upper flange 21t and lower flange 21d of the beam body 21.

[0069] The beam structures 10, 40, 50, and 60 in each of the above embodiments are configured to include beam end members 16 fixed to square steel pipe columns 15, but the type of column to which the beam end members 16 are provided is not limited to this. Instead of square steel pipe columns, they may be provided to, for example, round steel pipe columns or reinforced concrete columns. [Explanation of Symbols]

[0070] B1, B2... Bolt, C1... Center of beam, J1... Joint member, GP1... Gusset plate, L0... Total length of beam, L1, L5, L6, L7... Length, L8... Total length, 10, 40, 50, 60... Beam structure, 15... Column, 16... Beam end member, 16d, 21d... Lower flange, 16t, 21t... Upper flange, 16w, 21w... Web, 20, 70... Beam member, 21... Main beam body, 25, 26, 75... Side reinforcement plate (lateral buckling stiffening member), 26a... Joint reinforcement (joint reinforcement member), 30... Joint section, 30Ea... Inner end, 31, 32, 33... Splice plate, 36... Joint reinforcement plate (joint reinforcement member), 72, 73, 74... Small beam.

Claims

1. The beam body of a steel beam having an upper flange and a lower flange, The beam end member connects the main beam body to the column, A beam structure comprising a connecting member that connects the beam body portion and the beam end member, Both ends of the beam body each form a joint that is joined to the beam end member using the connecting member. The beam structure is provided with a lateral buckling stiffening member only in the main beam portion. The beam structure is characterized in that the lateral buckling stiffening member connects the upper flange and the lower flange.

2. The beam structure according to claim 1, characterized in that the lateral buckling stiffening member is a side reinforcing plate that connects the upper flange and the lower flange in the range from the inner end of one of the joint portions to the inner end of the other joint portion.

3. The beam structure according to claim 1 or 2, characterized in that the lateral buckling stiffening member is provided in a portion of the range from the inner end of one joint to the inner end of the other joint.

4. The beam structure further comprises a secondary beam and a gusset plate for the secondary beam, The beam structure according to claim 3, characterized in that the secondary beam is located in an area of ​​the main beam where the lateral buckling stiffening member is not provided.

5. The main beam section is made of H-shaped steel, The beam structure according to claim 2, further comprising a joint reinforcing member arranged across the beam body portion and the joint portion.

6. The beam structure according to claim 5, characterized in that the joint reinforcing member is a joint reinforcing portion formed by extending the side reinforcing plate toward the beam end member.

7. The aforementioned joint reinforcing member has a plate shape, It is fixed to at least one of the positions corresponding to the upper flange and the lower flange on the side reinforcement plate, The beam structure according to claim 5, characterized in that it is a joint reinforcing plate provided so as to protrude from the beam body portion in the beam width direction.

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