Steel beams and structures containing them

Abstract

To provide a steel beam which is provided with a vertical haunch at a beam end, can mitigate occurrence of stress (strain) concentration, provide through holes for equipment piping at the beam end, and eliminate need for processing through holes for equipment piping at a beam center, and to provide a structure having the same.SOLUTION: In a steel beam having a web and flanges connected to the top and bottom of the web, both end portions of the steel beam in a material axial direction are provided with beam height expansion portions whose beam height is expanded than at the center portion in the material axial direction, and openings are provided in the web of the beam height expansion portions.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a steel beam and a structure having the same. [Background technology]

[0002] In structures in which a steel beam made of H-shaped steel is joined to the side of a steel pipe column, it is common to provide a diaphragm in the steel pipe column and join the steel beam to the steel pipe column via this diaphragm in order to increase the rigidity of the steel pipe column and efficiently transfer the load from the steel beam to the steel pipe column.

[0003] In addition, there are many cases where multiple steel beams are connected around a steel pipe column at the same height. For example, in a structure where steel plate columns and steel beams are combined in a lattice pattern, up to four beams are connected to the left and right and front and back of the steel plate column at the same height of the steel pipe column.

[0004] 5(a) and 5(b) show a side view and a plan view of a column-beam joint in which steel beams 5 made of H-shaped steel with the same beam depth are joined to the left and right sides of a steel pipe column 9. In this way, when steel beams 5 with the same beam depth are joined to the sides of a steel pipe column 9, two diaphragms 91 are provided on the steel pipe column 9 so as to correspond to the respective heights of the upper flange 52 and the lower flange 53 of the H-shaped steel that constitutes the steel beam 5.

[0005] In addition, due to reasons such as different spans of the multiple steel beams joined around the steel pipe column, the beam depths of these multiple steel beams may not be the same. In such a case, as shown in Fig. 6, the heights of at least one of the bottom flanges 53, 63 and the top flanges 52, 62 of the steel beams 5, 6 do not match between the multiple steel beams 5, 6, so it becomes necessary to add an additional number of diaphragms 91 to the steel pipe column 9.

[0006] In this way, when the beam depths of the multiple steel beams joined around the steel pipe column do not match, the number of diaphragms provided on the steel pipe column increases, and the fitting of the column-beam joint becomes complicated. Therefore, when the difference in beam depths of multiple steel beams joined around the steel pipe column at the same height of the steel pipe column is less than about 150 mm, a vertical haunch (beam depth expansion part) 7a that gradually expands the beam depth of the beam end is provided in the steel beam 7 with the smaller beam depth among the multiple steel beams 5, 7, as shown in Figure 7. In this way, the beam depth of the steel beam 7 with the smaller beam depth among the multiple steel beams 5, 7 at the joint position to the steel pipe column 9 matches the beam depth of the other steel beams 5, so there is no need to add the number of diaphragms 91, and the fitting of the column-beam joint can be simplified. Furthermore, providing a vertical haunch 7a at the end of the steel beam 7 increases the section modulus of the beam end, thereby alleviating stress (strain) concentration at the beam end and suppressing fracture at the welded joints of the steel beam to the steel pipe column, thereby improving the earthquake resistance of the structure.

[0007] However, in a steel beam 7 having a vertical haunch 7a at the beam end as shown in Fig. 7, stress (strain) concentration is likely to occur at the position where the cross section of the steel beam 7 starts to change, as shown in the shaded area in Fig. 10. In addition, the greater the gradient of the vertical haunch 7a, i.e., the greater the change in the beam depth per unit length of the steel beam 7, the greater the stress (strain) concentration that occurs at the position where the cross section of the steel beam 7 starts to change.

[0008] For example, Patent Document 1 discloses a structure for reducing the concentration of stress (strain) occurring at the position where the cross section of a steel beam with a vertical haunch starts to change. Specifically, a stiffener is provided in a direction perpendicular to the flange and web near the position where the cross section of the steel beam starts to change, and the installation position of this stiffener is adjusted within a predetermined range, so that the concentration of stress (strain) can be reduced even when the gradient of the vertical haunch is large. Also disclosed is a structure in which a vertical haunch is provided without bending the beam flange by arranging and welding the haunch flange and the web of the haunch part so as to span between the outside of the flange at the beam end of a steel beam made of H-shaped steel and a steel pipe column.

[0009] In addition, in order to effectively utilize the space under the beams (floor height), through holes are sometimes provided in the webs of the steel beams to pass equipment piping through. In order to provide the steel beams with sufficient earthquake resistance, it is preferable that the steel beams have no cross-sectional defects. Therefore, when through holes are provided, reinforcement work needs to be performed around the through holes to compensate for the cross-sectional defects caused by the through holes. Therefore, in addition to the opening process for the through holes themselves, there is a problem that the number of man-hours required for the reinforcement work around the through holes increases.

[0010] Here, when a horizontal force such as an earthquake force acts on a structure, a large bending moment is generated at the beam end of the steel beam, so from the viewpoint of ensuring the strength and bending deformation capacity of the steel beam, it is generally considered that providing a through hole at the beam end of the steel beam should be avoided. On the other hand, from the viewpoint of efficient installation of equipment piping, providing a through hole at the beam end is more convenient than providing a through hole at the center of the steel beam.

[0011] As a method for providing through holes at the beam ends of steel beams, for example, Patent Document 2 discloses a structure in which the beam depth is expanded only at the center of the steel beam and equipment piping is arranged in the space under the beam end. In this structure, no through holes for passing equipment piping are provided in the steel beams, so no cross-sectional loss occurs due to the through holes.

[0012] Providing a through hole in a steel beam may reduce the strength and bending deformation capacity of the steel beam due to a loss of cross section, but providing an opening in the steel beam may have the effect of mitigating the concentration of stress (strain) generated in the steel beam. For example, Patent Document 3 discloses a structure in which a hole is provided in the widened part of a horizontal haunch in a steel beam in which the flange at the beam end is widened in the beam width direction. In this structure, the hole provided in the widened part of the horizontal haunch relieves the concentration of stress (strain) generated at the position where the flange width changes suddenly, and fracture at the welded part of the widened part of the horizontal haunch can be suppressed. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2012-057449 A [Patent Document 2] Patent No. 4016759 [Patent Document 3] JP 2013-204306 A Summary of the Invention [Problem to be solved by the invention]

[0014] However, in the technology disclosed in Patent Document 1, stiffeners, haunch flanges, webs of the haunch portion, etc. are welded to reinforce the steel beam near the position where the cross-section of the steel beam begins to change, which causes problems such as the occurrence of welding distortion, an increase in the weight of the steel beam, and an increase in the number of steps required to manufacture the steel beam.

[0015] In addition, in the technology disclosed in Patent Document 2, the beam depth of the steel beam at the center of the beam is increased and the beam depth at the beam end is decreased, thereby securing a steel pipe for arranging equipment piping in the space under the beam at the beam end. However, by reducing the cross-sectional area of ​​the steel beam at the beam end, the plastic section modulus Zp of the steel beam at the beam end is also reduced, and the total plastic strength Mp of the steel beam is reduced. For this reason, the technology disclosed in Patent Document 2 needs to be used in combination with a seismic wall structure so that a large bending moment is not generated at the beam end of the steel beam when a horizontal force such as an earthquake force acts, and the cross-sectional design of the steel beam needs to be performed taking into account the horizontal force borne by the seismic wall. Patent Document 2 also discloses a structure in which equipment piping is arranged so as to penetrate the web at the center of the beam, but in this case, there is a problem that the number of steps required for opening the through hole increases.

[0016] Furthermore, the technology disclosed in Patent Document 3 discloses that a stress (strain) concentration can be alleviated by providing a hole in the widened portion of the horizontal haunch provided at the beam end of the steel beam. However, the hole provided in the widened portion of the horizontal haunch cannot be used as a through hole for passing equipment piping through the beam. Therefore, in order to pass equipment piping through the steel beam, a through hole for equipment piping must be provided separately in the web of the steel beam, which increases the construction work. In addition, the technology disclosed in Patent Document 3 cannot alleviate the stress (strain) concentration that occurs at the position where the cross section of the steel beam starts to change in the steel beam provided with a vertical haunch.

[0017] In view of the above-mentioned problems, the present invention aims to provide a steel beam having a vertical haunch at the end of the beam, which can reduce the occurrence of stress (strain) concentration, and which can provide a through hole for equipment piping at the end of the beam, eliminating the need to process a through hole for equipment piping in the center of the beam, and a structure having the same. [Means for solving the problem]

[0018] In order to solve the above problems, the steel beam and the structure having the same of the present invention have the following features.

[0019] [1] A steel beam having a web and flanges connected above and below the web, wherein both ends of the steel beam in the material axial direction have beam depth expansion sections in which the beam depth is expanded compared to the central part in the material axial direction, and the web of the beam depth expansion section has at least one opening.

[0020] [2] A steel beam as described in [1] having an H-shaped cross section formed by the web and the flange.

[0021] [3] A steel beam as described in [1] or [2], wherein the beam depth of the beam depth expansion portion is gradually expanded from the center portion toward the tip in the material axis direction.

[0022] [4] A steel beam described in any of [1] to [3], wherein the openings are formed in a circular shape, and the cross-sectional area of ​​the web in the material axis direction and perpendicular to the material axis direction at the center position of each of the openings is equal to or greater than the cross-sectional area of ​​the web in the material axis direction and perpendicular to the material axis direction at the central portion.

[0023] [5] A steel beam described in any of [1] to [4], wherein the opening is formed in a circular shape and the periphery of the opening is positioned so as to be away from the flange by a distance equal to or greater than the diameter of the opening.

[0024] [6] A steel beam described in any of [1] to [5], wherein the opening is formed in a circular shape and the center of the opening is located at the center of the height of the beam depth of the beam depth expansion portion.

[0025] [7] A steel beam described in any of [1] to [6], wherein a plurality of the openings are provided in each of the beam depth expansion sections, and the spacing between the plurality of openings is set to a size that does not cause mutual interference of the stresses or strains generated in the web by each of the openings.

[0026] [8] A steel beam as described in [7], wherein, of the multiple openings provided in each of the beam depth expansion sections, the diameter of the opening located at the tip side in the material axis direction is larger than the diameter of the opening located at the central side in the material axis direction.

[0027] [9] A steel beam described in any one of [1] to [8], wherein the opening has a shape that can be used as a through hole for equipment piping.

[0028]

[10] A structure having a steel beam described in any one of [1] to [9]. Effect of the Invention

[0029] According to the steel beam and the structure having the same of the present invention, the opening is provided in the web of the beam depth expansion part, and the web around the opening becomes plastic, so that the stress (strain) concentration occurring in the flange and the web at the position where the cross section of the steel beam starts to change can be alleviated. As a result, the deformation performance of the steel beam can be improved.

[0030] In addition, in the steel beam and the structure having the same of the present invention, the beam depth at the center of the beam is smaller than the beam depth at both ends in the material axial direction, so that a space for equipment piping can be secured under the beam at the center of the beam. In other words, when equipment piping is passed through the steel beam so as to cross the center of the beam, there is no need to provide a through hole in the web at the center of the beam, and the man-hours required for opening and reinforcing the through hole can be omitted.

[0031] Furthermore, in the steel beam and structure having the same of the present invention, the openings provided in the beam depth enlarged portions at both ends in the material axis direction to relieve stress (strain) concentration can also be used as through holes for equipment piping. Since these openings are provided in the beam depth enlarged portions at both ends in the material axis direction of the steel beam, they are more convenient for efficiently installing equipment piping than through holes provided in the center of the steel beam. Furthermore, since there is no need to reinforce the periphery of the openings provided in the beam depth enlarged portions, no man-hours are required for reinforcement processing.

[0032] In addition, in the steel beam and structure having the same of the present invention, the total plastic strength of the steel beam can be set to a desired value by adjusting the diameter of the opening in the beam depth expansion section, the position of the opening, and the gradient of the vertical haunch, making it possible to rationalize the structure as a whole. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1(a) is a side view of a beam-column joint between a steel beam and a steel pipe column in one embodiment of the present invention, and FIGS. 1(b) to 1(e) are cross-sectional views of the steel beam shown in FIG. 1(a). [Diagram 2] 2(a) and 2(b) are diagrams for explaining a plastic region that occurs in a steel beam according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram showing stress (strain) concentration locations occurring in an example of a steel beam according to one embodiment of the present invention. [Figure 4] FIG. 4 is a side view of a beam-column joint between a steel beam and a steel pipe column according to another embodiment of the present invention. [Diagram 5] FIG. 5(a) and FIG. 5(b) are a side view and a plan view, respectively, of a beam-column joint between two steel beams having the same beam depth and a steel pipe column. [Figure 6] FIG. 6 is a side view of a column-beam structure consisting of two steel beams with different beam depths and a steel pipe column. [Figure 7] FIG. 7 is a side view of a column-beam structure made of a steel beam provided with a vertical haunch (beam depth expansion portion) and a steel pipe column. [Figure 8] 8(a) and 8(b) are diagrams for explaining the plastic region that occurs in a steel beam with a uniform cross section. [Figure 9] 9(a) and 9(b) are diagrams for explaining a plastic region that occurs in a steel beam provided with a vertical haunch (beam depth expansion portion). [Figure 10] FIG. 10 is a diagram showing locations of stress (strain) concentration occurring in a steel beam provided with a vertical haunch (beam depth expansion portion). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, embodiments of a steel beam and a structure having the same according to the present invention will be described in detail with reference to the drawings.

[0035] Fig. 1(a) shows a side view of a steel beam 1 according to one embodiment of the present invention and a beam-column joint in which the steel beam 1 is joined to a steel pipe column 9. Fig. 1(b) to Fig. 1(e) respectively show a bb cross-sectional view, a cc cross-sectional view, a dd cross-sectional view, and an ee cross-sectional view of the steel beam 1 shown in Fig. 1(a).

[0036] As shown in Fig. 1(a), the steel beam 1 of this embodiment is composed of an H-shaped steel having an H-shaped cross section, with a web 11 and flanges 12, 13 connected above and below the web 11. Both ends in the axial direction of the steel beam 1 (only one of the ends is shown in Fig. 1(a)) are provided with expanded beam depth portions 1a in which the beam depth is larger than that of the central portion in the axial direction. The beam depth of the expanded beam depth portion 1a is gradually expanded from the central portion in the axial direction of the steel beam 1 toward the tip in the axial direction.

[0037] The steel beam 1 may be assembled by welding steel plates, or it may be constructed by using an H-shaped steel beam manufactured by rolling in the center of the steel beam 1 in the axial direction, and assembling steel plates by welding only at both ends in the axial direction, and joining the two in the axial direction.

[0038] As shown in FIG. 1(a) and FIG. 1(c), a circular opening 11a is provided in a web 11 of the beam depth enlarged portion 1a.

[0039] In this embodiment, the opening 11a has a shape that can be used as a through hole for equipment piping (not shown), such as a duct, a drain pipe, or an electrical pipe. Specifically, the diameter Φ of the opening 11a and the position of the opening 11a in the steel beam 1 are set to a size and position suitable for passing the equipment piping. For example, in order to pass a duct, a drain pipe, or an electrical pipe, it is preferable to set the size of the diameter Φ of the opening 11a within a range of 0.5 times the beam depth. Also, in order to increase the degree of freedom in designing the equipment piping and to enable changes in the arrangement when updating the equipment piping, the size and number of the openings 11a provided in the web 11 of the beam depth expansion portion 1a of the steel beam 1 may be set to be large.

[0040] In this embodiment, the thickness of the web 11 of the beam depth expansion portion 1a of the steel beam 1 is equal to the thickness of the web 11 of the other portion (central portion in the material axis direction), and the diameter Φ of the opening 11a is set to be equal to or smaller than the beam depth expansion amount ΔH of the beam depth expansion portion 1a at the central position of each opening 11a. In other words, the diameter Φ of the opening 11a is set so that the cross-sectional area of ​​the web 11 in the material axis direction and the vertical direction at the central position of each opening 11a is equal to or larger than the cross-sectional area of ​​the web 11 in the material axis direction and the vertical direction at the central portion in the material axis direction. This is preferable because the provision of the opening 11a makes it difficult for the cross-sectional performance of the steel beam 1 to be reduced.

[0041] Also, in another form, the cross-sectional area of ​​the web 11 in the material axis direction and the vertical direction at the center position of each opening 11a can be made equal to or larger than the cross-sectional area of ​​the web 11 in the material axis direction and the vertical direction at the center part in the material axis direction, and the same effect can be obtained. For example, a form in which the thickness of the web 11 at the beam depth expansion part 1a of the steel beam 1 is made larger than the thickness of the web 11 in the other part (center part in the material axis direction) is possible. For example, even in the case where the diameter Φ of the opening is not made equal to or smaller than the beam depth expansion amount ΔH at the center position of each opening 11a in order to pass a relatively large diameter equipment piping through the opening 11a, the same effect can be obtained by adopting the above form.

[0042] Furthermore, in this embodiment, the opening 11a is disposed so that the periphery of the opening 11a is spaced apart from the flanges 12, 13 by a distance equal to or greater than the diameter Φ of the opening 11a. This is preferable because it prevents the flanges 12, 13 from being drawn in by the deformation of the web 11 around the periphery of the opening 11a and deforming, thereby preventing a decrease in the bending strength of the steel beam 1.

[0043] In addition, in this embodiment, the center of the opening 11a provided in the beam depth expansion portion 1a is disposed at the center of the beam depth of the beam depth expansion portion 1a. This is preferable because it makes it difficult for the stress transmitted in the material axis direction of the steel beam 1 to be biased to either the upper or lower side of the opening 11a.

[0044] The above-mentioned steel beam 1 is joined to the side surface of a steel pipe column 9 via a diaphragm 91, thereby forming a structure 10 of this embodiment.

[0045] The effect of mitigating stress (strain) concentration in the steel beam 1 of this embodiment will be described below.

[0046] First, Fig. 8(a) shows a simplified mechanical model of a cantilever beam with one end fixed in half of the steel beam 5(6) with a uniform cross section shown in Fig. 5(a), Fig. 5(b) and Fig. 6 in the axial direction. The dotted and solid lines in the graph in Fig. 8(b) show the bending moment M acting at each position in the axial direction of the steel beam 5(6) when a concentrated load is applied to the free end of the mechanical model shown in Fig. 8(a). The vertical axis of the graph in Fig. 8(b) shows the bending moment, and the horizontal axis shows the distance from the fixed end (the position of connection to the steel pipe column 9) (L is the total length of the steel beam 5(6) in the axial direction).

[0047] The bending moment M acting on each position in the axial direction of the steel beam 5(6) increases in proportion to the distance from the free end (center position in the axial direction) of the steel beam 5(6), and is maximum at the fixed end (joint position with the steel pipe column 9). Meanwhile, the total plastic strength Mp at each position in the axial direction of the steel beam 5(6) is the plastic section modulus Zp determined by the cross-sectional shape of the beam multiplied by the yield stress σy of the steel material constituting the steel beam 5(6) (Mp = σy x Zp). If the steel type is the same, the larger the cross-sectional area of ​​the steel beam 5(6), the greater the total plastic strength Mp of the beam.

[0048] Here, when the concentrated load acting on the free end of the mechanical model shown in Figure 8(a) is gradually increased, the bending moment M acting on each position in the axial direction of the steel beam 5(6) increases at each position in the axial direction of the steel beam 5(6) while maintaining the proportional relationship described above, while keeping the bending moment M at the free end position at 0. Then, when the bending moment M acting on each position in the axial direction of the steel beam 5(6) reaches the full plastic strength Mp at that position, the steel beam 5(6) starts to become plastic at this position. Figure 8(b) shows that for a steel beam 5(6) with a uniform cross section, the steel beam 5(6) starts to become plastic at the fixed end (the joint with the steel pipe column 9).

[0049] Next, Fig. 9(a) shows a simplified mechanical model of a cantilever beam with one end fixed support, in which half of the steel beam 7 in the axial direction is provided with the vertical haunch (beam depth expansion portion) 7a shown in Fig. 7. The bending moment M acting on each position in the axial direction of the steel beam 7 when a concentrated load is applied to the free end of the mechanical model shown in Fig. 9(a) and the full plastic strength Mp of each position in the axial direction of the steel beam 7 are shown by dotted lines and solid lines, respectively, in the graph of Fig. 9(b). As shown in Fig. 9(b), in the steel beam 7 provided with the vertical haunch 7a, the full plastic strength Mp of the vertical haunch 7a is larger than that in the case where the vertical haunch 7a is not provided.

[0050] Then, when the concentrated load acting on the free end of the mechanical model shown in Fig. 9(a) is gradually increased, the bending moment M acting on each position in the axial direction of the steel beam 7 increases, and at some position in the axial direction, the full plastic strength Mp is reached, and plasticity of the steel beam 7 starts from this position. From Fig. 9(b), it can be seen that in the steel beam 7 provided with the vertical haunch 7a, plasticity of the steel beam 7 starts at the position where the cross section of the steel beam 7 starts to change (the boundary position between the vertical haunch 7a and other parts).

[0051] In this way, in the steel beam 5 (6) with a uniform cross section, plasticization of the steel beam 5 (6) begins at the axial end where it is joined to the steel pipe column 9, and stress (strain) is concentrated at this position. Since the axial end of the steel beam has a weld for joining the steel beam to the steel pipe column, if stress (strain) is concentrated at this position, there is a risk that the weld will break, and it is therefore desirable to alleviate such stress (strain) concentration.

[0052] In addition, in a steel beam 7 provided with a vertical haunch 7a, plastic deformation of the steel beam 7 begins at the position where the cross section of the steel beam 7 starts to change (the boundary between the vertical haunch 7a and the other parts). It can be seen that at the time when this plastic deformation starts, there is still some margin of strength at the end of the steel beam 7 in the axial direction. However, as shown by the hatched area in Fig. 10, stress (strain) concentration occurs at the position where the cross section of the steel beam 7 starts to change, that is, the boundary between the vertical haunch 7a and the other parts.

[0053] Fig. 2(a) shows a simplified mechanical model of a cantilever beam with one end fixed, in which half of the steel beam 1 in the axial direction of this embodiment is supported. In addition, the bending moment M acting on each position in the axial direction of the steel beam 1 when a concentrated load is applied to the free end of the mechanical model shown in Fig. 2(a) and the full plastic strength Mp of this steel beam 1 at each position in the axial direction are shown by dotted lines and solid lines, respectively, in the graph of Fig. 2(b).

[0054] When the concentrated load acting on the free end of the mechanical model shown in FIG. 2(a) is gradually increased, the bending moment M acting on each position in the material axis direction of the steel beam 1 increases, and reaches the full plastic strength Mp at some position in the material axis direction, and plasticization of the steel beam 1 starts from this position. From FIG. 2(b), it can be seen that in the steel beam 1 of this embodiment, plasticization of the steel beam 1 starts first at the web 11 around the opening 11a in the beam depth enlargement portion 1a (at the time of "small acting moment" in FIG. 2(b)). Then, when the bending moment M acting on each position in the material axis direction of the steel beam 1 further increases, plasticization starts at the position where the change in the cross section of the steel beam 1 starts, that is, the boundary position between the beam depth enlargement portion 1a and the other parts, following the web 11 around the opening 11a (at the time of "large acting moment" in FIG. 2(b)). That is, as shown by the hatched area in Fig. 3, the areas where plasticization occurs in the steel beam 1 are distributed between the web 11 on the periphery of the opening 11a in the beam depth enlargement portion 1a and the position where the change in the cross section of the steel beam 1 begins (the boundary position between the beam depth enlargement portion 1a and other portions). By providing the opening 11a, the stress (strain) concentration at the position where the change in the cross section of the steel beam 1 begins (the boundary position between the beam depth enlargement portion 1a and other portions) is alleviated more than when the opening 11a is not provided (see Fig. 10).

[0055] Also, by adjusting the size of the diameter Φ of the opening 11a, it is possible to advance the start of plasticization at the position where the change in the cross section of the steel beam 1 begins (the boundary position between the beam depth enlargement portion 1a and the other portion) and subsequently cause plasticization of the web 11 around the opening 11a. In this way, with the steel beam 1 of the present invention, it is possible to alleviate stress (strain) concentration at the axial end portion welded to the steel pipe column 9 and at the position where the change in the cross section of the steel beam 1 begins in various ways.

[0056] In addition, the opening 11a provided in the beam depth expansion portion 1a on the beam end side can be used not only to relieve stress (strain) concentration, but also as a through hole for passing equipment piping, thereby improving the freedom of equipment planning.

[0057] 4 shows a side view of a steel beam 2 according to another embodiment of the present invention and a beam-column joint in which the steel beam 2 is joined to a steel pipe column 9. A structure 20 of this embodiment is configured by joining the steel beam 2 to the side of a steel pipe column 9 via a diaphragm 91.

[0058] As shown in FIG. 4, in the steel beam 2 of this embodiment, a plurality of openings 21a, 21b are provided in one beam depth enlarged portion 2a. The intervals between the plurality of openings 21a, 21b are set to a size that does not cause mutual interference of the stress or strain generated in the web 21 by each of the openings 21a, 21b. Here, "mutual interference of stress or strain" means that the stress or strain generated in the web 21 around the periphery of the opening 21a and the stress or strain generated in the web 21 around the periphery of the opening 21b interfere with each other and combine to be greater than the stress or strain generated in the web 21 when there is only one opening. Thus, the number of openings 21a, 21b provided in one beam depth enlarged portion 2a is not limited to one. That is, a plurality of openings 21a, 21b may be provided in one beam depth enlarged portion 2a, provided that the openings are spaced apart so as not to cause mutual interference between the stress or strain generated in the web 21 by each of the openings 21a, 21b.

[0059] Among the multiple openings 21a, 21b provided in each of the beam depth expansion portions 1a, the diameter of the opening 21a located at the tip side (the steel pipe column 9 side) in the material axis direction is set to be larger than the diameter of the opening 21b located at the center side in the material axis direction. Since the larger the diameter of the opening, the greater the effect of mitigating stress (strain) concentration, the above-mentioned method is preferable because it effectively mitigates stress (strain) concentration at the beam end and effectively suppresses fracture at the welded portion of the steel beam 2 to the steel pipe column 9.

[0060] 4, in the steel beam 2 of this embodiment, the equipment piping P is arranged under the beam at the center in the material axis direction. In this way, when the equipment piping P is arranged so as to intersect with the material axis direction of the steel beam 2 at a position other than both ends of the steel beam 2 in the material axis direction, it is also possible to fix the equipment piping P under the beam at the center in the material axis direction of the steel beam 2 by using a hanging metal fitting (not shown) or the like.

[0061] In the above embodiments, the steel beams 1 and 2 have an H-shaped cross section formed by a web and a flange, but the steel beam of the present invention is not limited to this and may have a web and flanges connected to the top and bottom of the web. For example, the present invention can be applied to a steel beam having a C-shaped cross section or a steel beam having a rectangular cross section. [Explanation of symbols]

[0062] 1, 2 Steel beam 1a, 2a Beam depth expansion section 9 Steel pipe column 91 Diaphragm 10, 20 structures 11, 21 Web 12, 22 Upper flange (flange) 13, 23 Lower flange (flange) 11a, 21a, 21b opening Φ Diameter of opening ΔH Beam depth expansion amount P Equipment piping

Claims

1. A steel beam having a web and flanges connected to the top and bottom of the web, The steel beam has an expanded beam depth portion at both ends in the material axis direction, the expanded beam depth portion being larger than the central portion in the material axis direction, At least one opening is provided in the web of the beam expansion portion, and no opening is provided in the web other than the beam expansion portion; A steel beam in which the diameter and position of the opening are set so that when a concentrated load is applied to the free end of a mechanical model in which half of the steel beam in the axial direction is a cantilever beam with one end fixed and the concentrated load is gradually increased, plasticization of the steel beam first begins at the web on the periphery of the opening in the beam depth expansion portion.

2. The steel beam of claim 1 having an H-shaped cross section defined by said web and said flange.

3. 3. The steel beam according to claim 1, wherein the beam depth of the beam depth enlarged portion is gradually enlarged from the central portion toward the tip in the material axis direction.

4. The steel beam according to any one of claims 1 to 3, wherein the openings are formed in a circular shape, and the cross-sectional area of ​​the web in the material axis direction and perpendicular direction at the center position of each of the openings is equal to or greater than the cross-sectional area of ​​the web in the material axis direction and perpendicular direction at the central portion.

5. The steel beam according to any one of claims 1 to 4, wherein the opening is formed in a circular shape and the periphery of the opening is positioned so as to be spaced apart from the flange by a distance equal to or greater than the diameter of the opening.

6. The steel beam according to any one of claims 1 to 5, wherein the opening is formed in a circular shape and the center of the opening is positioned at the center of the height of the beam depth of the beam depth expansion portion.

7. A steel beam as described in any one of claims 1 to 6, wherein a plurality of the openings are provided in each of the beam depth expansion sections, and the spacing between the plurality of openings is set to a size that prevents a situation in which the stress or strain generated in the web by each of the openings interferes with each other to cause a resultant stress or strain greater than the stress or strain generated in the web when there is only one opening.

8. The steel beam according to claim 7, wherein, of the plurality of openings provided in each of the beam depth expansion sections, the diameter of the opening located at the tip side in the material axis direction is larger than the diameter of the opening located at the central side in the material axis direction.

9. The steel beam according to any one of claims 1 to 8, wherein the opening has a shape that can be used as a through hole for equipment piping.

10. A structure having a steel beam according to any one of claims 1 to 9.

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