JP7655211B2 - Steel beams and structures containing them - Google Patents

Description

The present invention relates to a steel beam and a structure having the same.

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 on 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.

In addition, multiple steel beams are often connected around a steel pipe column at the same height. For example, in a structure in which 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.

Figures 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 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.

In addition, the heights of multiple steel beams joined around a steel pipe column may not be the same due to reasons such as different spans of the multiple steel beams. In such cases, as shown in Figure 6, the heights of at least one of the lower flanges 53, 63 and upper 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 more diaphragms 91 to the steel pipe column 9.

In this way, if 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, making the fitting of the column-beam joint complicated. Therefore, if the difference in beam depth between the multiple steel beams joined around the steel pipe column at the same height is less than about 150 mm, as shown in Figure 7, a vertical haunch (beam depth expansion section) 7a is provided in the steel beam 7 with the smaller beam depth among the multiple steel beams 5, 7, which gradually expands the beam depth at the beam end. 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 joining 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, mitigating stress (strain) concentration at the beam end and suppressing breakage at the welded joints of the steel beam to the steel pipe column, thus improving the earthquake resistance of the structure.

However, as shown in Figure 7, in a steel beam 7 with a vertical haunch 7a at the beam end, stress (strain) concentration is likely to occur at the position where the cross-section of the steel beam 7 begins to change, as shown in the shaded area in Figure 10. In addition, the greater the gradient of the vertical haunch 7a, i.e., the greater the change in 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 begins to change.

For example, Patent Document 1 discloses a structure that reduces the concentration of stress (strain) that occurs in a steel beam with a vertical haunch at the position where the cross section of the steel beam begins to change. Specifically, a stiffener is provided near the position where the cross section of the steel beam begins to change, in a direction perpendicular to the flange and web, and the installation position of this stiffener is adjusted within a specified range, making it possible to reduce the concentration of stress (strain) 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 positioning and welding the haunch flange and the web of the haunch so that they 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.

In addition, to make effective use of the space under the beams (floor height), through holes are sometimes provided in the webs of steel beams to allow equipment piping to pass through. In order to provide 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 done around the through holes to compensate for the cross-sectional defects caused by the through holes. This creates a problem in that in addition to the opening process for the through holes themselves, the labor required for the reinforcement work around the through holes increases.

When horizontal forces such as earthquake forces act on a structure, a large bending moment is generated at the ends of the steel beams. Therefore, from the viewpoint of ensuring the strength and bending deformation capacity of the steel beams, it is generally considered that providing through holes at the ends of the steel beams should be avoided. On the other hand, from the viewpoint of efficient installation of equipment piping, providing through holes at the ends of the beams is more convenient than providing a through hole in the center of the steel beam.

As a method of providing through holes at the 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.

Providing through holes in steel beams can reduce the strength and bending deformation capacity of the steel beam due to cross-sectional loss, but providing openings in steel beams can also have the effect of mitigating stress (strain) concentration in the steel beam. For example, Patent Document 3 discloses a structure in which holes are provided in the widened portion of a horizontal haunch in a steel beam in which a horizontal haunch is provided by widening the flange at the beam end in the beam width direction. In this structure, the holes provided in the widened portion of the horizontal haunch mitigate the stress (strain) concentration that occurs at the position where the flange width changes suddenly, and fracture at the welded portion of the widened portion of the horizontal haunch can be suppressed.

JP 2012-057449 A Patent No. 4016759 JP 2013-204306 A

However, the technology disclosed in Patent Document 1 involves welding stiffeners, haunch flanges, webs of the haunch portion, etc., to reinforce the steel beam near the position where the cross-section of the steel beam begins to change, which creates problems such as 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.

In addition, in the technology disclosed in Patent Document 2, the beam depth of the steel beam is increased in the center and decreased at the beam end, 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 also decreases, and the total plastic strength Mp of the steel beam decreases. For this reason, the technology disclosed in Patent Document 2 must be used in combination with a seismic wall structure so that a large bending moment does not occur 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 must 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 labor required for opening the through hole increases.

Furthermore, the technology disclosed in Patent Document 3 discloses that the stress (strain) concentration can be alleviated by providing holes in the widened portion of the horizontal haunch provided at the end of the steel beam. However, the holes provided in the widened portion of the horizontal haunch cannot be used as through holes for passing equipment piping through the beam. Therefore, in order to pass equipment piping through the steel beam, it is necessary to provide a separate through hole for the equipment piping 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 begins to change in a steel beam provided with a vertical haunch.

In view of the above problems, the present invention aims to provide a steel beam with a vertical haunch at the end of the beam that can reduce the occurrence of stress (strain) concentration, and can provide through holes for equipment piping at the end of the beam, eliminating the need to machine through holes for equipment piping in the center of the beam, and a structure having the same.

To solve the above problems, the steel beam and the structure having the same of the present invention have the following features.

[1] A steel beam having a web and flanges connected to the top and bottom of the web, in which an expanded beam depth portion is provided at both ends of the steel beam in the material axis direction, the beam depth being expanded compared to the central portion in the material axis direction, and the web of the expanded beam depth portion has at least one opening.

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

[3] A steel beam according to [1] or [2], in which the beam depth of the beam depth expansion portion is gradually expanded from the center toward the tip in the material axis direction.

[4] A steel beam according to any one of [1] to [3], in which the openings are formed in a circular shape, and the cross-sectional area of the web in the axial 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 axial direction and perpendicular direction at the center.

[5] A steel beam according to any one of [1] to [4], in which 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] A steel beam according to any one of [1] to [5], in which the opening is circular and the center of the opening is located at the center of the height of the beam depth of the beam depth expansion section.

[7] A steel beam according to any one of [1] to [6], in which 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 between the stress or strain generated in the web by each of the openings.

[8] A steel beam according to [7], in which, of the multiple openings provided in each of the beam depth expansion sections, the diameter of the opening located at the tip end in the material axis direction is larger than the diameter of the opening located at the center in the material axis direction.

[9] A steel beam according to any one of [1] to [8], in which 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 [1] to [9].

According to the steel beam and structure having the same of the present invention, an opening is provided in the web of the beam depth expansion section, and the web around the opening becomes plastic, thereby mitigating the concentration of stress (strain) that occurs in the flange and web at the position where the cross section of the steel beam begins to change. As a result, the deformation performance of the steel beam can be improved.

In addition, in the steel beams and structures having the same of the present invention, the beam depth at the center of the beam is smaller than the beam depth of the expanded beam depth at both ends in the material axial direction, so space can be secured under the beam at the center of the beam for equipment piping. In other words, when passing equipment piping so that it crosses the center of the steel beam, there is no need to make a through hole in the web at the center of the beam, and the labor required for opening and reinforcing the through hole can be saved.

Furthermore, in the steel beams and structures having the same of the present invention, the openings provided in the beam depth expansions at both ends in the material axial direction to relieve stress (strain) concentration can also be used as through holes for equipment piping. Because these openings are provided in the beam depth expansions at both ends in the material axial direction of the steel beam, they are more convenient for efficiently installing equipment piping than providing a through hole in the center of the steel beam. And because there is no need to reinforce the area around the openings provided in the beam depth expansions, no man-hours are required for reinforcement processing.

In addition, in the steel beams and structures having the same of the present invention, the full plastic strength of the steel beams 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 magnitude of the gradient of the vertical haunch, making it possible to give the entire structure a rational structure.

FIG. 1(a) is a side view of a column-beam joint between a steel beam and a steel pipe column according to 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). 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. FIG. 3 is a diagram showing stress (strain) concentration locations occurring in an example of a steel beam according to an embodiment of the present invention. 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. 5(a) and 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. FIG. 6 is a side view of a column-beam structure having two steel beams with different beam depths and a steel pipe column. FIG. 7 is a side view of a column-beam structure including a steel beam having a vertical haunch (beam depth expansion portion) and a steel pipe column. 8(a) and 8(b) are diagrams for explaining a plastic region that occurs in a steel beam having a uniform cross section. 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). 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).

Below, we will explain in detail the embodiments of the steel beam of the present invention and the structure having the same with reference to the drawings.

Figure 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. Figures 1(b) to 1(e) show the b-b cross-sectional view, c-c cross-sectional view, d-d cross-sectional view, and e-e cross-sectional view of the steel beam 1 shown in Figure 1(a), respectively.

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. At both ends of the steel beam 1 in the material axis direction (only one of the ends is shown in FIG. 1(a)), there is a beam depth expansion section 1a in which the beam depth is expanded compared to the center in the material axis direction. The beam depth of the beam depth expansion section 1a is gradually expanded from the center in the material axis direction of the steel beam 1 toward the tip in the material axis direction.

The steel beam 1 may be assembled by welding steel plates, or the central part of the steel beam 1 in the axial direction may be made of H-shaped steel manufactured by rolling, and only both ends in the axial direction may be assembled by welding steel plates, and the two may be joined in the axial direction.

As shown in Figures 1(a) and 1(c), a circular opening 11a is provided in the web 11 of the beam depth expansion section 1a.

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. In addition, in order to increase the degree of freedom in designing the equipment piping and to enable changes in the placement 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 larger.

In addition, in this embodiment, the thickness of the web 11 of the beam thickness 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 less than the beam thickness expansion amount ΔH of the beam thickness expansion portion 1a at the center 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 perpendicular direction at the center position of each opening 11a is equal to or greater than the cross-sectional area of the web 11 in the material axis direction and perpendicular direction at the center portion in the material axis direction. This is preferable because it is less likely that the cross-sectional performance of the steel beam 1 will be reduced by providing the opening 11a.

In addition, the same effect can be obtained by using a different method in which the cross-sectional area of the web 11 in the axial direction and perpendicular direction at the center of each opening 11a is equal to or greater than the cross-sectional area of the web 11 in the axial direction and perpendicular direction at the center of the axial direction. For example, a method is possible in which the thickness of the web 11 in the beam depth expansion portion 1a of the steel beam 1 is made greater than the thickness of the web 11 in other parts (center of the axial direction). For example, the above method can be used to obtain the same effect even when the opening diameter Φ is not set to the beam depth expansion amount ΔH at the center of each opening 11a in order to pass a relatively large diameter equipment piping through the opening 11a.

Furthermore, in this embodiment, the opening 11a is positioned so that the periphery of the opening 11a is separated from the flanges 12, 13 by at least 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.

In addition, in this embodiment, the center of the opening 11a provided in the beam depth expansion portion 1a is positioned at the center of the beam depth of the beam depth expansion portion 1a. This is preferable because it makes it less likely that the stress transmitted in the material axis direction of the steel beam 1 will be biased to either the upper or lower side of the opening 11a.

The structure 10 of this embodiment is constructed by joining the above-mentioned steel beam 1 to the side of the steel pipe column 9 via a diaphragm 91.

The effect of mitigating stress (strain) concentration in the steel beam 1 of this embodiment is described below.

First, FIG. 8(a) shows a simplified mechanical model of a cantilever beam with one end fixed, in which half of the steel beam 5(6) with a uniform cross section shown in FIG. 5(a), FIG. 5(b), and FIG. 6 is axially supported. In addition, 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 full plastic strength Mp at each position in the axial direction of the steel beam 5(6) is also shown. 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 in the axial direction of the steel beam 5(6)).

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). On the other hand, the total plastic strength Mp of each position in the axial direction of the steel beam 5 (6) is the value obtained by multiplying the plastic section modulus Zp determined by the cross-sectional shape of the beam 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.

Now, as 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 remaining 0 at the free end position. 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) begins to become plastic at this position. From Figure 8 (b), it can be seen that in the steel beam 5 (6) with a uniform cross section, the steel beam 5 (6) begins to become plastic at the fixed end (the joint with the steel pipe column 9).

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 with the vertical haunch (beam depth expansion portion) 7a shown in FIG. 7 is similarly simplified. In addition, the dotted line and solid line in the graph of FIG. 9(b) show the bending moment M acting at 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 at each position in the axial direction of the steel beam 7. As shown in FIG. 9(b), in the steel beam 7 with the vertical haunch 7a, the full plastic strength Mp of the vertical haunch 7a is greater than when the vertical haunch 7a is not provided.

When the concentrated load acting on the free end of the mechanical model shown in Figure 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 plastic deformation of the steel beam 7 begins at this position. From Figure 9(b), it can be seen that 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 begins to change (the boundary position between the vertical haunch 7a and other parts).

In this way, in a 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 contains 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 desirable to alleviate such stress (strain) concentration.

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 begins to change (the boundary between the vertical haunch 7a and other parts). It can be seen that at the time when this plastic deformation begins, there is still some strength left at the end of the steel beam 7 in the axial direction. However, as shown by the shaded area in Figure 10, stress (strain) concentration occurs at the position where the cross-section of the steel beam 7 begins to change, that is, the boundary between the vertical haunch 7a and other parts.

Figure 2(a) shows a simplified mechanical model of a cantilever beam with one end fixed support for half of the steel beam 1 in the axial direction of this embodiment. When a concentrated load is applied to the free end of the mechanical model shown in Figure 2(a), the bending moment M acting at each position in the axial direction of the steel beam 1 and the full plastic strength Mp at each position in the axial direction of this steel beam 1 are shown by dotted and solid lines, respectively, in the graph in Figure 2(b).

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 at some position in the material axis direction, the full plastic strength Mp is reached, and plasticization of the steel beam 1 begins 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 begins first at the web 11 around the opening 11a in the beam depth expansion 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, following the web 11 around the opening 11a, plasticization also begins at the position where the change in the cross section of the steel beam 1 begins, that is, the boundary position between the beam depth expansion portion 1a and the other parts (at the time of "large acting moment" in FIG. 2(b)). That is, as shown by the shaded area in FIG. 3, the areas where plasticity occurs in the steel beam 1 are distributed between the web 11 around the periphery of the opening 11a in the beam depth expansion 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 expansion portion 1a and other parts). And, 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 expansion portion 1a and other parts) is mitigated more than when the opening 11a is not provided (see FIG. 10).

In addition, 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 cross-section of the steel beam 1 begins to change (the boundary position between the beam depth expansion portion 1a and other parts), followed by plasticization of the web 11 around the edge of the opening 11a. In this way, with the steel beam 1 of the present invention, it is possible to alleviate stress (strain) concentration in various ways at the axial end welded to the steel pipe column 9 and at the position where the cross-section of the steel beam 1 begins to change.

In addition, the opening 11a in the beam depth expansion section 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, improving the freedom of equipment planning.

Figure 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. The structure 20 of this embodiment is constructed by joining the steel beam 2 to the side of the steel pipe column 9 via a diaphragm 91.

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 expansion portion 2a. The spacing between the plurality of openings 21a, 21b is 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. In this way, the number of openings 21a, 21b provided in one beam depth expansion portion 2a is not limited to one. In other words, multiple openings 21a, 21b may be provided in one beam depth expansion section 2a, as long as they are spaced apart so that the stress or strain generated in the web 21 by each of the openings 21a, 21b does not interfere with each other.

In addition, of the multiple openings 21a, 21b provided in each beam depth expansion section 1a, the diameter of the opening 21a located at the tip side in the material axis direction (the steel pipe column 9 side) 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, doing so as described above is preferable because it effectively mitigates stress (strain) concentration at the beam end and effectively suppresses fracture at the welded part of the steel beam 2 to the steel pipe column 9.

Furthermore, as shown in FIG. 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 using a hanging bracket (not shown) or the like.

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 beams of the present invention are 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 also be applied to steel beams with a C-shaped cross section or a rectangular cross section.

Reference Signs List 1, 2 Steel beam 1a, 2a Beam depth expansion section 9 Steel pipe column 91 Diaphragm 10, 20 Structure 11, 21 Web 12, 22 Upper flange (flange)
13, 23 Lower flange (flange)
11a, 21a, 21b Opening Φ Opening diameter ΔH Beam depth expansion amount P Equipment piping

Claims (10)

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 . The steel beam of claim 1, having an H-shaped cross section formed by the web and the flange. A steel beam according to claim 1 or 2, in which the beam depth of the beam depth expansion section is gradually expanded from the center toward the tip in the material axis direction. A steel beam according to any one of claims 1 to 3, in which the openings are formed in a circular shape, and the cross-sectional area of the web in the axial direction and perpendicular direction at the center position of each opening is equal to or greater than the cross-sectional area of the web in the axial direction and perpendicular direction at the center. 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 from the flange by a distance equal to or greater than the diameter of the opening. A 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 located at the center of the height of the beam depth of the beam depth expansion section. A steel beam according to any one of claims 1 to 6, in which 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 a state in which the stress or strain generated in the web by each of the openings interferes with each other and the resultant stress or strain is greater than the stress or strain generated in the web when there is only one opening. The steel beam according to claim 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 center side in the material axis direction. A steel beam according to any one of claims 1 to 8, in which the opening has a shape that can be used as a through hole for equipment piping. A structure having a steel beam according to any one of claims 1 to 9.

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