WO1992009767A1

WO1992009767A1 - Structural member provided with reinforcement against local buckling

Info

Publication number: WO1992009767A1
Application number: PCT/JP1991/001650
Authority: WO
Inventors: Toshiro Suzuki
Original assignee: Toshiro Suzuki
Priority date: 1990-11-30
Filing date: 1991-11-29
Publication date: 1992-06-11

Abstract

With structural members consisting of an I-beam, round bar, square bar, slab element and the like for use in a pillar, beam, pile and the like, plate buckling of the structural member is prevented by restraining a deformation in directions other than the surfaces of the slab element by use of reinforcing members and stable plastic deformation can be obtained even after the structural member is subjected to yielding. The reinforcing member or members are attached to one side or both sides of the slab member to be restrained. The reinforcing member does not substantially share a force produced in the structural member in such a manner that loose holes and bolts are combined together to allow the surfaces in contact with each other to slide on each other, so that the plastic deformation capability of the structural member can be fully displayed. Furthermore, when the reinforcing member gives little influence to the whole strength in such a case that the sectional area of the reinforcing member is small, the reinforcing member or members can be firmly fastened to the structural member by bolts or welding. Particularly, when the structural member is formed of a high tension steel, the yield load is high and the yield strength is decreased abruptly due to occurrence of the plate buckling after the yielding so that the reinforcing construction according to the present invention can prevent the plate buckling, thereby effectively utilizing the plastic deformation capability.

Description

Specification

Structural members with local buckling stiffening

Technical field

The present invention relates to a stiffening structure for preventing local buckling of structural members (columns, beams, piles, etc.) used in buildings, civil engineering structures, and the like, in particular, for preventing buckling. Background art

For example, when the I-shape is used as a beam or the like, if plate buckling occurs at the flange portion of the material end where yielding proceeds, the proof stress of the structural member suddenly decreases, and the plastic deformation capacity of the member is designed. I can't make the most of it. The sudden decrease in proof stress due to buckling occurs not only in I-beams but also in various structural members.

There is a possibility that stiffeners or reinforcing ribs may be provided at parts receiving large bending moments to stiffen or cause buckling as a member in columns and beams that make up the framework of the structure, or piles used as foundations In such cases, it is common practice to provide a reinforcing rib or the like to increase the rigidity. In such conventional stiffening with stiffening ribs, stiffening against buckling is increased by providing stiffening ribs at required intervals and shortening the buckling length.

However, in conventional buckling stiffening, once buckling occurs due to large deformation, the strength of the structural member suddenly deteriorates, and it may not be structurally feasible. It is not based on the idea of utilizing it in a global way.

One of the objects of the present invention is to provide a buckling of a plate element by attaching a stiffening member which restrains the plate element in a plane to a portion of the structural member composed of the plate element which may cause the plate buckling. An object of the present invention is to provide a structural member capable of utilizing the plastic deformation capability of the member without deteriorating the resistance to large deformation while suppressing the deformation.

Further, another object of the present invention is to attach a stiffening member for reducing the occurrence of plate buckling to a part of the structural member with respect to a structural member having an opening, and to use the stiffening member to reduce a cross-sectional defect of the opening. An object of the present invention is to provide a structural member which is capable of effectively utilizing the plastic deformation capability of the member and has excellent heat resistance. Still another object of the present invention is to form a double pipe by covering a thin outer pipe having an inner diameter substantially the same as the outer diameter of the inner pipe as a stiffening member on the outer circumference of the inner pipe as a structural member. However, there is a need to introduce structural members that can effectively utilize the plastic deformation of the inner pipe, which is the original structural member.

Still another object of the present invention is to provide a structural member capable of preventing corrosion of the inner tube by the outer tube and cutting negative peripheral friction when used as a pile or the like, with respect to the double tube. Disclosure of the invention

The present invention provides a method for preventing structural buckling of a structural member made of a 扳 element by restraining deformation of the plate element in an out-of-plane direction by a stiffening member, and after a structural member constituting a building framework or the like has yielded. Can also be stably deformed plastically.

Restricting the deformation in the out-of-plane direction here does not necessarily mean that the deformation in both the inner and outer surfaces must be constrained.Either the protrusion to the inner surface or the protrusion to the outer surface is required. Is included. That is, if there is an effect to change the buckling mode, for example, stiffening only on one side is sufficient.

Structural members consisting of 扳 elements to be projected include I-shape, groove-shape, box cross-section members, square-shape pipes, round-shape pipes, and other plates that are used for columns, beams, girders, piles, etc. It is a member with it. Further, a concrete or the like may be filled inside a structural member composed of a plate element, such as a concrete filled pipe column, a concrete filled pipe pile, or the like.

The reinforcing member is attached to one or both sides of the plate element to be restrained, and the buckling of the structural member is planarly restrained, thereby preventing plate buckling. The stiffening member should be attached to the portion where buckling is likely to occur due to the iS force, depending on the load acting on the structural member. For example, when used as a beam, buckling stiffening only at the end of the structural member Is often sufficient. The contact surface between the stiffening member and the 扳 element is substantially changed, for example, in a form in which the stiffening member sandwiches the 扳 element, or in a form in which a combination of a loose hole and a bolt allows sliding on the contact surface. The structure does not stick, and the force generated in the structural members is not substantially shared. By attaching, the structural member can exhibit its plastic deformation ability sufficiently without causing plate buckling. However, bolts may be penetrated or partially welded to the extent that displacement is prevented.

Further, since it is sufficient to stiffen the local buckling of the structural member, the stiffening member may be small depending on the cross section of the structural member. In some cases, the plate element of the structural member is restrained by a thin stiffening member, and the plate buckling can be sufficiently prevented. In such a case, even if the stiffening member is fixed to the structural member, the overall strength is not significantly affected. Therefore, the stiffening member may be firmly fixed by boltless welding.

As described above, the structural member according to the present invention can sufficiently exert the plastic deformation capability of the member as an effect of local buckling stiffening, and therefore, by incorporating this plastic deformation capability into the design Therefore, the cross section of members can be rationalized, and weight and cost can be reduced.

Further, when the structural member is {tensile} or the like, the yield load is large, the stress in the cross section at that time is high, and the buckling occurs after yielding, and the proof stress rapidly decreases. Is particularly effective.

As the stiffening member, shapes or the like corresponding to the cross section of the structural member to be stiffened are used alone or in combination, and reinforcing ribs or the like for increasing the rigidity of the stiffening member as necessary. It is attached. The material of the stiffening member is not particularly limited as long as it has a strength required to restrain the out-of-plane deformation of the plate element of the target structural member.

In addition, openings may be formed in the pipes of I-shaped beams for the purpose of passing equipment piping. Although the conventional method is to reinforce the web around the opening due to the loss of the cross section due to the web opening, the present invention rather restricts the deformation of the flange near the opening so that the beam is a structural member Is maintained. In this case, as a method of attaching the stiffening member, in addition to loosely fixing with a port etc., it is conceivable that the stiffening member is firmly fixed with bolts or welding and a force bar is used to reduce the amount of power resistance due to the opening.

Further, in the present invention, a stiffening member is provided for a portion where plate buckling may occur. Attaching does not mean that the stiffening member must be attached to all the parts that may cause buckling, but depending on the application and cross-sectional conditions of the structural member, a part of the structural member may be localized. Buckling deformation may be allowed. For example, in I-shaped beams, the bending strength due to local buckling of the compression flange is not abruptly reduced as compared with columns, and the majority of the web, that is, about 0.5 h on J¾ (h is the web), as an example. By stiffening the portion of about 7 to 0.8 h, the deterioration of the proof stress of the compression flange can be compensated for by the sound rib and the tension flange.

In the case of a stiffening structure in which a structural member such as a rectangular pipe or a round pipe is used as a column or a pile, there is conventionally known a case in which buckling and stiffening are performed from the inside by filling the inside with concrete. Have been. However, as is clear from the experimental results described later, the restraining effect of the stiffening member sealed in the tubular member in the case of internal restraint is extremely small. On the other hand, when the outer periphery is constrained, it can be provided by the tension of the thin-walled pipe, and the restraining effect prevents local buckling of the pipe member and sufficiently designs the plastic deformation capability of the pipe member. You can make use of it.

In the stiffening structure described above, the width of the local buckling stiffening is considered to be at least one or one or three or three, depending on the length of the structural members and the stress gradient. In the case of large I-shaped crepe, which is often used for beams that are relatively long, it is about ~ 3 times the width of the flange, but about 1 to 1.5 times the width of the web. Since it is necessary, it is a guideline to use about 1 to 5 cases with respect to the flange width in mutual ffi series. In the case of H-sections mainly used for pillars, etc., and closed section members such as round pipes and rectangular pipes, the guideline is about 1 to 3 times the cross-sectional width.

In addition, the buckling stiffening of the tube member as a structural member is further developed, and the outer periphery of the inner tube as a structural member is made of a thin outer tube for local buckling stiffening. It is conceivable to construct a double pipe surrounding it. In order to make full use of the plastic deformation capacity of the inner pipe, it is necessary to make sure that the inner pipe and the outer pipe do not allow the forces in the members to flow together, for example, the inner circumference of the inner pipe and the inner circumference of the outer pipe. It is desirable to provide a slight clearance between them and to use an anti-friction material such as asphalt or grease if necessary.

This double pipe can be used for supports or piles, etc. It can be used to prevent corrosion with outer pipes and to avoid negative peripheral friction, which is a problem with piles driven into viscous ground.

In addition, at the joints between columns and beams consisting of pipe members, or at the joints between the main and sub pipes of a truss, etc., stiffen an outer pipe with a joint at the outer periphery of the structural member with other structural members By setting the member at a predetermined position, it is possible to configure a connection part for transmitting force while preventing local buckling near the joint. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a front view showing an embodiment in which the present invention is applied to an I-shaped beam, and FIG. 2 is a sectional view thereof.

FIG. 3 is a front view showing another embodiment in which the present invention is applied to an I-shaped beam, and FIG. 4 is a sectional view thereof.

FIG. 5 is a front view showing an embodiment in which the present invention is applied to an I-shaped beam having a relatively high beam, and FIG. 6 is a sectional view thereof.

FIG. 7 is a front view showing still another embodiment in which the present invention is applied to an I-shaped beam, and FIG. 8 is a sectional view thereof.

FIG. 9 is a front view showing an embodiment in which the present invention is applied to an I-shaped steel beam having an opening, and FIG. 10 is a sectional view thereof.

Fig. 11 is an ice-plane sectional view showing an embodiment in which the present invention is applied to a square mesh tubular column, Fig. 12 is a front view thereof, Fig. 13 is a vertical sectional view, and Fig. 14 is a vertical sectional view of a different embodiment. It is. FIG. 15 is a horizontal sectional view showing an embodiment in which the present invention is applied to a pipe pile, FIG. 16 is a front view thereof, and FIG. 17 is a vertical sectional view.

FIG. 18 is a perspective view showing an embodiment when the present invention is applied to a double pipe structure. FIG. 19 is a front view showing the outline of the test piece used in Experiment 1, FIG. 20 is a cross-sectional view, and FIG. 21 is a graph showing the results of the experiment. .

Fig. 22 shows the outline of the test specimen used in Experiment 2, and Fig. 23 is a graph showing the experimental results.

FIG. 24 is a graph showing the experimental results of Experiment 3. BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of the present invention will be described with reference to the drawings.

Figs. 1 and 2 show an embodiment in which the present invention is applied to an I-shaped beam. C In this embodiment, the material end where a large bending stress acts, that is, the vicinity of the beam-column joint is shown. The stiffening member 3 is attached so as to sandwich the I-shaped beam 2 from both sides.

The catch member 3 of this embodiment includes a groove 3a and a reinforcing rib 3b interposed between the flange and the rib. The flanges at both ends of the stiffening member 3 are in contact with the inner surfaces of the upper and lower flanges of the I-beam 2 as a structural member, and the ribs are in contact with the web surface of the I-beam 2. The stiffening member 3 is attached with bolts 4 penetrating the web.

Deformation of the flange of I-shaped beam 2 in the out-of-plane direction (inward of the flange) is restricted, but the groove as stiffening member 3 is not fixed to the flange of 3a, and stable plastic deformation Is possible. The port of the I-beam 2 is penetrated by the port 4, and the bolt 4 is firmly tightened so that the stiffening member 3 shares a part of the force acting on the I-beam 2. Alternatively, the stiffening member 3 may be of such a form that it does not substantially bear the force acting on the rib of the I-shaped beam 2 by merely attaching it. In any case, in the case of the present embodiment, the I-shaped beam 2 can function rationally by allowing the flange of the I-shaped beam 2 to be plastically deformed stably after yielding.

3 and 4 show another embodiment in which the present invention is applied to an I-shaped beam.

In the present embodiment, the above-mentioned embodiment applied to the flange of the I-shaped beam 2 and restrained the deformation in the out-of-plane direction from only one side. Ports 3a and 1 3b are connected by Ports 14 to restrain the deformation of the flange of I-Guo Beam 2 from both sides to ensure the picking effect. Further, in the present embodiment, the grooves 13a provided between the upper and lower flanges of the I-beam 2 do not restrict the ribs of the I-beam 2 and form a pox cross section.

FIGS. 5 and 6 show an embodiment in which the present invention is applied to a relatively high-profile I-beam.

In the case of high-profile I-shaped beams 2, the four corners between the web and the flange By merely attaching the stiffening member 23 made of such a material, the deformation of the flange of the I-shaped beam 2 in the out-of-plane direction can be restricted, and local buckling can be effectively prevented. Thereby, stable plastic deformation is possible even after the flange of the I-shape beam 2 yields, and the strength and deformability as a member of the I-shape beam 2 can be sufficiently exhibited.ゥヱ If the plate thickness is thin, it is necessary to place a stiffener 23 b between the upper and lower flanges.

The fastening of the stiffening member 23 having such a simple structure does not have to bother with a loose hole, and has little to do with the overall strength, and can be stopped by port 24 or welding.

FIGS. 7 and 8 show still another embodiment in which the present invention is applied to an I-shaped beam.

As described above, in the case of beams, the reduction of the bending strength due to local buckling of the compression flange is not abrupt compared to that of columns, and if the majority of the web 2a is stiffened, a sound tube 2a and a tension flange 2c can be obtained. Thus, the deterioration of the compression flange 2b can be compensated for. Therefore, in this embodiment, at the end of the I-shaped beam 2, stiffening members 33 having a grooved cross section are attached to both surfaces of the web 2 a, and a plurality of bolts 3 4 passed through the elongated holes 35 are used for both. By fixing them, the deformation of the middle part in the out-of-plane direction is restricted, except for both ends where the flanges 2b and 2c are attached. By allowing local buckling of the compression flange 2b and part of the tube 2a (upper end), a large plastic deformation is generated while maintaining the plastic bending moment, and the force of the plastic deformation of the structural member is positively increased. It can be used in a practical way.

9 and 10 show an embodiment in which the present invention is applied to an I-shaped beam having an opening.

The conventional method is to reinforce the web plate around the opening 5 in order to avoid the gap in the cross section due to the web opening 5, but in the present invention, rather, by restraining the deformation of the flange near the opening 5, However, the properties of the beam 2, which is a structural member, are maintained. In this case, as a method of attaching the stiffening member 43, in addition to loosely fixing with the bolts 44 or the like, it is also conceivable that the bolts 44 or the welding is properly performed so as to cover the reduction in power due to the opening.

FIGS. 11 and 12 show an embodiment in which the present invention is applied to a square steel tubular column 51. It was done.

In the present embodiment, the stiffening member 53 is attached to the upper and lower ends of the square 鑭 column 51 where a large bending force acts so as to surround the square 鐮 column 51.

The stiffening member 53 of this embodiment is obtained by connecting two members 53 a with a substantially groove-shaped cross section provided with joining pieces 53 b for port joining at both ends by means of a port 54. On the other hand, FIG. 13 shows a case where the auxiliary member 53 is partially welded to the square pipe 51, but the welded portion 55 is merely for preventing the displacement. And does not substantially fix the contact surface with the rectangular column 51. That is, the stiffening member 53 restrains the plate buckling due to the protrusion of the rectangular steel tubular column 51 subjected to the bending stress, thereby enabling stable plastic deformation at the upper and lower ends of the rectangular tubular column 51. Figure 14 shows the use of bolts 56 instead of partial welding to prevent the displacement of the stiffening member 53.One of the bolt holes provided in the catching member 53 is a vertically long hole. By setting it to 57, the stiffening member 53 does not substantially share the force generated in the square 鐧 column 51. FIG. 15 to FIG. 17 show an embodiment in which the present invention is applied to a pipe pile 61.

In this example, short piles as stiffening members 6 3, 6 4 were provided inside and outside of the steel pipe pile 61, and plate buckling was performed on the pile head of the steel pipe pile 61 on which a large bending stress acts. Is being stiffened. In this case as well, the upper end is welded to prevent displacement (welded portions 65, 66), but the stiffening members 63, 64 do not constitute the cross section of the pile when viewed functionally .

Fig. 18 shows a further development of the buckling and stiffening of the pipe member described above. The outer circumference of the inner tube 71 as a structural member is a thin outer tube 7 for the purpose of local buckling and stiffening. This shows the double pipe surrounded by 2. In order to make full use of the plastic deformation capacity of the inner pipe 71, the inner pipe 71 and the outer pipe 72 must be designed so that the forces in the members do not flow together, such as the outer surface of the inner pipe 71. It is conceivable to provide a slight clearance between the outer pipe 72 and the inner peripheral surface of the outer pipe 72, and to use a friction material such as asphalt or darrys as necessary. This double tube can be used for pillars or piles, etc. For example, use a thin stainless steel pipe for the outer pipe to prevent corrosion, or use a pile that is cast on viscous ground, etc. Can be used to avoid peripheral friction.

Hereinafter, an experiment on a structural member subjected to local buckling stiffening according to the present invention will be described.

Experiment 1 (constant-axis shear bending experiment of box-shaped column)

Fig. 19 is a front view showing the outline of the test specimen used in Experiment 1, Fig. 20 is a cross-sectional view of the stiffening part, and Fig. 21 is a graph showing the experimental results.

As the test specimen, a square tube with an outer diameter of 150 mm X 15 O mm. Thickness of 6 mm and a yield point of the member of _y = 58 kg / ram ² (髙 tensile rope) was used. Experiments The Teijikuka P = 0 to the test body. 15 P _{_y} (P _y is the yield axial force) under increases the bending mode one instrument M, was determined deformation angle. In the graph of FIG. 2 1, bent vertical axis relates moment M at Zaitan plasticity bending moment M _P, it is dimensionless by plastic deformation angle e _p a horizontal axis on deformation angle ^.

In FIG. 21, the solid line indicates the case without stiffening, and the chain line indicates the case with the stiffening shown in FIGS. 19 and 20. In both cases, the yield strength decreases with deformation after yielding, but in the case of the dashed-dotted line corresponding to the present invention, the deterioration in resistance after yielding is slight, whereas in the case without the solid line stiffening, the local seat Sudden deterioration of power due to bending is observed.

Experiment 2 (Web opening beam shear bending experiment)

Figure 22 is a schematic diagram of the test specimen used in Experiment 2, and Figure 23 is a graph showing the experimental results.

The specimens are height 400 mm, flange width 14.7 mm, tube thickness 6 mm, flange thickness 12 mm, yield point of the member ff _y = 35 kg / mm ² (mild steel)鑭 was used. In the experiment, the shear force Q acting on the specimen as a beam was increased, and the displacement S was determined. In the graph of FIG. 2 3, the vertical axis on shear force Q in yield load Q _y, the horizontal axis about the deformation δ is dimensionless in yield modified 5 _y.

In FIG. 23, the solid line shows the case where there is no opening, the dashed line shows the case where stiffening at the opening shown in FIG. 22 is performed, and the broken line shows the case where there is an opening and stiffening is not performed. In the case of the dashed line corresponding to the present invention, the force flows through the mounting bolt of the stiffening member, It compensates for the decrease in strength due to the web. Deformation performance has also been significantly improved. Experiment 3 (Short tube compression experiment on tube)

Figure 24 is a Draf showing the experimental results of Experiment 3.

As the test ft, a round tube with an outer diameter of 101.6 mrn, a pipe thickness of 4.2 strokes, and a yield point of the member ff _y = 31 kg / mm ² (soft) was used as the main material. In the figure, the chain line at one end shows a case where an outer pipe with an outer diameter of 114.3 mm and a pipe thickness of 6.0 mra is covered on the outer side of the main pipe, and the clearance is equal to 0.35 mm. The dashed line similarly shows the case where an outer tube with an outer diameter of 1U. 3 π) π) and a wall thickness of 4.5 strokes is covered, and the clearance Δ = 1.8 mra. The solid line is the case of only the main material without stiffening. The dotted line shows the case where an inner pipe with an outer diameter of 89 lram and a pipe thickness of 4.2 mm was inserted inside the round pipe of the main material, and the clearance Δ = 2.Iran. In the case of a tubular body, the primary waveform of local buckling protrudes outward, so the effect of the inner restraint is small, while the effect of the outer restraint is remarkable. Industrial applicability

INDUSTRIAL APPLICABILITY The structural member according to the present invention prevents local plate buckling and exhibits stable plastic deformation ability. Therefore, when used as a structural member such as a column, a beam, a girder, a pile, etc. Streamlining can be achieved.

In addition, when the structural member is composed of {tensile force} in which the proof strength rapidly decreases after yielding, the effect of maintaining the power resistance due to the plastic deformation dragon force is always remarkable.

By simply attaching a simple stiffening member, it is possible to sufficiently exert the plastic deformation force of the structural member body, and it is easy to apply the existing structure to the structural member.

Claims

The scope of the claims

1. For a portion of a structural member made of a plate element that may cause plate buckling, a stiffening member made of a plate element is brought into contact with one or both sides of the plate element in a plane with the plate element of the structural member Characterized in that the stiffening member restrains out-of-plane deformation of the 扳 element of the structural member by local buckling.

2. The structural member subjected to local buckling stiffening according to claim 1, wherein the structural member and the stiffening member are not substantially fixed at an abutting surface.

3. The structural member has an I-shape, and the stiffening member has a flange portion at both ends in contact with the inner surfaces of the upper and lower flanges of the I-shaped steel, and a groove in which the abutment is in contact with the rib surface of the I-shape. 3. The structural member subjected to local buckling stiffening according to claim 2, which is a member.

4. The structural member is an I-shaped member, and the stiffening members are four angle-shaped cross-sectional members abutting at four corners between the upper and lower end portions of the upper and lower flanges of the I-shaped member. Item 2. A structural member subjected to local buckling stiffening according to item 2.

5. The structural member is an I-shaped member, and a stiffening member made of a plate element is attached to the inner and outer surfaces of the upper and lower flanges of the I-shaped member so that the stiffening member is made of a plate element. 3. The structural member subjected to local buckling stiffening according to claim 2, which restrains the shape.

6. The structural member is an I-shaped member, and the stiffening member is in contact with a surface of the I-shaped rope so as to be in contact with the surface, and restrains an out-of-plane deformation of the I-shaped web. 3. The structural member according to claim 2, wherein the local buckling is stiffened.

7. The structural member provided with local buckling stiffening according to claim 6, wherein the stiffening member is provided only at an intermediate portion except for both end portions of the I-shaped web to which a flange is attached.

8. The structural member is an I-shaped member having an opening in a web, and the stiffening member is attached to a flange near the opening to restrain deformation of the flange in an out-of-plane direction. Structural member with local buckling stiffening.

9. The structural member according to claim 2, wherein the structural member is a steel pipe.

10. The structural member according to claim 1, wherein the structural member and the stiffening member are fixed at an abutting surface.

1. The structural member has an I-shape, and the stiffening member has a flange at its end abutting on inner surfaces of upper and lower flanges of the I-shape, and a web abuts on a web surface of the I-shape. 10. The structural member subjected to local buckling and stiffening according to claim 10, which is a channel-shaped cross-sectional member.

2. The structural member is an I-shaped member, and the stiffening members are four angled cross-sectional members abutting at four corners between the upper and lower flange inner surfaces of the I-shaped member and the upper and lower flanges. A structural member provided with local buckling stiffening according to claim 1 (3).

3. The structural member is an I-shaped member, and a stiffening member made of a plate element is attached to the inner and outer surfaces of the upper and lower flanges of the I-shaped forceps so as to be in contact with the surface, thereby restraining the deformation of the upper and lower flanges in the out-of-plane direction. 10. The structural member having local buckling stiffening according to claim 10, wherein:

4. The claim wherein the structural member is an I-shaped steel, and the stiffening member is attached so as to be in contact with the rib of the I-shape in a plane, and restrains the deformation of the I-shape of the I-shape in an out-of-plane direction. Item 10. A structural member subjected to local buckling stiffening according to item 10.

5. The structural member provided with local buckling stiffening according to claim 10, wherein the stiffening member is provided only at a middle portion except for a rain end portion of the I-shaped net to which a flange of the web is attached.

6. The structural member is an I-shaped member having an opening in a web, and the stiffening member is attached to a flange near the opening to restrain deformation of the flange in an out-of-plane direction. A structural member provided with the local buckling reinforcement according to 0.

7. The structural member subjected to local buckling stiffening according to claim 10, wherein the structural member is a forceps tube.

8. A thin outer pipe having an inner diameter substantially the same as the outer diameter of the inner pipe is covered as a stiffening member on the outer circumference of the inner pipe as a structural member, and the inner pipe and the outer pipe are allowed to slide in the axial direction. In this state, a structural member subjected to local buckling stiffening, characterized in that the deformation of the inner tube to the outside is restrained.