JPH04149345A - Double steel pipe type structure member for truss - Google Patents

Abstract

PURPOSE:To restrain the elastic and plastic buckling so as to allow an axial plastic deformation to increase, and to stabilize the same by inserting a bend- resistant steel pipe in a steel pipe structure member in a free condition with respect to the latter. CONSTITUTION:A bend-resistant steel pipe 3 is inserted in a steel pipe structure member 2 in a free condition with respect to the latter so as to prevent axial compression forces P, P acting upon the steel pipe structure 2, from being transmitted to the pipe 3. At this time, the steel pipe 3 is set to be close to the steel pipe structure member 2 so that the gap alpha between the bend resistant pipe 3 and the steel pipe structure 2 is set as small as possible. When the axial compression forces P, P act upon the steel pipe structure member 2 so that the steel pipe structure member initiates deforming, the bend-resistant steel pipe 3 restrains the pipe structure member 2 from flexing perpendicularly to its center axis. Further, even though the steel pipe structure member 2 initiates plastically deforming, it is deformed only in the axial direction so that the deformation can be large and stable.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a double steel pipe type structural member for a truss, and more specifically, to a structure made of long steel pipes used to form a truss structure or a sill structure. The present invention relates to a double capillary type structural member that suppresses elastic-plastic buckling of the member and can increase the amount of plastic deformation in the axial direction.

[Conventional technology]

When constructing a large structure using a large number of structural members made of long steel pipes, a truss structure or a sill structure is often adopted. For example, when designing a truss structure that can withstand axial compressive force caused by dynamic external forces such as earthquakes, the ideal performance of structural members is to maintain their strength and deform sufficiently before buckling. It is true. That is, if a steel pipe buckles, its yield strength generally decreases rapidly. Therefore, structural members are designed based on a force that is less than their buckling strength, or stiffeners are installed inside steel pipes for reinforcement, but in such cases, structural members cannot withstand dynamic external forces. It becomes an elastic response.

As a result, larger design stresses must be assumed than when using plastic deformation of structural members.

In addition, in the waterway structure similar to the truss structure,
If an attempt is made to maintain a compressed insulator in the elastic region, large stresses will be generated in the insulator in the event of an earthquake, and a very large force will be applied to adjacent columns and beams, causing design problems. It is often possible. Although there is a method of designing by evaluating the strength of compressed water pipes after buckling, it is important to properly evaluate the sudden drop in strength after buckling to give the truss structure the required seismic performance. This is not easy at the current level of technology.

(Problems to be Solved by the Invention) Therefore, the present inventors have
(filed on December 28, 2009) proposed a structural member in which weakened parts that are plastically deformed by an external force smaller than the buckling strength of a steel pipe are formed at the left and right ends. In this case, the weak parts at the left and right ends are intentionally allowed to undergo plastic deformation when an axial compressive force of a predetermined value or more is applied.

Compressed materials using single pipes such as steel pipes suddenly and drastically lose their yield strength when exceeding the buckling load according to buckling theory, as shown by the solid line in Figure 13, and the amount of deformation is extremely small. On the other hand, in the structural member provided with the above-described fragile portion, the amount of axial deformation of the steel pipe can be increased in the direction shown by the broken line. However, since plastic deformation is not performed over the entire length of a long steel pipe, there is a limit to the amount of deformation of the structural member. Another problem is that a complicated and expensive mechanism must be employed at the end of the steel pipe in order to form the weakened portion.

The present invention was made in view of the above problems, and its purpose is to be able to manufacture structural members at low cost without providing fragile parts with complicated shapes, and to easily suppress lateral deflection due to buckling of long structural members. The amount of deformation in the axial direction can be extremely large, and it is possible to easily handle large deformations in only the required structural members of the truss structure. It is possible to prevent steel structures from suddenly collapsing during an earthquake and provide great earthquake resistance through plastic deformation like a rigid frame structure, and furthermore, it can overcome the buckling load of structural members that bear axial force. Another object of the present invention is to provide a double steel pipe type structural member for a truss that can withstand compressive force in the axial direction with a large yield strength.

[Means to solve the problem]

INDUSTRIAL APPLICATION This invention is applied to the steel pipe structural member used for the truss which forms a net structure. Its characteristics include, for example, referring to FIG. 1, a bending resistant steel pipe 3 which is in a free state with respect to the steel pipe structural member 2 so that the axial compressive force P acting on the steel pipe structural member 2 is not transmitted. However, steel pipe structural member 2
The bending resistance steel pipe 3 is placed close to the steel pipe structural member 2 so that the gap α facing the steel pipe structural member 2 is made as small as possible. And steel pipe structural member 2
When the compressive force P in the axial direction acts on the steel pipe structural member 2 and the steel pipe structural member 2 begins to deform, the steel pipe structural member 2
The bending resistance steel pipe 3 can suppress bending in the direction perpendicular to m (see FIG. 3).

Note that the bending resistance steel pipe 3 may be inserted into the steel pipe structural member 2, or may be inserted outside the steel pipe structure member 2 as shown in FIG.

Furthermore, as shown in FIG. 8, the total length P3 of the bending resistance steel pipe 3 is increased by a predetermined axially set deformation β that is allowed when the steel pipe structural member 2 is plastically deformed in the axial direction. Full length of 2! It may be made shorter than 2. It is only necessary that the yield strength of the steel pipe structural member 2 and the yield strength of the bending resistance steel pipe 3 be able to resist the compressive force in the axial direction after the steel pipe structural member 2 has shrunk by the axially set deformation β. .

[For production]

Even if an axial compressive force P acts on the steel pipe structural member 2, which causes buckling and deflection in a direction perpendicular to the pipe axis 2m, the restraining force due to the bending resistance steel pipe 3 does not transmit the compressive force. Thus, the bending deformation of the steel pipe structural member 2 is regulated. Therefore, even if the steel pipe structural member 2 begins to undergo plastic deformation, it deforms only in the axial direction. The amount of deformation is large and stable, and the truss structure 4 employing the double steel pipe type structural member 1
(See Figure 4), sudden collapse is avoided. Even if the steel pipe structural member 2 is plastically deformed, the buckling deformation of the steel pipe structural member 2 is induced by the bending resistance steel pipe 3 into an axially symmetrical lantern buckling 12 (see, for example, Fig. 10), and the deformation is also stabilized. Therefore, the occurrence of bending deformation buckling that would cause the steel pipe structural member 2 to buckle is prevented. In addition, whether the bending resistance steel pipe 3 is inserted into the steel pipe structural member 2 or inserted into the steel pipe structural member 2, substantially the same deformation can be performed.

The total length of the bending resistance steel pipe 3 is 3, and the total length of the steel pipe structural member 2 is the predetermined axially set deformation β that is allowed when the steel pipe structural member 2 is plastically deformed in the axial direction! If it is made shorter than 2, after the steel pipe structural member 2 has shrunk by the axially set deformation β, the axial compressive force will also reach the bending resistance steel pipe 3, and the yield strength of the steel pipe structural member 2 will eventually increase. Combined with the strength of the bending resistance steel pipe 3, the double steel pipe type structural member 1 is effectively
It is possible to increase the proof strength of the truss structure and further ensure the safety of the truss structure.

〔Effect of the invention〕

According to the present invention, the bending of the steel pipe structural member is suppressed by the restraining action of the bending resistant steel pipe, so that large axial deformation can occur with little deformation in the direction perpendicular to the pipe axis of the steel pipe structural member. Furthermore, when the deformation progresses, axially symmetrical lantern buckling can occur in the locally significantly plasticized portion. Therefore, stable plastic deformation of the steel pipe structural member can be obtained, large deformation can be sustained with little reduction in proof strength, and even if the truss structure receives a large external force, it can be prevented from immediately collapsing.

In addition, if the total length of the bending resistance steel pipe is set to a length that takes into account the amount of lantern buckling deformation of the steel pipe structural member in addition to the amount of plastic deformation in the axial direction, the deformation of the double steel pipe type structural member will be further increased. can be done.

In order to manufacture a double steel pipe type structural member having the above configuration, it is sufficient to insert and insert a bending resistant steel pipe, and it is possible to obtain a structural member for a truss that is inexpensive and capable of large deformation.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to drawings of embodiments thereof.

FIG. 1 is a sectional view of a double steel pipe type structural member 1 forming a steel structure to which the present invention is applied. A bending resistant steel pipe 3 is placed in a free state relative to the steel pipe structural member 2 so that the axial compressive force P acting thereon is not transmitted to the steel pipe structural member 2 constituting the double steel pipe type structural member 1. As shown in FIG. 2, it is inserted into the steel pipe structural member 2 in advance.

This bending resistant steel pipe 3 is not connected to the steel pipe structural member 2 in any way, and therefore, the bending resistant steel pipe 3 is only fitted into the steel pipe structural member 2. In this bending resistance steel pipe 3, the steel pipe structural member 2 subjected to the compressive force begins to buckle, and as shown in FIG.
It exhibits a bending resistance function that suppresses bending in a direction perpendicular to the tube axis 2 m. Therefore, the bending-resistant steel pipe 3 has a cross-sectional shape and cross-sectional size suitable for exhibiting resistance capable of resisting the bending of the steel pipe structural member 2.

Returning to FIG. 1, the gap α between the inner surface 2a of the steel pipe structural member 2 and the outer surface 3b of the bending resistance steel pipe 3 is extremely small. A bending resistant steel pipe 3 with an outer diameter of 53.6 nv is used for the member 2. In other words, each gap α is set to, for example, 0.25 mm, and therefore the inner diameter of the steel pipe structural member 2 is The difference between the outer diameter of the bending resistance steel pipe 3 and the outer diameter of the bending resistance steel pipe 3 is 0.5 mm.

The reason why the diameter difference is so small is that the bending resistance steel pipe 3 can be easily inserted into the steel pipe structural member 2. In addition, as described below,
When the steel pipe structural member 2 receives a buckling load due to the compressive force P, the steel pipe structural member 2 yields and deforms in the lateral direction as shown in Fig. 3, and the bending resistance steel pipe 3 receives an axial force. This is to allow the steel pipe structural member 2 to function as a perfect bending member without any bending, and to immediately restrain lateral displacement of the steel pipe structural member 2.

Incidentally, if a drawn copper tube is used as the bending resistance copper tube 3, it can be easily processed to obtain the required dimensions.

Note that the steel pipe structural member 2 may be rectangular as shown in FIG. 4, for example, as long as a gap α is ensured between it and the circular bending resistance copper pipe 3.

By the way, the above-mentioned bending resistance steel pipe 3 may be inserted into the steel pipe structural member 2 as shown in FIG. In this case, it goes without saying that a gap α is secured between the outer surface 2b of the steel pipe structural member 2 and the inner surface 3a of the bending resistant steel pipe 3.

Double steel pipe type structural member 1 having either of the configurations shown in Fig. 1 and Fig. 5
However, in the truss structure 4 shown in Fig. 6, it is applied to, for example, three structural members 5.5 on one side, which are represented by two solid lines, and the structural members 6, which are represented by two broken lines, and another one, which is represented by a single line. It does not necessarily have to be applicable to the structural members 7 and 8 that have been used. That is, when an external force due to an earthquake or the like acts on the truss structure 4, the stress in the structural members 5.5 becomes extremely large, and it is sufficient to deal with the stress only in at least the required structural members.

Incidentally, the bending resistance steel pipe 3 does not need to be inserted over the entire length of the steel pipe structural member 2, and as shown in FIG. The resistance steel pipe 3 may be interposed. In this case, in order to hold the bending resistant steel pipe 3 at a desired position, any one point 9 of the bending resistant steel pipe 3 may be welded to the steel pipe structural member 2 in advance. If the connection is made at the - point, the axial compressive force P acting on the steel pipe structural member 2 will not be applied to the bending resistance steel pipe 3 in the axial direction.

By the way, when the steel pipe structural member 2 is provided with an end member 11 having an end screw mechanism 10 as shown in FIG. 8, and the steel pipe structural members 2 are connected to each other using screws (not shown), After the bending resistant steel pipe 3 is inserted into the steel pipe structural member 2, the end member 11.11 may be attached to the tip of the steel pipe structural member 2 by welding.

When the truss structure 4 employing the double steel tube type structural member 1 configured as described above is subjected to an external force such as an earthquake, an axial compressive force is applied to the double steel tube type structural member 11 shown in the two solid lines shown in FIG. When P acts, each steel pipe structural member 2 begins to buckle and bends in a direction perpendicular to its pipe axis 2m, as shown in FIG. Since the bending resistance steel pipe 3 is in a free state with respect to the steel pipe structural member 2, it exerts resistance in the lateral direction, and the bending of the steel pipe structural member 2 is suppressed.

If the structural member is, for example, a simple single pipe, the point at which it begins to buckle under compression is the delicate point where the single pipe will yield or not. Therefore, if the lateral deformation and axial deformation at that time are borne by a single pipe,
Its ability to withstand deformation becomes smaller. However, as described above, if the axial deformation is borne by the steel pipe structural member 2 and the bending deformation is borne by the bending resistance steel pipe 3, and the respective loads are separated, lateral deformation, that is, bending can be suppressed. However, the deformation in the axial direction can be increased.

In order to construct such a double steel pipe type structural member 1, it is sufficient to simply fit the bending resistance steel pipe 3 into the steel pipe structural member 2, and the production of the double steel pipe type structural member 1 becomes extremely easy. Furthermore, the bending resistance steel pipe 3 only needs to be interposed in the necessary portions, and an increase in the amount of flanged pipes used is also suppressed.

Here, the outer diameter of the steel pipe structural member 2 is 60.5m+n, the wall thickness is 3.211II11, and the cross-sectional area A2 is 5.76C111.
”, buckling stress σ.

3. Ot/cm", and the moment of inertia I2 is 23.
7cm+', section modulus 22 is 7.84cm', length 1
2 is 2030 mm, calculate the cross-sectional area of the bending resistance steel pipe 3 to prevent buckling even if the steel pipe structural member 2 yields. The steel pipe structural member 2 is a fairly elongated structural member with a slenderness ratio of 100,
It shall be elastically buckled.

The yield axial force Py of the steel pipe structural member 2 is σyX Az=5.76X3.0=17.3, and the buckling strength p cr of the steel pipe structural member 2 is fcxA2×ν=0.954X5.76X1.9=10. 4 twhere rc is the degree of buckling stress and ν is the buckling safety factor.

Furthermore, if the steel pipe structural member 2 is allowed to bend by 5 mm, then from the balance of forces shown in Fig. 9,
Lateral force PL is 2XP, Xtanθ=2 x17.3x
o, 5/101.5 = 0.17t.

In short, if a lateral restraining force of about 0.171 tons, that is, a reaction force of 0.17 tons from the bending resistance steel pipe 3 when the steel pipe structural member 2 is deformed by 5 mm, this double steel pipe structural member 1 will continue to deform without buckling.

Next, with reference to FIGS. 3 and 9, the bending resistance steel pipe 3
Find the required moment of inertia I3. In addition,
The relationship between the amount of deformation δ and the moment of inertia lz is δ-PL×12”/48E
I3, that is, I3 is 28.2 cm'. From this calculation result, the moment of inertia lz of the bending resistance steel pipe 3
It can be seen that approximately 20% increase from 23.7 crn' of the steel pipe structural member 2 is enough.

Also, yield stress σ = 3. Assuming Ot/cn+2,
Necessary section modulus Z for the bending resistance steel pipe 3 to be in the elastic region
, is 3.0 = 0. from the relationship σ, −M/Z.
17X203 / (Z, X 4 ), that is, Z, = 2
．． It becomes 37cm3. It can be seen that the section modulus 73 of the bending resistance steel pipe 3 in this case may be smaller than the section modulus 22 of the steel pipe structural member 3.

From the above considerations, the bending resistant steel pipe 3 does not need to be dimensionally larger than the steel pipe structural member 2, and can be sufficiently used as the bending resistant steel pipe of the double steel pipe type structural member 1.

Normally, the steel pipe structural member 2 of the double steel pipe type structural member 1 undergoes lantern buckling 12 as shown in FIG. 10 or FIG. 11 after its hoof-shaped cross section and reaches its maximum yield strength.
A large amount of deformation is obtained immediately after yielding until the lantern buckles 12. In this case, it is possible for the steel pipe structural member 2 to shrink by about 1% of the total length (approximately 20 mm for a steel pipe structural member having the above dimensions) just before the lantern buckles. The bending resistance steel pipe 3 described above always guides the direction in which lantern buckling of the steel pipe structural member 2 occurs outward or inward in an axially symmetrical manner, and its deformation becomes extremely stable. Therefore, the bending deformation 13 as shown in FIG. 12 does not occur and the bending condition does not occur, and the yield strength does not suddenly decrease. Due to such stable deformation, the truss structure is also greatly deformed, but it does not collapse immediately, and it is possible to secure time to notice the large deformation and evacuate from the structure.

By the way, as shown in Fig. 8, the total length of the bending resistance steel pipe 3! 3 is a predetermined axially set deformation β (=β/
2+β/2) shorter than the total length 12 of the steel pipe structural member 2. In this way, after the steel pipe structural member 2 is deformed by the axially set deformation β, the double steel pipe structural member 1
The compressive force in the axial direction acting on the steel pipe can be counteracted by the combined force of the proof stress of the steel pipe structural member 2 and the proof stress of the bending resistant steel pipe 3.

In other words, if the steel pipe structural member 2 yields in cross section while the bending resistant steel pipe 3 is preventing the steel pipe structural member 2 from bending, it will be restrained by the bending resistant steel pipe 3 as shown in FIGS. 10 and 11. The steel pipe structural member 2 reaches its maximum strength while causing the axially symmetrical lantern buckling 12. If the steel pipe structural member 2 deforms by the axially set deformation β exceeding its maximum proof stress, the subsequent compressive force will also reach the bending resistance steel pipe 3, and the proof stress of the steel pipe structural member 2 and the proof stress of the bending resistance steel pipe 3 will increase. It is countered with. As a result, the effect of substantially increasing the yield strength of the double steel tube type structural member 1 is exhibited, and the safety of the truss structure is further ensured.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a double steel pipe type structural member in a horizontally arranged state when a bending resistance steel pipe is inserted into the steel pipe structural member;
Figure 2 is a cross-sectional view of Figure 1, Figure 3 is a cross-sectional view of a double steel pipe type structural member in an elastic buckling state, and Figure 4 is a double steel pipe type structure in which steel pipe structural members of different shapes are adopted. A cross-sectional view of a structural member, FIG. 5 is a longitudinal cross-sectional view of a double steel pipe type structural member when a bending resistance thin tube is extrapolated to a steel pipe structural member, and FIG. 6 is a vertical cross-sectional view of a double steel pipe type structural member partially An overall schematic diagram of the adopted truss structure, Figure 7 is an enlarged view of the main part of Figure 6, and Figure 8 is a double steel pipe type structural member in which a bending resistance steel pipe is inserted into a steel pipe structural member having an end member. 9 is a schematic diagram of a steel pipe structural member for calculating the lateral force that opposes lateral deflection in a buckled state. Figures 10 and 11 are two diagrams schematically showing lantern buckling. A partial cross-sectional view of a heavy steel pipe type structural member,
FIG. 12 is a schematic diagram of a structural member that has undergone bending deformation, and FIG. 13 is a graph showing the amount of axial deformation of a single pipe with respect to the buckling load. 1-Double steel pipe structural member, 2-・-Steel pipe structural member, 2m
- one pipe axis, 3 - bending resistance steel pipe, P - axial compressive force, α - clearance, β - axial direction set deformation length. Patent applicant Kawatetsu Kenzai Kogyo Co., Ltd. Agent Patent attorney Katsutoshi Yoshimura (and one other person) Figure 10 Figure 11

Claims (4)

[Claims] (1) In a steel pipe structural member used in a truss forming a steel structure, a bending resistant steel pipe is placed in a free state with respect to the steel pipe structural member so that the axial compressive force acting on the steel pipe structural member is not transmitted. , the bending resistance steel pipe is fitted into the steel pipe structural member, and the bending resistance steel pipe is disposed close to the steel pipe structural member so that the gap facing the steel pipe structural member is as small as possible; When the steel pipe structural member begins to deform due to compressive force in the direction, the bending resistant steel pipe can suppress the bending of the steel pipe structural member in a direction perpendicular to the pipe axis. A double steel pipe type structural member for truss, which is characterized by: (2) The double steel pipe structural member for a truss according to claim 1, wherein the bending resistance steel pipe is inserted into the steel pipe structural member. (3) The double steel pipe structural member for a truss according to claim 1, wherein the bending resistance steel pipe is extrapolated onto the steel pipe structural member. (4) The total length of the bending resistance steel pipe is made shorter than the total length of the steel pipe structural member by a predetermined axially set deformation length that is allowed when the steel pipe structural member undergoes plastic deformation in the axial direction, and the steel pipe structural member After shrinking by the set deformation length in the axial direction, the compressive force in the axial direction can be counteracted by the proof stress of the steel pipe structural member and the proof stress of the bending resistant steel pipe. The double steel pipe type structural member for a truss according to claim 2 or 3.