JPH0742759B2 - Double steel pipe type structural member for truss - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a double steel pipe type structural member for a truss, and more particularly, to a long steel pipe used for forming a truss structure or a stiff structure. The present invention relates to a double steel pipe type structural member capable of suppressing the elastic-plastic buckling of the structural member and increasing the amount of plastic deformation in the axial direction.

[Conventional technology]

When a large structure is constructed by using a large number of structural members made of long steel pipes, a truss structure or a fine structure is often adopted. For example, when designing a truss structure that can withstand an axial compressive force based on a dynamic external force such as an earthquake, the ideal performance of structural members is to maintain the yield strength before buckling and to be sufficiently deformed. Is. That is, if the steel pipe buckles, its yield strength generally decreases rapidly. Therefore, structural members are designed based on the force below the buckling resistance, or stiffeners are installed in the steel pipe to reinforce, but in that case, the structural members are elastic against dynamic external force. It will be a response.
As a result, a large design stress must be assumed in comparison with the case where the plastic deformation of the structural member is used.

In addition, even in the squid structure similar to the truss structure,
If an attempt is made to hold the compression line in the elastic region, a large stress will be generated in the line in the event of an earthquake, and a very large force will be applied to the adjacent columns or beams, resulting in a design failure. Often possible. Although there is also a method of designing by evaluating the proof stress after buckling of the compression strands, it is not possible to properly evaluate the sudden decrease in proof stress after buckling and to provide the truss structure with the required seismic performance. , It is not easy at the current technical level.

[Problems to be Solved by the Invention]

Therefore, the inventor of the present invention discloses in Japanese Patent Laid-Open No. 3-199560.
We proposed a structural member in which fragile parts that are plastically deformed by an external force smaller than the buckling strength of steel pipe are formed at the left and right ends. In this case, it is intentionally permitted to plastically deform the fragile portions at the left and right ends when an axial compression force of a predetermined value or more is applied.

In the case of a compressed material using a single pipe such as a steel pipe, generally, as shown by the solid line in Fig. 11, when the buckling load according to the buckling theory is exceeded, the yield strength is rapidly lost and the amount of deformation is extremely small. on the other hand,
In the structural member provided with the fragile portion, the amount of axial deformation of the steel pipe can be increased in the direction indicated by the broken line. However, there is a limit to the amount of deformation of the structural member because it is not to plastically deform the entire length of a long steel pipe. In addition, there is a problem that a complicated and costly mechanism must be adopted at the end of the steel pipe to form the fragile portion.

The present invention has been made in view of the above problems, and an object thereof is to be able to manufacture a structural member at low cost without providing a weak portion having a complicated shape, and to easily suppress lateral bending due to buckling of a long structural member. Therefore, the amount of axial deformation can be made extremely large, and it is possible to easily deal with only the required structural members of the structural members that make up the truss structure, so that large-scale deformation can be achieved. It is possible to suppress the rapid collapse of steel structures during an earthquake and to provide great earthquake resistance due to plastic deformation such as a rigid frame structure, and to exceed 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 realizes the ability to withstand a compressive force in the axial direction with a large proof stress.

[Means for Solving the Problems]

The present invention is applied to a steel pipe structural member used for a truss forming a steel structure. The characteristic point is, for example, referring to FIG. 1, a bending resistance steel pipe 3 which is in a free state with respect to the steel pipe structural member 2 so that an axial compressive force P acting on the steel pipe structural member 2 is not transmitted. But steel pipe structural member 2
The bending resistance steel pipe 3 is inserted into the steel pipe structural member 2 so as to minimize the gap α facing the steel pipe structural member 2 as much as possible.

As shown in FIG. 7, the total length l of the bending resistance steel pipe 3
It is preferable that the length ₃ of the steel pipe structural member 2 is shorter than the total length l ₂ of the steel pipe structural member 2 by a predetermined axially set deformation length β that is allowable when the steel pipe structural member 2 is plastically deformed in the axial direction.

[Action]

Even if an axial compressive force P acts on the steel pipe structural member 2 and it begins to buckle and bends in a direction perpendicular to the pipe axis 2 m, the compressive force is not transmitted.
The bending force of the steel pipe structural member 2 is restricted by the restraining force of Therefore, the steel pipe structural member 2 is deformed only in the axial direction even when plastic deformation starts. The amount of deformation is large and stable, and in the truss structure 4 (see FIG. 5) in which the double steel pipe type structural member 1 is adopted, abrupt 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 swelled outward by the bending resistance steel pipe 3 which prevents the steel pipe structural member 2 from deforming inward. (Refer to FIG. 3), the deformation becomes stable, and the bending deformation buckling such that the steel pipe structural member 2 bends at the waist is prevented.

Bending the entire length l ₃ of the resistance steel tube 3, steel structural member 2 only axial setting deformation length β of predetermined acceptable when plastically deformed in the axial direction, Oke made shorter than the total length l ₂ of the steel pipe structural member 2 For example (see FIG. 7), after the steel pipe structural member 2 contracts by the axially set deformation length β, the axial compressive force also reaches the bending resistance steel pipe 3, and eventually the yield strength of the steel pipe structural member 2 It is possible to substantially increase the proof stress of the double steel pipe type structural member 1 by the combined force of the proof stress of the bending resistant steel pipe 3 and further secure the safety of the truss structure.

〔The invention's effect〕

According to the present invention, since the bending of the steel pipe structural member is restrained from bending by the action of restraining the bending deformation by the inserted bending resistance steel pipe, the deformation of the steel pipe structural member in the direction perpendicular to the pipe axis is small. Thus, a large axial deformation can be caused, and at the time of the deformation, a locally symmetric lantern buckling can be caused in the locally largely plasticized portion. Therefore, a stable plastic deformation of the steel pipe structural member can be obtained, a large deformation with a small decrease in yield strength can be sustained, and even if the truss structure receives a large external force, it is possible to prevent the truss structure from immediately collapsing.

In addition, if the total length of the bending resistance steel pipe is set to a length that allows for 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 made.

In order to manufacture the double steel pipe type structural member having the above-mentioned structure, it is sufficient to insert a bending resistance steel pipe, and it is possible to obtain a structural member for a truss that is inexpensive and very feasible.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings of the embodiments. 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. The steel pipe structural member 2 constituting the double steel pipe type structural member 1 includes
A bending resistance steel pipe 3 which is in a free state with respect to the steel pipe structural member 2 so as not to transmit an axial compressive force P acting thereon is preliminarily inserted in the steel pipe structural member 2 as shown in FIG. There is.

This bend-resistant steel pipe 3 is not connected to the steel pipe structural member 2 at all, so that the bend-resistant steel pipe 3 is only fitted into the steel pipe structural member 2. The bending-resistant steel pipe 3 begins to buckle when the steel pipe structural member 2 that receives a compressive force begins to move laterally, that is, as shown in FIG.
It has a bending resistance function of suppressing bending in a direction perpendicular to the tube axis 2 m. Therefore, bending resistance steel pipe 3
Has a cross-sectional shape and a cross-sectional dimension suitable for exerting 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 resistant steel pipe 3 is extremely small. For example, in the steel pipe structural member 2 having an outer diameter of 60.5 mm and a thickness of 3.2 mm. On the other hand, a bending resistance steel pipe 3 having an outer diameter of 53.6 mm is adopted. That is, for example, 0.25 mm is secured for each gap α, and therefore, the difference between the inner diameter of the steel pipe structural member 2 and the outer diameter of the bending resistant steel pipe 3 is 0.5 mm.

The reason why the diameter difference is small in this way is that the bending resistant steel pipe 3 can be easily inserted into the steel pipe structural member 2. In addition, as described later, when the steel pipe structural member 2 receives a buckling load due to the compressive force P,
When the steel pipe structural member 2 yields and is deformed in the lateral direction as shown in FIG. 3, the bending resistant steel pipe 3 functions as a complete bending restraint member without receiving an axial force, and the steel pipe structural member This is because the lateral displacement of 2 can be immediately restrained.

By the way, if a drawn steel pipe is adopted as the bending resistance steel pipe 3, the work for obtaining the required dimension is easy.
The steel pipe structural member 2 may be rectangular as shown in FIG. 4, for example, as long as a gap α is secured between the steel pipe structural member 2 and the circular bending resistance steel pipe 3.

By the way, the double steel pipe type structural member 1 of FIG. 1 is applied to, for example, the structural members 5 and 5 at three positions on one side, which are represented by two solid lines in the truss structure 4 shown in FIG. 5, and are represented by two broken lines. It is not always necessary to apply to the structural member 6 described above or the structural members 7 and 8 represented by other single lines. That is, when an external force such as an earthquake acts on the truss structure 4, the structural members 5, 5
This is because the stress in (1) becomes extremely large, and it is sufficient to deal with at least required structural members.

By the way, the bending resistance steel pipe 3 does not need to be fitted over the entire length of the steel pipe structural member 2, and as shown in FIG. 6, only one portion of the horizontal long structural member 5 which is subject to buckling resists the bending resistance. The 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 it is a single point connection,
The axial compressive force P acting on the steel pipe structural member 2 does not extend in the axial direction of the bending resistant steel pipe 3.

By the way, in the case where the steel pipe structural member 2 is provided with the end member 11 having the end screw mechanism 10 as shown in FIG. 7 and the steel pipe structural members 2, 2 are mutually connected by using a screw (not shown), After inserting the bending resistance steel pipe 3 into the steel pipe structural member 2,
The end members 11, 11 may be attached to the tip of the steel pipe structural member 2 by welding.

The truss structure 4 that adopts the double steel pipe type structural member 1 configured as described above is applied to the double steel pipe type structural members 1 and 1 shown in FIG. When the compressive force P acts, as shown in FIG. 3, each steel pipe structural member 2 begins to buckle and bends in a direction perpendicular to the pipe axis 2 m. Since the bending resistance steel pipe 3 is in a free state with respect to the steel pipe structural member 2, the bending resistance steel pipe 3 exerts lateral resistance and the bending of the steel pipe structural member 2 is suppressed.

If the structural member is, for example, a simple single pipe, there is a delicate point where the single pipe yields or not when it begins to buckle under a compressive force. Therefore, when the lateral deformation and the axial deformation at that time are applied to one single pipe,
The ability to withstand that deformation is reduced. However, as described above, when the axial deformation is applied to the steel pipe structural member 2 and the bending deformation is applied to the bending resistance steel pipe 3 to separate the respective loads, lateral deformation, that is, bending is suppressed. However, the axial deformation can be increased.

In order to configure such a double steel pipe type structural member 1, it is sufficient to simply insert 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.
Further, it is sufficient to interpose the bending resistance steel pipe 3 only in a necessary portion, and an increase in the amount of steel pipe used can be suppressed.

Here, the outer diameter of the steel pipe structural member 2 is 60.5 mm, and the wall thickness is 3.2 m.
m, sectional area A ₂ is 5.76 cm ² , buckling stress σ _y is 3.0 t / cm ² , moment of inertia I ₂ is 23.7 cm ⁴ , sectional modulus Z ₂ is 7.84 cm ³ , and length l ₂ is 2,030 mm. Then, the cross-sectional area of the bending-resistant steel pipe 3 for preventing buckling even if the steel pipe structural member 2 yields is calculated. The steel pipe structural member 2 is a considerably elongated structural member having a slenderness ratio of 100 and elastically buckles.

The yield axial force P _y of the steel pipe structural member 2 is σ _y × A ₂ = 5.76 × 3.0 = 17.3 (t) The buckling strength P _cr of the steel pipe structural member 2 is f _c × A ₂ × ν = 0.954 × 5.76 × 1.9 = 10.4 (t) where f _c is the buckling stress level and ν is the buckling safety factor.

Further, assuming that the steel pipe structural member 2 is yielded in a state where the bending is allowed to be 5 mm, the lateral force P _L is 2 × P _y × tan θ = 2 × 17.3 × 0.5 / 101.5 from the balance of forces shown in FIG. = 0.17 (t).

In short, the lateral restraining force of about 0.17 tons, that is,
If a reaction force of 0.17 tons acts from the bending resistance steel pipe 3 when the steel pipe structural member 2 is deformed by 5 mm, this double steel pipe type structural member 1
Will not buckle and will continue to deform.

Next, referring to FIG. 3 and FIG. 8, the bending resistance steel pipe 3
Find the moment of inertia of area I ₃ required by. The relationship between the deformation amount δ and the second moment of area I ₃ is δ = P _L × l ³
/ 48E is a × I _3, by substituting each ^{value, 0.5 = 0.17 × 203 3/} 48 × 2,100 × I 3 i.e., I ₃ becomes 28.2cm ^4. From this calculation result, it is understood that the second moment of area I ₃ of the bending resistant steel pipe 3 may be increased by about 20% of 23.7 cm ⁴ of the steel pipe structural member 2.

Further, assuming that the yield stress σ _y = 3.0 t / cm ² , the section modulus Z ₃ required for the bending-resistant steel pipe 3 to be in the elastic region is σ _y =
From the relationship of M / Z ₃ , 3.0 = 0.17 × 203 / (Z ₃ × 4), that is, Z ₃ = 2.87 cm ³ . It is understood that the sectional modulus Z ₃ of the bending resistant steel pipe 3 in this case may be smaller than the sectional modulus Z ₂ of the steel pipe structural member 2.

From the above consideration, the bending resistance steel pipe 3 does not have to be dimensionally larger than the steel pipe structural member 2, and is sufficiently established as the bending resistance steel pipe of the double steel pipe type structural member 1.

Normally, the steel pipe structural member 2 in the double steel pipe type structural member 1 causes axisymmetric lantern buckling 12 as shown in FIG. 9 after the cross section yielding to reach the maximum proof stress. A large amount of deformation is obtained before the buckling 12. In this case, a contraction deformation of about 1% of the total length of the steel pipe structural member 2 (about 20 mm for the steel pipe structural member having the above-described size) is possible immediately before the lantern buckling. And the above-mentioned bending resistance steel pipe 3
Means that the direction in which the lantern buckling of the steel pipe structural member 2 occurs is always guided in the outward direction in an axially symmetrical manner, and the deformation thereof becomes extremely stable. Therefore, the bending deformation 13 as shown in FIG. 10 does not occur and the waist is not bent, and the proof stress does not drop sharply. Although the truss structure is also largely deformed by such stable deformation, it does not immediately collapse, and it is possible to secure a time to notice the large deformation and evacuate to the outside of the structure.

By the way, as shown in FIG. 7, the total length l ₃ of the bending resistance steel pipe 3 is determined by a predetermined axially set deformation length β (= β / = when the steel pipe structural member 2 is plastically deformed in the axial direction. 2+
Only β / 2) is made shorter than the total length l ₂ of the steel pipe structural member 2. In this way, after the steel pipe structural member 2 is deformed by the axially set deformation length β, the axial compressive force acting on the double steel pipe type structural member 1 is changed to the proof stress of the steel pipe structural member 2 and the bending resistance steel pipe. It can be countered by the total strength with the proof strength of 3.

That is, when the steel pipe structural member 2 yields in section while preventing the bending of the steel pipe structural member 2 by the bending resistant steel pipe 3, as shown in FIG. The steel pipe structural member 2 reaches its maximum proof stress while causing the lantern buckling 12. If the steel pipe structural member 2 is deformed by the axially set deformation length β beyond its maximum proof stress, the subsequent compressive force also extends to the bending resistant steel pipe 3 and the proof stress of the steel pipe structural member 2 and the proof stress of the bending resistant steel pipe 3. Will be opposed by.
As a result, the substantial strength increasing effect of the double steel pipe type structural member 1 is exerted, and the safety of the truss structure is further ensured.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a horizontal arrangement state of a double steel pipe type structural member in which a bending resistance steel pipe is inserted in a steel pipe structural member, FIG. 2 is a transverse sectional view of FIG. 1, and FIG. 3 is an elastic buckling state. 4 is a cross-sectional view of a double steel pipe type structural member, FIG. 4 is a cross-sectional view of a double steel pipe type structural member in which steel pipe structural members of different shapes are adopted, and FIG. Fig. 6 is an overall schematic view of the truss structure adopted in Fig. 6, Fig. 6 is an enlarged view of a main part of Fig. 5, and Fig. 7 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. Fig. 8 is a schematic view of a steel pipe structural member for calculating lateral force against lateral bending in a buckling state, and Fig. 9 is a double steel pipe type that schematically shows lantern buckling. Partial sectional view of structural member, 10th
FIG. 11 is a schematic diagram of a structural member that is bent and deformed, and FIG. 11 is a graph showing the amount of axial deformation of a single pipe with respect to a buckling load. 1 ... Double Tube type structural member, 2 ... steel structural member, 3 ... bending resistance steel tube, P ... axial compressive force, alpha ... clearance, beta ... axial setting deformation length, total length of l ₂ ... steel structural members, l ₃ … The total length of the bending resistant steel pipe.

Claims (2)

[Claims] 1. A steel pipe structural member used for a truss forming a steel structure, wherein bending is in a free state with respect to the steel pipe structural member so that axial compressive force acting on the steel pipe structural member is not transmitted. A resistance steel pipe is inserted into the steel pipe structural member, and the bending resistance steel pipe is arranged close to the steel pipe structural member so that a gap facing the steel pipe structural member is as small as possible. Double steel pipe type structural member for truss. 2. The total length of the bending resistant steel pipe is shorter than the total length of the steel pipe structural member by a predetermined axially set deformation length which is allowed when the steel pipe structural member is plastically deformed in the axial direction. The double steel pipe type structural member for a truss according to claim 1.