JP7230630B2 - weld joint - Google Patents

Description

The present invention relates to welded joints.

Generally, steel structures contain many welded joints. Welded joints are prone to stress concentration due to sudden changes in shape, and the introduction of tensile residual stress and deterioration of the material structure due to welding heat can also cause fatigue cracks to start when fluctuating loads are applied. be. In particular, when a load that deforms the plate-shaped member in the out-of-plane direction of the joint surface is applied to the welded joint, the amount of deformation and the generated stress are significantly larger than when the load is similarly applied in the in-plane direction. In many cases, the possibility of fatigue crack initiation also increases. For this problem, for example, as described in Patent Document 1, the surface of the weld is cut to reduce stress concentration, and as described in Patent Document 2, the tensile residual stress is removed by impact treatment, and the compressive residual stress is removed. Techniques for introducing stress have been proposed.

JP-A-5-69128 JP 2013-71140 A

However, although the techniques described in, for example, Patent Documents 1 and 2 are effective in preventing the occurrence of cracks, they increase the number of manufacturing processes for steel structures, and the locations where crack initiation points cannot be accessed from the surface (welding roots) The problem was that it could not be applied to cases such as inside a closed cross section, etc.).

SUMMARY OF THE INVENTION Accordingly, the present invention provides a new and improved welded joint capable of reducing localized stress in a welded joint subjected to an out-of-plane load on the joint surface without requiring an additional process. intended to

According to one aspect of the present invention, the joint surface has a first direction and a second direction perpendicular to each other as in-plane directions, and the first Young's modulus in the first direction is the second direction in the second direction. A welded joint is provided comprising a first member having a Young's modulus of less than 2 and a second member joined to the faying surfaces and transmitting loads in an out-of-plane direction of the faying surfaces. The second member may be a member having a dimension in the first direction that is greater than a dimension in the second direction. Also, the first Young's modulus may be 10% or more smaller than the second Young's modulus.
Forming the first member from an anisotropic steel sheet that has different Young's moduli between first and second in-plane directions to reduce localized stress in directions of relatively low Young's modulus In addition, it is possible to prevent the occurrence of cracks when a load in the out-of-plane direction acts.

In the welded joint described above, the first member is a rectangular plate-like member whose displacement is constrained at both ends in the first direction and at both ends in the second direction. Of the dimension and the dimension in the second direction, the longer dimension may be at least twice the shorter dimension. More specifically, the first member may be a web of H-section members having webs and flanges and joined at longitudinal ends to other members. Alternatively, the first member may be a web of H-section members having a web and a flange where the web and flange are joined to the rib at two longitudinal locations across the weld joint. Alternatively, the first member may be one side of a polygonal steel tube having three or more sides and joined to other members at both ends in the longitudinal direction.
When the first member satisfies the above conditions, the relationship between the dimensional ratio (aspect ratio) of the plate-like member in two directions and the rate of change of Young's modulus in the anisotropic steel sheet is analyzed to determine an appropriate design. It is easy to Note that even in cases other than such cases, when the Young's modulus is different between the two directions in the plane of the joint surface, the effect of reducing the stress in the direction with the smaller Young's modulus is the same. The scope of application is not limited to welded joints satisfying the above conditions.

As described above, according to the present invention, it is possible to reduce the local stress in a welded joint on which a load acts in the out-of-plane direction of the joint surface without requiring an additional process.

FIG. 4 is a diagram for explaining the relationship between the direction of a load and potential fatigue crack initiation sites in a welded joint according to an embodiment of the present invention; FIG. 2 is a sectional view taken along line II-II of FIG. 1; FIG. 4 is a diagram showing a model of a plate-like member that receives an out-of-plane load at a joint. FIG. 4 is a diagram modeling the welded joint described in FIGS. 1 and 2 in the same manner as the example of FIG. 3 ; FIG. 10 is a diagram showing another example of a welded joint; FIG. 10 is a diagram showing another example of a welded joint; 7 is a graph showing the relationship between the stress reduction effect and the aspect ratio of the plate member based on analysis results. 7 is a graph showing the relationship between the stress reduction effect and the aspect ratio of the plate member based on analysis results. It is a graph which shows the relationship between the stress reduction effect and change rate of a Young's modulus based on an analysis result.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

FIG. 1 is a diagram for explaining the relationship between the direction of load and the location of potential fatigue crack initiation in a welded joint according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line II--II of FIG. In the example shown in FIGS. 1 and 2, the welded joint 1 extends in a direction perpendicular to the web 2W (first member) of an H-section member 2 having a web 2W and a flange 2F. It is formed between the gusset plate 4 (second member) joined to the T-section member 3 . A first direction (x-direction in the drawing) and a second direction (y-direction in the drawing) that are orthogonal to each other are defined as the in-plane directions of the surface (joint surface) where the gusset plate 4 is joined to the web 2W. .

Here, when the load P is applied in the longitudinal direction of the T-shaped cross-section member 3, the gusset plate 4 transmits the load in the out-of-plane direction of the joint surface of the web 2W. In this case, as particularly shown in FIG. 2, fatigue cracks C may occur in the web 2W due to the local stress S in the direction parallel to the plate surface of the gusset plate 4 (x direction). More generally speaking, if the member bonded to the bonding surface of the first member is a member whose dimension in the first direction (x direction) is greater than its dimension in the second direction (y direction), the dimension Fatigue cracks C can occur due to local stress S along the direction in which is relatively large (the x-direction in the example shown).

In one embodiment of the present invention, in the welded joint 1 as described above with reference to FIGS. 1 and 2, the web 2W is formed of anisotropic steel to reduce the local stress S and fatigue cracks. Prevents the generation of C. In this specification, an anisotropic steel sheet has a lower Young's modulus in a first in-plane direction than a normal steel sheet (isotropic steel sheet), and a second direction perpendicular to the first direction in the plane. A steel sheet with a higher Young's modulus than ordinary steel sheets. That is, in the anisotropic steel sheet, the first Young's modulus in the in-plane first direction is smaller than the second Young's modulus in the second in-plane direction perpendicular to the first direction.

More specifically, in the case of the examples shown in FIGS. 1 and 2, the Young's modulus in the direction (x direction) in which the dimension of the gusset plate 4 is relatively larger among the in-plane directions of the joint surfaces is By using an anisotropic steel sheet having a Young's modulus smaller than that in the orthogonal direction (y direction), the local stress S can be reduced without requiring an additional process. The reduction of the local stress S by such a method is not limited to the case where the member (second member) to be joined to the joint surface has a plate-like cross section such as the gusset plate 4, for example, a rectangular cross section, an elliptical cross section, This is possible in the case of a shape such as an elliptical cross-section, which has different dimensions in two directions in the plane of the joint surface.

FIG. 3 is a diagram showing a model of a plate member that receives an out-of-plane load at a joint. FIG. 3 shows a rectangle having a length a in the first direction (x-direction) and a length b in the y-direction (second direction), and whose displacement is constrained at both ends in the x-direction and y-direction, respectively. is shown. In the case of this plate member, the direction within the xy plane including the x direction and the y direction is the in-plane direction, and the direction perpendicular to the xy plane is the out-of-plane direction.

In the above model, when the load P acting in the out-of-plane direction of the plate-like member is constant, the deformation of the plate-like member is the bending deflection of the support length a or the support length b in each of the x and y directions. It can be thought of as a variant. In this case, the stresses σ _x and σ _y generated in the x and y directions are affected by the Young's moduli E _x and E _y in the x and y directions of the plate member. Thus, for example, if E _x <E _y , the force flowing in the direction of higher Young's modulus will result in a lower stress σ _x and a higher stress σ _y than if E _x =E _y . In this case, when the Young's modulus of the plate member changes, the amount of deformation of the plate member in the out-of-plane direction also changes.

On the other hand, in the above model, if the amount of deformation δ in the out-of-plane direction caused by the load P is constant, even if the Young's modulus of the plate-like member changes, it is considered that the magnitude of the strain ε in the plate-like member does not change. be able to. In this case, between the stresses σ _x and σ _y generated in the x and y directions and the Young's moduli E _x and E y of the plate member in the x and _y directions, σ _x =εE _x and σ _y =εE _y holds. Thus, for example, if E _x <E ₀ <E _y , the stress σ _x will be lower and the stress σ _y will be higher than if E _x =E _y =E ₀ . Here, _E0 is the Young's modulus of a normal steel plate (isotropic steel plate). In this case, as the Young's modulus of the plate member changes, the magnitude of the load P also changes.

FIG. 4 is a diagram of the welded joint described in FIGS. 1 and 2 modeled in the same manner as the example of FIG. Assuming that the longitudinal direction of the H-shaped cross-sectional member 2 is the x direction and the height direction is the y direction, the joint surface of the web 2W extends along the xy plane. That is, the direction in the xy plane including the x direction and the y direction is the in-plane direction of the bonding surface, and the direction perpendicular to the xy plane is the out-of-plane direction of the bonding surface. Assuming that the H-section member 2 is joined to other members such as pillars at both ends in the longitudinal direction, the web 2W is displaced at both ends in the x-direction to be joined to other members, similar to the model of FIG. It becomes a rectangular plate-shaped member that is restrained by the member and whose displacement at both ends in the y direction is restrained by the flanges 2F. The gusset plate 4 is joined so that the plate surface is parallel to the x direction.

_{In the} example _of FIG _. 4 above, similarly to the example of FIG. The stress σ _x in the x direction can be smaller and the stress σ _y in the y direction can be larger. Therefore, for example, when it is desired to reduce the stress σ _x in the x direction parallel to the plate surface of the gusset plate 4, the web 2W is formed of an anisotropic steel plate having a Young's modulus of E _x <E _y , so that cutting or impact treatment is performed. The stress σ _x can be reduced without requiring additional steps such as

5 and 6 are diagrams showing other examples of welded joints. In the example shown in FIG. 5, a welded joint 1A is formed between the web 2W of the H-section member 2 and the gusset plate 4 as in the example of FIG. 5, the web 2W and the flange 2F of the H-section member 2 are joined to the rib 5 at two locations in the longitudinal direction sandwiching the welded joint 1A. In this case, the web 2W is restrained by the ribs 5 against displacement at both ends in the longitudinal direction (x direction) of the H-shaped cross-section member 2, and is constrained by the flanges 2F at both ends in the height direction (y-direction) of the H-shaped cross-section member. It becomes a constrained rectangular plate-like member, and can be modeled in the same way as the example in FIG.

In the example shown in FIG. 6, a welded joint 1B is formed between one side 6S of a square steel pipe 6 having four sides and joined to other members at both ends in the longitudinal direction and the gusset plate 4. . In this case, the displacement of both ends in the longitudinal direction (x direction) of the square steel pipe 6 is constrained by other members to be joined, and the displacement of both ends in the cross-sectional direction (y direction) of the square steel pipe 6 is adjacent to the other member. , and can be modeled in the same way as the example in FIG.

Using the model described above with reference to FIG. 3, the stress reduction effect of the welded joint according to the embodiment of the present invention was analyzed. The load P was applied to the centroid of the joining surfaces of the plate members, that is, the position of (x, y)=(a/2, b/2), and the stress reference point was also the centroid. The Young's modulus of a normal steel sheet (isotropic steel sheet) is E ₀ =200 GPa, and the Young's modulus E _x and E _y in the x and y directions of an anisotropic steel sheet are E _x =E ₀ ×(1−k), respectively. , E _y =E ₀ /(1−k). where k is the rate of change in Young's modulus. In the analysis, while changing the rate of change k of Young's modulus and the aspect ratio a/b of the plate-like member, the analytical solution of the out-of-plane bending deflection of the orthotropic plate was used to convert the plate-like member into anisotropic The rate of change in the x-direction stress when formed with a steel plate was calculated.

7 and 8 are graphs showing the relationship between the stress reduction effect and the aspect ratio of the plate member based on the analysis results. As shown in the graph, when the load P is constant and the Young's modulus change rate k is the same, the larger the aspect ratio a/b, that is, the longer the plate-shaped member in the x direction, the more the x-direction stress and the amount of deformation δ is greatly reduced. As for the x-direction stress, as the aspect ratio a/b decreases, the width of reduction gradually decreases. Even if b becomes smaller than 1 and the plate-shaped member becomes longer in the y direction, it does not reach the value (1 on the vertical axis) for the isotropic steel plate. Regarding the amount of deformation δ, when the aspect ratio a/b is less than 1, the value for the anisotropic steel plate exceeds the value for the isotropic steel plate. This is because the Young's modulus in the direction of the short side of the rectangle has a greater effect on the deformation amount δ than the Young's modulus in the direction of the long side. From the above analysis results, when the load P is constant, for example, the aspect ratio a/b≧2.0 can be specified as a region with a higher stress reduction effect.

On the other hand, when the deformation amount δ is constant, the x-direction stress and the load P are reduced when the aspect ratio a/b is small, that is, when the plate-like member is long in the y-direction, when the Young's modulus change rate k is the same. Wide. Regarding the x-direction stress, the width of reduction changes greatly in the range of 0.5<a/b<2.0, but even if the aspect ratio a/b exceeds 1 and the plate-like member is elongated in the x-direction, , does not reach the value for isotropic steel (1 on the vertical axis). Regarding the load P, when the aspect ratio a/b exceeds 1, the value for the anisotropic steel plate exceeds the value for the isotropic steel plate. This is because the Young's modulus in the direction of the short sides of the rectangle has a greater effect on the load P than the Young's modulus in the direction of the long sides, as in the case where the load P is constant. From the above analysis results, when the deformation amount δ is constant, for example, the aspect ratio a/b≦0.5 can be specified as a region with a higher stress reduction effect.

In the analysis results for the case where the load P shown in FIG. 7 is constant, the area with the aspect ratio a/b≧2.0 is shown in FIG. A range of b≦0.5 was identified as a region with a higher stress reduction effect. These ranges have in common that the longer dimension of a and b is at least twice the shorter dimension. In other words, when the longer dimension of the joint surfaces a and b is at least twice the shorter dimension, if the direction in which the Young's moduli E _x and E y are smaller is selected appropriately from the x direction and the _y direction, A large stress reduction effect can be obtained by using an anisotropic steel sheet.

FIG. 9 is a graph showing the relationship between the stress reduction effect and the rate of change of Young's modulus based on the analysis results. As shown in the graph, when the aspect ratio a/b of the plate member is fixed to 10, the rate of change of Young's modulus k and the y-direction The relationship with stress becomes almost linear. Therefore, for example, from the analysis results shown in FIGS. 7 and 8, the results for an arbitrary change rate k of Young's modulus can be predicted by linear interpolation.

Here, for example, when it is desired to improve the fatigue life of a welded joint by about 20%, it is sufficient to reduce the local stress by about 6%. In this case, the change rate of the Young's modulus in the anisotropic steel sheet is adjusted so that the x-direction stress reduction rate is 6% (0.94 on the vertical axis) or more with respect to the aspect ratio a/b of the plate member. k can be determined. For example, referring to the graph in FIG. 7, the deformation amount δ is constant in the range of aspect ratio a / b ≤ 0.5, and when k = 0.05, the reduction rate of stress in the x direction is 6% That's it. At this time, the Young's modulus E _x (E ₀ ×(1−k)=0.95E ₀ ) in the x direction is given by the Young's modulus E _y (E ₀ /(1−k)≈1.05E ₀ ) in the y direction. is also about 10% smaller. If the _difference in Young's modulus is increased, the stress reduction rate is also increased, so in this example (depending on the aspect ratio a/ _b ), the stress reduction rate is 6% or more. As a more preferable range, E _x may be smaller than E _y by 20% or more, or E _x may be smaller than E _y by 30% or more.

The above analysis was performed for the case where the plate-like member is rectangular plate-like and the displacement is constrained at both ends in the x direction and the both ends in the y direction. In this case, as described above, it is easy to analyze the relationship between the aspect ratio a/b of the plate-shaped member and the rate of change k of Young's modulus to make an appropriate design. Such an example is specifically described with reference to FIG. 5, the example of a web of H-section members whose longitudinal ends are joined to other members as described above with reference to FIG. Examples include a web of H-section members to which ribs are joined, and an example of a square steel tube profile as described with reference to FIG. The square steel pipe shown in FIG. 6 is an example of a steel pipe having a polygonal cross section and having four sides. The number of sides is not particularly limited as long as it is three or more. Other than this, analysis and design by modeling as described above are possible when similar conditions are established.

Also, the scope of application of the present invention is not limited to welded joints that can be modeled as shown in FIGS. When the Young's modulus is different between the two directions in the plane of the joint surface, the stress is reduced in the direction with the smaller Young's modulus. be done. Therefore, the welded joint according to the embodiment of the present invention can be applied, for example, to the flange of an H-shaped cross-section member or the case of joining other members to the peripheral surface of a circular steel pipe by welding. In the case of a circular steel pipe, the first and second in-plane directions of the joining surfaces correspond to the longitudinal direction and circumferential direction of the steel pipe, respectively.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1, 1A, 1B... Weld joint, 2... H-shaped cross-section member, 2F... Flange, 2W... Web, 3... T-shaped cross-section member, 4... Gusset plate, 5... Rib, 6... Square steel pipe, 6S... Side.

Claims (6)

A joint surface having a first direction and a second direction perpendicular to each other as in-plane directions, wherein the first Young's modulus in the first direction is smaller than the second Young's modulus in the second direction a first member;
a second member that is joined to the joint surface and transmits a load in the out-of-plane direction of the joint surface ,
The welded joint, wherein the second member is a member whose dimension in the first direction is greater than the dimension in the second direction . 2. The welded joint of claim 1, wherein said first Young's modulus is 10% or more less than said second Young's modulus. The first member is a rectangular plate-shaped member whose displacement is constrained at both ends in the first direction and at both ends in the second direction,
The welded joint according to claim 1 or 2 , wherein the longer dimension of the plate member in the first direction and the dimension in the second direction is at least twice the shorter dimension. 4. Any one of claims 1 to 3 , wherein the first member is a web of H-section members having webs and flanges and joined to other members at both longitudinal ends. welded joints. 3. The first member is a web of H-section member having a web and a flange, wherein the web and the flange are joined to the rib at two longitudinal locations across the welded joint. Item 4. The welded joint according to any one of Item 3 . 4. The first member according to any one of claims 1 to 3, wherein the first member is one side of a polygonal steel pipe having three or more sides and joined to other members at both ends in the longitudinal direction. Welded joints as described.

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