JP4537621B2 - Steel tube column base and method for strengthening steel tube column base - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel pipe column base for fixing a steel pipe column such as a road lighting pole or a road sign pole to a housing such as a road and a method for strengthening the steel pipe column base.
[0002]
[Prior art]
As a steel pipe column base for fixing a steel pipe column such as a road lighting pole or a road sign pole to a frame made of concrete or the like, a base plate 11 is welded to the lower end of the steel pipe column 10 as shown in FIG. A structure in which the space between the steel pipe column 10 and the base plate 11 is reinforced by a plurality of ribs 12 is common. Each rib 12 is a flat triangular rib whose upper end is inclined, and each rib 12 is T-welded to the steel pipe column 10. And the steel pipe column 10 is supported vertically by fixing the base plate 11 to the housing using the anchor bolts 13.
[0003]
However, in the conventional steel pipe column base as described above, when a bending moment is applied to the steel pipe column 10 due to wind or traffic vibration, a large stress concentration occurs in the vicinity of the weld toe, which is the upper end portion 14 of the rib 12. Further, there is a possibility that the strength of this portion is lowered due to repeated stress. Further, there is a problem in that the turning welded portion of the upper end portion 14 of the rib 12 is likely to be a structural defect due to the overlap between the tensile residual stress due to the welding heat and the deterioration of the heat-affected member material, and the proof stress and fatigue characteristics are lowered.
[0004]
Such a problem is common to structures in which reinforcing ribs are T-welded to structural members, and gusset is fillet welded by the Japan Steel Structure Association's “Fatigue Design Guidelines for Steel Structures”. It has been pointed out that the designed joints give consideration to the design, because the joints reduce the yield strength and fatigue properties of steel members.
[0005]
The present invention solves the above-described conventional problems, and even when a bending moment is repeatedly applied to a steel pipe column, it is possible to suppress a decrease in strength of the weld toe portion of the rib, and to turn weld the upper end portion of the rib. It is made in order to provide the reinforcement method of the steel pipe column base and the steel pipe column base which can prevent the yield strength of a part and the fall of fatigue performance.
[0006]
[Means for Solving the Problems]
The steel pipe column base of the present invention made to solve the above problems is a steel tube column base reinforced by a T-welded rib at the base of the steel tube column, and the rib is the reverse of the bent upper end portion. It is a U-shaped or inverted V-shaped rib, and a bar-shaped tool is vibrated in the axial direction by ultrasonic waves at the weld toe end of the rib, and the surface is recessed by applying the tip to the metal surface to be processed. It is characterized by being subjected to peening treatment by ultrasonic vibration. Also, the steel pipe column base strengthening method of the present invention is such that a reverse U-shaped or reverse V-shaped rib whose upper end is bent is welded to the base of the steel tube column, and then the weld toe of each rib is super welded. The bar-shaped tool is vibrated in the axial direction by sound waves, and a peening process is performed by ultrasonic vibration that dents the surface by applying the tip to a metal surface to be treated.
[0007]
In addition, the reinforcing effect can be further enhanced by performing a peening process by ultrasonic vibration in a state where a load that causes a tensile stress in the axial direction of the steel pipe acts on the base material of the processing section is applied to the base of the steel pipe column. . Preferred conditions for the peening treatment by ultrasonic vibration are an amplitude of 20 to 50 μm and a frequency of 10 to 50 kHz.
[0008]
As described above, in the present invention, by using an inverted U-shaped or inverted V-shaped rib having a bent upper end serving as a weld toe, the upper end of the rib is perpendicular to the main stress direction of the steel pipe column. The rigidity of the upper end of the rib is reduced. As a result, when a bending stress is applied to the steel pipe column, the stress concentration generated at the weld toe is remarkably relieved, and the tensile residual stress due to welding heat can be remarkably relieved.
[0009]
Furthermore, in this invention, the peening process by the ultrasonic vibration was performed to the weld toe part of the rib. This treatment is a method in which a bar-shaped tool is vibrated in the axial direction by ultrasonic waves, and the tip is applied to a metal surface to be treated to dent the surface. As a result, high-density energy is applied to the weld toe portion, plastic deformation occurs, and compressive residual stress is applied. For this reason, the weld toe which was a weak point of the steel pipe column base is further strengthened, and even when a bending moment is repeatedly applied to the steel pipe column, it is possible to suppress a decrease in strength of the weld toe of the rib and It is possible to prevent a decrease in yield strength and fatigue performance of the rotating welded portion of the upper end portion of the steel plate.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention are shown below.
In FIG. 1, 10 is a steel pipe column used as a road lighting pole or a road sign pole, 11 is a base plate welded to the lower end of the steel pipe column 10, and 12 is a reinforcement between the steel pipe column 10 and the base plate 11. In order to do this, it is a plurality of ribs which are T-welded. In this embodiment, the rib 12 has an inverted U-shape, but may be an inverted V-shaped rib 12 as in another embodiment shown in FIG. The base plate 11 is fixed to a frame such as a road by anchor bolts 13 and holds the steel pipe column 10 vertically.
[0011]
The main stress direction of the steel pipe column 10 is the vertical direction, and the ribs 12 also extend in the main stress direction of the steel pipe column 10 as a whole. However, the upper portion of the rib 12 is gently bent in an arc shape, and the upper end portion 14 of the rib 12 serving as the weld toe portion is bent until it is perpendicular to the main stress direction of the steel pipe column 10.
[0012]
Thus, the upper end portion 14 of the rib 12 can be made to have a low-rigidity structure by gently bending the upper end portion 14 of the rib 12 in a direction to escape from the main stress direction of the steel pipe column 10. As a result, the stress concentration at the upper end portion 14 of the rib 12 is alleviated, and the welding residual thermal stress of the welded portion is also remarkably reduced, so that the yield strength and fatigue performance as a welded structure are greatly improved.
[0013]
In order to sufficiently exhibit such an effect, it is preferable to set the radius of curvature of the upper end portion 14 of the rib 12 to be three times or more the thickness of the rib 12. When the radius of curvature is smaller than this, material deterioration is liable to occur when the rib 12 is bent, and the effect of lowering rigidity is also reduced.
[0014]
For reference, FIG. 3 and FIG. 4 show stress concentration diagrams obtained by FEM analysis of the steel pipe column base shown in FIG. 1 and the conventional steel pipe column base shown in FIG. In these drawings, the generated stress distribution around the rib 12 when a horizontal load equal to the upper end of the steel pipe column 10 is applied is shown by contour lines, and the unit in the figure is MPa. As apparent from a comparison between FIG. 3 and FIG. 4, it can be seen that by bending the upper end portion 14 of the rib 12, the maximum value of the concentrated stress is halved compared to the conventional structure.
[0015]
In addition, in the present invention, the weld toe portion of the bent rib 12 is further subjected to peening by ultrasonic vibration. As shown in an enlarged view in FIG. 1, the peening processing unit 20 is a region having a central angle α on both sides of the center line of the rib 12 and generally has a range of 30 ° ≦ α ≦ 60 °. . In FIG. 1, α is approximately 45 °.
[0016]
In this peening process by ultrasonic vibration, as shown in FIG. 5, the tip of the bar-shaped tool 22 of the ultrasonic impacting device 21 is applied to the metal surface to be processed and ultrasonically vibrated in the axial direction to hit the processing target part. It is a method to give the surface and dent. The tip of the rod-shaped tool 22 is generally circular in cross section, and its diameter is preferably about 1 to 6 mm. This is because if the diameter is less than 1 mm, the strength is insufficient and sufficient impact cannot be applied, and if the diameter exceeds 6 mm, the mass increases, making it difficult to perform ultrasonic vibration.
[0017]
The bar-shaped tool 22 preferably has a frequency of 10 to 50 kHz and an amplitude of 20 to 50 μm. This is because the energy of impact given to the steel material is efficiently increased in this frequency range. On the other hand, if the amplitude is less than 20 μm, a sufficient impact cannot be given. On the other hand, if the amplitude exceeds 50 μm, plastic deformation entering the steel material may become too large, which is not preferable.
[0018]
The metal surface treated under the conditions as described above is plastically deformed by high-density energy and is recessed to a depth of about 0.1 to 0.5 mm, and compressive stress is introduced from the surface layer to a depth of 10 mm or more. Can do. In addition, a large change is caused in the metal structure from the surface layer to a depth of about 100 μm, and a structure layer called a white layer is formed, and good corrosion resistance, wear resistance, and reduction in frictional resistance can be achieved.
[0019]
In the present invention, the peening processing part 20 by such ultrasonic vibration is formed at the weld toe part of each rib 12 as shown in FIGS. As a result, the stress concentration at the weld toe is alleviated, and a compressive stress is introduced into the weld toe, and the fatigue strength is dramatically improved. Further, as described above, the weld toe portion of the rib 12 is a portion that tends to become a structural defect due to the overlap of the tensile residual stress due to welding heat and the deterioration of the heat-affected material, but it causes a structural change by peening treatment by ultrasonic vibration. As a result, it is possible to repair structural defects such as fine cracks.
[0020]
Thus, the steel pipe column base portion of the method of the present invention is obtained by subjecting the weld toe end of the inverted U-shaped or inverted V-shaped rib 12 with the upper end portion 14 bent to a peening process by ultrasonic vibration. Therefore, the effects of the respective configurations are combined. As a result, the stress concentration generated near the weld toe portion of the rib 12 when a bending moment acts on the steel pipe column 10 due to wind or vibration can be relieved significantly, and is shown in the data of the examples described later. Thus, the fatigue strength of this part can be remarkably improved. Moreover, the present invention does not require ancillary equipment other than the ultrasonic hitting device 21 and has an advantage that it can be easily constructed on site.
[0021]
Normally, the peening process may be performed by applying the tip of the rod-like tool 22 of the ultrasonic striking device 21 to the weld toe end of each rib 12 welded to the base of the steel pipe column 10, but the base material of the processing section Peening treatment by ultrasonic vibration can be performed in a state where a load (for example, bending load) on which a tensile stress in the axial direction of the steel pipe acts is applied to the steel pipe column base. In this way, if a peening process is performed in a state where an external force is applied and a tensile stress is applied to apply a compressive stress to the weld toe, a larger compressive stress may remain in the weld toe 14 when the external force is removed. It becomes possible. For this reason, it becomes possible to obtain a further excellent reinforcing effect.
[0022]
In the above description, only the weld toe portion of each rib 12 has been subjected to peening treatment by ultrasonic vibration, but it goes without saying that other weld portions may be subjected to peening treatment. However, the lower portion of the rib 12 is not a portion that directly affects the fatigue strength of the steel pipe column base portion, so it is considered that there is not much profit.
[0023]
【Example】
A fatigue strength test was performed by repeatedly applying bending stress to the steel pipe column base of the present invention shown in FIG. The material used is SM490 for both steel pipe and rib. For comparison, a fatigue strength test was performed in which tensile stress was repeatedly applied to partial test pieces around the steel pipe base rib having the structure shown in FIG. As a result, as indicated by black circles in FIG. 6, the fatigue characteristics of the conventional structure shown in FIG. 7 corresponded to E grade to D grade of the design life curve of the railway bridge design specification. On the other hand, the fatigue characteristics of the product of the present invention greatly increased to the A grade of the design life curve as shown by white circles. The amplitude of the tip tool was 40 μm, and the frequency was 30 kHz.
[0024]
In addition, when peening treatment by ultrasonic vibration is applied with a tensile stress acting on the steel tube column base, its fatigue characteristics rise to A grade or higher of the design life curve as shown by white triangles. did. Note that the arrow pointing upward in FIG. 6 means that loading has ended because no change was seen in the specimen at that time. Here, the weld quality of the partial test piece of the conventional structure used in this test is very high grade, and the fatigue life should be slightly lower at the level of normal industrial products.
[0025]
【The invention's effect】
As described above, according to the present invention, by applying a peening process by ultrasonic vibration to the weld toe of the inverted U-shaped or inverted V-shaped rib whose upper end is bent, the rotation of the upper end of the rib is performed. It is possible to greatly prevent a decrease in yield strength and fatigue performance of the welded portion. As a result, even when a bending moment is repeatedly applied to the steel pipe column, there is no decrease in strength near the weld toe portion of the rib, and there is no safety problem even if it is used for a long period of time. And since this invention does not need to change the structure of a steel pipe pillar base, there exists an advantage which can be easily applied also to the existing installation.
[Brief description of the drawings]
FIG. 1 is a front view showing a first embodiment of the present invention.
FIG. 2 is a perspective view showing a second embodiment of the present invention.
FIG. 3 is a stress concentration diagram obtained by FEM analysis of a steel pipe column base portion using inverted U-shaped ribs.
FIG. 4 is a stress concentration diagram obtained by FEM analysis of a steel pipe column base portion having a conventional structure.
FIG. 5 is a side view of the ultrasonic striking device.
FIG. 6 is a SN curve showing the results of fatigue strength tests in Examples.
FIG. 7 is a perspective view showing a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Steel pipe pillar 11 Base plate 12 Rib 13 Anchor bolt 14 Upper end part 20 Peening process part 21 Ultrasonic hitting device 22 Bar-shaped tool

Claims (4)

A steel pipe column base portion in which a base portion of a steel pipe column is reinforced by a rib welded to a T-shape, wherein the rib is an inverted U-shaped or inverted V-shaped rib having a bent upper end portion, and welding of the rib is stopped. It is characterized in that a bar-shaped tool is vibrated in the axial direction by ultrasonic waves at the end , and subjected to peening treatment by ultrasonic vibration that dents the surface by applying the tip to the metal surface to be treated. Steel pipe column base. After T-welding an inverted U-shaped or inverted V-shaped rib whose upper end is bent at the base of the steel tube column, a rod-shaped tool is vibrated in the axial direction by ultrasonic waves at the weld toe of each rib. A method for strengthening a steel pipe column base, characterized by performing a peening process by ultrasonic vibration that dents a surface by applying a tip to a metal surface to be processed.   A method for strengthening a steel pipe column base, comprising performing a peening process by ultrasonic vibration in a state where a load that causes a tensile stress in the axial direction of the steel pipe acts on a base material in a processing section is applied to the base of the steel pipe column.   The steel pipe column base strengthening method according to claim 2 or 3, wherein peening treatment by ultrasonic vibration is performed under conditions of an amplitude of 20 to 50 µm and a frequency of 10 to 50 kHz.

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