JP2012158883A - Out-of-plane gusset for steel bridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an out-of-plane gusset for a steel bridge, which increases fatigue strength of a scallop end by a simple constitution.SOLUTION: An out-of-plane gusset 12 for a steel bridge comprises a scallop 15 that is welded in the state of rising with respect to a main plate 11 in the steel bridge and that is notched so that vertical stiffeners 13 similarly welded in the state of rising with respect to the main plate 11 can cross each other. The scallop 15 is designed in such a manner that a width b from the vertical stiffener 13, which is in a width-direction central position thereof, to a welding stop end of a scallop end 20, which is welded to the main plate 11, is a value greater than 35 mm.

Description

  The present invention relates to an out-of-plane gusset that stands up and is welded to a steel plate in a steel bridge, and more particularly, to an out-of-plane gusset having a scallop through which a vertical stiffener passes during welding.

  One of the joints used in steel bridges is out-of-plane gusset. FIG. 10 is a view showing an out-of-plane gusset provided in the steel bridge. The out-of-plane gusset 101 is welded while standing upright in the orthogonal direction to the main girder web 102, and the vertical stiffener 103 that is also upright and welded to the main girder web 102 is located at the center of the out-of-plane gusset 101. Through. Therefore, a scallop 110 for avoiding the vertical stiffener 103 is formed on the out-of-plane gusset 101. A beam member 105 is coupled to the out-of-plane gusset 101 from three directions.

JP 2007-107185 A

  When this out-of-plane gusset 101 receives a load, fatigue cracks are likely to occur at the scalloped end portion 120 and the end-to-end portion 130 where stress is particularly concentrated among the welded portions. Therefore, a fillet 131 projecting in an arc shape is formed at the end portion 130 to reduce stress concentration. However, since the scallop 110 having a small notch has a narrow working space for welding, it has been difficult to form a fillet to be an overhang portion at the scallop end 120. Patent Document 1 discloses a structure in which an L-shaped attachment plate is fastened to a beam plate having a scallop with a bolt. However, this complicates the structure, and if it is configured for each scallop 110 present in the steel bridge, it takes work and costs.

  Accordingly, an object of the present invention is to provide an out-of-plane gusset for a steel bridge in which the fatigue strength of the scallop end portion is improved with a simple configuration in order to solve such a problem.

The out-of-plane gusset for a steel bridge according to the present invention is welded upright to the main plate in the steel bridge, and the vertical stiffeners that are upright and welded to the main plate similarly intersect. The scallop is provided with a notched scallop, the scallop from the vertical stiffener disposed at the center in the width direction to the weld toe of the scalloped end welded to the main plate. The width is designed with a value exceeding 35 mm.
Further, in the out-of-plane gusset for a steel bridge according to the present invention, the scallop may be designed with a value from the vertical stiffener to the weld toe of the scalloped end up to 50 mm. preferable.

  According to the present invention, the scalloped end of the out-of-plane gusset is designed to have a width exceeding 35 mm, which is wider than 35 mm. It is possible to improve the fatigue strength of the conventional one.

It is the figure which showed the test body made into object in performing a three-dimensional FEM analysis, and is the figure which looked at the out-of-plane gusset from the orthogonal direction. It is the figure which showed the test body made into object in performing a three-dimensional FEM analysis, and is the figure which looked at the out-of-plane gusset from the horizontal direction. It is the figure which showed the parameter considered to influence the stress distribution of a test body. It is the figure which showed the example of element division of a test body. It is the figure which showed the stress distribution in the board width center of a main board in the graph. It is the figure which showed the maximum value of the stress concentration coefficient about the analysis case in the graph. It is the figure which showed the stress distribution of the thickness direction of the main board on the graph. It is the figure which showed the result of fatigue crack growth life analysis. It is the figure which showed the distance when taking the intersection of a scallop and a main board as the origin. It is the figure which showed the out-of-plane gusset provided in the steel bridge.

  Next, an embodiment of the out-of-plane gusset for a steel bridge according to the present invention will be described below with reference to the drawings. First, JSSC (Japan Steel Structure Association) fatigue design guidelines classify the fatigue strength of out-of-plane gussets into EG grades depending on the shape and the presence or absence of finish. It is not done. Therefore, when it is necessary to set the out-of-plane gusset to the E grade, the start / end section 130 can satisfy the E grade by providing the fillet 131 as shown in FIG.

  However, since the fillet cannot be formed on the scalloped end portion 120 as described above, it is necessary to finish the toe end by complete penetration welding. However, it is considered difficult to satisfy the E grade even with such welding finish. For example, when the R portion 111 of the scallop 110 shown in FIG. 10 is set to 80 mm and the modeled FEM analysis and fatigue crack growth life analysis are performed, the fatigue strength of the scalloped end portion 120 is approximately the same as that of the start / end portion 130. There is an announcement that a certain result was obtained. However, since it is expected that the fatigue strength varies depending on the scallop shape or the like, it cannot be said that the setting of the size of the R portion 111 is effective for the fatigue strength of the end portion of the scallop.

  Therefore, the inventor of the present application analytically examined factors that affect the fatigue strength of the scalloped end. That is, a three-dimensional FEM analysis was performed in order to grasp the stress state at the scallop end. FIGS. 1 and 2 are views showing a test body that is a target for performing a three-dimensional FEM analysis. FIG. 1 is a view of an out-of-plane gusset viewed from an orthogonal direction, and FIG. It is the figure seen from the horizontal direction. The test body 1 is welded with an out-of-plane gusset 12 standing upright in a direction perpendicular to the main plate 11 corresponding to the main girder web 102, and a scallop 15 is formed at the center thereof by an angled notch opened on the main plate 11 side. ing. Further, a vertical stiffener 13 that is erected in the orthogonal direction and passes through the scallop 15 so as to intersect the out-of-plane gusset 12 is welded to the main plate 11. The main plate 11, the out-of-plane gusset 12 and the vertical stiffener 13 are all rectangular steel plates.

  The parameters that are considered to affect the stress distribution of the specimen 1 are shown in FIG. tw is the plate thickness of the main plate 11, hv is the height of the scallop 15, tv is the plate thickness of the vertical stiffener 13, b is the width from the surface of the vertical stiffener 13 to the weld toe of the scallop 15, and r is This is the radius of curvature of the R portion of the scallop 15. For each, analysis was performed with the numerical values shown in FIG. The main plate 11 shown in FIG. 2 has a vertical dimension of 300 mm and a horizontal dimension of 1000 mm. The out-of-plane gusset 12 has a plate thickness of 9 mm, and the lateral dimension welded to the main plate 11 is 600 mm. FIG. 4 is a diagram showing an example of element division of the test body 1. The element size in the vicinity of the turn welding for calculating the stress concentration factor is 0.1 mm. In consideration of symmetry, a 1/4 model was used.

  First, FIG. 5 is a graph showing the stress distribution at the center of the plate width of the main plate 11. The horizontal axis indicates the distance from the scalloped end 20, and the vertical axis indicates the stress concentration factor. Note that the distance x from the scallop end 20 is a distance when the intersection (the weld toe of the scallop 15) of the scallop 15 and the main plate 11 is taken as the origin, as shown in FIG.

  Here, the relationship of the parameter tw-tv-b shown in FIG. 3 was analyzed in the case of 11-10-35 (case 1) and in the case of 11-10-50 (case 2) (both are numerical values). Unit is mm). That is, the width b from the surface of the vertical stiffener 13 to the weld toe of the scallop 15 is set to a different value. As a result of the analysis, the value of the stress concentration coefficient changed according to the distance from the weld toe (origin) of the scallop 15, and peaks occurred at three locations A to C as shown in the figure. Peak A is the starting end 21 of the out-of-plane gusset 12 (see FIG. 1), and peak B is the scalloped end 20, that is, the weld toe of the scallop 15 that is the origin. Peak C is the position of the vertical stiffener 13.

  Since the value of the peak B is larger than the peak A, it can be seen that the stress concentration coefficient at the weld toe (scallop end 20) of the scallop 15 is larger than the stress concentration coefficient at the start / end part 21 of the out-of-plane gusset 12. . This is considered to be related to the fact that the main plate 11 is deformed out-of-plane to the side where there is no out-of-plane gusset 12 but is deformed to the out-of-plane gusset 12 side at the scallop 15 portion. Further, when comparing the cases 1 and 2 at the peak B, the case 2 having a large width b from the surface of the vertical stiffener 13 to the weld toe of the scallop 15 has a small stress concentration coefficient. That is, the larger the width of the scallop 15 is, the smaller the stress concentration factor is, and if the value of b is sufficiently wide, the scalloped end portion 20 is expected to approach the stress distribution of the start / end portion 21. Note that the stress concentration coefficient of the start / end portion 21 was substantially constant regardless of the shape of the scallop 15.

  Next, FIG. 6 is a graph showing the maximum value of the stress concentration factor for other analysis cases. In this analysis graph, the horizontal axis represents the plate thickness tv of the vertical stiffener 13 and the vertical axis represents the stress concentration coefficient at the scalloped end portion 20, and in particular, the plate thickness tv of the vertical stiffener 13 is 10 mm. , 15 mm, and 25 mm, the maximum value of the stress concentration coefficient is shown. The relationship between the parameters tw-b shown in FIG. 3 is the case of 11-35 (case 11) and 11-50 (case 12), and the case of 25-35 (case 21) and 25-50. (Case 22) was analyzed (in both cases, the numerical unit is mm).

  In any case, as the plate thickness of the vertical stiffener 13 was increased, the stress concentration factor at the scalloped end 20 increased. This can be considered that the restraint state of the main plate 11 by the vertical stiffener 13 influences. When attention is paid to the plate thickness tw of the main plate 11, in this case, the plate thickness is increased from 11 mm to 25 mm, the rigidity of the main plate 11 is increased, and the plate thickness effect that the stress concentration coefficient at the scalloped end portion 20 is increased is recognized. It was. In each of the cases 11 and 12 and the cases 21 and 22 in which the plate thickness tw of the main plate 11 is the same, the case 12 has a large width b from the surface of the vertical stiffener 13 to the weld toe of the scallop 15. No. 22 had a smaller stress concentration factor.

  Next, FEM analysis was performed in consideration of the toe radius of the weld toe (R of the weld formed by welding finish) for the case with the largest and smallest scallop stress concentration factor. The toe radii were 2 mm (2R) and 5 mm (5R), and both the start / end and scallop ends were modeled. In addition, 2R is a state of welding as it is, and 5R assumes a welding finish. FIG. 7 is a graph showing the stress distribution in the plate thickness direction of the main plate 11. In the graph, the horizontal axis represents the distance in the plate thickness direction from the surface of the main plate 11 welded with the out-of-plane gusset 12, and the vertical axis represents the stress concentration factor at the scalloped end 20 and the start / end portion 21.

  Then, when the relationship of the parameter tw-tv-b shown in FIG. 7 is 11-10-50 (both numerical units are mm), the toe radius of the scalloped end 20 is 5 mm (5R) ( Case 31) and 2 mm (2R) (case 32), and the toe radius of the start / end portion 21 was 5 mm (5R) (case 33) and 2 mm (2R) (case 34). Here, the values of the plate thickness tw of the main plate 11, the plate thickness tv of the vertical stiffener 13 and the width b to the weld toe of the scallop 15 are smaller from the results of FIGS. The case was selected.

  When the cases 31 and 33 and the cases 32 and 34 were compared with each other, no difference in stress distribution was observed between the scalloped end portion 20 and the start / end portion 21 when the toe radius was the same. On the other hand, when the toe radii are 2R and 5R, in the vicinity of the surface of the main plate 11, the case 32 having the toe radius of the scallop end 20 of 2R has the largest stress concentration coefficient, and the toe radius of the scallop end 20 is 5R. The difference from the case 31 was large.

  Based on the above FEM analysis results, fatigue crack growth life analysis was performed using a fracture mechanics technique. The analysis was performed on the scalloped end portion 20 and the start / end portion 21 in 2R and 5R cases considering the toe radius of the weld toe portion. As the design curve, the safest design curve of the fatigue design guideline is used, and the stress intensity factor range ΔK (MPa√m) is Fg. Fe. Fs. Ft. It calculated by (DELTA) (sigma) (pi). At that time, the crack shape was assumed to be a semi-ellipse, and the ratio of the crack length in the plate thickness direction to the plate width direction was 1/3. The initial crack length in the thickness direction of the main plate 11 was set to 0.1 mm, and the limit crack length was set to the plate thickness of the main plate 11 × 0.8.

  Here, FIG. 8 is a diagram showing the results of fatigue crack growth life analysis, and the fatigue strength of 2 million times was obtained for each case. The horizontal axis represents the toe radius, and the vertical axis represents the fatigue strength of 2 million times. The fatigue crack growth life is calculated by calculating the number of repetitions until fracture when the fatigue crack that enters the welded part is repeatedly subjected to a predetermined stress. Is a value obtained by determining the predetermined stress that breaks when the predetermined stress is repeatedly applied 2 million times. Therefore, it can be seen from this analysis result that the strength increases as the toe radius increases. Further, the plate thickness tw of the main plate 11 and the plate thickness tv of the vertical stiffener 13 were thin, and the strength was greater as the width b to the weld toe of the scallop 15 was larger.

  Therefore, from the above, it has been found that the stress concentration factor of the scallop 15 of the out-of-plane gusset 12 can be lowered by increasing the width b from the vertical stiffener 13 to the weld toe of the scallop end 20. . Conventional scallops for out-of-plane gussets are generally formed with a width b value of 35 mm. In this embodiment, the width b is formed wider than the conventional scallop and is designed to have a value exceeding 35 mm. Further, when the value of the width b is too large, the distance from the scalloped end portion 20 to the start / end portion 21 is shortened, and the welding width of the out-of-plane gusset 12 is decreased. Therefore, the value of the width b is set to 50 mm. Thereby, the out-of-plane gusset of the present embodiment can improve the fatigue strength of the scallop end portion as compared with the conventional out-of-plane gusset.

As mentioned above, although an example was shown about the out-of-plane gusset for steel bridges concerning the present invention, the present invention is not limited to this.
For example, the main plate 11 has been described as corresponding to the main girder web 102 shown in FIG. 10, but the main plate 11 is not limited to the main girder web as long as the out-of-plane gusset is a target to be welded.

1 Test body 11 Main plate 12 Out-of-plane gusset 13 Vertical stiffener 15 Scallop 20 Scallop end 21 Start / end

Claims (2)

Steel bridges with cut-out scallops so that vertical stiffeners that stand up to and welded to the main plate in the steel bridge and can also be welded to the main plate can intersect. For out-of-plane gussets,
The scallop is designed to have a width exceeding 35 mm from the vertical stiffener disposed at the center position in the width direction to the weld toe of the scallop end welded to the main plate. Out-of-plane gusset for steel bridge. In the out-of-plane gusset for a steel bridge according to claim 1,
The out-of-plane gusset for a steel bridge, wherein the scallop is designed with a width from the vertical stiffener to the weld toe at the end of the scallop up to 50 mm.

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