JP2021023947A - Method for improving fatigue life of weld zone in existing bridge and for repairing crack in weld zone therein - Google Patents

Abstract

To improve a fatigue life of a weld zone in an existing bridge and efficiently repair a crack existing in the weld zone.SOLUTION: A method for improving a fatigue life of a weld zone 60 in an existing bridge and for repairing a crack C in the weld zone therein is disclosed. The method includes: determining whether there is the crack C in the weld zone 60 or not; performing peening processing on the weld zone 60 when there is not the crack C in the weld zone 60; determining whether the crack C falls within a range of a predetermined reference or not when there is the crack C in the weld zone 60; performing peening treatment on the weld zone 60 including the crack C when the crack C falls within the range of the predetermined reference; and determining, after performing peening processing, whether a shape of an indentation formed by the peening processing satisfies a predetermined reference or not.SELECTED DRAWING: Figure 3

Description

The present application relates to a method for improving fatigue life and repairing cracks in a welded portion, more specifically, a welded portion of an existing bridge.

Conventionally, various methods for improving the fatigue life of metal materials have been proposed. For example, Patent Document 1 describes the fatigue life of various metal materials (for example, welded parts of large structures such as bridge girders of bridges, welded products of automobiles, and non-welded metal materials of automobiles) by ultrasonic impact treatment. Discloses methods for improving. In this method, first, in the crack inspection, it is determined whether or not there is a crack at the target location. If no cracks are detected, ultrasonic impact treatment is performed on the target area. When a crack is detected, ultrasonic impact treatment is performed on the target portion after repairing the crack. Specifically, first, cracks are removed by grinding or gouging, and then ultrasonic impact treatment is performed on the target portion. In such a conventional method, it is possible to delay the occurrence of fatigue cracks and improve the life by applying compressive residual stress to the toe of the weld, but the progress of cracks that have already occurred can be improved. It was not known if it could be suppressed.

Japanese Unexamined Patent Publication No. 2003-11418

Generally, bridges contain various welds and are exposed to various loads. Stress can be concentrated in the welds and therefore, in existing bridges, fatigue cracks can occur in many welds. Therefore, in order to use the existing bridge for a long time, it is necessary to repair the cracks generated in such welds. However, existing crack repair methods (eg, removing cracks by grinding or gouging as described above) require a long time (eg, several hours per location). Therefore, in order to use the existing bridge for a long time, a method that not only improves the fatigue life of the welded portion but also can efficiently repair the cracks generated in the welded portion is desired.

The load applied to the bridge is generally smaller than the load applied to a structure used in a more severe environment such as a crane runway girder (CRG) (for example, about 150 MPa). Under a repetitive load of this degree, the present inventor performs a peening treatment on the welded portion including the crack if the crack in the welded portion is within a predetermined range, thereby closing the opening of the crack. It was found that the cracks can be prevented from further developing and the cracks can be substantially repaired.

Therefore, one aspect of the present disclosure is a method for improving the fatigue life of a welded portion and repairing a crack, in which the welded portion is provided on an existing bridge, and the method has a crack in the welded portion. Judging whether or not there is a crack, performing a peening treatment on the weld when there is no crack in the weld, and when there is a crack in the weld, the crack is within the specified reference range. It is formed by determining whether or not it is inside, performing a peening treatment on the welded portion including the crack when the crack is within a predetermined reference range, and performing the peening treatment after the peening treatment. It is a method including determining whether or not the shape of an indentation meets a predetermined criterion.

According to the method of one aspect of the present disclosure, when there is no crack in the welded portion, a peening treatment is performed on the welded portion. As a result, the shape is improved so that the stress is not concentrated on the welded portion, and the tensile residual stress is removed and the compressive residual stress is applied (generally, the tensile residual stress reduces the fatigue life and the compressive residual stress is fatigue. Contributes to improved life). Therefore, the fatigue life of the welded portion can be improved. Further, even when there is a crack in the welded portion, if the crack is within a predetermined reference range, the welded portion is subjected to the same peening treatment, whereby the opening of the crack is closed. Therefore, further growth of the crack can be significantly suppressed or prevented, and the crack can be substantially repaired. The peening process requires less time (eg, several hours per site) than the time required for existing repair methods (eg, removing cracks by grinding or gouging) (eg, 1). A few minutes, a dozen minutes, or a few tens of minutes per location). Therefore, the fatigue life of the welded portion can be improved, and cracks in the welded portion can be efficiently repaired.

For example, the weld may be provided on the main plate of an existing bridge, and the predetermined criterion may be that the crack is in the toe and does not extend to the base plate of the main plate. According to the present inventor, when the welded portion of the main plate of some bridges has a size such that the crack does not extend to the base metal, the welded portion is subjected to a peening treatment to crack. It was found that further progress could be prevented. In addition, the criterion that the crack is inside the toe and does not extend to the base material of the main plate means that the size of the crack can be easily determined visually by the operator without using a specific device. to enable. Therefore, according to the method according to the above aspect, the crack can be repaired efficiently.

The method according to one aspect of the present disclosure may further include polishing the welded portion subjected to the peening treatment with an abrasive softer than the base metal. Generally, a coating is applied to the welded portion for a purpose such as rust prevention, and before the coating is applied, the welded portion is polished to remove an oxide film and dirt. However, if the welded portion subjected to the peening treatment is excessively polished, the portion to which the compressive residual stress is applied by the peening treatment is also removed, and the intended fatigue life may not be obtained. In the method according to this aspect, by using an abrasive material softer than the base material, only the oxide film and dirt can be removed without removing the base material portion to which the compressive residual stress is applied. Therefore, the welded portion can be polished after the peening process is performed. In addition, the coating needs to be reapplied once every few years or decades, and also needs to be polished. In the method according to this aspect, since only the oxide film and stains can be removed, it is not necessary to repeatedly carry out the peening treatment every time the coating is reapplied and the polishing accompanying the coating is reapplied. Therefore, the cost of reapplying the coating can be reduced.

For example, the welded portion may be a rotary welded portion. In some turn welds, cracks may arise from within the toe and then propagate to the base metal. In this case, the predetermined criterion may be, for example, that the crack is in the toe and does not extend to the base metal of the main plate, as described above. Therefore, it is possible to easily determine the size of the crack visually by the operator, and the crack can be repaired efficiently. The rotation welded portion exists at an end portion such as an out-of-face gusset of the main girder, a vertical rib or a horizontal rib of the main girder, an upper end portion of the vertical rib of the steel deck slab, and a vertical / horizontal rib intersection of the steel deck slab.

The peening process may be an ultrasonic impact process, and the ultrasonic impact process may use a single pin. In this case, since the target surface can be hit intensively with a single pin, the target surface can be compressed deeper.

According to one aspect of the present disclosure, it is possible to improve the fatigue life of the welded portion of an existing bridge and efficiently repair cracks in the welded portion.

It is a schematic perspective view which shows a part of the bridge to which the method which concerns on embodiment is applied. It is a schematic enlarged view which shows the part A in FIG. FIG. 3A shows an example of a crack in the toe. FIG. 3B shows an example of a crack extending to the base metal. It is the schematic which shows the UIT apparatus. It is a flowchart which shows the method which concerns on embodiment. It is a schematic cross-sectional view which shows the dent formed by UIT. FIG. 7A shows a top view of the test piece used in the fatigue test. FIG. 7B shows a side view of the test piece used in the fatigue test. FIG. 7C shows a front view of the test piece used in the fatigue test. It is a graph which shows the fatigue life of a PC test piece / the fatigue life of a JSSC-F grade test piece.

Hereinafter, the method according to the embodiment will be described with reference to the attached drawings. Similar or corresponding elements are designated by the same reference numerals, and duplicate description is omitted. The scale of the figure may have been changed for ease of understanding.

FIG. 1 is a schematic perspective view showing a part of a bridge 100 to which the method according to the embodiment is applied. The bridge 100 shows an example of an existing bridge. For example, a main girder 10 extending in the longitudinal direction of the bridge 100, a horizontal girder 20 extending at a right angle to the main girder 10, and the main girders 10 are connected to each other. A horizontal structure 30 for connecting and an anti-tilt structure 40 for connecting the main girders 10 are provided. The bridge 100 may include other components (eg, piers, piers, etc.) not shown.

Generally, bridges contain various welds and are exposed to various loads. In general, stress may be concentrated in welds, and therefore, in existing bridges, fatigue cracks can occur in many welds. The position and shape of cracks generated in each weld are generally determined according to factors such as the position of the weld. The present disclosure relates to a welded portion of a main plate of a bridge 100. The main plate is a main member that transmits the load used in the design. For example, the main girder 10, the main girder flange, the web, the cross girder flange, the cross girder web, the steel deck deck plate, and the steel deck vertical rib (U). (Including ribs), steel deck horizontal ribs are the main ones. However, depending on the situation of fatigue inspection, the gusset itself for connecting anti-tilt structures, cross girders, etc. may be treated as the main plate. In the present disclosure, as an example, the welded portion of the main girder 10 will be described. Hereinafter, as an example, a crack generated in a welded portion between the main girder 10 of the bridge 100 and the out-of-plane gusset (details will be described later) will be described.

FIG. 2 is a schematic enlarged view showing a part A in FIG. The main girder 10 and the horizontal structure 30, and the main girder 10 and the anti-tilt structure 40 are connected by an out-of-plane gusset 50, respectively. The out-of-plane gusset 50 is fixed to the main girder 10 by welding. The out-of-plane gusset 50 has a substantially plate shape, and is arranged so as to extend substantially vertically from the main girder 10 and parallel to the longitudinal direction of the bridge 100. The horizontal structure 30 and the anti-tilt structure 40 are fixed to the out-of-plane gusset 50 by welding, bolts, rivets, or the like.

Various repetitive loads are applied to the out-of-plane gusset 50. For example, a bridge on the Japanese Metropolitan Expressway receives a repetitive load of about 65 MPa or less. Cracks due to such repeated loads occur in the welded portion between the out-of-plane gusset 50 and the main girder 10.

FIG. 3 shows an example of a crack generated in the weld 60 between the out-of-plane gusset 50 and the main girder 10, (a) shows an example of a crack C in the toe 63, and (b). ) Indicates an example of a crack C extending to the base material of the main girder 10. As shown in FIG. 3A, the welded portion 60 includes the bead 61 and a region in the vicinity thereof (a portion of the main girder 10 and the out-of-plane gusset 50 in the vicinity of the bead 61). The weld 60 includes a toe 62 between the bead 61 and the out-of-plane gusset 50 and a toe 63 between the bead 61 and the main girder 10. It is known that in the welded portion 60, a crack C is typically generated along the end portion 51 of the plate-shaped out-of-plane gusset 50 at the toe 63 between the bead 61 and the main girder 10. If such a crack C is left unattended, the welded portion 60 may be damaged starting from the crack C. Therefore, in order to use the bridge 100 for a long time, such a crack C must be repaired.

As a result of diligent research, the present inventor performed a peening treatment on the welded portion including the crack if the crack was within a predetermined reference range, thereby closing the opening of the crack, thereby causing the crack. We have found that further development can be significantly suppressed or prevented and that cracks can be substantially repaired. Specifically, the "predetermined standard" may change depending on factors such as the position and material of individual welds, but for example, "crack depth" and "crack length". , Or "crack width" and the like. Further, as described above, the shape of a crack generated in each welded portion (for example, the relationship between the depth and length of the crack) is generally determined according to factors such as the position of the welded portion. By measuring the length of the crack, the depth of the crack can be estimated. Therefore, it is also possible to determine whether or not the crack depth is equal to or less than a predetermined value based on the crack length.

For example, the present inventor has a welded portion 60 between the out-of-plane gusset 50 and the main girder 10 included in some bridges on the Japanese capital highway (material of main girder 10: JIS G 3106 SM570Q, out-of-plane gusset). In 50 materials: JIS G3101 SS400, thickness of out-of-plane gusset 50: about 9 mm), as shown in FIG. 3 (b), the length of the crack C slightly extended to the base material of the main girder 10. (Depth of crack C at this time: about 3.8 mm), it was found that the crack C can be substantially repaired by carrying out the peening treatment (details will be described later). ). In other words, as shown in FIG. 3A, if the crack C has a length that fits within the toe 62, the crack C is surely repaired by performing a peening treatment. Can be done.

The peening treatment can be, for example, an ultrasonic impact treatment (hereinafter, may also be referred to as UIT). UIT is a method for hitting the target surface by changing ultrasonic waves (for example, 27 to 55 kHz) into mechanical striking vibrations. For the UIT, for example, an ultrasonic hammering impact device (hereinafter, may also be referred to as a UIT device) can be used.

FIG. 4 is a schematic view showing the UIT device 200. The UIT device 200 includes, for example, a main body 210, a cooling unit 220, and a power supply control device 230. The main body 210 has a size that can be carried by an operator, and has an ultrasonic oscillation unit 211, a wave guide 212, and a pin holder 213. The ultrasonic waves generated by the ultrasonic wave oscillating unit 211 are converted into mechanical vibrations by the spring 214 of the wave guide 212 and transmitted to the pin holder 213. The pin holder 213 holds a plurality of (three in FIG. 4) pins P so as to be movable (sliding) in the striking direction (longitudinal direction of the pins P). Therefore, the pin P repeatedly bounces between the pin holder 213 and the target surface. The target surface is hit by such an operation of the pin P. The number of pins P can be changed according to the application. Further, the shapes of the pin holder 213 and the pin P may also be changed according to the application. The cooling unit 220 is configured to cool the ultrasonic oscillator unit 211, and the power supply control device 230 is configured to supply electric power to the ultrasonic oscillator unit 211 and control the ultrasonic oscillator unit 211. There is.

In the method according to the present disclosure, the quality of the surface after the peening treatment is determined based on the shape of the dents formed by the peening treatment, particularly the depth (details will be described later). Therefore, the peening treatment is performed on the target surface. It may be carried out in such a manner that it is compressed as deeply as possible. For example, only one pin P may be set in the pin holder 213, or the target surface may be hit intensively with one pin P. In this case, since the compressive force can be concentrated on a specific portion of the target surface, the target surface can be compressed as deeply as possible. The quality of the surface after the peening treatment may be judged based on other shapes of dents other than the depth (for example, groove width).

Subsequently, the method according to the embodiment will be described.

FIG. 5 is a flowchart showing the method according to the embodiment. In the present disclosure, the method according to the embodiment will be described in relation to the welded portion 60 between the out-of-plane gusset 50 and the main girder 10.

First, it is determined whether or not there is a crack in the welded portion 60 (step S100). Specifically, the crack detection method may be, for example, visual inspection by an operator. Further, the detection method may be, for example, magnetic particle inspection (MT) or penetrant inspection (PT). In the case of MT, for example, a crack having a length of about 2 mm or more can be detected. In the case of PT, for example, cracks having a length of about 3 mm or more can be detected. When performing MT or PT, it is common to remove the coating in advance at the welded portion and its vicinity. It should be noted that many minute cracks that cannot be detected visually, MT or PT may already exist in the welded portion of the existing bridge, but the “crack” in the present disclosure is a selected detection method (for example, for example). Note that it means cracks with a size that can be detected visually, MT or PT) and does not include very small cracks that are undetectable by the detection method chosen. .. In addition, the welded part of an existing bridge is generally coated for the purpose of rust prevention, etc., but if fatigue cracks occur from the welded part under the coating, the coating will crack. Very often. Therefore, it is a common method to look for cracks in the coating as a primary screening method for investigating fatigue cracks that have already occurred. Conversely, if the coating is not cracked and is in a healthy state, it can be determined that there is a high possibility that fatigue cracks have not occurred in the welded portion underneath. Therefore, in some cases, peening can be performed directly without removing the coating for crack inspection.

When it is determined in step S100 that the welded portion 60 has a crack, it is determined whether or not the crack is within a predetermined reference range (step S102). Specifically, referring to FIGS. 3A and 3B, in the present embodiment, whether or not the crack C is contained in the toe 63 (the crack C is the base material of the main girder 10). Whether or not progress has been made) is determined. When the crack C is contained within the toe 63 (FIG. 3A), it is determined that the crack C is within a predetermined reference range. In contrast, if the crack C does not fit within the toe 63 and extends to the base metal of the main girder 10 (FIG. 3 (b)), the crack C is not within a predetermined reference range. It is judged. Such a determination can be performed, for example, visually by an operator.

With reference to FIG. 5, when it is determined in step S102 that the crack is within a predetermined reference range, a peening process is performed on the welded portion 60 including the crack to close the opening of the crack (step). S104). With reference to FIG. 3A, in this embodiment, the UIT is performed so as to compress the toe 63 between the bead 61 and the main girder 10. The UIT does not have to be applied to the entire weld 60, for example, the crack C actually generated and the location where the crack C is expected to occur, and the vicinity thereof (for example, the out-of-plane gusset 50). It may be implemented only at the toe 63) around the end 51. Usually, the processing range may be about 30 mm from the end portion 51 and the end portion 51 thereof, or about twice the plate thickness of the out-of-plane gusset 50.

FIG. 6 is a schematic cross-sectional view showing the dent dm formed by the UIT. The UIT maintains the pin P of the UIT device at a predetermined angle with respect to the target surface (for example, the surface of the main girder 10) so as to compress the target surface as deeply as possible (swings left and right in FIG. 6). It may be carried out along the toe 63 (without causing). Also, in the UIT, a single pin P may be used as described above to compress the target surface as deeply as possible. If there is a crack C, the UIT is performed so that the pin P directly compresses the crack C.

With reference to FIG. 5, when it is determined in step S100 that there are no cracks in the welded portion 60, the peening process of step S104 is directly proceeded without performing step S102.

If it is determined in step S102 that the crack is out of the predetermined reference range, it is determined that the method according to the embodiment is not applicable (step S106), and a series of operations is completed.

After the peening process in step S104, it is determined whether or not the depth of the dents formed by the peening process is equal to or greater than a predetermined value (step S108). Specifically, with reference to FIG. 6, a dent dm is formed at the boundary between the bead 61 and the main girder 10 by the peening process. The depth dm of the dent dm can be measured by various methods. For example, the depth dp may be measured by a gauge for welding undercut measurement or a laser length measuring device. In some welds 60 (material of main girder 10: JIS G 3106 SM570Q, material of out-of-plane gusset 50: JIS G3101 SS400, thickness of out-of-plane gusset 50: about 9 mm), the "predetermined value" is, for example, It can be about 0.2 mm (more on this later). As described above, in the existing bridge, the welded portion is generally painted, but since the coating is usually peeled off by the peening treatment, the thickness of the coating does not affect the measurement of the depth dp. Therefore, it is not necessary to polish the target surface to remove the coating prior to step S108. Further, if necessary, in order to measure the depth dp more accurately, step S108 may be performed after removing the coating by polishing similar to step S110 described later. In this case as well, polishing in step S110 may be additionally performed after step S108, depending on various factors such as the timing of painting.

Further, since the vicinity of the welded portion is easily corroded, even if only the coating film is removed, the steel material under the welded portion may be corroded or uneven. For this reason, when it is difficult to measure the depth of the dent because the installation part of the tool (for example, a straight line or a flat surface) such as a normal weld gauge cannot be in close contact with the surface in the vicinity of the weld part. There is. In this case, for example, a measuring device such as a micrometer having a smaller installation portion (for example, a thin installation foot) may be used. In this case, since the area of the installation portion is small, it is not easily affected by non-landing, and the depth dp of the dent dm can be accurately and easily measured. Further, the depth of the dent dm is obtained by obtaining the measured value of the bottom of the dent dm and the measured value of the surface in the vicinity of the dent dm with reference to the same position and calculating the difference between them. The dp can be measured more accurately.

With reference to FIG. 5, when it is determined in step S108 that the depth of the dent is equal to or greater than a predetermined value, the region where the peening treatment is performed and its vicinity are polished in order to adjust the base material for painting ( Also referred to as Keren) (step S110). For polishing, an abrasive material softer than the base material of the target surface (in this embodiment, the base material of the main girder 10) is used. Such an abrasive may be, for example, a wire brush (for example, made of stainless steel) or a grindstone (for example, made of ceramics having a particle size of 60). The abrasive can be rotated at, for example, about 25,000 rpm.

If it is determined in step S108 that the depth of the dent is not equal to or greater than the predetermined value, steps S104 and S108 are repeated until the depth of the dent is equal to or greater than the predetermined value.

Subsequently, the required coating is applied to the substrate-adjusted region (step S112), and the series of operations is completed.

In addition, the coating may be reapplied years, decades later, or when deemed necessary. In this case, steps S110 and S112 may be performed as shown in FIG. As described above, in step S110, since an abrasive material softer than the base material of the main girder 10 is used, it is possible to remove only the oxide film and dirt without removing the base material portion to which the compressive residual stress is applied. it can. Therefore, when the coating is reapplied, it is not necessary to carry out the peening process again.

As described above, according to the method according to the embodiment, when there is no crack in the welded portion 60 (when “NO” in step S100), the welded portion 60 is subjected to the peening process. As a result, the shape is improved so that the stress is not concentrated on the welded portion 60, the tensile residual stress is removed, and the compressive residual stress is applied. Therefore, the fatigue life of the welded portion 60 can be improved. Further, even when the welded portion 60 has a crack (when “YES” in step S100), if the crack is within a predetermined reference range (when “YES” in step S102), the welded portion A similar peening process is performed on 60, which closes the opening of the crack C. Therefore, further growth of the crack C can be prevented, and the crack can be substantially repaired. The peening process requires less time than the time required for existing repair methods (eg, removing cracks by grinding or gouging). Therefore, according to the method according to the embodiment, the fatigue life of the welded portion 60 can be improved, and the crack C in the welded portion 60 can be efficiently repaired.

Further, in the method according to the embodiment, the welded portion 60 is provided between the main plate of the bridge 100, specifically, the main girder 10 and the out-of-plane gusset 50, and the predetermined standard is that the crack C is formed. It is in the toe 63 and has not progressed to the base material of the main girder 10. The criterion that the crack C is in the toe 63 and does not extend to the base metal of the main girder 10 makes it easy for the operator to visually determine the size of the crack C without using a specific device. Allows you to. Therefore, according to the method according to the embodiment, the crack C can be repaired efficiently.

Further, the method according to the embodiment further includes polishing the welded portion 60 subjected to the peening treatment with an abrasive that is softer than the base material of the main girder 10 (step S110). Generally, a coating is applied to the welded portion for a purpose such as rust prevention, and before the coating is applied, the welded portion is polished to remove an oxide film and dirt. However, if the welded portion subjected to the peening treatment is excessively polished, the portion to which the compressive residual stress is applied by the peening treatment is also removed, and the intended fatigue life may not be obtained. Therefore, for example, Patent Document 1 proposes to perform a peening process at the end after completing all other processes related to the welded portion. In response to such a problem, the present inventor uses an abrasive that is softer than the base material to remove only the oxide film and dirt without removing the base material portion to which the compressive residual stress is applied. I found that I could do it. Therefore, according to the method according to the embodiment, the welded portion 60 can be polished after the peening treatment is performed. This is also beneficial when reapplying the coating. Specifically, the coating needs to be reapplied once every few years or decades, and also needs to be polished. The weld 60, which has been peened by the method according to the embodiment, may be intended to be used for a further decade, so that during the remaining life, multiple recoatings and the like. May require accompanying polishing. In the method of Patent Document 1, since it is necessary to perform the peening treatment at the end after completing all the other processes, it is necessary to carry out the peening treatment every time the coating is reapplied and the polishing associated therewith. However, according to the method according to the embodiment, only the oxide film and dirt can be removed without removing the base material portion to which the compressive residual stress is applied, so that when the coating is reapplied and the polishing is accompanied by the removal. It is not necessary to carry out the peening process. Therefore, it is possible to reduce the cost burden of the bridge owner when reapplying the coating.

Further, in the method according to the embodiment, the welded portion 60 is a turning welded portion. In such a welded portion 60, the crack C may be generated from within the toe 63 and then propagate to the base metal. Therefore, the predetermined criterion may be that the crack C is in the toe 63 and does not extend to the base metal of the main girder 10. Therefore, it is possible to easily determine the size of the crack C visually by the operator, and the crack C can be repaired efficiently. The rotation welded portion exists at an end portion such as an out-of-face gusset of the main girder, a vertical rib or a horizontal rib of the main girder, an upper end portion of the vertical rib of the steel deck slab, and a vertical / horizontal rib intersection of the steel deck slab.

Further, in the method according to the embodiment, the peening process is UIT, and UIT uses a single pin P. Therefore, the target surface can be intensively hit with a single pin P, and the target surface can be compressed deeper.

Although the embodiment of the method for improving the fatigue life and repairing cracks of the welded portion of the existing bridge has been described, the present invention is not limited to the above embodiment. Those skilled in the art will appreciate that various variations of the above embodiments are possible. Those skilled in the art will also understand that the above methods need not be performed in the above order and can be performed in other orders as long as there is no contradiction.

For example, in the above embodiment, the welded portion 60 between the main girder 10 and the out-of-plane gusset 50 is described as the welded portion of the existing bridge in which the method according to the present disclosure is implemented. However, the welded portion is not limited to the welded portion 60 described above, and the method according to the present disclosure may be implemented for other welded portions of an existing bridge. For example, the method according to the present disclosure may be carried out on the welded portion between the steel slab of the bridge and the vertical stiffener. The upper end of the vertical stiffener of the plate girder, the vicinity of the web gap plate, the vertical and horizontal rib intersections of the steel deck slab, and the like are welded portions having the same shape, and may be implemented in the same manner.

Further, for example, in the above embodiment, the peening process is UIT. However, in other embodiments, other methods may be used. For example, the peening process may be carried out using a portable pneumatic needle-peening device (so-called PPP process). The process uses compressed air as a power source and transfers the energy of the piston driven by the compressed air to the needle held at the tip of the tool. The target surface is peened by the needle continuously colliding with the target surface. Similarly, needle peening such as air type and motor type, and hammer peening may be used.

A fatigue test was conducted to investigate the effect of the method according to the present disclosure on welds.

7 (a), (b) and (c) show a top view, a side view and a front view of the test piece TP used in the fatigue test, respectively. A plurality of test specimen TPs imitating the welded portion of the existing bridge as shown in FIG. 7 were prepared. The main girder 10 was formed of JIS G 3106 SM570Q, and the out-of-plane gusset 50 was formed of JIS G3101 SS 400.

By conducting a preliminary fatigue test on the test piece TP, a crack (hereinafter referred to as a pre-crack) was generated in the welded portion 60. The test body TP having these pre-cracks is referred to as a PC (Pre-cracked) test body. Pre-cracks occurred in the same manner as crack C shown in FIGS. 3 (a) and 3 (b). Pre-cracks in the toe of some PC specimens occurred, and pre-cracks that extended to the base material of the main girder 10 occurred in the remaining PC specimens.

For all the PC test specimens, UIT was performed on the welded portion 60 in the same manner as in the above method (step S104 in FIG. 5). In addition, the depth of the dents formed by the UIT was measured for all the PC test specimens in the same manner as in the above method (step S108 in FIG. 5). Some PC test specimens had dents having a depth of 0.2 mm or more, and the remaining PC specimens had dents having a depth of less than 0.2 mm.

Fatigue tests were carried out using a PC test piece at stress ranges of 50 MPa, 65 MPa, 80 MPa, 100 MPa, and 120 MPa. In either test, repeated load is applied more than 10 ⁶ times. Some PC specimens did not break under repeated loads of applied times. By dividing the fatigue life of each PC test piece (the number of repetitions when the test piece breaks) by the fatigue life of similar JSSC-F grade test pieces subjected to the fatigue test in the same stress range, according to UIT. We investigated the improvement of fatigue life. The results are shown in FIG.

FIG. 8 is a graph showing the fatigue life of the PC test piece / the fatigue life of the JSSC-F grade test piece. In FIG. 8, the vertical axis shows the fatigue life of the PC specimen (Fatigue life after UIT) / the fatigue life of the JSSC-F grade specimen (Fatigue life of JSSC-F), and the horizontal axis shows the observation of the microscope. The pre-crack depth of each PC specimen measured by is shown. FIG. 8 shows that when Fatigue life after UIT / Fatigue life of JSSC-F is larger than 1, the fatigue life is improved over the fatigue life of the JSSC-F grade test piece. The results with upward arrows indicate that the PC test piece did not break under the repeated load of the applied number of times, and these results showed Fatigue life after UIT / Fatigue life of JSSC-F. Note that indicates the value obtained by dividing the number of repeated loads actually applied to the PC test piece by the fatigue life of the JSSC-F grade test piece.

As shown in FIG. 8, when the pre-crack is 3.8 mm or more, it can be seen that the pre-crack has propagated to the base metal (see the results shown by the black triangle and the white triangle). Also, PC specimens with pre-cracks in the toes (see results indicated by black and white circles) have a fatigue life improved by UIT over the fatigue life of JSSC-F grade specimens, while Some PC specimens with pre-cracks that have progressed to the base metal (see Fatigue life after UIT / Fatigue life of JSSC-F results shown by two black triangles without arrows less than 1) It can be seen that even if UIT is performed, the fatigue life is not improved to the fatigue life of the JSSC-F grade test piece. In addition, among the PC test specimens having a pre-crack in the toe, the PC specimens having a dent with a depth of 0.2 mm or more (processing depth 0.2 mm or more) (see the results shown by black circles). It can be seen that the fatigue life is improved by 5 times or more of the fatigue life of the JSSC-F grade test piece. Therefore, if the crack is in the toe and the UIT forms a dent having a depth of 0.2 mm or more, the UIT substantially repairs the crack and sufficiently improves the fatigue life. You can see that you can.

10 Main girder 50 Out-of-plane gusset 60 Welded part 63 Toe end 100 Bridge C Crack dm Dip dent pp Depth of dent

Claims (5)

It is a method for improving the fatigue life of welds and repairing cracks.
The welded portion is provided on an existing bridge and
The method is
Determining whether or not there is a crack in the weld
When there is no crack in the welded part, peening treatment is performed on the welded part, and
When there is a crack in the welded portion, it is determined whether or not the crack is within a predetermined reference range, and
When the crack is within the predetermined reference range, the welded portion containing the crack is subjected to a peening treatment.
After the peening process, it is determined whether or not the shape of the indentation formed by the process meets a predetermined criterion.
Including methods. The welded portion is provided on the main plate of an existing bridge.
The method according to claim 1, wherein the predetermined criterion is that the crack is in the toe and does not extend to the base material of the main plate. The method according to claim 1 or 2, further comprising polishing the welded portion subjected to the peening treatment with an abrasive softer than the base material. The method according to any one of claims 1 to 3, wherein the welded portion is a rotary welded portion. The method according to any one of claims 1 to 4, wherein the peening treatment is an ultrasonic shock treatment, and the ultrasonic shock treatment uses a single pin.

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