JP2024017508A - Maintenance method for steel bridge - Google Patents

Abstract

To provide a maintenance method for a steel bridge capable of preventing the reoccurrence of a crack generated in a steel material not temporarily but for a longer period of time.SOLUTION: A maintenance method of a steel bridge suppresses the growth of the crack 110 by forming a through-hole 100 at the tip part of the crack 110 to the crack 110 generated in the steel material 90 of the existing steel bridge and includes a through-hole forming step of forming the through-hole 100 by projecting a projection material and imparting compressive residual stress to the peripheral edge and the inner peripheral surface of the through-hole 100.SELECTED DRAWING: Figure 3

Description

The present invention relates to a steel bridge maintenance method for suppressing the growth of cracks that have occurred in the steel materials of an existing steel bridge by forming through holes at the tips of the cracks.

Existing steel bridges deteriorate over time (fatigue) due to vibrations caused by the passage of heavy vehicles and weather changes such as wind and snow, and cracks (fatigue cracks) may occur in the steel materials used. If the cracks are left untreated, the ends will stretch and grow, so it is necessary to deal with them as soon as possible upon discovery.

Several proposals have been made to date to deal with cracks in steel materials. The known ones are described below.

There is a method to prevent crack growth by applying a patch to cover the crack (plaster repair method). This has a high repair effect and is highly effective in preventing the occurrence of cracks again. However, preparing a caul plate of an appropriate size and fixing the caul plate is extremely time-consuming and increases maintenance costs.

There is also a re-welding method in which the cracked part is removed and the removed part is covered by welding. However, such a configuration also requires complicated repairs and increases maintenance costs.

Furthermore, when a crack has occurred in a welded part, there is a cutting removal method in which the crack in the welded part is removed by cutting. Such a configuration has a problem in that the parts that can be addressed are limited. Furthermore, since the strength of the removed portion is not improved, there is a risk that cracks will occur again.

There is also a peening method that closes cracks by performing peening treatment along the cracks. This needs to prevent the scattering of dust, but it can also be expected to have the effect of improving the fatigue strength of the steel material as well as dealing with cracks.

Furthermore, there is a stop hole method, as disclosed in Patent Document 1, in which a hole (stop hole) is formed at the tip of the crack to temporarily prevent the growth of the crack. In the stop hole method, a stop hole can be formed as soon as a crack is discovered, and it is very useful as a temporary solution because it does not require much effort or cost.

JP 2020-7713 Publication

However, the above-mentioned stop hole method is only a temporary measure, and cracks often re-occur from the stop hole in a short period of time.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a steel bridge maintenance method that can prevent cracks occurring in steel materials from reoccurring not temporarily but over a longer period of time.

The present invention is a steel bridge maintenance method that suppresses the growth of cracks by forming through holes at the tips of cracks that have occurred in the steel materials of existing steel bridges. A steel bridge maintenance method comprising a through hole forming step of forming the through hole in the steel material by projecting a projectile material and applying compressive residual stress to the peripheral edge and inner peripheral surface of the through hole. .

In such a configuration, since compressive residual stress is applied to the periphery of the through hole (stop hole) by the projection of the blast material, it is possible to effectively prevent cracks from reoccurring from the through hole. .

Further, before the through-hole forming step, a guide hole forming step of forming a guide hole having a predetermined hole diameter at or around the tip of the crack so as to penetrate the steel material, the through-hole In the forming step, a configuration is proposed in which a projection material is projected around the guide hole to enlarge the diameter of the guide hole to form the through hole.

With this configuration, when the projection material collides with the steel material and is reflected in the through-hole forming process, it is possible to suppress the collision between the reflected projection material and the projected projection material and a decrease in projection efficiency. can do. Furthermore, since the diameter of the hole increases along the guide hole, it is possible to prevent the through hole from being formed in an unintended direction or position.

Further, a configuration is proposed in which the blast material is a shot used in shot peening treatment for improving the fatigue strength of the steel material.

With this configuration, compressive residual stress can be effectively applied to the steel material.

Further, the method further includes a blasting step of performing a blasting treatment to condition the surface of the steel material, and a peening step of performing a shot peening treatment on the surface of the steel material to improve fatigue strength, and the peening step includes the step of performing a shot peening treatment to improve the fatigue strength. A configuration is proposed that includes a hole formation step.

By adopting such a configuration, it is possible to reduce the labor and cost of construction related to the steel bridge maintenance method of the present invention. Further, there is no need to perform finishing treatment on the inner circumferential surface of the through hole drilled in the peening process, which further saves time and effort.

The steel bridge maintenance method of the present invention has an excellent effect of preventing the recurrence of cracks over a long period of time.

FIG. 2 is a flow diagram showing the procedure for maintenance painting of a steel bridge according to an example. FIG. 1 is a schematic explanatory diagram illustrating a circulating blasting device according to an embodiment. It is an explanatory diagram showing a procedure of forming a stop hole for a crack according to an example, (a) is a state before forming a stop hole, and (b) is a state after forming a stop hole. . FIG. 3 is an explanatory diagram of another example, in which (a) shows a state after a guide hole is formed, and (b) shows a state after the guide hole is expanded in diameter and a stop hole is formed. FIG. 7 is an explanatory diagram showing a longitudinal section of a steel material in which guide holes are formed in another example.

Hereinafter, embodiments embodying the steel bridge maintenance method according to the present invention will be described in detail. Note that the present invention is not limited to the embodiments shown below, and design changes can be made as appropriate.

The steel bridge maintenance method of this embodiment is performed as part of repainting (maintenance painting) performed for the purpose of preserving an existing steel bridge. First, I will explain maintenance painting of steel bridges.

As shown in Figure 1, the procedure for maintenance painting of a steel bridge (steel structure) is to first temporarily erect scaffolding on the steel bridge that is to be painted. At the same time, preliminary preparations are made (S101) such as installing a dustproof sheet to prevent dust from leaking to the outside, curing unpainted areas, and installing equipment for blasting and shot peening.

Thereafter, the type and thickness of the old paint film applied to the steel bridge, the condition of the steel bridge, etc. are investigated (S102). Then, based on the survey results, the type of grit and shot to be used, the injection speed, etc. are determined. Here, the selected grit (non-spherical shape) and shot (spherical shape) are both defined in JIS Z 0311:2004.

Then, using the grit determined in S102, a blasting process is first performed (S103). Specifically, the coating film to be removed on the steel bridge is removed and the surface condition is adjusted. Such blasting constitutes the blasting step in the present invention. Note that peeled paint, rust, etc. and used grit are generated as dust by the blasting process, but since a dustproof sheet is installed in S101, the dust does not leak outside. is accumulating on the work site.

Subsequently, the shot determined in step S102 is loaded into the blasting device that has sprayed the grit, so that the shot can be sprayed. This process constitutes a shot replacement process.

Then, the shot peening process is performed on the blasted part where the base surface has been exposed by the blasting process using the apparatus replaced with the shot (S104). Such treatment constitutes a peening process that improves the fatigue strength and stress corrosion cracking resistance of the base surface. Note that the used shot generated by the shot peening process continues to accumulate as dust at the work site, mixed with the used grit in S103. Incidentally, the shot peening treatment may be performed on all the base surfaces that have been subjected to the above-mentioned blasting treatment, or it may be performed on a portion of the base surface that has been subjected to the above-mentioned blasting treatment, as appropriate, such as around welded areas or areas where the strength is uncertain.

Thereafter, the base surface that has been subjected to the blasting process and the shot peening process is confirmed (S105). Such confirmation includes not only visual confirmation but also, for example, comparison using an ISO8501 blast photo book or roughness confirmation using a surface roughness measuring device. This allows it to be confirmed whether there is any unpeeled paint remaining or whether the roughness of the base surface is within the specifications, and appropriate treatment can be carried out on any insufficient areas. For example, in areas where blasting cannot be performed, the surface is adjusted using hand tools.

A final finish coating is applied to the part whose base surface has been confirmed in this way to form a final coating film (S106). In addition, such coatings are generally applied in multiple layers, such as an undercoat as a rust-preventive coating, an intermediate coat to protect the rust-preventive coating, and a topcoat as a final finishing coat. .

When the painting work is completed, confirmation thereof is performed (S107). Such confirmation includes not only checking the film thickness after the coating has dried, but also, for example, checking the wet film thickness using a wetness gauge during the painting operation. Further, such confirmation is performed not only after the top coat, which is the final finishing coat, but also during the undercoat and intermediate coat.

When the painting work is completed according to the above confirmation, the site is cleaned up (S108). Specifically, the maintenance painting will be completed after collecting the scaffolding, dustproof sheets, etc., and removing the blast-shot peening equipment.

In addition to the above procedure, a dust collection step is also executed (S110). Specifically, the used grit generated in the blasting process (S103), the used shot generated in the shot peening process (S104), and the dust containing flakes and rust generated in each process are separated. We will collect it.

The collected used grit and used shot are both iron (metallic) abrasives specified in JIS Z 0310:2004, so even if they collide with a steel bridge during use, they will not be abrasive like almandite garnet or steel slag. It does not need to be crushed and can be reused. Among them, high-carbon cast steel can be reused approximately 600 times, making it extremely economical, and by separating it from peeled paint and other foreign matter, the amount of waste can be significantly reduced. .

Below, we will explain a circulating blasting device 1 that can spray grit and shot with a common device, and can collect and separate used grit, used shot, peeled paint, etc. This will be explained as an example.

As shown in FIG. 2, the circulating blasting apparatus 1 includes an apparatus main body part 2 installed adjacent to a work site α of a steel bridge K to be worked. Further, the main body 2 of the device includes a pressure hose 4, and an injector 3 is connected to the tip of the pressure hose 4. The injector 3 injects grit or shot. Further, the device main body 2 includes a suction hose 5, and the tip of the suction hose 5 is disposed at the work site α. Thereby, it is possible to suction the dust generated at the work site α, which consists of used grit, used shot, and foreign matter including peeled paint films, rust, etc., through the suction hose 5. In order to prevent dust from leaking outside, a dustproof sheet (not shown) is stretched over the work site α, and blowers, dust collectors, etc. are also installed as appropriate.

Further, as shown in FIG. 2, a grit hopper tank 10 and a shot hopper tank 20 are disposed adjacent to each other in the apparatus main body 2 of the circulating blasting apparatus 1. More specifically, the grit hopper tank 10 has the function of storing grit and used grit. Further, the shot hopper tank 20 has a function of storing shots and used shots. Furthermore, a grit pressurizing tank 11 is connected to the grit hopper tank 10 for pressure-feeding the grit stored in the grit hopper tank 10 to the work site α. Similarly, the shot hopper tank 20 is connected to a shot pressurizing tank 21 for pressure-feeding the shot stored in the shot hopper tank 20 to the work site α.

Further, a dry compressed air supply means 30 is connected to the grit pressurized tank 11 and the shot pressurized tank 21 via a dry compressed air pipe 31. The dry compressed air supply means 30 is composed of an air compressor and an air dryer for supplying dry compressed air. Further, the dry compressed air piping 31 is equipped with a switching valve 32, which allows dry compressed air to be selectively fed to the grit pressurizing tank 11 or the shot pressurizing tank 21, and shot instead of grit. It can be loaded and sprayed at will.

Further, the pressure feeding hose 4 is connected to the grit pressure tank 11 and the shot pressure tank 21. With this configuration, grit or shot is injected from the injector 3 via the pressure hose 4 by the air pressure of the dry compressed air supplied from the dry compressed air supply means 30, and is blasted onto the steel bridge K to be worked. treatment or shot peening treatment can be performed. Note that a blast-shot peening injection device is constituted by the circulating blasting device 1 having the conventional functions.

Dust containing foreign matter such as used grit, used shot, and peeled paint film accumulated at the work site α is sucked all together from one end of the suction hose 5. Then, the dust X sucked by the suction hose 5 reaches the separation chamber 40.

Further, a dust hose 51 is attached to the separation chamber 40, and a dust collection section 50 as a peelable coating film collection section is connected to the dust hose 51. Further, an air suction device 60 as a dust suction means is connected to the dust collection section 50. Therefore, the dust X can be sucked by the air suction force of the air suction device 60.

Here, a discharge section is provided on the downstream side of the separation chamber 40, and the discharge section is connected to the dust hose 51 and to the air suction device 60 via the dust collection section 50. has been done.

Here, the dust introduced into the separation chamber 40 from the suction hose 5 advances at a predetermined speed due to the air suction force of the air suction device 60, and foreign substances such as peeled paint films and rust that have a light specific gravity are removed. It is discharged as is along with the air flow. The discharged foreign matter is introduced into the dust collection section 50 via the dust hose 51, is deposited in the dust collection section 50, and is discharged into a waste bag 52 at a desired timing to be treated as industrial waste.

In addition, since the used grit and used shot are iron (metallic) abrasives, they have a heavy specific gravity, and when given a certain speed, they collide with a specified reflector, and based on the difference in the distance they bounce back, the used It becomes possible to separate out foreign substances including grit, used shot, and peeled paint. The used grit thus separated is returned to the grit hopper tank 10 located below the separation chamber 40 and reused. Similarly, used shots are also returned to the shot hopper tank 20 located below the separation chamber 40 for reuse. In this way, grit and shot can be cycled and used continuously.

In addition to the embodiments described above, the design can be modified as appropriate. For example, the switching valve 32 may be provided in the work site α so that the operator H at the work site α can switch it, or it may be remotely controllable. Moreover, the injector 3 and the suction hose 5 may be separate bodies or may be integrated (vacuum blast type). Further, the dry compressed air supply means 30 may be provided separately in the grit pressurizing tank 11 and the shot pressurizing tank 21, respectively. Further, the pressure feeding hose 4 may be provided separately for grit and shot. Further, the injector 3 may be similarly divided into one for grit and one for shot. Furthermore, the separation chamber 40 does not need to be placed directly above the grit hopper tank 10 and the shot hopper tank 20, and its position is not particularly limited. Furthermore, the method for realizing an airtight space within the flow path 41 is not particularly limited. For example, each hopper tank 10, 20 may be made airtight while communicating with the grit hopper tank 10 and shot hopper tank 20, or a dedicated tank for temporarily storing grit or shot may be arranged and Hopper tanks 10, 20 may be supplied with grit and shot. Further, it is desirable to be able to supply a new product when the amount of grit or shot in the circulating blasting device 1 becomes less than a specified value. Further, the device main body 2 may be placed on a vehicle and movable, for example.

Furthermore, in this embodiment, a common projection material having a spherical shape portion while having corners and ridges may be used without separating the grits and shots. For example, conditioned cut wire shot may be proposed as a common projection material.

The main parts of the present invention will be explained below.

In the above S102 (construction target survey), if cracks are found in the steel material, stop holes are installed to deal with the cracks in parallel with the surface treatment of the steel material performed in the blasting process in S103 or the shot peening process in S104. Form.

That is, when forming a stop hole in S103, when blasting the surface of the steel material, at the site where a crack has occurred, grit is projected onto the end of the crack using the blasting equipment that performs the blasting. and drill a stop hole in the shape of a through hole.

In addition, when forming a stop hole in S104, when performing shot peening treatment on the surface of the steel material, at the site where a crack has occurred, a shot peening treatment is performed at the end of the crack using a shot peening equipment. Project and drill a through-hole-shaped stop hole.

In either case, after the stop hole is formed, if necessary, finishing treatment such as deburring the hole edge of the stop hole is performed as appropriate.

In this way, the step of forming a stop hole consisting of a through hole by projecting the shot material and applying compressive residual stress to the periphery of the through hole corresponds to the through hole forming step in the present invention.

Compressive residual stress is applied to the hole edge and inner peripheral surface of the formed stop hole, which has higher fatigue strength than the conventional stop hole method and can effectively prevent crack recurrence.

The method of forming stop holes in this example will be explained below.

As shown in FIG. 3, the stop hole 100 is formed at the end of a crack 110 that has occurred in the steel material 90.

To form the stop hole 100, any of grit, shot, and common projectile material may be used.

Here, compressive residual stress is applied to the periphery of the stop hole 100 formed by projection of grit, shot, or common projection material. As a result, the fatigue strength of the steel material 90 at the periphery of the stop hole is improved, and recurrence of cracks can be effectively prevented.

As an example, a steel material (SS400) with a thickness of 6 mm was prepared as a test specimen, and drilling was attempted using grit. The test conditions are as follows.

Projection material Steel grit Same as those used in construction, and complies with JIS Z 0311:2004.
Projection conditions Nozzle diameter 8mm
Applied pressure 0.7MPa
Projection distance 50mm

As a result of carrying out the test under the above conditions, a through hole was formed in about 3 minutes. Further, at a position 1 mm away from the formed through hole, a maximum compressive residual stress of about -140 MPa was measured at a depth of 90 μm from the surface. It was confirmed that compressive residual stress was applied to a depth of 800 μm at the position.

At a position 2 mm and 3 mm away from the formed through hole, a maximum compressive residual stress of about -170 MPa was measured at a depth of 160 μm from the surface. In all of these positions, compressive residual stress could no longer be confirmed at a depth of about 300 μm from the surface.

Furthermore, when a stop hole was provided by projecting a shot for shot peening treatment as a projection material, no finishing treatment was required on the inner circumferential surface of the stop hole. In the fatigue test, cracks were observed at the edge of the stop hole after approximately 600,000 cycles at a stress range of 100 MPa.

Further, as the projection material, the same round cut wire (grain size of 0.8 mm or more and 1.0 mm or less) as used in construction can be used.

As shown above, it has been found that the present invention in which stop holes are formed by projecting a projectile material is very effective. In addition, by using shot for shot peening treatment as the shot material, there is no need for finishing treatment on the inner circumferential surface of the stop hole, and the effect is high.

In addition, in the steel bridge maintenance method of the present invention, before forming a through hole as a stop hole, a guide hole having a diameter smaller than that of the through hole is formed at the tip of the crack or around the tip of the crack. It may also include a step of forming a guide hole in advance so as to penetrate the steel material. In this case, in the through-hole forming step, the diameter of the guide hole is expanded by projecting a projection material around the guide hole, thereby forming the through hole as a stop hole.

More specifically, as shown in FIGS. 4A and 5, a small-diameter guide hole 140 is first provided in a penetrating manner at the end of a crack 130 that has occurred in the steel material 120. The guide hole 140 is formed using a known drill or the like. Then, by projecting the projection material toward the guide hole 140, the diameter of the guide hole 140 is expanded, and the guide hole 140 becomes a stop hole 150 as a through hole, as shown in FIG. 4(b).

Even in this case, compressive residual stress is applied to the edge of the stop hole 150, thereby improving fatigue strength.

In this way, by preliminary forming the guide hole 140 before forming the stop hole 150, it is possible to suppress the collision between the reflected projection material and the projected projection material and a drop in projection efficiency. I can do it. Further, it is possible to prevent the stop hole 150 from being formed in an unintended direction or at an unintended position.

In the steel bridge maintenance method of the present invention, compressive residual stress is applied to the edge of the stop hole, which improves fatigue strength and ensures safety over a long period of time rather than a temporary repair. I can expect it. The shot material used is preferably shot used in shot peening treatment to improve fatigue strength.

In the embodiments described above, the dimensions and shapes of each part can be freely selected as appropriate.

1 Circulating blasting device 40 Separation room 50 Dust recovery section (peeling paint film recovery section)
60 Air suction device (dust suction means)
90,120 Steel material 100,150 Stop hole (through hole)
110,130 Crack 140 Guide hole K Steel bridge

Claims (4)

A steel bridge maintenance method that suppresses crack growth by forming a through hole at the tip of a crack that has occurred in the steel material of an existing steel bridge,
The step includes a through hole forming step of forming the through hole in the steel material by projecting a blasting material around the tip of a crack that has occurred in the steel material, and applying compressive residual stress to the periphery and inner peripheral surface of the through hole. A steel bridge maintenance method featuring: Before the through hole forming step, a guide hole forming step of forming a guide hole having a predetermined hole diameter at the tip of the crack or around the tip so as to penetrate the steel material,
2. The steel bridge maintenance method according to claim 1, wherein in the through hole forming step, a projection material is projected around the guide hole to enlarge the diameter of the guide hole to form the through hole. 3. The steel bridge maintenance method according to claim 1, wherein the shot material is shot used in shot peening treatment for improving fatigue strength of the steel material. a blasting step in which blasting is performed to condition the surface of the steel material;
a peening step of subjecting the steel surface to shot peening treatment to improve fatigue strength;
further including;
The steel bridge maintenance method according to claim 1 or 2, wherein the peening step includes the through hole forming step.

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