JP3180117B2 - Corrosion protection method for cables for suspended structures - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing corrosion of cables for suspension bridges and cable-stayed bridges and cables for suspension structures used for suspension structures.

[0002]

2. Description of the Related Art In a cable for a suspended structure, it is extremely important to prevent corrosion of a large number of metal wires constituting the suspended cable. For this reason, various anticorrosion methods have been conventionally studied and put into practical use. In these anticorrosion methods, basically, a metal wire itself is galvanized, and the outer periphery of a bundled cable is coated or painted in multiple layers.

FIG. 18 shows an example of a conventional anti-corrosion structure. An anti-corrosion tape 3 made of synthetic resin or the like is wrapped around a cable 2 in which a large number of metal wires 1 are tightly bundled, and a cushion material 4 such as rubber is wrapped thereon. , And further covered with a plastic plate 5 and coated with a resin coating 6 such as epoxy on the final layer.
This is called a plastic wrapping method.

In another conventional example shown in FIG. 19, an anticorrosion paste 7 is applied to the outer surface of the cable 2 and 3 mm to 4 mm
A round wrapping wire 8 having a diameter of about mm is wound without any gap, and a resin coating 6 is applied to the final layer, which is called a wire wrapping method. Conventionally, a round wire is used as a wire used in the wire wrapping method. However, the wire can be meshed with an adjacent wire as shown in FIG.
A modified wire wrapping (modified wire) 10 having a substantially S-shaped cross section as shown in FIG. 0 has been proposed and put into practical use. The use of the deformed wire has an advantage that airtightness can be ensured because there is no gap between adjacent wires, so that the anticorrosion paste can be omitted.

[0005] As another conventional example, in order to further improve the airtightness, as shown in FIG.
There is also an advanced anticorrosion structure in which a rubber wrapping 12 is interposed. As described above, conventionally, a heavy-duty anticorrosion structure having a double or triple anticorrosion layer has been used for anticorrosion of a cable for a suspended structure.

The concept of cable corrosion protection in the above-described conventional corrosion protection technology is to block an external corrosive environment such as rainwater and moisture and an environment inside the cable by a covering layer on the cable surface.
It is intended to protect metal wires from corrosion. However, when these anticorrosive coatings are applied, moisture or moisture is trapped inside the cable, and dew condensation may occur on the surface of the metal wire. In addition, if the anticorrosion coating layer is deteriorated or damaged due to environmental factors such as ultraviolet rays, wind and rain, new moisture may enter the cable. For these,
For the first time, it can be protected from corrosion by galvanizing a metal wire. After applying the heavy corrosion protection described above, the applicants also set up an air chamber in the spray saddle part at one end of the suspension bridge cable, pass dry gas all at once to the spray saddle at the other end over the entire length, and dry the inside of the cable Japanese Patent Laid-Open No. 8-177012 discloses a means for preventing corrosion of a metal wire due to the state.

[0007]

However, the above-mentioned prior art is intended to dry a metal wire by sending dry gas from a single air chamber over the entire length of the suspension bridge cable, so that several thousand wires are required. In order to send the dry gas over a very small space made of metal wires of a very long cable of up to m, the dry gas entering the cable from the air chamber needs to be at a very high pressure, There is a possibility that the corrosion protection layer and the sealing portion of the cable surface layer may be damaged or malfunction may occur. Further, if there is a leak from a small gap such as a cable outer surface or a band portion, it is very difficult to supply air to the other end. The air chambers installed in the spray saddle section and the like are provided for every several hundred strands, so that the air chambers are large-scale. Further, since airtightness is required, a very complicated structure is required.

In the prior art, a suction device is provided on the outlet side to take measures to improve the flow of the dry gas.
If the inside of the cable becomes a negative pressure than the outside air, and there is a flaw in the coating, there is a problem that moisture or moisture easily enters from outside the cable particularly in rainy weather.

The present invention eliminates the above-mentioned problems by further improving the means for sending dry gas into the above-mentioned cable to prevent corrosion of the metal wire. It is an object of the present invention to provide an anticorrosion method for constantly drying the inside of a cable so that no moisture or dew is present on the surface thereof.

[0010]

According to the present invention, there is provided a method for preventing corrosion of a cable for a hanging structure according to the present invention, comprising the steps of bundling a number of metal wires and coating the outer periphery of the cable at appropriate intervals in the longitudinal direction of the cable for the hanging structure. The air supply unit and the exhaust unit that conduct inside the coating are exchanged.
It is characterized in that a plurality of dry gases are provided to each other , the dry gas is sent from the air supply section to the gap between the metal wires, and is exhausted from the exhaust section. The dry gas has a relative humidity of 60%
It is characterized by the following air or nitrogen gas. Further, the present invention is characterized in that the dry gas is continuously supplied while maintaining a pressure within a pressure range of the anticorrosion coating and a pressure equal to or higher than an external pressure.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1 to FIG. 6, an air supply unit 15 and an exhaust unit 16 that are electrically connected to the inside of the cable coating layer 14 are alternately attached at intervals of about 100 m in the longitudinal direction of the suspension structure cable 13. Air supply unit 15 and exhaust unit 16
Are formed by an air supply cover 17 and an exhaust cover 18 which are formed in a tubular shape by joining both ends of a half member of a tubular body.

More specifically, as shown in FIGS. 1 and 3, a drying dehumidifier 21 and a blower 22 are provided on the top 20 of a suspension bridge 19.
Is installed, and the drying gas is passed through a metal or plastic air supply pipe (pipe) 24 disposed along the cable 13 and branched from the air supply pipe 24. The branch pipe 25 is connected to the air supply cover 17 via a flow control valve 26 (shown in FIG. 2), and the dry gas flows from the air supply cover into the coating layer 14 of the cable 13.

The dry gas flowing into the cable 13 from the air supply cover 17 passes through the gap between the metal wires 1 through the cable 13.
, And is discharged from the exhaust port 27 of the exhaust cover 18, and a steady flow of dry gas is generated in the cable 13.

Due to the flow of the dry gas, the cable 1
3 to remove the existing water and moisture, etc.
To improve the wet ring inside. At the cable portion where the air supply cover 17 and the exhaust cover 18 are mounted, as shown in FIGS. 2 and 3, the coating layer 14 is not provided so that the air supply gas easily enters the gap between the metal wires 1 in the cable 13. A sealing material 28 such as a caulking material is applied to the joint portion between the end portions of the tubular air supply cover 17 and the exhaust cover 18, which are the same as the cable coating layer 14, and the cable coating layer 14 so as to be completely sealed. The exhaust cover 18 is provided with a temperature / humidity sensor 29. In the case of an existing cable, the cover wire layer is peeled off to expose the metal wire 1.

When air is supplied from the tower top saddle 20a, as shown in FIG. 7, the air supply cover members 30, 31 in which the upper surface of the tower top saddle 20a with the cable 13 exposed are formed of fiber-reinforced plastic. To completely cover and airtightly communicate with the cable covering layer 14 of the general part via the cable collar 32. This cable color 3
2, an end band 33 of the split cylinder is air-tightly attached to one of the air supply cover members 31 of the tower top saddle 20a, and the other end is air-tightly bonded to the cable covering layer 14 of the general portion with a sealing material 34. Airtightly installed through. The air supply pipe 24 passes through the one air supply cover member 31 and passes through the cable 13.
It is led along.

Cables for suspension structures used for suspension bridges and the like include:
As shown in FIG. 5, since the cable is a cable in which several hundreds to tens of thousands of metal wires having a diameter of about 5 mm are closely bundled in parallel, or a cable in which strands in which a number of metal wires are twisted are bundled in parallel. In the cable 13, a large number of small gaps 35 mutually formed by the metal wires 1 exist. Moreover, the gap 35 formed by the metal wire 1
Are not well-aligned and are generally irregular. The size of the gap 35 is about 0.5 mm to several mm in an equivalent diameter, and the gap existing in the cable is about 20% in terms of porosity with respect to the entire cable cross section based on the actual values of past suspension bridge cables. It is.
Therefore, although the entire space occupies a considerable area, the gas sent into the cable does not always flow uniformly over the entire cross section of the cable due to the unevenness of the space as described above.

On the other hand, moisture and moisture remaining in the gap 35 before the anticorrosion work are not easily removed naturally after the cable surface layer has been anticorrosive. In the present invention, as described above, by flowing a dry gas through the gap 35 between the metal wires 1 constituting the cable 13, high moisture due to moisture or moisture remaining inside the cable is changed, and the inside of the cable for the suspension structure is gradually changed. It changes to a dry environment and protects many metal wires that compose the cable from corrosion. In particular, by providing the air supply unit 15 and the exhaust unit 16 at predetermined intervals, the entire length of the long cable is reduced. The dry gas flows smoothly at an appropriate pressure.

[0018]

Embodiments of the present invention will be described below. As the dry gas, it is preferable to use air having a relative humidity as low as possible, and it is necessary to use dry air having a relative humidity of 60% RH or less. The reason for this is that, as shown in FIG. 8, in an environment having a relative humidity of 60% RH or less, the corrosion rate of the metal becomes extremely slow. Therefore, dry air having a relative humidity of less than this is used. If nitrogen gas is used as a dry gas, the air around the metal wire can be purged to be in an oxygen-free state, so that an environment free from corrosion can be obtained, and a high level of corrosion prevention can be performed.

Since the anticorrosion coating layer and the sealing portion of the cable band mounting portion are deteriorated or damaged by environmental factors such as ultraviolet rays and wind and rain over a long period of time, a gap communicating with the outside is required. Can be done. The dry gas flowing in the cable for the suspension structure flows through the gap between the metal wires while leaking from such a gap. Therefore, since it is important that the corrosion prevention layer on the cable surface is not destroyed by the internal pressure or the damaged portion is not enlarged, it is necessary to flow at a pressure as low as possible within the pressure resistance of the coating layer.
In general, the experimental results show that the pressure is highest near the air supply section as shown in FIG. 17, and decreases as the air flows through the cable. At the exhaust part, the pressure is finally adjusted to be equal to or slightly higher than the atmospheric pressure. Since the pressure depends on the cable specifications, the air supply length, the air supply flow rate, the leakage amount, and the like, the pressure is determined in consideration of these factors. Cable diameter 1m
When the air supply length is about 100 m at the actual bridge level, the air supply flow rate per location is about 3 m ³ / min, and the pressure is about 300 mmAq. If the pressure is on the order of magnitude, there is no problem at all on the anticorrosion coating layer, and since the internal pressure of the cable can be made higher than the external pressure, it is possible to prevent moisture and moisture from entering the cable.

The distance between the air supply and exhaust covers attached to the cable for the suspension structure is gradually reduced because the air flows through the gap between the metal wires with slight leakage from the outer periphery of the cable and the sealing portion of the cable band attachment portion. I do. For this reason, in order to dry the vicinity of the exhaust part, it is necessary to set an appropriate air supply section length. For example, when the outer periphery of the cable is covered by a wire wrapping method, which is a conventional cable anticorrosion method, the air supply length that can be dried is about 100 m. Therefore, in order to extend the air supply length, the outer surface of the cable is covered with a conventional wire wrapping method as described above with rubber wrapping, a wrapping method with a substantially S-shaped irregular cross section, or stainless steel or the like. It is desirable to adopt a method of coating a metal cover such as titanium to reduce leakage from the cable surface layer.

If the seal structure of the band portion is excellent in pressure resistance as shown in FIGS. 9 and 10, the airtightness of the cable can be further improved. That is, the pair of band members 36 are
By tightening at 7, both ends in the cable longitudinal direction of the cable band 38 for directly fastening the outer surface of the wire bundle of the metal wire 1, the wrapping wire 39 covering the metal wire 1, the cable coating layer 14, and the anticorrosion coating layer 40, an annular groove 41 is formed. The groove 41 is filled with a butyl rubber 42, and the anticorrosion coating layer 40 and the cable band 38 are formed.
A sealing material 43 is loaded between the sealing member 43 and the outer peripheral end face.
With this structure, the cable coating layer 14 and the anticorrosion coating layer 40
The gap between the end of the cable band 38 and the end face of the cable band 38 is sealed by the butyl rubber 42 and the sealing material 43, so that gas sent to the gap between the metal wires 1 does not leak from the cable band.

Once the moisture and / or moisture accumulated in the gap between the cable metal wires is dehumidified, the air supply flow rate thereafter can be reduced to such a degree that it flows slightly over the entire length of the air supply section.
It is preferable to adjust the air supply flow rate while controlling the temperature, humidity, and pressure with a temperature / humidity sensor or an exhaust cover attached to the exhaust unit, or a micro-pressure gauge attached near the exhaust cover.

The anticorrosion of the cable for the suspension structure supports the suspension bridge and the entire suspension structure, and it is very difficult to replace the cable in the future. Therefore, it is desirable to adopt the above-described anticorrosion method from the completion stage. Also in the cable for a suspension structure of a bridge, it can be sufficiently adopted because corrosion can be prevented or the progress can be delayed. Further, the present invention can be applied to a cable of a suspension bridge main cable, a cable-stayed bridge cable, a suspension roof building, and the like.

[Experimental Examples] Element tests and actual bridge tests on existing bridge cables were conducted with respect to the dehumidifying effect and gas flow in the cables, which are the points of the method of preventing corrosion of the cables for suspension structures according to the present invention. The results will be described below.

Dehumidification Effect FIGS. 11 and 12 show schematic diagrams of an experiment for dehumidification in a cable. In the experiment, about 5 mm of the same diameter as that used for the suspension bridge cable was used.
11,500 galvanized steel wires with a diameter of 2 mm and a length of 2 m are bundled in parallel to make the diameter of the cable 13 600 mm, the cable surface layer is covered with resin, and both end faces 44 are only partial cross sections (φ300 mm) in the cable. Other parts were sealed by a plate so that a dry gas could flow. Then, the drying gas from the drying air supply device including the blower 45 and the drying dehumidifier 46 is sent into the cable 13 from the cable end face 44 through the circulation hose 48 in which the flow meter 47 is interposed upstream, and from the other end 44a. An experiment was conducted by constructing a circulating system that flows again through the drying air supply device through a reducer and a hose. Put 3 liters of water in the cable in advance and make it wet, and supply air at a relative humidity of 24%.
The dry gas of about RH was adjusted to 1 m3 / min. The measurement was to measure the amount of dehumidification drained by the dehumidifier. In FIG. 12 , a micro pressure gauge 51 is provided at one end of the cable 13 on the dry gas inflow side, and the dehumidifier 46 is provided so as to be drained by a drain hose 52.

FIG. 13 shows the results of the air supply time and the dehumidification amount obtained in the above experiment. As can be seen from this result, the amount of dehumidification per unit time is very large for about ten and several hours from the start of the experiment, and then drops sharply and becomes almost steady at about ten and several g / hr after 25 hours, and at about 140 hours Water in the cable was removed. This is because the dry gas in the middle and upper part of the cable is easy to flow, and the water that has accumulated in the gap between the metal wires that is relatively easy to dehumidify is removed first, and then the hard-to-evaporate moisture that has accumulated in the lower part of the cable is removed. it is conceivable that. Therefore, the moisture present in the cable
It was confirmed that if the dry gas flowed even partially, it could be removed over time. FIG. 14 shows the results of an experiment on the change in the amount of dehumidification when the air supply flow rate was changed. It can be seen from this figure that the dehumidification rate depends on the flow rate of the dry gas.

Next, a description will be given of the results of an actual bridge experiment conducted with an existing suspension bridge cable. As shown in FIG. 16, an air supply cover is attached to the center of the center span to provide an air supply humidity inlet 53, from which dry gas produced by a dry air supply device is sent to both sides of the cable 13 at 1 m ³ / min. I noticed. The pressure of the air supply cover was kept constant at about 320 mmAq during the experiment. The measurement was carried out by installing a hygrometer and a micro pressure gauge at (a) an air supply section, (b) at a distance of 10 m, (c) at a distance of 50 m, and (d) at a position of 100 m. In addition, the micromanometer was further installed at a point 150 m, 200 m, and 240 m away. FIG. 15 shows a change in relative humidity at each point obtained in the experiment. By the dry gas sent from the air supply section provided in the cable, (c), (c),
(D) and the humidity in the cable gradually decreases, and (d) 10
At the 0 m position, it took about 45 days for the relative humidity, which was initially 90% RH or higher, to reach 60% RH or lower, which is a relative humidity level at which corrosion does not occur. Also, after 35 days, (b) at a position 50 m away, it drops to about 10% RH,
That state is maintained. The x mark in FIG. 15 indicates the relative humidity of the outside air, which fluctuated in the range of 90% to 40% RH during the experiment.

The moisture and moisture remaining in the cable even at a position 100 m away from the air supply section can be removed by flowing a dry gas through the cable, so that after about 1.5 months, the relative humidity of 60% RH at the corrosion limit is reached. It can be reduced to: During the experiment, it rained for three days, but since the relative humidity in the cable did not change, the pressure in the cable was higher than the outside air pressure while sending dry gas.
It was confirmed that new moisture did not enter the cable and was not affected by external humidity. It has been confirmed that a sufficiently dry state can be maintained by flowing a dry gas through the cable as described above.

Gas Flow in Cable for Suspended Structure FIG. 17 shows the measurement result of the pressure of the dry gas measured by the micro pressure gauge 51 in FIG. From this result, it was found that the pressure of the dry gas sent from the air supply section gradually decreased as the distance increased, but pressure transmission of about 240 m was possible even at a very low pressure of about 320 mmAq.

However, in the suspension bridge 19 shown in FIG.
Experimental results under various conditions in which the middle of the cable 13 erected between the tower tops was set to the air-supply / humidity inlet section 53 show that, from FIG. 15, near the tip of the gas flow, time was required for dehumidification and the efficiency was low. It is better to set a distance of about 100 m from the air supply unit to a dehumidifying distance. In this experiment, it is confirmed that a slight leak was detected from the cable surface layer or the sealing portion of the cable band. Therefore, it is considered that if the leakage to the outside of the cable is reduced and a highly airtight anticorrosive coating is used, the drying distance can be more efficiently extended.

[0031]

As described above, according to the present invention, the air supply portion and the exhaust portion which are conducted inside the coating are alternately arranged at appropriate intervals (hundred to several hundred m) in the longitudinal direction of the cable for the suspension structure. Each
Plurality, the dry gas steadily and air in the cable Re,
Since the gas containing moisture is exhausted, the dry gas flowing in the cable flows smoothly, and the moist environment in the structural cable can be improved to a dry environment that is less likely to rust. In addition, since the pressure of the dry gas is within the range of the pressure resistance of the anticorrosive coating and equal to or higher than the external pressure, even if the coating has damage or leaks, it prevents new intrusion water from outside in rainy weather etc. Thus, there is an effect that the function as a structure of the suspension structure cable can be maintained for a long time.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the entire structure of an example in which the anticorrosion method of the present invention is applied to a suspension bridge cable.

FIG. 2 is an explanatory side view showing a system outline of the anticorrosion method of the present invention in the suspension bridge cable of FIG. 1;

FIG. 3 is a cross-sectional view of the air supply unit in FIG. 2 in a direction perpendicular to the axis.

FIG. 4 is a sectional view of the general cable section in FIG. 1 in a direction perpendicular to the axis.

FIG. 5 is an enlarged sectional view showing a part of a metal wire bundle in a cable.

FIG. 6 is a diagram of an air-drying device provided at the top of a suspension bridge.

FIG. 7 is an explanatory diagram of an example of a cover structure of a tower top saddle portion.

FIG. 8 is a graph showing a relationship between a relative humidity and a corrosion rate of a metal wire.

FIG. 9 is a perspective view of an example of a seal structure of a cable band portion.

FIG. 10 is an enlarged sectional view of a portion A in FIG. 9;

FIG. 11 is a diagram showing a dimensional relationship of a full-size cable used in a dehumidification experiment.

12 is a configuration diagram of a dehumidification experiment using the full-size cable of FIG.

FIG. 13 is a graph showing experimental results of dehumidification time and dehumidification amount.

FIG. 14 is a graph showing a relationship between an air supply flow rate and a dehumidification amount.

FIG. 15 is a graph showing the relationship between the air supply time and the relative humidity based on the experimental results at the actual bridge.

FIG. 16 is an explanatory diagram showing a real bridge in the experiment of FIG.

FIG. 17 is a graph showing a result of a pressure distribution in an actual bridge.

FIG. 18 is a perspective view of a cable provided with anticorrosion specifications by a conventional plastic wrapping method.

FIG. 19 is a perspective view of a cable that has been subjected to anticorrosion specifications by a conventional wire wrapping method.

FIG. 20 (A) is a perspective view of a cable provided with anticorrosion specifications by a conventional S-shaped wire wrapping method, and FIG. 20 (B) is a partial cross-sectional view of part (A) of FIG.

FIG. 21A is a perspective view of a cable provided with anticorrosion specifications by a conventional rubber wrapping method, and FIG. 21B is a partial cross-sectional view of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 metal wire 2 cable 3 anticorrosion tape 4 cushion material 5 plastic material 6 resin coating 7 anticorrosion paste 8 wrapping wire 10 deformed wire wrapping 11 wrapping wire 12 rubber wrapping 13 cable 14 cable coating layer 15 air supply unit 16 exhaust unit 17 air supply cover 18 Exhaust Cover 19 Suspension Bridge 20 Tower Top 20a Tower Saddle 21 Dry Dehumidifier 22 Blower 23 Air Supply Drying Device 24 Air Supply Tube 25 Branch Pipe 26 Flow Rate Control Valve 27 Exhaust Port 28 Sealing Material 29 Temperature / Humidity Sensor 30 Air Supply Cover Member 31 Transmission Air cover member 32 cable collar 33 end band 34 sealing material 35 gap 36 band member 37 band bolt 38 cable band 39 wrapping wire 40 anticorrosion coating layer 41 concave groove 42 butyl rubber 43 sealing material 44 End surface 45 the blower 46 dehumidifier 47 flowmeter 48 hose 49 hygrometer 50 humidity meter 51 micromanometer 52 drain hose 53 air humidity inlet

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Morio Seio 2-3-6 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Steel Corporation (72) Inventor Tatsuya Eguchi 2-chome Otemachi, Chiyoda-ku, Tokyo No. 6-3 Inside Nippon Steel Corporation (72) Inventor Shoichi Saeki 4016-19 Tsuna, Tsuchiura City, Ibaraki Prefecture (72) Inventor Hiroki Matsumoto 3-13-19 Midorigaoka, Ogawamachi, Hiki-gun, Saitama Prefecture (72) Invention Motoki Okuda 2-2-5 Kyoyama, Okayama City Towa High Town Kyoyama 401 (72) Inventor Kazuhiko Furuya 3-18-5 Hanazono-ku Hanazono-ku, Chiba-shi Park Avenue 203 (72) Inventor Kyoichi Kaneda 3 1-1-13 Chome Inside Honshu-Shikoku Bridge Engineering Co., Ltd. (72) Inventor Shunichi Kuwamoto 1-3-18 Wakihama-cho, Chuo-ku, Kobe Inside Kobe Steel, Ltd. (56) Reference Document JP-flat 8-177012 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) E01D 19/08 E01D 11/00

Claims (3)

(57) [Claims] 1. A cable for a hanging structure having a plurality of metal wires bundled and coated on the outer periphery thereof at appropriate intervals in the longitudinal direction.
Alternating the air supply unit and exhaust unit conducting inside the coating
A method for preventing corrosion of a cable for a suspension structure, wherein a plurality of dry gases are provided from the air supply unit to a gap between the metal wires and exhausted from the exhaust unit. 2. The method according to claim 1, wherein the dry gas is air or nitrogen gas having a relative humidity of 60% or less. 3. While maintaining the dry gas at a pressure within the pressure range of the anticorrosion coating and at a pressure equal to or higher than the external pressure,
The method according to claim 1 or 2, wherein the air is supplied continuously.