maintenance of steel bridges on honshu-shikoku crossing

Journal of Constructional Steel Research 58 (2002) 131–150www.elsevier.com/locate/jcsr

Maintenance of steel bridges on Honshu-Shikoku crossing

Yukikazu Yanaka, Makoto Kitagawa*

Honshu-Shikoku Bridge Authority, 4-1-22 Onoedori, Chuo-ku, Kobe 651-0088, Japan

Abstract

This paper describes maintenance technologies of Honshu-Shikoku bridges in Japan. TheHonshu-Shikoku bridges feature many long-span cable supported bridges. Akashi Kaikyobridge is known as the longest-spanned suspension bridge, and Tatara bridge is known as thelongest-spanned cable stayed bridge. The Kojima-Sakaide route, the so-called Seto Ohashibridge, features highway and railway combined structures. Since the opening of the first bridge,maintenance technologies of Honshu-Shikoku bridges have been accumulated for about 20years.

The most important maintenance technology for steel bridges on the sea is how to protectsteel members from corrosion. In this paper, as examples of anti-corrosion methods for steelbridges, repainting of bridges by heavy-coated paint, the dehumidification method for thecables of suspension bridges, and the anti-corrosion method for the steel caissons in the seaare described.

Furthermore, a monitoring system to detect weld defects in the railway structures relatedto fatigue problems is described. Lastly, measurement of the static and dynamic behavior ofbridges to verify design assumptions on a bridge’s behavior and to ascertain a bridge’s sound-ness is described. 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Honshu-Shikoku bridges; Maintenance technology; Painting; Cable; Caisson; Fatigue;Monitoring

* Corresponding author. Tel.:+81-78-291-1053; fax:+81-78-291-1362.E-mail address: [email protected] (M. Kitagawa).

0143-974X/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved.PII: S0143 -974X(01)00031-1

132 Y. Yanaka, M. Kitagawa / Journal of Constructional Steel Research 58 (2002) 131–150

1. Introduction

1.1. Construction of Honshu-Shikoku bridges

The Honshu-Shikoku bridges comprise three routes that cross the Seto Inland Seabetween Honshu and Shikoku from north to south. A map of these three routes isshown in Fig. 1.

Kobe-Naruto route is an 89 km long expressway from Kobe City in Honshu viaAwaji Island to Naruto City, Tokushima Prefecture in Shikoku. There are two long-span suspension bridges on this route: Akashi Kaikyo bridge, which is the longestbridge in the world, and Ohnaruto bridge. Ohnaruto bridge was constructed earlier,being completed in June 1985, while Akashi Kaikyo bridge was completed inApril 1998.

The Kojima-Sakaide route is comprised of a 37.3 km expressway from HayashimaTown, Okayama Prefecture in Honshu via islands in the Inland Sea to Sakaide City,Kagawa Prefecture in Shikoku, and a 32.4 km ordinary JR railway from ChayamachiStation in Honshu to Udatsu Station in Shikoku. The bridges (13.1 km in total length)on this route are highway–railway combined bridges. The bridges comprise three

Fig. 1. View of the Honshu-Shikoku routes.

133Y. Yanaka, M. Kitagawa / Journal of Constructional Steel Research 58 (2002) 131–150

Table 1Suspension bridges of Honshu-Shikoku Bridge Authority

Bridge name Center span length (m) Completion (year)

Innoshima 770 1983Ohnaruto 876 1985Ohshima 560 1988Shimotsui-Seto 940 1988Kita Bisan-Seto 990 1988Minami Bisan-Seto 1100 1988Akashi Kaikyo 1991 19981st Kurushima Kaikyo 600 19992nd Kurushima Kaikyo 1020 19993rd Kurushima Kaikyo 1030 1999

long-span (1000 m class center spans) suspension bridges (Shimotsui-Seto, KitaBisan-Seto, and Minami Bisan-Seto bridges) and cable-stayed bridges (Hitsuishijimaand Iwakurojima bridges). These bridges are grouped together and called the SetoOhashi bridges. The construction of this route was started in October 1978 and com-pleted in April 1988.

The Onomichi-Imabari route is a 59.4 km expressway from Onomichi City, Hiro-shima Prefecture in Honshu via islands in the Inland Sea to Imabari City, EhimePrefecture in Shikoku. Kurushima Kaikyo bridge on this route is a box girder bridgewith 1000 m class center spans, and Tatara bridge is the longest cable-stayed bridgein the world. The bridges in this route feature pathways for bicycles and pedestrians.This route was constructed in stages because the bridges between the islands wereexpected to contribute to regional development. Ohmishima bridge, the first bridge,was completed in May 1979, followed by Innoshima bridge, Hakata-Oshima bridgeand Ikuchi bridge. In May 1999, the remaining three bridges, Shin-Onomichi, Tataraand Kurushima Kaikyo bridges were completed to connect Honshu and Shikoku byhighway transportation.

The completion years and center spans of the suspension bridges and the cable-stayed bridges in the Honshu Shikoku Bridge Project are shown in Tables 1 and 2,respectively. The tables suggest a rapid-paced advance of construction technologyin a short period of time.

Table 2Cable stayed bridges of Honshu-Shikoku Bridge Authority

Bridge name Center span length (m) Completion (year)

Hitsuishijima 420 1988Iwakurojima 420 1988Ikuchi 490 1991Shin-Onomichi 215 1999Tatara 890 1999


1.2. Basic policies of maintenance of long-span bridges

The followings are the basic policies of the maintenance of the Honshu Shikokulong-span bridges.

1. The long-span bridges in these three routes must remain in a safe and sound statefor more than 100 years, since they have been constructed at the expense ofenormous amounts of money and are invaluable elements of Japan’s social infra-structure.

2. These bridges have to be maintained for a long time by methods that are aseconomical as possible because investment in social infrastructure will be limitedin future with the birth dearth and the graying of Japan.

3. Maintenance work requiring halt of traffic has to be minimized because there areno alternative routes to these bridges.

Considering these factors, particular emphasis must be placed on preventive mainte-nance, by which method structures are maintained before they become susceptibleto deterioration. Long-span bridges over the sea are particularly difficult to maintainbecause of their specific conditions: a severe natural environment including strongwinds, strong tidal currents and salt air, a large degree of continuing deformation ofstructures, an extremely large variety of structural members and materials, and theneed to cope with the fatigue of structural steel especially in the case of the SetoOhashi bridges, which carry trains as well as road traffic.

Therefore, in order to maintain long-span bridges for a long period of time appro-priately and economically, we need to have all-round technology that encompassesdesign, construction and maintenance of such bridges along with expertise in relatedareas. The followings are typical examples of maintenance technologies applied toHonshu-Shikoku bridges.

2. Rust proofing of structural steel

2.1. Repainting of anti-corrosive coatings

2.1.1. Painting specificationsLong-span bridges over the sea employ massive quantities of structural steel, and

durable coating systems are used to prevent corrosion. The coating systems consistof rust-preventive thick inorganic zincrich paints as the primary coats and weatherresistant polyurethane resin paints or fluorocarbon resin paints as the top coats.

The application of thick inorganic zincrich paints requires a high degree of qualitycontrol and therefore it is extremely difficult to paint on construction sites. For thisreason, steel structures are painted mostly in shops, including the top coat, and onlyjoints are painted on-site. Painting specifications in shops are shown in Table 3.Repainting on the bridges is in principle limited to the deteriorated top and intermedi-ate coats, keeping the thick inorganic zincrich paint (primary coat) in a sound state.


Table 3Coating specifications in the factory

Application section New coating specification (since April 1990) (µm)

External surfaces Inorganic zinc rich paint 75High build epoxy resin undercoat 120Epoxy resin paint intermediate coat 30Flurocarbon resin paint top coat 25Total film thickness 250

Old coating specification (until March 1990)

External surfaces Inorganic zinc rich paint 75High build epoxy resin undercoat 120Epoxy resin paint intermediate coat 30Polyurethane resin paint top coat 30Total film thickness 255

The reason for adopting this method is that if the entire coated film has deteriorated,it would need blasting before repainting, which would be disadvantageous in termsof quality control, cost and environmental conservation. Repainting specificationsare shown in Table 4. In repainting, only fluorocarbon resin paints are used as thetop coat.

2.1.2. Monitoring of the coated filmsTo monitor any damage of the coated film and to touch up as required is the chief

process of maintenance, because with these coating systems early maintenance workis the best way to prevent the coated films from deteriorating and structural steelfrom corroding.

Consequently, the coated films are periodically inspected at observation pointslocated at strategic parts of each bridge. Time-based changes in the thickness of thecoated films, glossiness, chalking, FT-IR analysis, adhesion, salt deposit density, anddamaged structural members are examined in order to check for deterioration throughaging, to ascertain its mechanism, and to estimate the life of the coated films. Moni-toring to date has made it clear that the coated films of some bridges deterioratetwice as fast as those of other bridges due to differences in the natural environment.

Table 4Recoating specifications in the field

Application section Recoating specification (µm)

External surfaces Fourth surface treatment –Epoxy resin paint intermediate coat 30Fluorocarbon resin paint top coat 25Total film thickness 55


Also, it has proved that the early-type coating systems with polyurethane resin paintsas the top coat are considerably durable and need not be repainted for more than10 years.

2.1.3. Repainting workMaintenance vehicles are used for the monitoring and maintenance of the long-

span bridges over the sea, affording safety in work at high sites that would be other-wise hard to access. These include the girder vehicle to be attached to stiffeninggirders and the cable vehicle moving on a hand rope used for the maintenance ofcables, as shown in Figs. 2 and 3, respectively.

Ohmishima bridge, which was constructed earliest, was repainted in 1992. Innosh-ima and Ohnaruto bridges are now being repainted.

Many long-span bridges over the sea have trussed girders. The repainting of suchbridges is carried out using girder vehicles, but scaffolding is necessary to repaintsome parts that are inaccessible by vehicles. Compared with box girder bridges,trussed girder bridges need more temporary structures such as scaffolding forrepainting, which increases the cost. As a countermeasure, simple and prefabricatedscaffolding has been adopted. The scaffolding developed for Ohnaruto bridge, whichis a trussed girder bridge, is shown in Fig. 4.

Ohshima and Kurushima Kaikyo bridges, which are suspension bridges, and Tatarabridge, which is a cable-stayed bridge, have box girders. Compared with trussedgirders, box girders consist of simple plates and therefore are easier to paint bymachine. We have developed a device to paint box girders automatically. Basically,this device is composed of paint rollers mounted on a girder vehicle, which movesalong the girder and paints efficiently.

Since repainting work is expected to increase in the future, we are working toward

Fig. 2. Girder maintenance vehicle.


Fig. 3. Cable maintenance vehicle.

Fig. 4. Scaffolding for painting.

the development of simpler scaffolding and more effective quality control methodsfor the durability of the coated films in order to reduce costs.


2.2. Dehumidification system for cables

2.2.1. Survey on existing suspension bridgesThe main cable is one of the most important structural members of a suspension

bridge. Cables of the earlier suspension bridges were preserved by traditional rustpreventive methods used in Europe and America: steel rustproof paints (red lead,high molecular rust-preventive agents, etc.) were painted on tightly squeezed galvan-ized steel wires, the surface of which was protected by painted wrapping wires.

However, a survey of existing suspension bridges in Japan conducted before start-ing the construction of Akashi Kaikyo bridge showed that rust was found on steelwires, two to three layers below the outer surface of the main cables. This suggestedthat traditional rust preventive methods were not effective enough under Japan’sweather conditions with high humidity and large temperature change. The surfaceof a cable after the wrapping was removed is shown in Fig. 5.

2.2.2. Development of dehumidification systemIn order to solve this problem, experiments and analyses were conducted on the

mechanism of rusting and on new rust-preventive agents. Then, HSBA concludedthat an entirely new method of the preservation of main cables should be developed.The product of this effort is a dehumidification system, which forces air into spacesbetween wires to dry the cable and eliminate water in the cable, which is the causeof rust. The design of this system is based on the experimental result that galvanizedsteel wires are generally corrosion resistant when the relative humidity around themis under 60%. Since a main cable is composed of steel wires and has the space of17–20% of its cross section, it can be kept dry if dry air is forced into the space atappropriate intervals. The system includes a dry air generator, air supply covers, airexhaust covers, and the airtight shielding around the surface of the cable. The concept

Fig. 5. Corrosion situation, 6 years after completion (Oonaruto bridge).


Fig. 6. Schematic drawing of a dry air injection system.

illustration of the system is shown in Fig. 6, and its major parts are shown in Figs.7 and 8.

Shown in Fig. 9 is the relative humidity inside of the main cable of Akashi Kaikyobridge, which adopted this system from the start. The graph shows that the humidityreaches a steady state and the inside of the cable becomes dry after about 8 monthsfrom the start of the air supply. After that, the humidity is affected by the seasonalchange of the outside humidity, but it can be kept under 60% by operating the systemwith the target humidity of 40%.

For air tightness, neoprene rubber sheets and S-section wrapping wires were usedfor Akashi Kaikyo and Kurushima Kaikyo bridges, respectively. This system is beingintroduced to suspension bridges constructed earlier, in which case air tightness is

Fig. 7. Devices of a dry air injection system.


Fig. 8. Dry air injection cover.

secured by coating with flexible paint the surface of the wrapping systems that havebeen prepared by traditional methods. The outline of the method of ensuring airtightness is shown in Fig. 10.

2.3. Corrosion proofing of steel caissons

2.3.1. Survey of existing caissonsFor long-span bridges over the sea, foundations are constructed in water mostly

using the laying-down caisson method, by which pre-packed concrete or underwaterconcrete is placed inside of cylindrical steel caissons (as shown in Fig. 11).

A survey of the underwater foundations of the 11-year-old Seto Ohashi bridgesshowed that there were pitting corrosions on the skin plates of the caissons, whichare shown in Fig. 12. Corrosion had been expected to advance homogeneously, butit turned out to occur locally and to be likely to penetrate the skin plates in a shortperiod of time. Therefore, it is necessary to take early measures for ensuring thesoundness of the underwater foundations.

2.3.2. Development of an electro-deposit methodSpecial paints or electric anticorrosion methods are generally used for the protec-

tion of underwater steel structures.For Seto Ohashi bridges, however, we have developed an electro-deposit method

considering the conditions of the underwater foundations including the water depthand strength of the tide as well as the life cycle cost. This method is based on thefact that by passing an extremely weak current between a steel caisson and a positiveplate in water, ions of calcium and magnesium can be turned into calcium phosphateand magnesium hydrate, which will adhere to the surface of the caisson. The adhering


Fig. 9. Changes in relative humidity in the Akashi Kaikyo bridge cables.

Fig. 10. Three types of wrapping method.


Fig. 11. Towing of steel caisson.

Fig. 12. Situation of hole corrosion.

deposit has about the same strength and permeability as concrete. A conceptual illus-tration of the method is shown in Fig. 13.

Although this method was previously known as a means of protection of under-water structures, it had been used only on an exploratory basis for small-scale steelpipe piles. Application of this method on the steel caissons of Seto Ohashi bridgesneeded a few years of experiment before the execution of work in 1999, because ofthe large surface area, deep water and strong tide. The experiment made it possibleto determine the conditions such as the distance between the caisson and positiveplates, current density and welding time.

The deposit (rust, marine life, etc.) on the surface starts to come off in scales2000 h after the start of the passage of current. In order to eliminate these scales,


Fig. 13. Schematic drawing of the electro-deposit method.

the water jet device shown in Fig. 14 was developed. The necessary 5 mm of depositis obtained after 8000 h of energization.

3. Monitoring of fatigued structural members

3.1. Considerations at the time of construction

Seto Ohashi bridges, which are highway–railway combined bridges, are underheavy concentrated load every time a train runs over them. Therefore, it is absolutelynecessary to take into account metal fatigue in order to secure the soundness of thebridges. At the time of construction, fatigue was considered in the design of weldedjoints and in the quality control of structural members.

Fig. 14. Scale of removal device.


For this purpose, HSBA designed and built a large fatigue test facility, and conduc-ted fatigue tests on various specimens of materials and structures in order to verifyfatigue strengths and feed them back to design and fabrication. The process of thefatigue test is shown in Fig. 15.

For the corner weld of trussed members made of quenched and tempered hightensile strength steel (SM 58, HT 70 and HT 80), full-sized pilot members weremade in every shop in order to determine the execution conditions, groove precision,inspection methods and evaluation criteria.

Some members may pass the test in spite of their weld defects, especially verysmall blowholes made in the fabrication process, but they are susceptible to fatigueover a long period of time. For this reason, the positions and sizes of the blowholesare recorded and are to be monitored for maintenance purposes.

Fig. 15. Fatigue test.


3.2. Development of an ultrasonic detector

It was necessary to develop a new ultrasonic detector to be used for the inspectionof the members of the bridges because the welded defects had to be detected underconditions different from those in shops. The newly developed ultrasonic detectorcan be divided into parts so that it can inspect the members in upward and sidewayspositions. Its probe is made in such a manner that it is not too sensitive to paints.The detector attached to the underside of a girder is shown in Fig. 16.

The processor part of the detector has the functions to store, retrieve and analyzethe data. The system configuration of the ultrasonic detector is shown in Fig. 17.The monitoring of the structural members of the bridges started in 1990, and thesecond monitoring started 7 years later. So far, no fatigue crack has been detected.

4. Monitoring of static and dynamic bridge behaviors

4.1. Outline of monitoring

The Honshu-Shikoku bridges include long-span cable supported bridges, whichare susceptible to deformation and oscillation due to natural external forces such aswinds and earthquakes and have complex oscillation behaviors. For this reason, everybridge was designed to be wind-resistant and quakeproof, taking into account itsstatic and dynamic behaviors. However, the designs are based on a number ofassumptions, the validity of which can be verified only by observing the behaviorsof the actual bridges. Moreover, the observation of the static and dynamic behaviorsof the bridges and the analysis of their secular changes will provide data for theassessment of their soundness. For these reasons, focusing on the long-span bridges,

Fig. 16. Automatic ultrasonic flaw detector.


Fig. 17. Configuration of the automatic flaw detector.

HSBA has observed dynamic bridge behaviors and has precisely measured the bridgeshapes for the purpose of design validation and soundness assessment.

In this chapter, observations carried out at Akashi Kaikyo bridge are presented asan example. The measurement data items at Akashi Kaikyo bridge and the layoutplan of the measuring instruments are shown in Table 5 and Fig. 18, respectively.The special feature of the bridge is that receivers by the GPS (global positionigsystem) are set on stiffening girders, at the top of the tower and the top of theanchorage (mobile stations on girders and tower, and fixed stations on anchorage).The coordinates of the various parts of the bridge can be measured in real time andprecisely by the real time kinematics (RTK) measurement method that utilizes theGPS receivers. Using this method, the coordinates of the mobile stations are determ-ined in the following way. The fixed stations receive the data from the satellite andtransmit them to the mobile stations. Then, the mobile stations carry out measurementanalysis by interfering the data from the fixed station with the received data of theirown to determine the coordinates. This method insures a horizontal accuracy of 1cm and a vertical accuracy of 2 cm. In the following sections, measurement of thebridge shape and observation of the behaviors of the bridge exposed to strong windsare explained.

4.2. Measurement of the bridge shape

The shape of a long-span bridge is measured for the purpose of a macroscopicassessment of the soundness of the bridge by the time-based changes of its shape.However, comparison between different sets of data observed at different times isdifficult because the shape of a suspension bridge is heavily dependent on tempera-


Table 5Measurement items at Akashi Kaikyo bridge

Design verification item Points of main focus Variables to be measured

Earthquake characteristics Seismic motion and magnitude AccelerationEarthquake frequencycharacteristicsGround characteristicsPhase difference

Bridge response to earthquakes Acting seismic force Response acceleration (speed)Amount of displacement DisplacementNatural frequency Response acceleration (speed)Seismic motion input ontosuperstructure

Wind characteristics Basic wind speed Wind direction and wind speedDesign wind speedVariable wind speedcharacteristicsIntensity of turbulenceSpatial correlationPower spectrum etc.

Bridge response to winds Natural frequency of Response acceleration (speed)superstructureVibration mode configuration DisplacementStructural damping Predominant frequencyGust response Wind velocity and response

accelerationAction of main tower TMDsa Response displacement

a TMD: Tuned Mass Damper.

ture. If a certain correlation can be found between temperature and shape, then acorrection can be made to compensate for the effects of temperature and the secularchanges can be evaluated for the assessment of the soundness of a bridge.

From this point of view, the correlation between the vertical displacement of thecentral stiffening girder of Akashi Kaikyo bridge and the surface temperature of thecable was examined using the GPS measuring method for 1 year (from September1998 to August 1999). The surface temperature of the cable varies according to timeand place because it is strongly influenced by solar radiation. For this reason, thecorrelation is very difficult to find. By analyzing various data, however, a closecorrelation was found between the vertical displacement of the girder duringnighttime (from 22:00 to 03:00 hours) and the surface temperature of the cable atthe saddle of the tower 2P (see Fig. 19). Supposedly, the close correlation is due tothe fact that the surface temperature data were stable because of the measuring time(nighttime when air temperature is stable) and the measurement point (the part ofthe cable shrouded by the saddle cover and not exposed to the sun).

By conducting the same kind of measurement on other suspension bridges, arelation expression between the bridge shape and the surface temperature will beobtained. Time-based changes obtained from the continuous measurement of the


Fig. 18. Measurement system at Akashi Kaikyo bridge.

bridge shapes are expected to provide the necessary data for a macroscopic assess-ment of the soundness of bridges.

4.3. Observation of the responses of the girder to strong winds

Field observation is conducted on Akashi Kaikyo bridge using the afore-mentionedGPS receivers in order to examine the dynamic behavior of the bridge under theconditions of earthquakes and strong winds. As an example, we shall explain theobservation result of the responses of the girder to the winds of Typhoon No. 9807on 22 September 1998 (maximum 10 min mean wind speed at the center of thecentral span was 32.0 m/s) and how those data are utilized.

The observed values of the horizontal displacement of the girder at the center ofthe central span were compared with the analytical values derived from the designstandard using the data obtained during the time period when the wind was strongest.The wind direction during the time period was at a right angle to the bridge andwas best suited to the assumption of the wind resistant design. The average anddynamic horizontal displacements of the girder when the wind speed was over 20m/s are plotted in Fig. 20. Also shown in the figure are the average and dynamicdisplacements of the analytical values of the response to the natural wind derivedfrom the design standard. The figure shows that the average displacements of theobserved and analytical values are about the same but that as regards the dynamicdisplacement, the analytical value derived from the design standard is too large (fourtimes as large as the observed value).

In order to identify the factor that is the cause of the excessive analytical value,natural wind response analysis was conducted using the power spectra of the winds


Fig. 19. Relationship between cable temperature and girder displacement.

Fig. 20. Horizontal displacements of the girder of Akashi Kaikyo bridge (Typhoon No. 9807 in 1998).


Table 6Comparisons between measured values and calculated values for Typhoon No. 9807

Gust response analysis Actualmeasurements (m)

Using actually Using design codemeasured values for values for parametersparameters (m) (m)

Average displacement (1) 5.43 5.43 5.17Dynamic displacement 0.68 2.62 0.78(max. amplitude) (2)Maximum displacement (1)+(2) 6.11 8.05 5.95

and the observed values of the spatial correlation. The analytical value obtained asa result was approximately the same as the observed value (see Fig. 19). This showsthat the design standard assumes a too strong dynamic effect of wind and leavesroom for revising. It is expected that the accumulation of such dynamic observationdata will provide the grounds for reducing the present design wind loads, which arebased on assumed strength of wind gusts. The design wind loads for suspensionbridges in the future will be further rationalized on the basis of these dynamic obser-vation data (Table 6).

5. Summary

The maintenance of Honshu Shikoku bridges is carried out following the policyof ‘preventive maintenance’ . To realize this policy, several technologies describedin the paper are developed and employed. These technologies will furthermore berationalized by the experiences gained in carrying out maintenance works in thefield, as well as the experiences gained in the construction works of these bridgesin the future.

Further reading

Fujikawa, Kashima, Kawakami. Corrosion protection for suspension bridge cable. In: Second InternationalSuspension Bridge Operator’s Conference, 2000 April; New York.Furuya, Kitagawa, Suzumura. Corrosion mechanism and protection methods for suspension bridge cable.Structural Engineering International, Vol.10, No.3, August 2000.Murata, Okano, Takeguchi. Monitoring system for the Akashi Kaikyo bridge using GPS. In: First Inter-national Conference on Advances in Structural Engineering and Mechanics 99; August 2000.Kashima, Okano, Takeguchi, Mori. Monitoring system for the Akashi Kaikyo bridge. In: Workshop onResearch and Monitoring of Long Span Bridges, 2000 April; Hong Kong.

maintenance of steel bridges on honshu-shikoku crossing

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