a cable-stayed bridge with main span of 1088 meters

7/30/2019 A Cable-Stayed Bridge With Main Span of 1088 Meters

1/9

Sutong Bridge-A Cable-stayed Bridge with Main Span of 1088 Meters

Qingzhong YOUChief Director

J iangsu Provincial

Communications Dept.Nanjing, [email protected] 1957.

PingHEDeputy Site Director

Jiangsu Sutong Bridge

CCDNantong, [email protected] 1964.

Xuewu DONGDeputy Division Chief

J iangsu Sutong Bridge

CCDNantong, [email protected] 1967.

Xigang ZHANGDirectorHPDI Consultants, INC.Beijing, [email protected]

Born 1962.

Shouchang WUSite Chief Engineer

Jiangsu Sutong BridgeCCDNantong, [email protected] 1950

Summary

The Sutong Bridge is the longest spanning cable-stayed bridge in the world with a main span of1088 meters. In this paper, the design and construction concepts are briefly presented. Keytechnologies and innovative achievements are summarized. These focus mainly on pile foundationbearing capacity analysis, river bed scour protection and monitoring, superstructure wind-resistancestudy, mid-span closure method, as well as long cantilever structure construction control.

Keywords: cable-stayed bridge, foundation, pylon, steel box girder, cable stay,

construction control.

1IntroductionThe Sutong Bridge crosses the Yangtze River approximately 100 km upstream from Shanghai,China, connecting the cities Suzhou and Nantong located on the southern and northern banksrespectively. It is a key project for the coastal highways in China. The bridge is a seven span doublepylon and double cable plane steel box girder cabled-stayed bridge, and has a span arrangement of100+100+300+1088+300+100+100=2088 m (see Fig. 1). The Sutong Bridge sets the record ofbeing the longest spanning cable-stayed bridge in the world.

Fig. 1: Span Arrangement of the Main Bridge

The Chinese policy of reform and opening up to the outside world, as well as the strategic

development of Pudong in Shanghai began in 1990s, have boosted rapidly the economicdevelopment of the Yangtze River Delta in China. As a result, crossing the Yangtze River has


2/9

become a transportation bottle-neck for traffic directed to the new urban agglomerations north ofthe Yangtze River Delta, restricting economic development of those cities to the north of the

Yangtze River. Therefore, a proposal to build the Sutong Bridge was submitted for state approval asearly as 1991.

Starting from 1991, several long span bridges, including the Jiangyin Bridge, the Nanjing 2rd

Yangtze River Bridge, and the Runyang Bridge, were built in Jiangsu. At the same time, severalother famous bridges like the Yangpu Bridge and the Lupu Bridge were built in China. However,the Sutong Bridge is located very close to the estuary of Yangtze River where the width of the riveris 6 km, geological and meteorological conditions are complicated and moreover, river traffic hereis very heavy and the large scale construction is a great challenge from a technical perspective. Itwas not until 2001 that the Sutong Bridge project was approved by the State Council.

The bridge deck is 34 m wide and carries 6 traffic lanes in two directions, the design traffic speedbeing 100 km/h. The structural design life is 100 years and navigational clearance is 891 m 62 m.

The Jiangsu Provincial Sutong Bridge Construction Commanding Department is the owner of thebridge, who will act as general supervisor during construction of the bridge. The bridge is designedby a consortium composed of the China Highway Planning and Design Institute (HPDI), the

J iangsu Provincial Communication Planning and Design Institute (JSPCD), and the ArchitecturalDesign and Research Institute of Tongji University. Construction work is performed by contractorswhich include the 2nd Navigational Engineering Bureau of China Communications ConstructionCompany Ltd, the 2nd Highway Engineering Bureau of China Communications ConstructionCompany Ltd, China Railway Shanhaiguan Bridge Group Co., Ltd, and J iangyin Fasten Cable Co.,Ltd. As technical consultants, the China Railway Major Bridge Design Institute, COWI fromDenmark, Southwest University, Maunsell Hongkong, and Nippon Steel have provided technicalconsultation service during the construction period.

2. Foundation

At the Sutong Bridge site, the soil is

mainly alluvial with a sediment layerthickness of more than 270 m. Acomparison between variousalternatives such as caisson and pilefoundations was made during thedesign stage. Bored pile groupfoundations were finally selected onthe basis of study results from shipimpact, riverbed protection, andseismic fortification as well as inconsideration of aesthetics, structuralbehaviour, and construction (see Fig.2).

As the foundation was a large scalegroup pile foundation, a series ofmodel tests and real pile tests werecarried out at design stage so as todetermine the mechanism of pile-soilinteraction and analyze group pileeffects and bearing capacity of thepile group foundation. In addition, alarge number of high-precision stresssensors and strain gauges wereembedded in pile tip, pile top and pile

cap to track pile group settlements, pile cap stress, and pile axle force and deformation of group pilefoundation during construction, and to optimize pile-soil interaction models and carry out backwardanalysis of foundation force transfer and deformation. The results showed that the compaction

Fig. 2: General Arrangement of Foundation (Unit: m)


3/9

effect on the soil foundation from riverbed pre-protection, deep pile casting of fluid concrete andthe post-grouting sealing effect would contribute to enhancing the bearing capacity of the pile groupfoundations. Apart from that, these three factors also enabled the large pile group foundations toattain the bearing capacity as one solid piece. It was also found that the pile group effect was notsignificant and that settlement was less than predicted.

Hydraulic model tests showed that thepylon foundation was susceptible toformation of a 28 m scour pit inducedby a flood with a return period of 300years as the water flow velocity wasvery high and geological erosion-proofperformance was weak. The temporaryconstruction platform installed duringfoundation construction was to someextent risky due to scour and therefore,it was decided to provide scourprotection for the riverbed within thescope of the foundation and its

surrounding area.Riverbed scour protection is dividedinto two parts, i.e. pre-protection andpermanent protection. Pre-protectionmeans dumping of sandbags to ensuresafety of construction platforms and tofacilitate permanent scour protection.Permanent protection means dumpinggraded stones and armor stones

permanently on top of the sandbags so as to form a layer with strong erosion-proof performance inthe bottom of riverbed. Scour protection is divided into three areas, the central area (correspondingto size of construction platform), the outer area, and falling apron (see Fig. 3). Calculations and tests

were made to specify dimensions,size of materials and thickness oflayer for each area. Total quantity ofscour protection materials dumpedfor each foundation is approximately550,000 m3.

A long-term monitoring plan startedat the very beginning of scourprotection construction. The resultsshowed relatively obvious local scouroccurred at the edge of falling apronshortly after the scour protectionwork. It continued rapidly in thefollowing year and then becamestable after that. From October 2005to September 2008, local scour hadstabilized and even slightly backfilled.A slope of 1:2 to 2:2.2 was observedat the outer edge of falling apron,which coincided with model testresults. The scour shape validated thecorrectness of the pylon foundationscour protection design concept.

In addition, many critical technicalissues, including setup of theconstruction platform by steel casing,

Fig.3: Layout of Scour Protection Zone Distribution(Unit: m)

Fig. 4: Structural Details of the Pylon (Unit: m)


4/9

participation in force transfer of permanent structures by steel casing, pile tip grouting, lowering ofthe 6000 t steel cofferdam, and massive concrete casting of pile cap, were resolved based on testsand calculations. Foundation and pile cap construction started in June of 2003 and ended in May of2005, for a total duration of 24 months.

3PylonAt the design stage, several alternatives such as diamond-shaped, A-shaped, inverted Y-shaped(which resembles the Chinese character for human) towers, with or without a lower cross beamwere proposed for the pylons of the Sutong Bridge. A light, simple and graceful inverted Y-shapedpylon was finally chosen, which manifested harmony of heaven and human beings in Chinesetraditional culture. The pylon is 300.4 m high and is a reinforced concrete structure with hollowcross-section (see Fig. 4). Steel anchor boxes are arranged in cable anchorage zone at upper part ofpylon to bear and transfer cable forces.

Wind tunnel tests of the free standing pylon werecarried out during the design and constructionperiods (see photo 5) to determine the pylons

critical galloping wind speed, structural strength,and stability. In addition, as part of constructionengineering investigations, wind tunnel testing onthe aerodynamic performance of the pylon duringerection, taking full account of the influence oftower crane and formwork system, was conducted.

The tests aimed to evaluate wind-resistance safetyduring construction and wind effects onconstruction equipment, working conditions ofworkers, and to determine the correspondingdamping measures according to test results. Thewind tunnel test results showed that pylons of the

bridge could satisfy wind resistance requirementsand normal working requirements under theallowable construction wind speeds.

The pylons were built with an automatic hydraulicclimbing form system, in 68 sections. Eachstandard section is approximately 4.5 m high. Steelanchor boxes were fabricated in the workshop,pre-assembled, and erected by tower crane on site.

Tracking prisms were used for construction controlof pylon verticality during pylon construction so asto compensate such ambient factors as wind andtemperature influence on survey measurements.

Relative coordinates were used for constructionlayout so as to allow construction activities 24hours a day (see photo 6). Measured resultsshowed that verticality of the pylons was 1/40000and the maximum axial line deviation was 7 mm.

Technical issues as production of highperformance concrete, pumping technology, curingof concrete at height, and deviation correction ofthe steel anchor box were studied. Construction ofthe pylons started in May of 2005 and ended inSeptember of 2006 with duration of 16 months.

4Steel Box Girder and Cable Stays

Photo 5: Wind Tunnel Test at Free StandingPylon Stage

Photo 6: Pylon under Construction


5/9

The Sutong Bridge was designed to areference wind speed of 38.9 m/s at 10m height with a return period of 100years. Neither a fully floating nor afixed structural system were feasiblefor both wind and temperature effects.

A viscous damper system with adisplacement stopper was thereforeadopted following structural static anddynamic load analysis under wind,temperature, seismic, and vehiclebraking load. This resulted in asemi-floating system (see photo 7).

This system has the advantage ofbeing able to limit dynamic movement and load caused by turbulent wind, braking, and seismicloading by dissipating energy, but at the same time providing minimal restriction to the slowmovements caused by temperature, traffic and static wind. The function of the stopper is that thedampers provide no restriction to movement of the deck girder as long as the relative movement in

longitudinal direction is within the stroke length of the damper, whereas the damper will provide afixed connection between pylon and deck girder when the relative movement is beyond the strokelength of the damper.

According to fabrication technologies and conditions available to the manufacturer, force transfercharacteristics and site installation capability, parallel wire stay cables were selected. These cableswere made of galvanized high strength wires supplied by the Baosteel Group with a strength of1770 MPa and diameter of 7.0 mm. The stay cables were designed to have a service life of 50 yearsand have been tested for fatigue and water tightness. Adequate provisions were made in structural

details to facilitate future replacement of stays.

Cable wind tunnel tests and damping tests wereconducted to determine the wind drag

coefficient of the cables, study vibrationmitigation measures, and verify vibrationmitigation effects, since both the overallstructure and the stays of the Sutong Bridge areflexible, characterized by widely distributedvibration eigen-frequencies. The main concernwas vortex shedding of girder and pylon,parametric vibration and linear resonance ofstays, and wind/rain induced vibration of stays.It was decided to take aerodynamic measures tomitigate wind/rain induced vibration of thestays, i.e. to arrange concave pits on cable planeand to add external dampers to improve the

damping ratio of the stays and limit their amplitude of vibration. In addition, provisions forinstalling cross ties were made so the cross ties could be installed if necessary.

The bridge deck consists of a steel box girder with an aerodynamic streamlined shape, includingfairingssee Fig. 9.

Photo 7: Pylon and Deck Semi-floating System

Photo 8: Wind Tunnel Test at MaximumCantilever Stage


6/9

Fig. 9: General Structure of Steel Box Girder Cross Section (Unit: m)

For the girder section, section model wind tunnel tests with scales ranging from 1:70 to 1:13.5 wereconducted at the wind tunnel laboratories. These tests revealed the Reynolds number effect in thegirder and the obvious vortex shedding response in the girder at an angle of incidence of +3 insmooth flow. During detailed design, the position of inspection gantry rails at the bottom of thegirder was further optimized based on wind tunnel results. Gantry rails were to be placed onhorizontal bottom plate and fairing panels were to be placed at both sides of the rails.

During construction, the maximum cantilever of the bridge was 540 m long and wind bracing safetywas one of the most critical risks. Therefore, as part of the construction engineering investigations,wind tunnel tests were performed under the most unfavorable conditions for the completed bridgeand the erection stages (see photo 10). Test results from the completed bridge, the maximumbalanced cantilever and the maximum cantilever test configurations revealed that the bridge's testedcritical wind speed was much higher than the design critical wind speed and the structure had goodaerodynamic stability. However, due to the galloping effect, structural safety of some parts wasrelatively low under maximum design wind speed. Test results also revealed that tuned massdampers would not be effective as the structural vibration frequencies were relatively low. Based onwind tunnel test results, the following countermeasures were taken: (1) Planning was adjusted in a

comprehensive manner during construction to ensure that the maximum cantilever construction did

not take place during typhoon season and to ensure that main span closure was achieved before theonset of a typhoon, (2) A detailed anti-wind contingency plan, which included measures such aswithdrawal of erection devices and removal of objects increasing wind resistance, was created andrehearsed, and (3) Local parts of bottom slab and web plate of steel box girders were strengthenedtemporarily.

Steel box girders were fabricated in the shop. In order to speed up construction and reduce durationof balanced cantilever construction, steel box girder sections for the side spans were supported by

temporary piers and brackets and installed by floating crane (see photo 11) so that main spanclosure could be completed as soon as possible. The largest girder section installed by floating crane

Photo 10: Erection of Side Span Large BoxGirder Section Photo 11: Pylon and Deck Temporar


7/9

was 60 m long and weighed 1250 t. Standard girder sections were lifted by deck crane for fittingand then assembled and welded. After the stays were unreeled on the bridge deck, cable socketswere first attached at the pylon end and were then drawn into sockets at the girder end in threestages, soft and hard tensioning. The maximum traction length and traction force were 25 m and650 t respectively. Both tensioning and adjustment of the stays were made at the pylon end.

A scheme for main span closure by jacking was adopted. Pylon and deck temporary fixation duringconstruction was made by tie-down cable in the direction of the bridge, steel pier with skid plateinstalled on the top vertically, and transverse anti-wind bearings perpendicular to the bridgedirection (see photo 6). During closure, half the tension force of the vertical cable was released andat the same time tie-down cables along the bridge direction were tensioned and released, pullinghalf the span of the deck (1000 m) to move toward the bank side by 10 cm and expanding theclosure gap so that the closure segment could be easily lifted into place (see photo 12). During nighttime with relatively small temperature variation (ambient temperature approximately 20), the boxgirder was pulled towards the river side and matching ends of the cantilevers were adjusted and

fixed with temporary plates. Approximately 90percent of the required welding was completedbefore early morning of the next day whenambient temperature was rising. At the same time,

the temporary fixation between pylon and girderwas quickly released to complete the transfer ofstructural system.

Erection of the steel box girder and stays startedin September of 2006 and the main span closurewas achieved in June of 2007, for a duration of10 months. The erection cycle for standard girdersegments was about 5 days on average. Rivertraffic was temporarily stopped during liftingoperations.

5Construction control during Erection of SuperstructuresDue to the long span, long cantilevers and structural characteristics of the Sutong Bridge, specificgeometry control methods were adopted for construction control during fabrication and erection ofthe superstructure.

In order to avoid major deviation, CCD organized the designer and their consultants to verifycalculations performed by the contractor. More than three months were spent to reach a commonunderstanding of calculation parameters, boundary conditions, and loading procedures. In addition,a sensitivity analysis was carried out to identify the major parameters affecting constructiontolerance. Analysis results revealed that deviation of shrinkage and creep of the pylons, weight ofsteel box girder, length of steel box girder, length of the stays, elastic modulus of the stays all hadsignificant effects on geometry and all these parameters were primary control parameters. The

height of the steel anchor boxes, rigidity of box girder cross section, and weight of the stays had alesser effect on the structure. These parameters were regarded as secondary control parameters. Theelastic modulus of concrete in the pylons, verticality of steel anchor boxes, height of anchoragepoints at deck end, and differential shrinkage of welding between girder sections had negligibleeffects on the structure and these parameters could generally be neglected. In addition, theoreticalanalysis revealed that structural geometry was highly sensitive to wind and ambient temperature.Wind and temperature effects must be compensated and accordingly, environmental requirementsfor the construction survey were stipulated.

At the fabrication stage, the steel box girder and stay cables was fabricated according to data andrequirements supplied by the construction control calculations. In addition, geometry and weight ofeach steel box girder section were to be accurately measured under specified environmentalconditions. The elastic modulus and distance between two sockets were to be measured after

completion of each cable production.

Photo 12: Main Span Closure Segment Lifting


8/9

Erection was primarily controlled by cable length. In practice, forward analysis and intermediatepredicted geometry were compared to evaluate erection in a timely manner after each pair of steelbox girders and stays were erected. Any deviation during erection should be corrected by a forwardcorrection method to avoid sudden change or excessive compensation. In June 2007, whenmid-span closure was being performed,the closure segment was laid out to be in agreement withthe top plate, bottom plate, and web plate of the box girder as well as keeping the centreline of the

cantilever tip at both sides to within 1 mm while the geometry of the completed bridge was about

10cm higher than expected. In general, the bridge has a smooth geometry without any localdeviation (see Fig. 13), therefore the very innovative construction control implemented on thisproject was successful in achieving good results in this record-breaking cable-stayed bridgeconstruction.

6. Conclusion

Construction of the Sutong Bridge began in June 2003. The bridge was opened to traffic in May,

2008 (see photo 14). The whole construction process lasted for about five years, almost one yearahead of schedule. The total cost of the project is about 1.2 billion US dollars including 23 km ofapproach roads, 6 km of approach bridges, and the main bridge itself.

Heavy snowfall at the beginning of 2008 gave an even load distribution of 0.51 kN/m2 for thewhole bridge, which also provided a load test. Results from this test and dynamic and static loadtest performed before the bridge wasopened to traffic show that measuredvalues of stress and deformation of eachcontrol component of the steel box girderand bridge pylon are in accordance withtheoretical values, the bridge has abalanced load distribution, and structural

performance complies with design codeand standard with sufficient strength andrigidity. Monitoring of bridge duringoperation shows that stress anddeformation of each structural componentare in accordance with the design. TheSutong Bridge is working properly now tocreate enormous social and economicbenefits. Photo 14: Sutong Bridge Opened to Traffic

The Sutong Bridge project has brought about important advances in the theory and practice ofbridge aerodynamics and construction control. It encourages further developments in engineeringand project management, and has firmly established itself a visionary project which has benefited

from the wholehearted cooperation between Chinese construction units and international consultantfirms. By any standard, the Sutong Bridge project is a unique, recent outstanding achievement in

Deflection of South Pylon

0

50

100

150

200

250

300

-0.10 0.00 0.10 0.20 0.30 0.40 0.50 0.60

Deflection in X-dir [m]

Level,Z[m]

FINAL BRIDGE

COWI, THEO

Measured 25/06/2007 02:10

Vertical profile - Whole Bridge [m]

-0.100.000.100.200.300.400.500.600.700.800.901.001.101.201.301.401.501.601.701.801.902.002.10

-1100 -1000 -900 -800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700 800 900 1000 1100

COWI, THEO CENTRE LINE UPSTREAM DOWNSTREAM

South PylonNorth Pylon

Fig. 13: Geometry of Pylon and Deck after Closure


9/9

bridge engineering clearly demonstrating technical innovation, material innovation, high aestheticmerits, and harmony with the environment.

References

[1] China Highways Planning and Design Institute, Jiangsu Provincial Communications Planningand Design Institute, Building and Design Institute Subordinated to Tongji University,Construction Design of Sutong Main Bridge, July 2004.

[2] The Second Navigational Engineering Bureau of CHEC, Sutong Main Bridge ConstructionOrganizational Design for C3 Contract, May 2005.

[3] XIANG Z.S., Bridge Construction Control Technology, China Communications Press, May2001.

[4] HUA X.S., HUANG T., et al, Precise Works Survey Technology and Its Application, HehaiUniversity Press, October 2001.

[5] YOU Q.Z.; DONG X.W.;WU S.C.. Challenge and Innovation during Construction of SutongBridge Foundation, Engineering Science, Vol. 9, No.6.Chinese Academy of Science, June2007.

[6] JENSEN O. J ., TRUELSEN C, Assessment and Concept Design of Scour Protection forSutong Bridge, P.R. China, 3rd International Conference on Scour and Erosion,Amsterdam,NetherlandAugust, 2004.

a cable-stayed bridge with main span of 1088 meters

Documents