Tailor Made Concrete Structures – Walraven & Stoelhorst (eds)© 2008 Taylor & Francis Group, London, ISBN 978-0-415-47535-8

Precast segmental design and construction in China

Dong, Xu, Huichi Li & Chao LiuDept. of Bridge Engineering, Tongji University, Shanghai, China

ABSTRACT: In 2001, Liuhe River Bridge in Shanghai was the first span-by-span precast segmental bridgeconstructed by a launching gantry in China. In 2003, Humin Viaduct in Shanghai was the first project usingshort line segment casting for urban elevated viaducts. The biggest PC beam bridge using balanced cantileverprecast segmental construction in China is Jiujiang Bridge in Guangdong province, which has two 160 m mainspans and was completed in 1996. In July 2001, the first 4-span cable-stayed bridge in China, Yiling Bridgein Hubei province, using precast segmental PC box girder construction, was completed. Although China hasthese successful references, the precast segmental construction, originated from the contractor system, was notwell followed in time by design codes. Lack of specified design codes in China usually causes owners and evendesigners hesitate to use this construction method. Longitudinal mild reinforcing bars do not continue throughthe joints. The new concept of making closed horizontal shear reinforcement, with the addition of normallyarranged vertical stirrups, to carry the horizontal and vertical components of the diagonal tensile stress wasproposed in the reinforcement design of precast segments for the approach bridges of the Sutong Bridge.

1 INSTRUCTIONS

Precast segmental construction for prestressed con-crete bridges has been widely used in the world.This method has many advantages, such as quality-guaranteed standard precast segments, fast speedconstruction time and the least site work. Lots of pre-stressed concrete bridges in the world were built byprecast segmental construction method in recent 20years[1].

Although more and more precast segmental bridgeshave been successfully built in China, this construc-tion method is still relatively new to Chinese engineers.One reason is that the precise control of the dimensionsof the bridge makes the construction much more com-plicated. Another reason is that the precast segmentalconstruction method, originated from the contractorsystem, is not well followed in time by design codes.This construction method even well influences thestructural design including the profiles of internal andexternal prestressing tendons, the detail dimensions ofsegments and the arrangements of segments and devi-ators, etc. Due to these reasons, lack of the regardingspecified design codes usually causes owners and evendesigners to hesitate to use this construction method.

2 RECENT CONSTRUCTION REFERENCESIN CHINA

2.1 Precast segmental span by span construction

2.1.1 New Liuhe Bridge in ShanghaiThe new Liuhe Bridge in Shanghai consisted of3 × 42 m single spans. The bridge had dual carriage-ways, each of which included 3 lanes of traffic. Theupward bridge was 16.00 m in width, while the down-ward bridge was 18.80 m. In order to be familiarwith the design method of segmental constructionwith external prestressing, the precast segmental con-struction was adopted. The upward and downwardbridges consisted of two parallel single-cell box gird-ers, respectively. Each box girder was longitudinallydivided into 13 segments. The weight of a single spanwas 515 tons, and the weight of a 3.33 m standard seg-ment was 40 tons. The bridge segments were precastedwith long-line method. A launching gantry was usedto carry and install all the segments into a span.

This bridge was the first span-by-span precast seg-mental bridge constructed by a launching gantry inChina, as shown in Figure 1. Mixed tendons were usedfor the longitudinal prestressing in the bridge. Most

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Figure 1. New Liuhe River Bridge, installation of precastsegments.

Figure 2. New Liuhe River Bridge, external tendons.

of the prestressing tendons were internal bonded ten-dons, while four 19T15 external unbonded tendonswere used in each span, occupying 24% of the wholeprestressing in a single span, as shown in Figure 2. Thebridge was completed in Oct. 2001.

2.1.2 Humin Elevated Viaduct in ShanghaiHumin Elevated Viaduct in Shanghai was the secondbridge using span-by-span precast segmental con-struction using launching gantry in China, as shown inFigure 3. The total length of the viaduct was 5.56 kmand the average span was 30∼35 m. The 30 m spanswere made of 11 precast segmental box girders, whilethe 35 m spans were made of 13 ones. The girder seg-ments were 25 m in width, 2.1 m in height, 2 m, 2.5 mand 3 m in length. The weight of the precast segmentsat pier tops was up to 130 tons and the standard seg-ments were about 110 tons. The segments were shortline precasted. Figure 4 shows the external tendons anddeviators in this bridge.

Although half of the 5.56 km viaduct was designedto adopt this method, most of the spans were builtby the traditional monolithic scaffolding constructionbecause of the restricted construction period. Only

Figure 3. Humin Viaduct, installation of precast segments.

Figure 4. Humin Viaduct, external tendons and deviators.

Figure 5. Second Jiujiang Bridge.

two sections were left to use precast segmental con-struction, one in the main viaduct and another in aramp. Each section included ten spans. The wholeviaduct, which has an appealing arc bottom shape, wascompleted in the end of 2003.

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Figure 6. Approach bridges in deep water.

Figure 7. Precast segments storage yard.

2.2 Precast segmental balanced cantileverconstruction

2.2.1 Second Jiujiang BridgeAt present, the biggest bridge using precast segmen-tal balanced cantilever construction in China wasthe Second Jiujiang Bridge, completed in 1996 andlocated in Guangdong Province, as shown in Figure 5.The main bridge had 6 spans (50 m + 100 m + 2 ×160 m + 100 m + 50 m), including the two biggest160 m precast segmental spans. In this bridge, the max-imum cantilever length reached to 78.5 m, leaving a3 m cast-in-situ closure. The width of the deck seg-ments was 25.27 m. All the prestressing system wasinternally arranged.

2.2.2 Deep water approach bridges of theSutong cable-stayed bridge

Sutong Bridge, with a total length of 8146 m over theYangtze River including a 1088 m cable stayed mainspan, was completed on June 28, 2007 and will opento traffic at the end of April this year. The approach

Figure 8. Launching gantry to assemble the segments.

Figure 9. Installation of the deviator segment.

spans were wholly prestressed concrete continuousbeams including about 25 spans of 75 meters in deepwater (Fig. 6). Short line segment precasting and bal-anced cantilever construction were adopted (Fig. 7).Launching gantry was used to assemble the cantileversegments, as shown in Figure 8. The bridge is thelargest bridge project using precast segmental can-tilever construction, launching gantry assembling andshort line precasting in China.

Special segments, including the anchorage seg-ments and deviator segments (Fig. 9) were carefullydesigned and precasted. In order to keep the weightof all segments within 150 tons, the anchorage crossbeam, which occupies half of the weight of the piersegment, is casted in-situ. Each span consists of six25T15 external tendons. A new external prestressingsystem was adopted in this bridge. The adopted exter-nal prestressing system was developed by the jointR&D center supported by OVM (Liuzhou) MachineryCo. Ltd. and Tongji University, as shown in Figure 10and Figure 11.The system uses unbonded monostrandsand has two features. The first is the deviator device,which can comb the individual monostrands and guide

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Figure 10. External prestressing tendons.

Figure 11. External prestressing tendons.

Figure 12. Detail of the deviator of the system.

them one by one in deferent vertical and lateral cur-vatures (Figs 12–13). The second feature is that thestraight part of the tendon profile does not need tobe grouted (Fig. 14). It significantly reduces the selfweight of the tendons and facilitates the inspection andmonitoring of the strands during service time (Fig. 15).

2.3 Precast segmental cable-stayed bridge

2.3.1 Yunyang Bridge over the Hanjiang RiverYunyang Bridge, completed in 1993 and located inHubei Province, was a P.C. cable-stayed bridge withdouble pylons. The bridge was the first long span earthanchored prestressed concrete cable stayed bridges in

Figure 13. Profile of the deviator after testing.

Figure 14. Connection of the deviator and the straight part.

Figure 15. Easy inspection of the tendons.

China, with 3 spans (86 m + 414 m + 86 m). The con-crete girder was box-section with three cells, usingthree-dimension prestress technology. The length ofthe segments were 3.7 m and 4.3 m and the maximumweight of the precast segments was around 100 tons.(Fig. 16)

2.3.2 Yiling Bridge over the Yangtze RiverYiling Bridge, crossing Yangtze River in Yichang Cityin Sichuan Province, was a 4-span cable-stayed bridge

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Figure 16. Yunyang Bridge under construction.

Figure 17. Yiling Bridge.

with 2 main spans of 348 m and side spans of 120 mwith a total length of 936 m. The concrete girder wasthree cells box-girder, which was 23 m in width. Theprecast segments were 3 m in length. The cast-in-situlength of the main girder was 131 m on both sidespans and 22 m around the central pylons; the two324 m main spans were precasted and erected usingthe balanced cantilever method. (Fig. 17)

3 SOME TECHNICAL CONSIDERATIONS

3.1 Flexural behavior

For externally prestressed concrete structure, the flex-ural resistance in ultimate stage has relationship withmany factors, including span depth ratio, the distancebetween deviators, the type of external prestressingstrands, i.e., bonded or unbonded, etc. Joint is also amajor factor influencing the flexural behavior of pre-cast segmental structures. Although FEM method hasbecome popular for analysis, the numerical model forjoints is difficult to make. Meanwhile, designers used

to get a quick estimation of the flexural ultimate carry-ing capacity of the bridges, especially in preliminarystage.

As a matter of fact, section equilibrium methodcan be “borrowed” from the calculation of internallyprestressed concrete structures to calculate the flexu-ral ultimate carrying capacity of externally unbondedprestressed concrete structures. The key factor to usethis simplified method is to get the ultimate stressincrement of external prestressing tendons at the ulti-mate stage. Although many codes in the world includethose equations, they are quite different because manyparameters that have influences on the ultimate stressof external prestressing tendon cannot be totally sim-ulated in experiments.

Zero ultimate stress increment was recommendedfor the external tendons in Sutong approach bridges.Although a little bit conservative, it was practicaland not a controlling factor in this case because theunbonded monostrands external system were adoptedand much more internal tendons than external ten-dons were used in the mixed tendon arrangement inthe design.

In China, there are already some theoretical andexperimental achievements in the design theories ofthe flexural behavior for monolithic and precast seg-mental construction. Some numerical analysis modelsconsidering the geometric and material nonlinear, aswell as the joint mechanism have been developed. Inorder to create more precise numerical models, whichcan reflect the mechanism of joints between segments,further research and experimental tests are still beingmade. The technical guides are hopefully to be issuedbased on these researches in the following years.

3.2 Reinforcement design near joints of theprecast segments in Sutong Bridge

Although dry joints between precast segments havebeen used in a lot of bridges around the world, themechanism of this kind of construction is still not veryclear, especially the shear strength. Fortunately, if theglued and multiple-key joints are used between precastsegments, the web crack pattern will be the same asthat in the monolithic structures in ultimate stage[3].

Nevertheless, there is still a concern that becauselongitudinal mild reinforcing bars do not continuethrough the joints in precast segmental bridges,minor deficiency of shear resistance might happen inthe local areas along the joints. In order to minimize theuncertain area as much as possible, in the design of thereinforcement near joints of the precast segments inthe Sutong approach spans, horizontal reinforcementswere suggested to be made closed so as to get enoughdevelopment length similar to the vertical stirrups asin Figure 18.

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Figure 18. Reinforcement arrangement in a web near jointsof the precast segments.

4 CONCLUSIONS

Practical experiences gained from major engineeringprojects, especially in the approach spans of Sutong

Bridge, made Chinese Engineers to be more famil-iar with this construction method. At the same time,the theoretical and experimental research achieve-ments will further accelerate the establishment of thedetailed specifications for the design and constructionof precast segmental bridges.

REFERENCES

[1] Naaman, A.E. & Breen, J.E. 1990. External prestress-ing in bridge. ACI Detroit: SP–120.

[2] Xiang Hanfan. 2003. Major Bridges in China, Com-pilation Board of Major Bridges in China. Beijing,China: The People’s Transportation Press.

[3] Podolny, W. & Muller, J.M. 1982. Construction andDesign of Prestressed Concrete Segmental Bridges.New York, USA.

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