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Chongqing Chaotianmen Yangtze River Bridge(Ⅰ)



2012-10-10
Xiang Zhongfu


Chongqing is a typical city with hills and rivers. Yangtze River and Jialing River run around the main city. Chongqing cannot develop without bridge construction. At the end of 2008, Chongqing has built more than 8,000 bridges, and there are more than 50 bridges only above Yangtze River and Jialing River. Chongqing's bridges are not only in a large amount, but also of diverse forms, high technical difficulty and large influence in the world. Among these bridges, RC arch bridge, concrete-filled steel pipe arch bridge and steel bridge with the longest span in the world are all constructed in Chongqing, therefore Chongqing is honored as the Bridge City of China.

Main bridge of Chongqing Chaotianmen Yangtze River Bridge used half-through continuous steel truss tied arch bridge(190+522+190m) (Figure 2). The bridge is designed for both highway and railway traffics. The upper deck was provided with two-way six-lane and two sidewalks, 36m wide in total; the lower one was provided with urban railway transit in the center, with one 7-m-wide car lane reserved at either side (Figure 3). This bridge has created many new records in terms of bridge type, structural system, span, construction, control, function and so on.

Chaotianmen Yangtze River Bridge was invested by Chongqing Urban Construction Investment Company, designed by the design institute of China Railway Major Bridge Engineering Group and Chongqing Communications Research & Design Institute. China Communications Construction Company Ltd serves as BT owner. It was constructed by China Communications 2nd Navigational Bureau 2nd Engineering Co.,Ltd, supervised by Supervision Company of China Railway Major Bridge Engineering Group. The construction is controlled by Chongqing Jiaotong University and site tested by CCCC Wuhan Harbor Engineering Design & Research Institute. Construction of the bridge started at the end of 2005 and was completed in April, 2009.

                         

                          Figue1: The Yangtze River and Jialing River join in Chaotianmen of Chongqing


                       
                                                       Chongqing Chaotianmen Yangtze River Bridge in Sunset



                                          Figure 2: Diagram of Chaotianmen Yangtze River Bridge(Unit:m)


                                        Figure 3: Cross Section of Chaotianmen Yangtze River Bridge

New Breakthrough in Arch Span
Traffic demand and rapid technical development promote new breakthrough in span for arch bridges.
Span of Pont Saint Louis completed in 1874 is 158.6m; 42 years later, Hell Gate Bridge increased the span to 297m; after another 15 years(1931), Bayonne Bridge's span in U.S. reached up to 504m; span of New Valley Bridge in U.S. had increased to 518.3m in 1977. It is one leap that China built Shanghai Lupu Bridge in 2003, with main span as long as 550m. The table below gives some information about top ten large span steel arch bridges in the world.

                                          Table 1:Top Ten Large Span Steel Arch Bridges in the World

Number Name of the Bridge Country Years of Completion Span(m)
1 Chongqing Chaotianmen Yangtze River Bridge China 2009 552
2 Shanghai Lupu Bridge China 2003 550
3 New River Gorge America 1977 518.3
4 Baynooe Bridge America 1931 504
5 Sydney Harbour Bridge Australia 1932 503
6 Guangzhou Xinguang Bridge China 2003 428
7 Chongqing Caiyuanba Yangtze River Bridge China 2007 420
8 Fremont Bridge America 1973 383
9 Port Mann Bridge Canada 1964 366
10 Chongqing Wanzhou Railway Bridge China 2004 360


We can see that with the span of 552m, Chongqing Chaotianmen Yangtze River Bridge becomes the largest span arch in the world. The elegant shape of the bridge may be considered as one perfect combination of bridge and art, and it has already become the new landmark architecture of Chongqing.

Structural System Design
The main bridge is a three-span continuous-beam stress system, with main span of 552m and central span of 488m show the stress feature of tied arch, arch crest of midspan to middle pivot is 142m high, as shown in Figure 4.



                                                                                 Figure 4: Composition

Stress magnitude of members of the main truss of the bridge’s steel truss (arch) present large difference during construction and operational state after completion. To produce a safe and economical structure, from one hand, Q345q, Q370q and Q420q steels respectively with yield strength of 345Mpa, 370Mpa and 420Mpa were used to reduce member section size required by the maximum member stress during design. On the other hand, highly variable sections were adopted based on stress magnitude of the members. At the same time, as to member section width of main trussed girders (arch) were 1,600mm and 1,200mm. Members with different width were designed as horn-shaped transition through neighboring internodes.

Fully considering difficulty of manufacture and economy of manufacture cost, except for the central support node (Figure 5), the rest all used knock-down node structure. Within the scope of central support node, reinforcing ribs were set up and temporary lifting structures required for late maintenance and steel structure installation were provided. To ensure spatial structural positions of various members within the scope of the node, whole node structure was used to allow high strength bolt connection to be engineered outside of the node plate in view of large internal force of each member that the node linked with and a great deal of high strength bolts needed for load transmission, benefiting arrangement of other structural members.


                                                                              Figure 5: Central Support Node

As midspan of main trussed girder (arch) showed stress features of arch, in design double-layered tie member was used to horizontally push along the bridge. Upper and lower layers of tie members were respectively arranged within structural scope of deck system. To facilitate connection with truss structure and straight part load transmission, double-layered tie members were made up of shape steels consisting of steel plates. Tie members on the upper layer were H shaped, and those on the lower layer were王-shaped (like Chinese character "王") ones which were horizontally arranged. To reduce internal load values of lower tie members, external pre-stressing high strength steel strands were adopted in the lower tie members as auxiliary structure. (Figure 6)


                                               Figure 6: Cross section of tie members (Unit: mm)

Section sizes of some members of the main trussed girder (arch) were relatively large and to solve the problem of relatively large secondary stress of the members, theoretical system lines of some members were altered in the design, which made deviation between practice and theory. It went back to theoretical value through applying external force during installation, thereby forming one group of disturbance end moments in opposite direction that equal to constant moment of member end, fulfilling such a purpose that member end moment under structural completion state did not dominate member section design.

Each pier of the main bridge used hinge bearings (whose central pivot was up to 14,500t and was so far the bridge bearing with the maximum bearing capacity in the world) that support nodes of the main truss. For longitudinal support, central pivot at north side was provided with fixed hinged bearings, and the rest piers were provided with mobile hinged bearings. For transverse support, central and side pivots under the main truss were provided with transverse mobile bearings; however their transverse displacement values shall be limited. To ensure main truss to develop uniform transverse displacement at both sides with main structure under action of system temperature and avoid rails of the light railway developing transverse sidewise bending that would affect operation safety of the light railway. Two transverse limit bearings were set at center of lower cross beam under at side pivot. Bearings of main bridge were spherical cast-steel hinged bearings.

Upper and lower highway decks of this bridge utilize orthotropic steel decks with diaphragm provided longitudinally to the bridge. 6 and 2 longitudinal girders were set up respectively on upper deck transverse to the bridge and at either side of the lower deck. One transverse girder that linked the main truss was provided at the node of the main truss. After completion of the bridge, steel decks for highway constrained the tie or chord members that lied within the same segment and elevation range. design length of steel deck at different positions extended or shortened based on theoretical values, this different values were identical to the deformation of corresponding tie or chord members under action of total dead load and partial live load, so as to eliminate the adverse influence of indirect joint action that exists between deck and truss on deck system structure and main truss's linking members.






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