Recent Major Cable-Stayed Bridges in Shanghai

Transcription

1 34 Recent Major Cable-Stayed Bridges in Shanghai Q.E. Deng, C.Y. Shao Shanghai Municipal Engineering Design General Institute, China ABSTRACT: This paper presents three major cable-stayed bridges completed or under construction in Shanghai recently. The three bridges are located in the open sea, over the Yangtze River and the Huangpu River respectively with different characteristics. They are: (1) the main channel Donghai Bridge with 420m main span, a cable-stayed bridge with a composed box girder, (2) the main channel Shanghai Yangtze Bridge with 730 main span, a cable-stayed bridge with the stiffening girder composed of two separated steel boxes interconnected by numerous cross beams, and (3) the Minpu Bridge with 708m main span, a two-deck cable-stayed bridge with steel truss girder for the main span and composite truss girder for the side spans. The three bridges are introduced with the focus on the technical characteristics of their stiffening girders. Key Words: Donghai Bridge, Shanghai Yangtze Bridge, Minpu Bridge, cable-stayed bridge, stiffening girder, two separated steel boxes girder, composite box girder, composite truss girder, combined highway and railway bridge 1. THE MAIN CHANNEL DONGHAI BRIDGE 1.1 Donghiai Bridge Overview Donghai Bridge is an important complementary project of the Shanghai Yangshan Deep-water Harbor Project. It is the first super long-span bridge over open sea in China. The bridge starts from Shanghai Luchao Harbor, spans the vast sea to the Phase I junction of Xiaoyangshan Harbor. Its total length is 32.5 m. The project is characterized by its large scope, the poor natural conditions, the high technical difficulties, and the short construction period. The engineering design gave rise to a series of new problems that required analysis and study. In order to begin the project on a high note, maintain the high standards and provide high quality, upgrading past experience and bold vision were essential. The designers sought plans and techniques for safe and efficient over-sea construction. From June 2002 to October 2005, the construction of the bridge took merely 40 months. The bridge is designed according to the two-way six-lane expressway standard. The deck is 31.5 m wide. The vehicular load is designed according to the automobile super Class 20 and the trailer 120. In addition, the loads of densely arranged container trucks (center to center spacing of front to back wheels on adjacent cars equals 10m) were also examined. The bridge, crossing 26km-wide sea with the depth of 10~15m, is located at the loose stratum of the

2 35 Quaternary Period, which is over 130m thick. The sectional water velocity of the site is generally 2.0m/s ~ 2.5m/s. Waves larger than 6.0m in height has a return period of 100 years. The bridge is 32.5 km in length, of which 90% spans over the sea (illustrated in Fig. 1). It includes 1 main channel bridge, 3 auxiliary channel bridges, non-navigable span bridges as well as bridges near the harbor. View from Sea to Bank View from Bank to Sea Fig. 1 General View of Donghai Bridge 1.2 Main Channel Cable-stayed Bridge Bridge Proposal The main channel bridge is a 420m main span cable-stayed bridge, designed according to the navigation requirements. The main considerations include managing construction progress, ensuring structural durability and smooth operation under traffic loads. The design load is about 11t/m after considering the lane reduction, which is equal to 0.8 times the UIC load of the double-line railway. The steel box girder cable-stayed configuration allows for fast construction, but provides relatively low rigidity and causes high range of stresses in the cables and the main girder. When the concrete structure is adopted for the entire Donghai Bridge except for the main channel span, the pavement over the steel deck will become the weakest point during the operation period. Concrete girder cable-stayed configuration has good rigidity, but is slow to construct. Even if sectional cantilever construction method is used, it is difficult to meet the project deadline. The plate steel and concrete deck composite girder cable-stayed configuration has better rigidity and stress performance. The deck paving is unified with the whole bridge, and the project deadline can also be met. If the concrete deck is prefabricated in pieces, the resulting field joints can decrease the structure s corrosion resistance. If the concrete deck is cast in-situ, then the amount of work carried out over-sea increases, leading to increased risk and technical difficulty. In addition, large areas of steel are exposed for this kind of structure, and the configuration of plate steel girders is complicated, making maintenance work more difficult. In view of the above comparison, the steel-concrete composite box girder cable-stayed

3 36 configuration is chosen for the main channel bridge to satisfy the usage/environmental conditions and to meet the project deadline Bridge Design The main channel bridge is ( =)830m long and 33m wide. It is a five-span continuous cable-stayed bridge with double pylons, single cable plane, and auxiliary piers (illustrated in Fig.2). These piers are designed to improve the stiffness of the bridge and reduce stress applied to the girder and pylons. The pylon section above the deck is an inverted Y shape. Below the deck is a box structure with uneven width. Steel anchor girders are used for 2/3 of the stay-cables in the anchorage zone, and are rigidly connected to the pylon wall. The other 1/3 of the cables are anchored directly to the concrete pylon wall due to their smaller horizontal component force. Fig. 2 View of Main Bridge The 4.0m deep main girder is a steel concrete structure of single-box-three-cell section (illustrated in Fig.3). The top plate of the girder box, made from C55 concrete, is 33.0m wide with two 4.5m wide cantilevers. The rest of the girder box is made from Q345qD steel. The concrete plate is generally 28cm thick, and increases to 55cm on top of the web. The typical steel structure is composed of 16mm thick bottom plates & diagonal web plates, as well as 24mm thick vertical webs & web flanges. Other steel structures by the pylon bottom and on top of the side/auxiliary piers are thicker than the typical segment. The bottom plates and webs are stiffened by 8mm thick U-shaped ribs. The diaphragms of the main girder are steel trusses with 24mm thick top flanges. Two types of shear studs with 22mm diameter are adopted to connect the steel box structure to the concrete deck. One type is 450mm long and set at the edge of the top steel flange to counteract the transverse bending moments. The rest studs are 200mm long. Fig. 3 Cross Section of Composite Box Girder Fig.4 Cantilever Construction

4 37 The standard cable spacing is 8m on the girders and 2.2m on the pylons, totalling 224 cables overall. PE sheathing protected φ7 mm high-strength galvanized parallel metallic cables are used with cold-cast anchors. The main pylon is supported by pile groups composed of 38 bored piles, each 110m long and 2.5m in diameter. 2. THE MAIN CHANNEL SHANGHAI YANGTZE BRIDGE 2.1 Shanghai Yangtze Bridge Overview The Chongming Cross-River Passageway (illustrated in Fig. 5), in the northbound direction, traverses the southern waterway of the Yangtze River by tunnel, then crosses the northern waterway from Changxing Island to Chongming Island by bridge. Its total length is 25.5km. The Shanghai Yangtze Bridge spans the northern waterway with a total length of 16.55km, of which approximately 10km is over water. The whole project including bridges and tunnels are under construction now. Fig.5 The General View of the Chongming Cross-River Passageway The bridge design is based on the standard for dual-direction 6-lane expressway. The design vehicular speed is 100km/h and the width is 35.3m. In anticipation of the future development needs of Chongming Island and seeking to optimize the use of resources, the design takes into consideration railway traffic across the bridge. Therefore, the 3-m wide continuous emergency parking lanes on both sides are widened to 4.15m, resulting in a total deck width of 35.3m. This allows for future addition of two railway tracks beside the existing Fig.6 Present and Future Layout of Lanes lanes (illustrated in Fig. 6). The Class I Highway Vehicular Load Standard was used for this design. The design train load is taken to be: 10 carriages per train, with each train 16.5m in length and carrying 48-t (full load). The project is located at the entrance of the Yangtze River, thus is frequently influenced by typhoons. As a result, the bridge needs to have excellent wind-resistance properties. The

5 38 bridge site is situated in the alluvial plain of the delta of the Yangtze River, a typical soft soil region. The bridge design not only needs to overcome the challenges of complicated natural/construction conditions and of combining highway/railway traffic; as the symbolic structure at the mouth of the Yangtze River, it also needs to make an architectural statement. The over-water portion of the bridge consists of the main navigable span, sub-navigable spans and non-navigable spans. The overall view is shown in Fig.7. Fig.7 General View of the Shanghai Yangtze Bridge over Water 2.2 Main Channel Cable-stayed Bridge The main channel cable-stayed bridge is situated at the river center. The main channel is required to meet Fig.8 Layout of the Main Channel Cable-stayed Bridge Fig.9 General View of Main Channel Cable-stayed Bridge the two-way navigation clearance of 585m 52.7m for both a 30000t container cargo vessel and a t bulk cargo vessel. The main sub-channels on both sides are required to meet the one-way navigation clearance of 146m 36m for a 5000t vessel. The span arrangement is =1430m, as shown in Fig. 8 and Fig. 9. Fig.10 Layout of Pylon The bridge pylon is a concrete structure. Above the deck it takes on a single-column form, and below the deck it has an inverted V shape. Steel anchor boxes are used to anchor the cables on the pylon. The anchorage areas are lifted and assembled in sections. The structure of the pylon is shown in Fig. 10.

6 39 The steel box girder is 51.5 m wide, in detached form. The space between the detached steel boxes is 10 m. Steel box-section cross beams are used at 15m spacing to connect the girders. The height of the girder is 4 m. A typical cross section is shown in Fig. 8. Q345qD steel is used. The top plates are 16mm or 14mm thick. The bottom plates and webs are either 12mm, 16mm, 20mm or 30mm thick. The external anchorage webs are either 30mm, 40mm, 50mm or 60mm in thickness. A standard section of steel box girder is 15m in length. The individual sections are assembled with cantilever method. With the exception of bolted longitudinal stiffeners, all connections between the sections are welded. To reduce the turning angle at the end of the cable-stayed bridge girder, to create favourable conditions for trains passing the bridge, and to satisfy side span stability needs, 35cm-thick concrete slabs are attached to the bottom of the steel box girders within the 92m side spans to enhance their rigidity. Fig.11 Cross Section of Steel Girder The standard cable spacing is 15m on the girders and 2.3m on the pylons, totalling 192 cables overall. PE sheathing protected φ7 mm high-strength galvanized parallel metallic cables are used with cold-cast anchors. The main pylons are supported by large deep-water foundations. Each foundation consists 60-φ2500mm cast-in-situ piles with the length of about 105m. 3. MINPU BRIDGE 3.1 project background Shanghai A15 expresswsy, starting from the boundary of Shanghai City and Zhejiang Province in the west, ending at Pudong International Airport in the east, is about 83km long. This project will provide people from suburban area in Shanghai and peripheral cities a rapid way to enter Pudong International Airport. A15 expressway spans the Huangpu River at the Minhang District in Shanghai, on the other hand, the local urban transportation has the same demanding of crossing the river as well. As a result, Minpu Bridge, a two-deck bridge, is chosen to meet all the demandings. The two-deck bridge proposal can not only save the natural resource but also reduce the cost. The location of A15 expressway and Minpu Bridge is shown in Fig. 12.

7 40 Pudong International Airport Boundary of Shanghai City Fig.13 Lanes Layout for the Upper Deck Fig.12 Project Location Fig.14 Lanes Layout for the Lower Deck With a total deck width of 40.5m, the upper deck is designed for A15 expressway to carry 120km/h design speed on 8 traffic lanes in dual directions. And the lower deck with a total width of 26m is designed for the local urban transportation to carry 60km/h design speed on 6 traffic lanes in dual directions. Traffic loads for two decks are determined according to Grade I of Chinese code. The layouts for two decks are illustrated in Fig. 13 and Fig Bridge design The span arrangement is 4x x63=1212m, as shown in Fig. 15 and Fig. 16. It is a nine-span continuous cable-stayed bridge with two decks, double pylons, double cable plane, and auxiliary piers. Fig.15 Layout of Minpu Bridge Fig.16 General View of Minpu Bridge The H-shaped pylon (illustrated in Fig.17) is unique compared to other cable-stayed bridges over the Huangpu River. Steel anchor girders are used for 2/3 of the stay-cables in the anchorage zone, and are rigidly connected to the pylon wall. The other 1/3 of the cables are

8 41 anchored directly to the concrete pylon wall due to their smaller horizontal component force. Fig.18 Cross Section of Truss Girder for Main Span Fig.19 Cross Section of Composite Truss Girder for Side Span Fig.17 Layout of Pylon Truss girder with the steel deck and the truss framework integrated is adopted for the main span. The truss girder is N-shaped longitudinally in a space of 15.1m, and that the upper deck is wider than the lower deck results in an inverted trapezia cross-section (illustrated in Fig.18). The distance between the two decks is 9m. A standard section of the main span girder is 15.1m in length accordingly. The individual sections weighing about 500 tons for per section are assembled with cantilever method. All connections between the sections are supposed to be welded, and the welding solution is under research and investigation. In order to balance the main span and shorten the length of the side spans, a relative heavy composite truss girder (the cross-section is shown in Fig.19) for the side spans is an economic choice. The composite truss girder is N-shaped as well in a space of 10.5m. The configuration of the side span girder is almost the same as the main span except that the concrete decks are adopted for the side spans, while the steel decks are adopted for the main span. A temporary truss is used for the purpose of facilitating the concrete casting and the permanent web steel members positioning. The standard cable spacing is 15.1m and 10m on the girders of the main span and the side span respectively, and 2.3m on the pylons, totalling 176 cables overall. PE sheathing protected φ7 mm high-strength galvanized parallel metallic cables are used with cold-cast anchors. The main pylon is supported by pile groups composed of 385 driven tube steel piles, each 55m long and 0.9m in diameter.

9 42 4. CONCLUSION Designers should challenge the different bridge designing and constructing conditions and propose the appropriate solutions with creativity. The three major cable-stayed bridges presented in this paper show somewhat innovative solutions, especially on their stiffening girders. 5. REFERENCES [1] Shao, Lu, Deng, 2006, The Shanghai Yangtze Bridge, International Conference in Hong Kong 2006 on Bridge Engineering-Challenge in the 21st Century. [2] Shao, Deng, Yang, 2006, Donghai Bridge, International Conference in Hong Kong 2006 on Bridge Engineering-Challenge in the 21st Century.