An Overview of Modern Chinese Bridges

Man-Chung Tang, Chairman of the Board T.Y. Lin International, USA

Introduction

The modernization of China began around 1976. In this vastly huge country at that time, China had only a few major bridges. The more well-known ones are, the Qiantangjiang Bridge near Hangzhou Fig. 1, which was built in 1937 (before the World War II); the First Wuhan Yangtze River Bridge, which was completed in 1957; and the First Nanjing Yangtze River Bridge, which was completed in 1968. So, in 1976 there were only two major bridges crossing the Yangtze River, which is the longest river in China and divides the country roughly into two halves.

Infrastructure is the backbone of modernization, and bridges are a major element of infrastructure. Consequently, bridge construction took off as modernization and industrialization increased rapidly after 1976. However, most of the new bridges built during the first decade of modernization were relatively moderate spans, such as the 220m span Yellow River Bridge in Jinan; the 260m span Yonghe cable-stayed bridge in Tianjin; and the 170m concrete box girder, the Old Shibanpo Bridge crossing the Yangtze River, in Chongqing.


The modernization of China called for seven major east-west highways and five north-south highways. Currently, China has about 3.5 million kilometers of highways and 70,000 kilometers of freeways. Undoubtedly, many major bridges along these routes will be built.

Materials and Technology

Due to advancements in communi- cation and transportation, the world today is very interconnected. Technology can be leveraged and learned in a short period of time. Most construction materials and equipment are commercially available globally. Whatever technology we use to build a bridge in one part of the world can be easily reproduced in any other part of the world. Therefore, the bridges in China are not much different from bridges built in Europe or the United States, or any other country for that matter. The difference lies only in style and/or need.

The basic construction materials used to build bridges today include concrete and steel. The most commonly used concrete in China are C40 and C50, with cube strengths of 40 MPa and 50 MPa respectively. C60 and C70 have also been used but less frequently. The most commonly used steel types are Q235 and Q345 weldable steel with yield strengths of 235 MPa and 345 MPa respectively. These materials are comparable to what most other countries are using.

Beginning of the Modernization

The first major long-span bridge in China was the Nanpu Bridge in Shanghai. This 423m span cable-stayed bridge is a composite bridge, completed in 1991. Thereafter, the City of Shanghai immediately built the Yangpu Bridge, which also crosses the Huangpu River. It has a main span of 602m and was completed in 1994. It was the world's longest cable-stayed bridge span at the time of its completion. Then came yet another cable-stayed bridge—the Xupu Bridge, also crossing the Huangpu River in Shanghai with a main span of 590m. These three bridges Fig.2, all have composite decks with precast concrete panels on top of the steel frames of two edge girders connected by transverse floor beams. Composite action between concrete panels and the steel frame is through shear studs on the steel beams at the cast-in-place joints between the precast deck panels. These bridges serve as the main connector between the old metropolitan Shanghai and Pudong, the new development across the Huangpu River. Today, Pudong is a booming area filled with skyscrapers.


Several major concrete cable-stayed bridges were also built during the same period, after completion of the Nanpu Bridge. The Second Yangtze River Bridge in Wuhan has a shallow concrete box girder with a main span of 400m. Then came the Yangtze River Bridge in Tongling, with a main span of 420m. It has a concrete beam and slab, or plate girder type main girder cross section. Both were completed in 1995. The Lijiatuo Bridge in Chongqing over the Yangtze River followed shortly thereafter, in 1996. It has a similar configuration, but it has a main span of 440m.

Steel decks were not used during this early period of construction because of their high cost. In those days, China did not produce a sufficiently high quality, or sufficient quantity of steel required for bridge construction. As a result, a majority of the steel for the aforementioned composite bridges was imported. Moreover, steel box girders were not a competitive product at that time. Concrete, on the other hand, can be sourced locally. Even though China had imported cement in the beginning, since supply could not satisfy demand, many new cement factories were soon established to satisfy China's need for this highly sought after material.

During the same period, many long-span arch bridges were constructed. In the beginning, most arches were made of concrete, such as the 200m span Wujiang Bridge in Fulin and the 330m Jiangjiehe Bridge in Guizhou.


It is worth mentioning that several concrete arches were constructed by the horizontal rotation method. The arch ribs were typically constructed on falsework on the slope of a hill. They were then rotated to their final position horizontally. Each half arch was stabilized by a tie back cable at the height of its crown, Fig. 4.


Concrete-filled steel tube arch are very popular in China. The 200m span Sanshanxi Bridge in Guangdong was built in 1995, Fig. 5. The arch rib consists of four 750mm diameter steel pipes that were filled with concrete after their erection. The diagonals and verticals connecting these four ribs are 350mm diameter steel pipes. Many Chinese fabricators have acquired the necessary equipment, hardware and software to accurately fabricate the pipe connections, despite their complicated geometry. Therefore, the cost of fabrication has been greatly reduced. This type of arch bridge is now a very competitive bridge type in China.

For the construction of very long-span concrete arches, one popular method is to build a skeletal steel truss arch to serve as support for the formwork of the arch rib. The steel truss is embedded in the final concrete arch. This construction method was used for the 312m span Yongning Bridge over the Yongjiang in Guangxi. Currently, the longest span concrete arch is the 400m span Wanxian Bridge,Fig.6.



China also built several suspension bridges in that period of time. However, the spans were, for the most part, rather moderate in size, Fig. 7. The two longest suspension bridges were the Humen Bridge and the Xiling Bridge. The Humen Bridge over the Pearl River in Guangdong has a main span of 888m and was completed in 1996. The 900m span Xiling Bridge over the Yangtze River near the Three Gorges Dam was built in 1996. Both have a steel box girder deck and concrete towers.


A suspension bridge with a concrete deck girder and a main span of 452m in Shantou is yet another interesting case study. The deck utilizes precast concrete segments.

Many concrete box girder bridges were also built as well. The longest span is over the auxiliary shipping channel of the Humen Bridge and it has a main span of 270m, a world record at the time of its completion.

Current Records

The 552m span Chaotianmen Bridge in Chongqing is now the world's largest arch span. It crosses the Yangtze River. The 420m span concrete arch in Wanxian is the world's longest concrete arch span.

The Xihoumen Bridge over the Bay in Zhoushan has a main span of 1650m. The towers are 211.3m tall. It is a suspension bridge with concrete towers and features an orthotropic steel box girder deck. The girder is 36m wide and 3.50m deep. It was completed in 2009. It is presently the longest suspension bridge in China, and it is the second longest in the world, Fig. 8.


The Sutong Bridge has a main span of 1088m, and it is the longest cable-stayed span in the world. It features two concrete towers and an orthotropic steel box girder deck. The cables are parallel wire strands with Hi-Am type anchorages. The wires are galvanized and have an extruded layer of high density polyethylene over them.

The longest box girder bridge is the 330m span Shibanpo Bridge in Chongqing. This bridge crosses the Yangtze River connecting the southern district with the central business district in Yuzhong Pennisula. It is located next to an existing box girder bridge. But the Waterway Department specified that the new bridge had to have a larger navigation opening, thus resulting in a 330m span. Such a bridge would have been more economical were it a cable-stayed or an arch bridge. But aesthetics were an important consideration and the Owner decided that the bridge must be a girder bridge because it was located too close to the existing girder bridge. To reduce the weight of the bridge, the 103m central portion of the girder is a steel box with an orthotropic deck. This steel girder was fabricated 1000km downstream and towed to the site, and then lifted to its final position using strand jacks.

Currently, China holds three world records out of the four major categories of bridges— cable-stayed bridge, arch bridge and girder bridge. The world record for suspension bridges is still the Akashi Kaikyo Bridge in Japan, while the 3300m span Messina Bridge in Italy is under construction. There is no indication that China will build the world's longest span suspension bridge. With navigation requirements today, it is difficult to justify building any bridge span over 2,000 meters except under very special circumstances, as in the case of the Messina Bridge.

Besides major spans, China has also completed several long bay and sea crossings. The Hangzhou Bay Bridge is 36km long and it was opened to traffic in 2008. It has two navigation channel spans, each with a cable-stayed bridge, and the rest are long stretches of concrete viaducts. The Qingdao Bay Bridge is 42km long and was opened to traffic in 2011. It is the world's longest bay crossing today.

The Donghai (East Sea) Bridge connects Shanghai with Yangshan Island, where a deep water port will eventually be built. It is 32.5km long. It has two navigation channel spans of 332m and 420m span respectively.

Signature Bridges

As the standard of living rises rapidly in China, the pursuit of a better quality of life becomes exceedingly important. Bridge aesthetics is an integral part of city planning, and it is a key ingredient in creating a good living environment. More aesthetics are forming a critical component in the design of a bridge.


For the Caiyuanba Bridge, Fig. 9, a significant effort expended during the conceptual design to produce the most beautiful configuration of the tied arch. The bridge carries six lanes of city traffic on the upper deck and two tracks of monorails on the lower deck. A truss girder was selected to offer the monorail passengers a grand view of the river valley. The girder is 12m deep, accommodating the monorail. A trapezoidal shaped cross section was used so the girder looks much more slender.

As mentioned above, the 330m box girder was selected for the Shibanpo Bridge mainly for aesthetic reasons. It is a parallel structure sitting next to the existing Shibanpo Bridge, which is a box girder bridge, built in 1981. The Owner rejected all cable-stayed, suspension and arch bridge alternatives because they did not complement the existing bridge.

For the Dagu Bridge in Tianjin, Fig.9, the Owner requested a signature bridge that could be a symbol for the City. The bridge connects to the local streets; thus, the deck elevation is fixed. The navigation clearance of the river restricts the girder depth to only 1.40m at the centerline of the deck. Combined with a high seismic performance requirement and the existence of soft soil layers on both river banks, designing the bridge was a challenge. The resulting asymmetrical tied arch is a distinctively artistic structure uniquely harmonious with its surroundings. The very slender arch ribs were made possible using two planes of hangers, forming a three-dimensional structure that restrains the arch ribs from lateral buckling.


The Sanhao Bridge in Shenyang is another signature bridge requested by the Owner. The bridge deck is 29.50m wide. It has two main spans of 110m each. The original design was based on a conventional cable-stayed bridge concept that would require a steel box girder to reduce its weight. A steel girder is much more expensive than a concrete box girder in China. But a concrete girder would have been too heavy for the delicate tower. To solve this problem, a new bridge concept, the “partially cable-supported girder bridge” was developed and applied for the design of this bridge. The innovative concept makes use of the capacity of the concrete box girder in that it is basically designed as a girder bridge. The cables are used to pick up the difference between the load that girder can carry and the actual load requirement. In the case of the Sanhao Bridge, the cables carry approximately half of the total loads acting on the bridge. The cables are made up of epoxy-filled, seven wire strands protected by a high density PE pipe. Each strand can be stressed and replaced individually.

Another signature bridge, the Taijiang Bridge in Sanming City, was also designed based on the concept of the partially cable-supported girder bridge. The bridge deck is 34m wide and has two 100m main spans. The girder is made of prestressed concrete and the tower is steel. The cables are placed in an inverted arrangement adding a certain intrigue. All cables anchor at the middle of the deck. Hence, the cables do not exert any asymmetrical loads on the tower. All torsional moment due to asymmetrical loads on the bridge is carried by the concrete box. The girder was built first using local falsework. The towers were then erected with the help of a steel frame and a big winch traveling on top of the frame. Cables were prefabricated with galvanized parallel wires encased in a high density PE pipe. All cables were stressed from the tower end.

Conclusion

China is mountainous with deep valleys and big gorges. It is also bisected by many big rivers, such as the Yangtze River and the Yellow River. Development of new highway and railway systems will undoubtedly require the construction of many major bridges. As the Chinese economy is roaring ahead at a spectacular speed, bridge construction in China is understandably progressing with unprecedented vigor as well. For engineers who really want to work on bridges, this is a dream come true!