Why has the Nanpu Bridge, which is over 30 years old, become so popular?

Recently, a video of Nanpu Bridge went viral online.

Netizens exclaimed: "Ah! It's worthy of being the Magic City!"

Image source: 021 Video

Although a closer look reveals that this is processed through special effects, this does not affect everyone's feelings towards the Nanpu Bridge.

Image source: TikTok

As the first bridge across the Huangpu River in downtown Shanghai, Nanpu Bridge has a history of 30 years. It is like a harp on the Huangpu River, playing the city's music and telling the story of Shanghai's urban development.

The grand occasion on the opening day of Nanpu Bridge

Source: Xinmin Evening News

01

Building an “open channel” for Pudong

From the opening of the port in the late Qing Dynasty, to the large number of factories gathered on both sides of the Huangpu River in the early 20th century, to its transformation into a world-class metropolis, Shanghai's development is closely related to the natural advantages of its port.

However, while the concentration of population has promoted the development of Shanghai's economy, it has also made the central urban area very crowded. The transfer of traditional industries has also required Shanghai to find new economic growth points.

Therefore, the Party Central Committee decided to develop Pudong and set up five comprehensive areas in the Pudong planning.

Source: Planning and Construction of Pudong New Area

To strengthen the connection and cooperation between the east and the west, a modern transportation network is indispensable. In the Pudong planning, modern transportation facilities such as the inner ring road, outer ring road, subway, tunnel, bridge, etc. are required to achieve unified standards and connect the east and the west. It was in this context that the construction of Nanpu Bridge began.

In early 1988, the former Shanghai Construction Committee held a meeting and decided to independently build the Nanpu Bridge. On December 25, 1988, the construction of the Nanpu Bridge started. It was called "Nanpu" because it connects Nanshi District and Pudong, and Nanshi District was incorporated into Huangpu District in 2000.

02

Suspension bridge? Cable-stayed bridge? How to choose?

The first challenge in building a bridge over the Huangpu River is the span of the bridge (the distance between the center lines of the piers). Since the Huangpu River is busy with shipping, if piers are set up in the middle of the river, it will affect navigation, so the bridge needs to "cross the river in one span."

The Huangpu River is located in the urban area, and its narrowest part is about 400 meters wide. At that time, there was no bridge in China that could achieve such a span, and there were only two types of bridges that could be used for large spans, namely suspension bridges and cable-stayed bridges. Which one should I choose?

Among modern bridges, suspension bridges are the record holders for span. The towering bridge towers, curved main cables, and solid anchors constitute its most basic load-bearing system, which is also its most distinctive appearance feature.

The cables of a suspension bridge are perpendicular to the bridge deck, so no matter how long the span is, there will be no axial force to squeeze the main beam. The anchor is the main load-bearing structure of the suspension bridge, resisting the tension from the main cable and transferring it to the foundation. According to scholars' calculations, the span of a suspension bridge can reach at least 5,000 meters.

Schematic diagram of suspension bridge

However, building a suspension bridge requires a solid anchor foundation. The geology on both sides of the Huangpu River is soft. If a suspension bridge is chosen, not only will the foundation work be huge, but the cost will also be very high.

A cable-stayed bridge is a bridge that uses many inclined cables to pull the main beam directly onto the bridge tower. It is composed of a pressure-bearing tower, tensioned cables, and a pressure-bending beam. When the bridge is overhead, the beam will bend or even break due to the weight of the bridge deck and the load (pedestrians, vehicles). The cable can provide a strong pulling force to hold the main beam, and then transfer the pulling force to the bridge tower, converting it into downward pressure.

Schematic diagram of cable-stayed bridge

A very important feature of cable-stayed bridges is "self-anchoring", which means that the cables do not need additional anchors and can be directly anchored on their own main beams. This feature makes cable-stayed bridges very suitable for Shanghai's soft geological conditions. In addition, cable-stayed bridges have high rigidity, good wind and earthquake resistance, low cost, and a tall and beautiful shape. After considering many factors, engineers finally decided to adopt the cable-stayed bridge solution.

Nanpu Bridge adopts a composite beam cable-stayed bridge structure, with a main span of 423 meters, a six-lane bridge deck, a width of 30.35 meters, and a bridge tower of 155 meters. The bridge tower is a broken H-shaped hollow column, leaving enough space in the upper part of the tower to fix the steel cables. The main beams are connected to each other on both sides of the bridge tower with steel cable-stayed cables, and the distributed cable surfaces form a fan-shaped cable surface with alternating virtual and real surfaces.

Picture丨TuChong Creative

The Nanpu Bridge also has a striking design - the spiral approach bridge. Why is it designed like this? Is it for aesthetics? In fact, it is mainly because the west bank of the bridge is a densely populated area. In order to reduce the area occupied by the bridge and the cost of demolition, the approach bridge is designed to be spiral.

Picture丨TuChong Creative

03

Turn danger into safety and create a precedent

The composite beam cable-stayed bridge structure used by the Nanpu Bridge actually had a precedent in the world at that time, which was the Annasis Bridge in Canada. Therefore, when selecting the scheme, engineers often drew lessons from the Annasis Bridge.

Annacis Bridge, Canada, built in 1986

Image source: structurae.net

Considering that the Annasis Bridge was built less than two years ago, engineers decided to go to Canada for a field survey and found cracks on the bridge. After returning from the survey, Chief Engineer Lin Yuanpei immediately conducted theoretical calculations, and the results also showed that cracks would occur.

"Since I can calculate it, it means there is a pattern, and it is not the result of careless work by workers. If there are cracks, rainwater will seep in. There are steel nails and steel beams connecting them. If the steel nails rust over time, the bridge will collapse!"

After repeated research, Lin Yuanpei believed that the cracks on the Annasis Bridge were caused by improper design and construction. He divided the cracks into four categories and decided to change the design to resolve them one by one. Finally, after the engineers modified more than 3,000 drawings one by one, they made the Nanpu Bridge stand over the Huangpu River.

Bridge builders hold a meeting to discuss the construction plan

Image source: Red Voice

Nanpu Bridge pioneered the independent construction of modern large-span bridges in my country and laid the foundation for the subsequent construction of Yangpu Bridge and Xupu Bridge. Among them, Yangpu Bridge, which opened to traffic in October 1993, has a span of 602 meters and became the world's largest cable-stayed bridge at that time.

The Nanpu Bridge not only connects the traffic on both sides of the Huangpu River, but also connects the economy and people's livelihood on both sides, making an important contribution to the development of Pudong.

When the Nanpu Bridge was first built, the Pudong section was full of pastoral scenery.

Source: Xinmin Evening News

Author: Jade Cucumber

Editor: Tinker Bell

Scientific review: Zhu Ledong, researcher at the Department of Bridge Engineering, School of Civil Engineering, Tongji University; Ma Xiaogang, engineer at Shanghai Pudong Architectural Design and Research Institute Co., Ltd.

Source: Shanghai Science and Technology Museum

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