What new concepts are reflected in the concept of "strengthening the body and keeping fit"? For the first time in the history of Shanghai Lupu Bridge, structural maintenance has been quietly completed for the Lupu Bridge | Bridge | Concept

The Lupu Bridge, the sixth bridge on the Huangpu River in Shanghai and known as the "world's largest arch," has recently completed its first structural repair since its construction.

Since 2015, Shanghai's urban bridges have entered a peak maintenance period, with several iconic bridges undergoing maintenance and renovation, including Zhejiang Road Bridge, Nanpu Bridge, Yangpu Bridge, Songpu Bridge, etc. Why did the Lupu Bridge, which is younger than them, start "strengthening and keeping fit" early on? The Jiefang Daily Shangguan News reporter learned that after this maintenance, the Lupu Bridge still needs to consider upgrading, reflecting the new concept of urban municipal facility operation.

How long can disease removal last?

June 28th is the 20th anniversary of the opening and operation of the Lupu Bridge. Why did a young bridge who had just turned 20 start maintenance work early?

"The design period of the main structure of the Lupu Bridge is 100 years. Through testing, we found that the main structure of the bridge is still very healthy, but some ancillary facilities are nearing their service life and need to be replaced." Wang Ruilong, the person in charge of the Lupu Bridge overhaul design at the Shanghai Municipal Engineering Institute, said that the bridge is like a person. If you have a minor illness, you need to take medicine and undergo daily physical examinations to maintain long-term health.

Construction site

Bridge experts told reporters that some of the maintenance work this time is related to the special structure of the bridge. The Lupu Bridge is the world's first fully welded steel structure arch bridge and still the largest steel box arch bridge in the world. As is well known, the bridge is close to the water surface and requires rust prevention and corrosion. The previously built Nanpu Bridge and Yangpu Bridge were both cable-stayed bridges, which incorporated concrete in their structures and were not easily corroded. In contrast, the Lupu Bridge, which uses steel structures, requires special attention to rust prevention issues.

Among the 5 items of this structural repair, two are related to rust prevention, namely the upgrade of dehumidification system and inner surface coating. In addition, the daily average traffic volume of the two-way lanes of the Lupu Bridge reaches 130000 vehicles. After 20 years of high load operation, the horizontal cable system, side span drainage, and sound barrier street lights of the bridge have also experienced defects and diseases.

In order to maintain a youthful appearance, the Lupu Bridge started maintenance work in June 2022. Unlike other cross river bridges, when the Lupu Bridge was built, a dehumidifier was specially installed inside the bridge to slow down the corrosion rate by removing moisture.

Wang Ruilong introduced that as the number of years of bridge use increases, the internal "moisture" of the bridge will affect the overall safety and quality of the bridge body, and it is necessary to always maintain the "moisture removal" efficiency. Therefore, the design team upgraded the air supply circuit, replaced it with 42 dehumidification devices, and kept it on for 24 hours to control the humidity inside the bridge below 45%. "According to our research findings, when the humidity inside the bridge is below 45%, even without the use of anti rust coatings, there will be no large-scale rust," said the designer.

Bridge dehumidification monitoring system

Modular assembly of dehumidifiers, but for the sake of "double safety", the design team synchronously replaced all internal coatings of the bridge. These coatings not only prevent rust and corrosion, but are also very environmentally friendly. It does not contain harmful solvents such as benzene, which is not only friendly to construction personnel, but also effectively reduces the risk of explosion and avoids fire hazards.

How long can the bridge last after removing the disease this time?

Wang Ruilong introduced that bridges are a century long project, and according to the design period, the main structure can be maintained for 100 years. But different ancillary facilities have different service lives, including expansion joints, suspension rods, coatings, and horizontal cables. For example, painting takes about 10 to 15 years, and the suspension rod takes about 20 years.

To build a century old bridge, it is necessary to rely on daily maintenance. In fact, the Lupu Bridge has undergone minor repairs and repairs in the past few years. From 2016 to 2020, the Lupu Bridge underwent horizontal cable anchor head renovation, road milling and covering, exterior painting maintenance, landscape improvement, and replacement of large displacement expansion and contraction devices.

What new concepts will future upgrades reflect?

Why is the first structural overhaul in the history of Lupu Bridge so quiet?

Wang Ruilong said that this repair does not involve landscape, but mainly focuses on improving functionality, also known as "strengthening the body", with the aim of removing diseases from the bridge. On the other hand, construction should be carried out in the early morning as much as possible to avoid affecting citizens and traffic.

For example, taking multiple measures to reduce noise pollution, replacing sound barriers in the project, optimizing the connection process of sound barriers, reducing noise pollution, and significantly reducing construction time. During the construction process, the generator is covered with sound-absorbing cotton to reduce noise, and nighttime construction is utilized to minimize the traffic impact caused by disturbance to residents and road closures.

At the same time, the road lighting has been transformed from high-pressure sodium lamps to LED energy-saving lamps, which can save energy and reduce emissions by 41%. It can also better simulate natural light, illuminate the road surface more clearly, and ensure nighttime driving safety. At the same time, LED lights have a smaller volume and flexible design, which can be well integrated into urban landscape design and enhance the beauty of the city.

The 16 horizontal cables that run horizontally through the bridge deck and body are the "life cables" of the Lupu Bridge, mainly used to balance the strong horizontal thrust transmitted by the main arch of the Lupu Bridge, about 20000 tons. However, after years of wind and frost, the vertical bracket used to support the horizontal cable is prone to detachment and damage. The team has independently developed a "saddle shaped" bracket with adjustable height, significantly increasing the load-bearing area, ensuring that the vertical bracket does not become empty, and reducing safety hazards caused by the stability of the bracket.

A new type of saddle shaped bracket

Before updating

After update

With the peak period of urban construction receding, Shanghai has entered the era of urban renewal. Not only does construction need to be updated, but municipal facilities also need to continuously improve their efficiency through operation and maintenance. The reporter learned that after the maintenance of the Lupu Bridge was completed, the major repairs of several iconic cross river bridges in Shanghai have temporarily come to an end. Up to last year, more than ten bridges have been built on the Huangpu River, and these large-scale municipal facilities are also facing management challenges.

"The future focus on municipal facilities should also include subsequent operation and maintenance management, and improve management efficiency through cross-border use of digital technology and artificial intelligence technology," said bridge experts.

It is reported that the Lupu Bridge is considering upgrading its digital management system. In order to conduct future inspections, during this major overhaul, the maintenance team has also added temperature and humidity sensors and video cameras inside the Lupu Bridge, which can view the internal situation of the bridge in real time and monitor its health. "The Yangpu Bridge has now achieved digital twins, displaying the bridge's' vital signs' in real-time through various sensing devices. Next, the Lupu Bridge will also consider doing digital twins," said Wang Ruilong.