NANNING, June 12 (China News Service) — What has China's arch bridge contributed to the world?

— An exclusive interview with Zheng Jielian, Academician of the Chinese Academy of Engineering and Professor at the School of Civil Engineering and Architecture, Guangxi University

By Huang Yanmei and Chen Qiuxia

In February this year, the world's largest-span arch bridge — the Tian'e Longtan Grand Bridge on the Nandan–Tian'e–Xialao Expressway in Guangxi — was completed and opened to traffic. It is the world's first arch bridge with a span exceeding 600 meters, achieving a "century-span leap" for concrete arch bridges, becoming another milestone in the history of world arch bridge development and a new national "calling card" for Chinese bridges.

At present, China's arch bridges have advanced to the front ranks of the world in both construction technology and number. As the chief designer of the Tian'e Longtan Grand Bridge, Zheng Jielian, Academician of the Chinese Academy of Engineering and Professor at the School of Civil Engineering and Architecture, Guangxi University, recently gave an exclusive interview to China News Service's "East-West Question" program, interpreting the design and construction innovation highlights of China's modern arch bridges as well as the development achievements of China's arch bridge technology.

　　The following is a summary of the interview:

CNS Reporter: China has a long history of bridge construction. Bridge structures can basically be divided into four major types: arch bridges, cable-stayed bridges, beam bridges, and suspension bridges, among which arch bridges have the longest history. What development course have Chinese arch bridges gone through? At what level is China's arch bridge construction at present?

Zheng Jielian: Around 282 AD, stone arch bridges appeared in China. In 605 AD, China built the world's first open-spandrel stone arch bridge — the Zhaozhou Bridge, with a span of 37.02 meters. There are four small arches on the arch ring, which can reduce the self-weight of the superstructure and improve the stress at the arch springing. It found a correct path for increasing the span of arch bridges. This stone arch bridge span record lasted in China for more than 1,300 years and was not broken until after the founding of New China.

In New China, stone arch bridges continued to be built in large numbers. The largest span was the Danhe Bridge on the Shanxi Jincheng–Henan Jiaozuo Expressway, completed in 2000, with a clear span of 146 meters. Although it ranks among the world's front ranks, because of the safety and high cost of arch centering, there is little point in continuing to increase the span of stone arch bridges.

However, the spans of China's steel arch bridges and concrete arch bridges lagged far behind the world for a long time. Among concrete arch bridges, the former Yugoslavia had already completed the 390-meter-span KRK Bridge before 1980, while China completed the Fuling Wujiang Bridge in 1985 with a span of only 200 meters. Among steel arch bridges, the United States completed the New River Gorge Bridge in 1977 with a span of 518 meters, while China completed the main span of the Jiujiang Yangtze River Bridge at 216 meters in 1993, only then breaking the 200-meter mark.

It was not until the past 20 years that China's arch bridges of various categories — steel arch bridges, concrete-filled steel tube arch bridges, and concrete arch bridges — all exceeded foreign spans and ranked first in the world. Ranked by span, China accounts for 8 of the world's top ten arch bridges, including the top six. In particular, the Tian'e Longtan Grand Bridge, completed and opened to traffic in February 2024, raised the world record for concrete arch bridges by 155 meters at one stroke, and China owns the intellectual property rights for all the technology. The Tian'e Longtan Grand Bridge costs 125 million yuan less than the cable-stayed bridge option at the same site in terms of budget estimate, and its stiffness is 7 times greater. In short, China's arch bridge construction technology is currently among the world's front ranks overall.

The world's largest-span arch bridge — the Tian'e Longtan Grand Bridge. Photo courtesy of Guangxi Communications Investment Group

CNS Reporter: Guangxi is one of the representative provinces for arch bridge design and construction. What major technical difficulties have modern arch bridges represented by the Guangxi Pingnan Third Bridge and the Tian'e Longtan Grand Bridge overcome? What breakthrough technological innovations have been achieved?

Zheng Jielian: In the 1960s and 1970s, Guangxi already used the cable-stayed buckling and suspension assembly technology for precast arch rib segments to build more than 40 reinforced concrete arch bridges with spans of about 100 meters. Their unit cost was on par with that of 30-meter simply supported beams, making Guangxi one of the provinces with the most arch bridges in China. In recent years, Guangxi has made a series of major breakthroughs, represented by the Pingnan Third Bridge and the Tian'e Longtan Grand Bridge.

The main bridge of the Pingnan Third Bridge is a concrete-filled steel tube arch bridge with a calculated span of 560 meters, ranking first among all types of arch bridges in the world by span at the time of completion. The main technological innovations of the Pingnan Third Bridge include: the invention of a composite abutment foundation of "diaphragm wall + concrete pile cap + pebble layer grouting" suitable for non-rock foundations; the invention of active force control replacing traditional passive stiffness control, reducing the horizontal displacement at the tower top during arch truss suspension assembly from the decimeter level to the centimeter level while greatly slimming down the lifting and buckling towers; the invention of the technology of one-time tensioning without cable adjustment and one-time removal of buckling cables during arch truss suspension assembly; and the development of shrinkage-controllable in-tube concrete, solving the biggest technical bottleneck restricting the development of concrete-filled steel tube arch bridges. Deng Wenzhong, Academician of the US National Academy of Engineering and Foreign Academician of the Chinese Academy of Engineering, pointed out that the construction technology of the Pingnan Third Bridge represents the highest level of concrete-filled steel tube arch bridges.

The Pingnan Third Bridge. Photo by Zhong Jian

The Tian'e Longtan Grand Bridge is the world's first concrete arch bridge with a span of 600 meters. On the basis of two core technologies for concrete arch bridges previously invented by Chinese engineers — using a concrete-filled steel tube skeleton instead of a shaped steel skeleton, and regulating the time-history stress of the skeleton during the pouring of the outer concrete and reducing the permanent stress — the Tian'e Longtan Grand Bridge mainly solved the following technical problems during construction: first, it proposed reasonable selection criteria for the stiffness and strength of the stiff skeleton; second, through reasonable ring division and scientific arrangement of multiple working faces for simultaneous pouring, it balanced the suppression of structural time-history stress with on-site construction efficiency, achieving safe and rapid construction of the arch rib outer concrete; third, through both fine design of shrinkage compensation and regulation of working performance, it achieved no cracking in the 28,000 cubic meters of arch ring outer concrete; fourth, comprehensive structural optimization measures were taken so that the stress level of the completed 600-meter-span concrete arch bridge was on par with that of the completed 416-meter-span concrete arch bridge; fifth, an optimization method for longitudinal reinforcement of the arch rib was established, reducing the longitudinal reinforcement to 1/16 of the original scheme. After completion, the bridge also withstood the test of a magnitude 4.4 earthquake at the epicenter, and the bridge remained intact.

CNS Reporter: From the Zhaozhou Bridge, "China's first stone arch bridge," to the completion of the Tian'e Longtan Grand Bridge, "the world's largest-span arch bridge," what is the internal driving force behind the leapfrog development of China's arch bridge construction?

Zheng Jielian: First, China has an arch bridge gene; 1,400 years ago it built the world-famous Zhaozhou Bridge. Arch bridges have very reasonable force behavior, high stiffness, and good durability. However, for 1,400 years the arch rings of masonry arch bridges had to be constructed with centering, making it difficult to increase spans, and the cost of centering became increasingly high — until 1968, when Chinese engineers created the centering-free construction method, making it possible to increase arch bridge spans. Through long-term research, Chinese engineers have fairly well solved the problems of construction risk in arch bridges and of reducing the construction cost of long-span arch bridges. In addition, the large-scale development of China's expressways and high-speed railways over the past 30 years has created an urgent demand for arch bridge construction.

The above factors together have driven China's rapid development in the number and span of arch bridges, creating a miracle in the history of world bridge development.

In March 2023, Zheng Jielian, Academician of the Chinese Academy of Engineering and Professor at the School of Civil Engineering and Architecture, Guangxi University, briefed guests attending the on-site observation meeting of the Second World Conference on Construction Technology of Long-Span Arch Bridges on the construction of the Tian'e Longtan Grand Bridge. Photo by Chen Guanyan

CNS Reporter: What impact have Chinese arch bridges had on world bridge architecture? Compared with other bridge-building powers, what room for improvement remains in China's arch bridge construction?

Zheng Jielian: Centering-free construction is the watershed between traditional and modern arch bridges. Centering-free construction technology for arch bridges originated in China and has also been widely adopted abroad, greatly improving construction safety and economy. China's progress and practical experience in arch bridge construction technology have provided foreign countries with a comparative option of high stiffness, good durability, and low cost when building long-span bridges.

Specifically, the concrete-filled steel tube arch bridge originated in the Soviet Union, but because it failed to leverage the structural and construction advantages of this bridge type, it lost its economic advantage and was eliminated by the market after only two were built. Since the 1990s, Chinese engineers have used their own developed cable-stayed buckling technology and rotation technology to erect steel tube arch trusses, and vacuum-assisted continuous pressure grouting for in-tube concrete, improving quality, reducing cost, and shortening construction periods. Nearly 500 concrete-filled steel tube arch bridges have been built, with the largest span reaching 560 meters. Therefore, there is ample reason to say that the concrete-filled steel tube arch bridge with engineering value was developed by Chinese engineers.

Chinese engineers' contributions to stiff-skeleton concrete arch bridges are also multifaceted, including replacing steel arch trusses with concrete-filled steel tube arch trusses as stiff skeletons, reducing steel consumption by 50%; and developing ring division, multi-working-face pouring of outer concrete, and cable-stayed load adjustment technology, promoting an increase in the number of arch bridges built and the continuous increase of spans.

However, it must be recognized that China still lags behind foreign countries in structural calculation software and construction intelligence, and we need long-term efforts to catch up and surpass.

CNS Reporter: Chinese arch bridge construction technology has spread to Japan, India, Sri Lanka, and other countries. What role have Chinese arch bridges played in promoting cultural exchange between China and other countries?

Zheng Jielian: Bridges are extremely charming in China's cultural corridor. They not only have practical functions but are also cultural specimens of various historical periods and cultural symbols of communication and exchange between countries. The construction technology of ancient Chinese stone arch bridges was far ahead of the world, demonstrating the wisdom of the ancient Chinese to the world. "The Travels of Marco Polo" praised the Lugou Bridge as unparalleled in the world.

In recent years, China's concrete-filled steel tube arch bridges and concrete arch bridges have ranked among the world's front ranks in span and construction technology, greatly enhancing the competitiveness of Chinese bridge technology in overseas engineering construction markets. At present, transportation infrastructure construction under the "Belt and Road" initiative is in full swing. As Chinese bridge construction enterprises continue to build large arch bridges in countries around the world, they will also build cultural "bridges" for exchanges and mutual learning among Chinese and foreign civilizations. (End)

Profile of the interviewee:

Zheng Jielian, Academician of the Chinese Academy of Engineering and Professor at the School of Civil Engineering and Architecture, Guangxi University, gives an exclusive interview to China News Service's "East-West Question" program. Photo by Chen Guanyan

Zheng Jielian, road and bridge engineering expert, Academician of the Chinese Academy of Engineering, Professor-level Senior Engineer, Professor and Doctoral Supervisor at the School of Civil Engineering and Architecture, Guangxi University. In 1968, he pioneered a new centering-free construction technique for double-curvature arch bridges in China, solving the problem of building arch bridges without erecting centering. His research and practice in regulating the instantaneous stress occurring during the pouring of arch ring concrete for stiff-skeleton concrete arch bridges and reducing the permanent stress of the arch ring achieved major breakthroughs, guiding the successful construction of the world's largest-span concrete-filled steel tube arch bridge and stiff-skeleton concrete arch bridge. His achievements have won 3 National Science and Technology Progress Awards and 2 National Patent Excellence Awards, and he has received the Li Guohao Bridge Original Technology Award and the Mao Yisheng Science and Technology Award — Bridge Grand Prize.