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李国豪（邬海佳画）▲

LI Guohao

LI Guohao (1913-2005) has his ancestral family from Meizhou in Guangdong province. He was an expert in bridge engineeringand mechanics, educator and social activist. In 1936, he graduated from Tongji University. From 1938 to 1945, he studied in Darmstadt University of Technology in Germany, specializing in bridge engineering and structural mechanics. After returning to China in 1946, he was appointed as engineer of Shanghai Municipal Bureau of Works and professor of Tongji University.

After the founding of the New China, he served in succession as vice president and president of Tongji University and chairman of the sixth session of the Shanghai CPPCC. He was successively employed as member and director of the Technical Committee of Wuhan Yangtze River Bridge and Nanjing Yangtze River Bridge, chief adviser of the Engineering Technical Committee of Baoshan Iron and Steel Plant, expert group leader of Shanghai Nanpu Bridge, advisory group leader of Shantou Bay and Humen Pearl River. In 1994 he was elected as one of the first academician of Chinese Academy of Engineering. The discipline of bridge engineering he has been specializing in has reached the leading level in China and has a significant impact in the international arena. He is one of the world’s top ten well-known structural engineering experts.

Unraveling the Mystery of“ Bridge Vibration”

On October 15, 1957, Wuhan Yangtze River Bridge, China’s first bridge across the Yangtze River, was completed and opened to traffic. Mighty crowds jostled each other and swarmed to the bridge. Suddenly the bridge vibrated. What caused the bridge to rock? He thought about this problem for a long time. Because of his national defense research missions in those years, he had no time to study it and put it aside. In 1968, the news that Nanjing Yangtze River Bridge was opened to traffic reached him. He worried that the bridge would vibrate once again. Years ago, Wuhan Yangtze River Bridge vibrated at its opening to traffic. This time, in order to be on the safe side, the construction of Nanjing Yangtze River Bridge widened the steel truss girders by 4 meters and used more steelby 4,000 tons. However, everybody was still unsure about the result. Would this work?

He decided to solve this problem. Methods he used when he studied in Germany crossed his mind. He converted a complex bridge of multi-column diamond truss system into a continuous one, successfully deduced the equivalence relation of stiffness conversion by using differential equation and verified it with model tests. Yes, he told himself to adopt this idea to study the stability and vibration of the bridge. In this way, he made use of the basic data of the two bridges to start calculation on the basis of a powerful memory and a solid foundation.

In April 1971, he theoretically gave the answer to bridge vibration. But he knew that theoretical calculations alone could not work and they must be verified by tests. At that time, however, there was no tool to make a steel bridge model. On a second thought, he decided to use celluloid instead. His son-in-law helped buy a lot of celluloid from the central mall. At that night, he could scarcely wait to prepare a stove to boil water. The celluloid he put into the stove softened. After pressing, cutting and pulling, he began to make bridge models. A year later, his test data finally came out, which was completely consistent with theoretical results. In 1974, he reported the results at the National Conference on Steel Vibration: the vibration when Wuhan Yangtze River Bridge was opened to traffic was due to the fact that the crowd of people suddenly gushed onto the bridge, resulting in a load which caused vibration and torsional resonance. But there was no problem with the structure of the bridge. Therefore, there was no necessity to use additional 4,000 tons of steel in the construction of Nanjing Yangtze River Bridge. “The mystery which troubled us for 17 years was solved!” The applause burst out at the conference.

Years later, he used plain language to explain the reasons for the bridge vibration: “This is like a small wooden boat. When you put one foot on it, it will shake; when you put both feet on it, it will not shake any more in a while. The bridge vibrated is due to the fact that a lot of people suddenly swarmed onto it, while there was no problem with the bridge structure itself.

In 1975, the book A Theory of Truss Torsion: Its Torsion, Stability and Vibration was published, which covered 110,000 words. In 1983, this achievement won the third prize of National Natural Science Award. His theory greatly saved manpower and material resources for later man-made bridge.