Case Study 1 (ePDF) The Story of the Koror Bridge

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The Story of the Koror Bridge
Koror Babeldaob Bridge, also called Koror Babelthuap Bridge or simply Koror Bridge, connects the islands of Koror and Babeldaob in the Republic of Palau. The design of the bridge began in 1974 and was based on the prevailing AASHO Standard Specifications at that time and was supplemented by ACI and CEB-FIP design recommendations on an as-needed basis. When the Koror Bridge was opened to traffic in April 1977, it was the world’s longest concrete girder span. A few years later, the bridge began to deflect more than had been anticipated. The owner commissioned a Japanese engineering firm in 1985 and then a US engineering firm in 1993 to conduct in-depth investigations of the structure. Both firms came to the same conclusion that the bridge was structurally safe and that the excessive deflection was an unexplainable phenomenon. Nevertheless, in order to improve the driving quality of the bridge deck, the owner decided to repair the bridge. The repair scheme made changes to the structural system and added a large amount of post-tensioning force to the bridge. Unfortunately, less than three months after the repair, late in the afternoon on 26 September, 1996, nineteen and a half years after it was opened to traffic, the bridge collapsed. Thereafter, most of the documents were sealed as a result of litigation between the various parties and the debris was cleared. For a long time, it was impossible to study the facts surrounding the bridge’s collapse. Only recently, through continuous probing by a group of engineers, were these documents made accessible to researchers.

ISBN 978-3-85748-136-9


Description

Koror Babeldaob Bridge, also called Koror Babelthuap Bridge or simply Koror Bridge, connects the islands of Koror and Babeldaob in the Republic of Palau. The design of the bridge began in 1974 and was based on the prevailing AASHO Standard Specifications at that time and was supplemented by ACI and CEB-FIP design recommendations on an as-needed basis. When the Koror Bridge was opened to traffic in April 1977, it was the world’s longest concrete girder span. A few years later, the bridge began to deflect more than had been anticipated. The owner commissioned a Japanese engineering firm in 1985 and then a US engineering firm in 1993 to conduct in-depth investigations of the structure. Both firms came to the same conclusion that the bridge was structurally safe and that the excessive deflection was an unexplainable phenomenon. Nevertheless, in order to improve the driving quality of the bridge deck, the owner decided to repair the bridge. The repair scheme made changes to the structural system and added a large amount of post-tensioning force to the bridge. Unfortunately, less than three months after the repair, late in the afternoon on 26 September, 1996, the bridge collapsed. Thereafter, most of the documents were sealed as a result of litigation between the various parties and the debris was cleared. For a long time, it was impossible to study the facts surrounding the bridge’s collapse. Only recently, through continuous probing by a group of engineers, were these documents made accessible to researchers. Engineering is not science. The aim of science is to search for truth. The aim of engineering is to serve human society’s needs. Based on what they already know, scientists make discoveries about nature that are pre-existing. Based on an accumulation of experience, engineers improve the built environment of human beings. Experience is never complete, but engineers obviously cannot wait for scientific discoveries of all the necessary truths they need to design and build. At the time of the construction of the Great Wall of China, the Pyramids of ancient Egypt and many other great structures, the laws of gravity had not yet been discovered and an understanding of the physical properties of building materials did not yet exist. Engineers must design and build based on their present-day experience. This was the case 2000 years ago. And so this is the case today!