The Story of the Koror Bridge
IABSE Bulletins
Case Studies
1
M.-C. Tang
Man-Chung Tang
The Story of the Koror Bridge
1
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.
IABSE Bulletins/ Case Studies
The Story of the Koror Bridge
International Association for Bridge and Structural Engineering (IABSE)
Case Studies
1 Man-Chung Tang
The Story of the Koror Bridge
International Association for Bridge and Structural Engineering (IABSE)
Copyright © 2014 by International Association for Bridge and Structural Engineering All rights reserved. No part of this book may be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the publisher. ISBN 978-3-85748-139-0 Publisher: IABSE c/o ETH Zürich CH-8093 Zürich, Switzerland Phone: Fax: E-mail: Web:
Int. + 41-44-633 2647 Int. + 41-44-633 1241 secretariat@iabse.org www.iabse.org
Preface
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!
The foundation of engineering is what we learn from past experience; this includes both successful and unsuccessful experiences. Learning from our mistakes is especially useful, as it can teach us what can be done and what cannot be done. But, for the past to be useful, we must present the facts carefully and honestly. This is the reason why I have written this book.
Man-Chung Tang
Table of Contents
Chapter 1: A Brief History Republic of Palau Bidding Process
Chapter 2: The Original Design Design Concept Prestressing System Structural Safety of the Bridge Creep and Shrinkage Prestress Loss Overturning Safety Factor Prediction of Creep Deflection
Chapter 3: Construction Field Change
Chapter 4: Bridge Performance Test Results
Chapter 5: The Repair Repair Scheme
Chapter 6: The Collapse Forensic Observations Failure Mechanism Questions Raised after the Collapse
Chapter 7: What Would Have Happened If No Repairs To The Bridge Had Been Made?
1 1 3
5 5 9 9 18 20 20 20
23 31
33 37
41 41
45 45 54 56
57
Chapter 8: Why Was The Deflection of The Bridge So Much Larger Than Anticipated?
59
Calculation of Creep and Shrinkage Current AASHTO/LRFD Model The 1990 CEB-FIP Model Discussion of Creep Estimate The fib 2010 Model Code (Final Draft 2014) The Time Function The fib 2010 Model Code Creep Under Tension Calibration of Creep Models B3 Model ACI, AASHTO and CEB-FIP The Question of the Loading Age Other Effects on Deflection Effect of Differential Shrinkage Effect of Main Pier Settlement Effect of Prestress Loss Effect of Cracks on Deflection Interpretation of Test Results Experience from Another Bridge – the Pine Valley Creek Bridge, California A Worldwide Survey
59 59 60 61 62 62 63 64 64 64 65 67 70 71 71 72 74 77 78 81
Chapter 9: Initiation of the Collapse
83
Chapter 10: Other Failure Hypotheses
87
Chapter 11: Discussions
91
Purpose of This Book The Koror Bridge Was Structurally Safe Long-Term Deflection Prestress Loss Was the Most Probable Culprit
91 91 91 92
Summary
95
Acknowledgement
97
Units
99
References
101
1 Chapter
1 A Brief History
Republic of Palau The Koror Bridge, also called Koror Babelthuap Bridge, or Koror Babeldaob Bridge, or Palau Bridge (see Fig. 1), is located in the Republic of Palau, a country that consists of about 300 islands in the South Pacific Ocean, and is a part of the Caroline Island group. In 1899, Spain sold these islands to Germany. In 1914, the Germans ceded them to Japan. During the Second World War, there were several severe battles between the US and the Japanese armies on these islands that led to the death of over 12,000 soldiers. After the war, the United Nations trusted these islands to the US in 1947 as the US Trust Territory of Pacific Islands. In 1979, the entire Caroline Island group declared independence from the US. Palau did not join them and established the Republic of Palau in 1981. When the islands were under US trusteeship, the US navy had a military base there. The construction of the Koror Bridge was, in part, financed by the US government.
Fig. 1: Koror Babeldaob Bridge
2
CHAPTER 1. A BRIEF HISTORY
The Koror Bridge connected the Islands of Koror and Babeldaob (Babelthuap); it was the only fixed link between these two islands. The majority of the population lived on Koror Island but the only airport was located on Babeldaob Island. Before the bridge was built, the main form of transportation between the islands was by ferries (see Fig. 2a,b). The country of Palau is very remote; it is about 800 km away from the Philippines. The temperature ranges from 23oC to 32oC. The average temperature is about 28oC. The average relative humidity is about 82%. Palau receives more than 2300 hours of sunshine in a year. Annual rainfall is about 3670 mm. The Republic of Palau has a total land area of 459 km2, with a total population of slightly more than 20,000. Tourism is the main economic industry.
(a) Mariana Islands Luzon
Philippine Sea
Saipan Rota Gaum, U.S.
Manila Philippines
Sulu Sea
Mindanao Palau Islands
Sulu Archipelago Celebes Sea
Caroline Islands Helen Islands Halmahera
Indonesia Vicinity Map Not to scale
(b)
Fig. 2: Location map
Project location
Trust te
rritory
of the Pacific Islands (U.S.)
BIDDING PROCESS
3
Bidding Process The original bid documents for the construction of the Koror Bridge were prepared by the Hawaii consulting engineering firm, Alfred Yee and Associates (AYAA) [1–3]. The original design featured a three span prestressed concrete girder with a centre span of 560 ft (170.68 m). The deck provided two lanes of traffic and a pedestrian path on one side. The bid documents permitted the successful contractor to modify the design to a 760 ft (231.65 m) span bridge in order to clear the channel and avoid building the piers in the channel. The successful bidder was Ajoo Construction Company from Korea. Their bid price was US$ 4.5 million. However, Ajoo was not able to start construction for many months and so the bonding company transferred the contract to Socio Construction Company, a firm originally from Korea with headquarters in Guam. Because the bid price was considered to be too low, the bonding company provided an extra US$ 800,000, bringing the total contract price to US$ 5.30 million [4]. Socio decided that the construction of the two deep-water piers would be too expensive because the water was about 30 m deep and the tidal current was very swift. It would have required heavy equipment that was not available in the area. Renting and transporting equipment from the Philippines or other countries would have been too costly to build two relatively small piers. Therefore, Socio decided to follow the suggestion of the engineer to extend the span to 760 ft. It was acknowledged that $5.3 million was still reasonable for a 760 ft span bridge. Therefore, economy was an important consideration in the redesign of the bridge [5]. Socio hired the German firm, Dyckerhoff&Widmann, AG (Dywidag) to carry out the redesign. The redesign started with a 760 ft span. However, just short of its completion, it was found that the 760 ft span would still require the two main piers to be placed in the water and on the slope. The span was then increased to 790 ft (240.792 m) (see Fig. 3). The redesign was reviewed and approved by the original designer, AYAA. In the meantime, AYAA had merged with another firm, Leo Daly. Leo Daly was responsible for supervision during the bridge construction. Sand and stone were the only construction materials available in Palau. Almost everything else had to be imported including prestressing steel from the US, cement and reinforcing steel from Japan, and the form travelers from the US [5]. The travelers were adapted from those used in the Pine Valley Creek Bridge in California. The workers were mostly from Korea. The Pine Valley Creek Bridge was the first long-span prestressed concrete segmental bridge in the US, and had a main span of 450 ft (137.16 m). Its construction began in 1972 and was
Fig. 3: Koror Bridge
4
CHAPTER 1. A BRIEF HISTORY
completed in 1975. The design was based on guidelines of the American Association of State Highway Officials (AASHO) of the US. (AASHO was later changed to American Association of State Highway and Transportation Officials, AASHTO [6]). At that time, long-span segmental prestressed concrete bridges were relatively new in the US; the AASHO design specifications were not complete; and the design had to be supplemented by the American Concrete Institute, USA (ACI) [7], the German DIN (German Industry Norms) and the European ComiteEuropeen du Beton- Federation Internationale de la Precontraine (CEB-FIP) Recommendations [8]. At the time of redesign, Japan had just completed the 236 m span Hikoshina Bridge and the 240 m span Hamana Bridge. So the span of the Koror Bridge was not outside the realm of engineers’ understanding of what was possible. The 790 ft (240.792 m) span Koror Bridge, was longer than the Hamana Bridge by less than 1 m and is also a world record (see Figs. 1 and 3).
About the Author
Case Studies Objective:
Man-Chung Tang, PE
Dr.-Ing., Dr.-Ing. Eh, Hon. Dr. Litt., Hon. Architect, Hon. Professor Member, National Academy of Engineering, USA, Foreign member, Chinese Academy of Engineering, PRC Chairman of the Board, T.Y. Lin International
To provide in-depth information to practicing stuctural engineers in reports of high scientific and technical standards on a wide range of structural engineering topics.
IABSE Bulletin Editorial Board: J. Sobrino, Spain (Chair); H. Subbarao, India (Vice Chair); M. Bakhoum, Egypt; C. Bob, Romania; M. Braestrup, Denmark; M.G. Bruschi, USA; R. Geier, Austria; N.P. Hoej, Switzerland; S. Kite, Hong Kong; D. Laefer, Ireland; R. Mor, Israel; H.H. (Bert) Snijder, The Netherlands; R. von Woelfel, Germany.
Topics: Structural analysis and design, dynamic analysis, construction materials and methods, project management, structural monitoring, safety assessment, forensic investigations, maintenance and repair, and computer applications.
Readership: Practicing structural engineers, teachers, researchers and students at a university level, as well as representatives of owners, operators and builders.
Publisher: The International Association for Bridge and Structural Engineering (IABSE) was founded as a non-profit scientific association in 1929. Today it has more than 3500 members in over 90 countries. IABSE’s mission is to promote the exchange of knowledge and to advance the practice of structural engineering worldwide. IABSE organizes conferences and publishes the quarterly journal Structural Engineering International, as well as conference reports and other monographs, including the SED, Case Study series and Guidelines. IABSE also presents annual awards for achievements in structural engineering.
For further Information: IABSE c/o ETH Zürich CH-8093 Zürich, Switzerland Phone: Int. + 41-44-633 2647 Fax: Int. + 41-44-633 1241 E-mail: secretariat@iabse.org Web: www.iabse.org
About the Author
Case Studies Objective:
Man-Chung Tang, PE
Dr.-Ing., Dr.-Ing. Eh, Hon. Dr. Litt., Hon. Architect, Hon. Professor Member, National Academy of Engineering, USA, Foreign member, Chinese Academy of Engineering, PRC Chairman of the Board, T.Y. Lin International
To provide in-depth information to practicing stuctural engineers in reports of high scientific and technical standards on a wide range of structural engineering topics.
IABSE Bulletin Editorial Board: J. Sobrino, Spain (Chair); H. Subbarao, India (Vice Chair); M. Bakhoum, Egypt; C. Bob, Romania; M. Braestrup, Denmark; M.G. Bruschi, USA; R. Geier, Austria; N.P. Hoej, Switzerland; S. Kite, Hong Kong; D. Laefer, Ireland; R. Mor, Israel; H.H. (Bert) Snijder, The Netherlands; R. von Woelfel, Germany.
Topics: Structural analysis and design, dynamic analysis, construction materials and methods, project management, structural monitoring, safety assessment, forensic investigations, maintenance and repair, and computer applications.
Readership: Practicing structural engineers, teachers, researchers and students at a university level, as well as representatives of owners, operators and builders.
Publisher: The International Association for Bridge and Structural Engineering (IABSE) was founded as a non-profit scientific association in 1929. Today it has more than 3500 members in over 90 countries. IABSE’s mission is to promote the exchange of knowledge and to advance the practice of structural engineering worldwide. IABSE organizes conferences and publishes the quarterly journal Structural Engineering International, as well as conference reports and other monographs, including the SED, Case Study series and Guidelines. IABSE also presents annual awards for achievements in structural engineering.
For further Information: IABSE c/o ETH Zürich CH-8093 Zürich, Switzerland Phone: Int. + 41-44-633 2647 Fax: Int. + 41-44-633 1241 E-mail: secretariat@iabse.org Web: www.iabse.org
The Story of the Koror Bridge
IABSE Bulletins
Case Studies
1
M.-C. Tang
Man-Chung Tang
The Story of the Koror Bridge
1
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.
IABSE Bulletins/ Case Studies
The Story of the Koror Bridge
International Association for Bridge and Structural Engineering (IABSE)