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Lrfd Calibration of Bridge Foundations Subjected to Scour

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Lrfd Calibration of Bridge Foundations Subjected to Scour LRFD CALIBRATION OF BRIDGE FOUNDATIONS SUBJECTED TO SCOUR AND RISK ANALYSIS A Dissertation by CONGPU YAO Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved by: Chair of Committee, Jean-Louis Briaud Committee Members, Paolo Gardoni Stefan Hurlebaus Mark E. Everett Head of Department, John Niedzwecki May 2013 Major Subject: Civil Engineering Copyright 2013 Congpu Yao ABSTRACT Bridge scour is the loss of soil by erosion due to water flowing around bridge supports. Scour has been the number one cause of bridge collapse in the United States with an average rate of 22 bridges collapsing each year. This dissertation addresses three topics related to bridge scour. First, three sets of databases are used to quantify the statistical parameters associated with the scatter between the predicted and measured scour depth as well as the probability that a deterministically predicted scour depth will be exceeded. The analysis results from these databases will also be used to provide the bias factors in the scour depth predictions in practice. In the second part of the dissertation, these statistical parameters are used to develop a reliability-based Load and Resistance Factor Design (LRFD) for shallow and deep foundations subjected to scour. The goal is to provide a design procedure for the bridge foundations, where the reliability of the foundation is the same with or without scour. For shallow foundations, the key of the design issue is the location of the foundation depth and the probability that the scour depth will exceed the foundation depth. Therefore, for shallow foundations, the proposed LRFD calibration is based on the probability of exceedance of the predicted scour depth. However for deep foundations, the key of the design issue is the resistance factor associated with the axial capacity of a pile. Hence, the proposed LRFD calibration for deep foundations is based on a reliability analysis using First-Order Reliability Method (FORM). The dissertation is broadened in the third part by analyzing ii the risk associated with bridge scour, where the risk is defined as the probability of failure times the value of the consequences. In the third part, the risk associated with bridge scour is compared to risks associated with other engineering structures as well. Target values of acceptable risk are recommended as part of the conclusions. The outcome of the research will modify the current “AASHTO LRFD Bridge Design Specifications” developed by the American Association of State Highway and Transportation Officials (AASHTO) and help the practitioners design foundations of bridges over rivers for a uniform probability of failure in the case of scour. The risk of bridge scour is also quantified in the dissertation, and compared with common societal risks and civil engineering risks. It will help engineers understand the risk level associated with bridge scour. iii DEDICATION To my parents for bringing me into this beautiful world and teaching me the wisdom of life iv ACKNOWLEDGEMENTS I would like to express my heartfelt gratitude to my academic advisor and Committee Chair, Dr. Jean-Louis Briaud. It has been a true blessing to be able to study under Dr. Briaud’s supervision. Not only did I receive financial support through the whole PhD study from him, but also I learned from him an active and humorous attitude towards life, a hard-working spirit, and dedication in physical exercise. Dr. Briaud is always available to students whenever we need his advice. He has helped me go through a lot of difficult times in the research. Without his guidance, support and encouragement, this dissertation would not have been accomplished. I would like to thank him heartfully. I also would like to thank Dr. Paolo Gardoni for his dedication and valuable guidance during my research. He is such a quick, smart and knowledgeable professor that he could always figure out what I was trying to express during our weekly conference call. His knowledge in reliability field really inspired me. It has been my privilege to be able to work with him on this research topic, and I really appreciate his help. Great appreciation also goes to my other two committee members, Dr. Stefan Hurlebaus and Dr. Mark E. Everett, for serving on my committee. I really appreciate their advice and help during the preparation of this dissertation draft. I owe a lot of thanks to Dr. Vahid Bisadi, who provided me with great advice and help on understanding reliability theory. His kindness and helpful advice is very much appreciated. v I would like to thank Winchell Auyeung and Michael Sullivan from New York State Department of Transportation (NYSDOT) for providing the NYSDOT Database. The database was used in Section 6 of the dissertation to quantify the bridge scour risk. Mr. Auyeung’s great help and patience with my detailed questions regarding the items in the database is very much appreciated. I also appreciate colleague-and-friend Negin Yousefpour’s help on studying the Florida Department of Transportation (FDOT) Unknown Foundation Bridges Database. It has been a pleasant experience to share the same office with her for two years. I owe thanks to Dr. Seung Jae Oh for providing the Bridge Pier Scour Database, which involves the deterministic pier scour depth predictions of more than 500 data points. I would also like to acknowledge Dr. Andrzej Nowak at the University of Nebraska-Lincoln for the conference call with me discussing the Load and Resistance Factor Design (LRFD) in Structural Engineering field. I would also like to thank all the professors and staff in our department for their help and assistance during my PhD study. Special thanks go to Ms. Theresa Taeger for her great help on printing the dissertation draft and on taking care of the paperwork for me while I was not around. I would also like to thank Ms. Maxine Williams for her great assistance and help during my PhD study. I would like to acknowledge our laboratory manager Mr. Mike Linger for his great help and encouragement during my PhD study. It has been a great experience to be able to work with him in the laboratory for two years. vi Great appreciation goes to Mr. Mike Downey at Texas A&M University for proofreading the whole dissertation. I also would like to thank the support and encouragement from all my friends. It is their consistent encouragement that helped me go through the whole PhD study. Great thanks go to Dr. Yi Dong, Dr. Qian Li and Dr. Xi Cui for their enormous support, understanding and precious long-term friendship. Particularly I would like to acknowledge their help and advice on the format of the dissertation in the draft preparation process. Thanks go to Dr. Chin Leung, Dr. Deeyvid Saez, Ghassan Akrouch, Xin Guo and Yunhuang Zhang for being true friends in need for the last five years. I would like also to acknowledge my friends-and-co-workers Colin Darby and Dr. Hrishikesh Sharma for bringing me pleasant research experience. I would also like to acknowledge Stacey Tucker, Dr. Xingnian Chen, Amir Hessami, Ryan Dalton, Vishal Dantal, and Ajay Shastri for their support and help. I would like to thank my brother Dr. Conglun Yao and sister-in-law Ms. Duoduo Liu for their support and love. Special thanks go to my brother for growing up with me and sharing his personal opinion on the PhD and work with me. Finally, I would like to show my great gratitude to my dear parents, Mr. Zengmin Yao and Ms. Rongxiang Jing, for their constant love and unconditional support. Without their encouragement and love, this dissertation would not have been finished. I would like to thank both of them for teaching me the wisdom of life and providing me the courage to face difficult times in life. This dissertation is dedicated to my parents. vii TABLE OF CONTENTS Page ABSTRACT .......................................................................................................................ii DEDICATION .................................................................................................................. iv ACKNOWLEDGEMENTS ............................................................................................... v TABLE OF CONTENTS ............................................................................................... viii LIST OF FIGURES ..........................................................................................................xii LIST OF TABLES ........................................................................................................ xxiv 1 INTRODUCTION ...................................................................................................... 1 1.1 Problem Statement ............................................................................................. 1 1.1.1 Scour ...................................................................................................... 1 1.1.2 Schoharie Creek Bridge Failure Study .................................................. 2 1.1.3 Bridge Scour Current Study .................................................................. 5 1.1.4 Bridge Failure Modes due to Scour (Briaud et al. 2011b) .................... 7 1.1.5 Bridge Design ...................................................................................... 16 1.1.6 Bridge Scour Risk ................................................................................ 19 1.2 Objectives .......................................................................................................
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