EVALUATION OF MODEL UNCERTAINTIES IN LRFD CALIBRATION PROCESS OF DRILLED SHAFT AXIAL DESIGN by Mohammad Rakib Hasan Presented to the Faculty of the Graduate School of The University of Texas at Arlington in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY THE UNIVERSITY OF TEXAS AT ARLINGTON August 2019 Copyright © by Mohammad Rakib Hasan 2019 All Rights Reserved i This dissertation is dedicated to my parents for their constant support and motivation throughout my life. ii ACKNOWLEDGEMENTS At first, I would like to express my deepest gratitude and acknowledgement to my advisor Dr. Xinbao Yu for his endless guidance and encouragement during my doctoral research. I am thankful to him for providing me the opportunity of working under his supervision. This research would not come to fruition without his counseling. I also would like to thank my committee members Dr. Shahadat Hossain, Dr. Laureno Hoyos and Dr. Samantha Sabatino for their valuable comments, help and time. I am thankful to Dr. Xinbao Yu, Dr. Laureano Hoyos, Dr. Sahadat Hossain, Dr. Aera LeBoulluec, Dr. Dong-Jun Seo and Dr. Chein-Pai Han for fulfilling my experience at University of Texas at Arlington by sharing their knowledge during my course works required for the doctoral program. Finally, I would like to thank my parents, my siblings and my beloved wife for their endless love and encouragement which kept me motivated. None of these would happen without them. July 29, 2019 iii ABSTRACT OPTIMIZATION OF LRFD CALIBRATION OF DRILLED SHAFTS by Mohammad Rakib Hasan The University of Texas at Arlington, 2019 Supervising Professor: Xinbao Yu The Federal Highway Administration (FHWA) released a policy in 2000 that required all new federally funded bridges to be designed using the AASHTO LRFD specifications by October 2007. The transition from ASD to LRFD posed a challenge due to the lack of area specific resistance factors. Though several studies were performed to calibrate area specific resistance factors, they did not improve from the resistance factors suggested in AASHTO 2012. The objective of this study is to analyze the uncertainties in LRFD calibration and to calibrate more accurate and improved resistance factors. A drilled shaft load test database from Mississippi and Louisiana has been selected to carry on the research. Osterberg Cell load test was a majority among the load tests in the database. Extrapolation is required in most Osterberg cell load test which may cause errors in the calibration. An analysis of the error due to the extrapolation can result in more accurate LRFD calibration of resistance factors. The analysis was performed on 8 drilled shaft cases from Louisiana and Mississippi. 4 of the 8 drilled shafts reached 5% of the shaft diameter (D) failure criterion and 4 of the drilled shafts were close to 5%D. For each of the cases, extrapolation was performed on tip and side resistance curves to get the equivalent top-down curve. iv Data points were removed systematically from the end of top and bottom movement curves and extrapolation was performed for each trial to get an equivalent top-down curve. Bias and error values was measured for each of the trial top down scurves for both 5% of the drilled shaft diameter (D). 80 extrapolation cases were achieved from this analysis. Finally, multiple linear regression analysis was performed on the extrapolated data set in order to reduce the effect of the extrapolation error on the resistance factor. Applying bounded bias distribution may also result in more accurate resistance factors, since the bias values have significant role in the calibration process. As the probability of failure significantly depends on the lower tail of the distribution of the resistance values and there is a physical presence of a lower limit of the resistance of a drilled shaft, introducing a lower bound to the resistance distribution will ensure more realistic calibration of the resistance factors. An analysis by simulation of load tests to failure on will also help to understand the reasons for low resistance factor values. The objective of this study is also to minimize effect of extrapolation by means of finite element modelling of the bidirectional load tests included in a database collected from Louisiana and Mississippi. The finite element modelling was performed in PLAXIS 2D until the top and the bottom movement curves reach the measured loads corresponding to the failure criteria. LRFD calibration of resistance factors was performed based on the simulated bidirectional load test database and the results were compared to the results from conventional approach. v Table of Contents ACKNOWLEDGEMENTS ........................................................................................................... iii ABSTRACT ................................................................................................................................... iv LIST OF ILLUSTRATIONS .......................................................................................................... x LIST OF TABLES ....................................................................................................................... xiv Chapter 1 INTRODUCTION .......................................................................................................... 1 1.1. General ............................................................................................................................ 1 1.2. Problem Statement .......................................................................................................... 6 1.3. Objective ......................................................................................................................... 7 1.4. Organization of the Dissertation ..................................................................................... 7 Chapter 2 LITERATURE REVIEW ............................................................................................... 9 2.1. Introduction ..................................................................................................................... 9 2.2. Drilled Shaft Design Practice ....................................................................................... 10 2.2.1. Side and Tip Resistance in Cohesive Soil................................................................. 12 2.2.2. Side and Tip Resistance in Cohesionless or Granular Soil ....................................... 15 2.2.3. Side and Tip Resistance in Intermediate Geomaterial .............................................. 17 2.2.4. Side and Tip Resistance in Rock .............................................................................. 20 2.2.5. Nominal Axial Resistance ......................................................................................... 25 2.2.6. Settlement of Drilled Shafts ...................................................................................... 26 2.3. Load Tests on Drilled Shafts ........................................................................................ 29 vi 1.1.1. Static Load Test ........................................................................................................ 30 1.1.2. Bidirectional Load Test............................................................................................. 33 2.4. LRFD Calibration of Resistance Factors ...................................................................... 45 2.4.1. Load and Resistance Factor Design .......................................................................... 45 2.4.2. Resistance Factor Development ................................................................................ 47 3.5. Studies on Calibration of Resistance Factor ................................................................. 53 3.5.1. Florida DOT .............................................................................................................. 53 3.5.2. Iowa DOT ................................................................................................................. 59 3.5.3. New Mexico DOT..................................................................................................... 65 3.5.4. Louisiana DOTD ....................................................................................................... 72 2.5.5. Nevada DOT ............................................................................................................. 78 2.5.6. FHWA Recommendations ........................................................................................ 84 2.6. Studies on Uncertainties in LRFD Calibration ............................................................. 86 2.6.1. Studies on Extrapolation ........................................................................................... 88 2.6.2. Studies on Outliers .................................................................................................... 98 2.7. Summary ..................................................................................................................... 100 Chapter 3 DATABASE............................................................................................................... 102 3.1. Introduction ................................................................................................................. 102 3.2. Background ................................................................................................................. 102 3.3. Breakdown of the Database .......................................................................................