S - Kam Ng PhD Dissertation Final.pdf - Digital Repository of CCEE ...

822.7. LRFD Resistance Factors for Dynamic Analysis Methods2.7.1 IntroductionA study by Transportation Research Board (TRB) in 1987 concluded that theAmerican Association of State Highway and Transportation Officials (AASHTO) standardspecifications for highway bridges contain gaps and inconsistencies and did not use the latestdesign philosophy and knowledge, the limit state design or also known as Load andResistance Factor Design (LRFD). The relative slow LRFD development in deep foundationis associated with the challenges of high variability in soil properties and the ability inpredicting realistic pile resistance. The initial LRFD resistance factors calibration was carriedout by Barker et al. (1991). A review of worldwide LRFD codes for deep foundations wasperformed by Goble (1999), and the short summary of each code was described byPaikowsky et al. (2004). LRFD gains acceptance over the conventional allowable stressdesign (ASD) in the recent several decades, because LRFD provides uniform level of safetyand reliability by calibrating the resistance and load factors from actual bridge databases. Inaddition, a more uniform level of safety that should ensure superior bridge serviceability andlong term maintainability. Most importantly, LRFD is believed as a more cost effective andefficient design method. Because of the LRFD’s impact on the safety, reliability, andserviceability of National Bridge Inventory (NBI) which contains more than 590,000 bridgesin the United States, the AASHTO in concurrence with the Federal Highway Administration(FHWA) has mandated that all bridges initiated after October 1, 2007, must be designed inaccording to the LRFD specification. According to the AASHTO Oversight Committee(OC) 2005 survey, sixteen (16) States have fully implemented LRFD, and the remainingStates are in the transition of full implementation. In 2007, the AASHTO OversightCommittee (OC) updated that forty-four (44) of fifty (50) states will fully implement LRFDfor all new bridges by October 1, 2007. In response to the recommendation by FHWA toimprove the AASHTO LRFD specifications that have a better represent of local soil andlocal experience, the Iowa Department of Transportation (Iowa DOT) in cooperation withIowa State University (ISU) began the LRFD foundation research project TR-573 in July2007. The main objective of this research project is to examine current pile design and