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

83construction procedures used by the Iowa DOT, and recommend changes and improvementsto the current AASHTO LRFD bridge design specification. In addition to TR-573, dynamicanalysis methods using PDA, CAPWAP, and WEAP for pile design and construction controlwere added in the research project TR-583 that allows the development and/or improvementof LRFD foundation design for dynamic analysis methods. The fundamental difficulties ofdeveloping LRFD resistance factors for dynamic analysis methods are correct identificationof pile penetration, static resistance calculation, and time dependent pile resistance(Paikowsky et al., 2004). Many studies have been made on developing LRFD for deepfoundations in the recent years, especially by Paikowsky et al. (2004) and Allen (2005),which were adopted in the recent AASHTO (2010) Bridge Design Specifications.2.7.2 Reliability theory approachesThe principle of LRFD is to incorporate the margin of safety through the combinationof load and resistance factors. The uncertainties involve in the load and resistance arequantified using statistical based methods to achieve a consistent level of reliability.Uncertainties in loads are small compared with soil resistances. This fundamentalrelationship can be given by Eq. (2.41). As noticed from this equation, partial safety factorsare applied separately to the load (Q) and resistance (R).∑ (2.41)where,η iγ iQ iφR= a modifier factor to account for effects of ductility, redundancy andoperational importance,= load factor,= load, kN or kip,= resistance factor, and= ultimate resistance, kN or kip.