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

12correction factors to estimated pile resistances using the Iowa in-house method, theconstruction control was assimilated in pile designs with the intentions to improve theaccuracy of pile resistance estimation using the Iowa DOT in-house method and to reduce thediscrepency of pile resistances estimated during designs and measured during constructions.1.5.5. Task 5: LRFD calibrationRegional LRFD resistance factor calibrations are allowed by FHWA to maintainconsistent and reliable pile performances, to represent local soil condition and constructionpractices, and to design cost effective pile foundations. LRFD resistance factors for WEAPanalysis were calibrated based on five different soil input procedures for sand, clay andmixed soil profiles, and the five procedures are DRIVEN, soil type based method (ST), SPTN-value based method (SA), Iowa in-house design chart, and current Iowa DOT approach.The soil profile input procedure that gives the highest efficiency coefficient (φ/λ), a ratio ofthe resistance factor and the corresponding resistance bias, at each soil profile wasrecommended. These comparisons provide a rational basis for pile designers to adopt variessoil input procedures for different soil profiles in WEAP. Besides, LRFD resistance factorswere calibrated for CAPWAP. These newly and regionally calibrated LRFD resistancefactors were compared with the latest AASHTO (2010) recommendations and with theresistance factors proposed by other researchers, such as Paikowsky et al. (2004) and Allen(2005).Furthermore, a new procedure was developed to enabling incorporation of aresistance factor separately for pile setup such that the setup effect can be accounted inaddition to the design resistance estimation for a pile at the End of Driving (EOD) for achosen target reliability index. The procedure, which uses the First Order Second Moment(FOSM) method, not only allows incorporation of any form of setup estimate to theestimated pile resistance at EOD, but also facilitates inclusion of two resistances affected byeach other to reach a target reliability level in accordance with the LRFD framework. Themain benefit of this approach is that it eliminates the inappropriate means to use the sameresistance factor for both setup and pile resistance estimation at EOD, which could result in