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

7pile performances can be ensured. Currently, twenty-seven states have implemented theLRFD approach to foundation design while seventeen other states including Iowa are intransition from ASD to LRFD (AbdelSalam et al., 2008).1.2.5. Dynamic soil parametersThe accuracy of dynamic analysis is dependent upon the proper input of suitabledynamic soil parameters: damping coefficient (c) and stiffness (k). The damping coefficient(c) was recommended by Smith (1962) as a product of ultimate static soil resistance (R u ) andSmith’s damping factor (J). The spring stiffness (k) was assumed as the ratio of ultimatestatic soil resistance (R u ) and Smith’s soil quake (q). Currently, the Smith’s soil parametersare implemented in WEAP analysis. On the other, Goble et al. (1975) proposed the dampingcoefficient (c) as a product of Case damping factors (J c ) and pile impedance (Z) for use inPDA analysis. The Case damping factors were reported by Hannigan et al. (1998). Note thatall the recommended dynamic soil parameters are only correlated with simple soil typesand/or pile geometry, and no relationship has been developed to correlate them withmeasurable soil properties. Furthermore, Svinkin and Woods (1998) recognized that thepresent dynamic soil parameters cannot reflect the time dependent variation in the pileresponses. They believed the use of variable dynamic soil parameters as a function of timewill improve the pile resistance prediction.1.3. Problem StatementThe Federal Highway Administration (FHWA) has mandated all new bridgesinitiated after October 1, 2007 should follow the LRFD design approach. Unfortunately, thecurrent AASHTO LRFD Bridge Design Specifications (2010) have been developed forgeneral soil conditions and pile types. Also, the current Iowa DOT pile design manual doesnot comply with the LRFD design philosophy. Even though AASHTO allows the use ofregional calibrated resistance factors in LRFD pile designs, Iowa DOT has insufficient usablepile database, such as pile driving data with PDA records, for developing resistance factorsfor dynamic analysis methods. In recognizing the problems, the Iowa Highway Research