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

209procedure in pile designs. Two construction bridge sites at the locations of recentlycompleted field tests in Iowa listed in Table 5.1 (data sets 1 and 4) were selected for acomparative study. The soil profile at each of these sites is cohesive, and a total dead load of3000 kN (674 kips) and total live load of 1500 kN (337 kips) were assumed for all bridgeabutments. HP 250×63 (HP 10×42) production piles were driven with embedded lengths of29 m (95 ft) and 21 m (69 ft) closed to test sites ISU2 and ISU5, respectively.Four factored pile resistances based on: (1) EOD condition (φ EOD R EOD ); (2) a singleresistance factor as described in Case 3 of Table 5.2 (φ(R EOD +R setup )); (3) the proposedprocedure (φ EOD R EOD +φ setup R setup ); and (4) SLTs (φ SLT R SLT ) were determined by establishingthe minimum number of piles required to support the assumed applied loads. Forcomparison purposes, each computed number of piles was not rounded to the next higherinteger number. A fixed time of 7 days elapsed after pile installation was assumed in the pilesetup calculations in Eq. (5.1a). The respective resistance factors are given in Figure 5.6.The φ setup values were calculated using Eq. (5.13) based on the recommended probabilisticcharacteristics of the loads recapitulated in Eq. (5.2) and of the pile resistances given in Table5.2. The φ SLT of 0.80 for measured pile resistances using SLTs was adapted from theAASHTO (2010) recommendations. These resistance factors were selected based on a targetreliability index (β T ) of 2.33.Figure 5.6 clearly shows that the incorporation of pile setup reduces the number ofpiles needed, comparing the EOD condition with others. On average the proposed procedurereduces the number of piles required by about 8.6% when compared to the EOD condition(φ EOD R EOD ). The procedure using a single resistance factor for both initial pile resistance andpile setup (φ(R EOD +R setup )) requires the least number of piles, which is less than thosedetermined based on the measured pile resistances (φ SLT R SLT ). This approach will lead to alower reliability index than that targeted because it is implied in Figure 5.6 that the resistantfactor is not the same for both R EOD and R setup. On the other hand, the proposed procedure(φ EOD R EOD +φ setup R setup ) compares compatibly with those from measured pile resistances as thenumber of piles determined based on both combinations are almost similar. This implies that