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37 5 0.3 4.5 0.275 4 0.25 0.225 3.5 0.2 Number of Pile-Cases 3 Relative Frequency 0.175 log-normal distribution 2.5 mlnx = -0.197 0.15 lnx = 0.464 2 0.125 normal distribution 0.1 1.5 mx = 0.901 0.075 1 0.05 x = 0.374 0.5 0.025 0 0 0 0.5 1 1.5 2 2.5 3 KSX = Ratio of Static Load Test Results over the Pile Capacity Prediction using the -API method Figure 19. Histogram and frequency distributions of Ksx for 16 cases of H piles in clay. methods by comparisons of factors of safety and the efficiency can be done by the simplified, closed form FOSM approach, factors. Additional evaluations are described in section 3.5. with the obtained resistance factors on the low side; and (2) the resistance factors obtained in this study (as presented in Tables 16 through 18) can be directly compared to the current speci- 3.2.2 FOSM Versus FORM fications and other LRFD codes based on FOSM. As the existing AASHTO specifications are based on FOSM (see section 18.104.22.168), the relationship between the fac- 3.2.3 Equivalent Factors of Safety tors obtained by FOSM and those obtained by the current methodology, FORM, needed to be checked. Figure 41 pre- The fact that the resistance factors using FORM approxi- sents these relationships for the different categories of the ana- mate those obtained by FOSM allows the use of a simplified lyzed methods for all three databases and for a reliability index relationship between resistance factor and FS based on of = 2.33. The data in Figure 41 suggest that FORM results FOSM and provided by Barker et al., 1991: in resistance factors consistently higher than those obtained by FOSM. The ratio between the two suggests that, as a rule of QD D+ L thumb, FORM provides resistance factors approximately 10% QL FS = (32) D + 1 higher than those obtained by FOSM. Two practical conclu- Q sions can be drawn from these data: (1) first evaluation of data QL