49_HWKTTE 4004c - n m Ri R R = (5-10) where Ri Bias Factor...

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39 Equation 5-9 is the resulting calibration equation for ASD fitting to the LRFD or vice versa. For deep foundation design, the values of γ D and γ L recommended by LRFD Highway Bridges Design Specifications (AASHTO, 1994) are 1.25 and 1.75 respectively. The Q D /Q L definition and values will be presented in more detail in latter sections. Calibration by fitting is recommended when there is insufficient statistical data to perform a more sophisticated calibration by optimization. When statistical data is available it is recommended to make use of reliability theory. Reliability Calibration Statistical data In order to perform a reliability calibration for deep foundations (obtain resistance factor, φ ), such as piles and drilled shafts, the designer must have available statistical data for the method of interest. This statistical data must include real or measured capacities and the estimated or nominal capacities of the shafts. Next, the bias is defined as
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Unformatted text preview: n m Ri R R = (5-10) where Ri Bias Factor R m Measured Resistance R n Predicted (nominal) Resistance The biases for all history cases using the same design procedure are subsequently determined for the database and the values of mean, standard deviation and coefficient of 40 variance are then found. Equations 5-11, 5-12 and 5-13 are used for this purpose (Withiam et al., 1997). N Ri R = (5-11) ( 29 1 2--= N T Ri R (5-12) R R R COV = (5-13) where R Average Resistance Bias Factor N Number of Cases R Resistance Standard Deviation COV R Resistance Coefficient of Variance For calibrations of the methods that predict driven pile capacity, the values of the measured resistance (R m ) were obtained from in-situ load test employing the Davissons capacity. The nominal resistances (R n ) were obtained from the various dynamic equations under study (Chapter 3)....
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49_HWKTTE 4004c - n m Ri R R = (5-10) where Ri Bias Factor...

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