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47_HWKTTE 4004c

# 47_HWKTTE 4004c - factor that result in equivalent...

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37 3. The most rigorous method for developing and adjusting resistance factors to meet individual situations requires availability of statistical data and probabilistic design algorithms. Calibration of LRFD Calibration is defined as the process of assigning values to resistance factors and load factors, which are indispensable for the LRFD approach. This process can be performed by use of engineering judgement, fitting to other codes (e.g. ASD method), use of reliability theory, or a combination of them. In the following sections these approaches will be discussed. Engineering Judgement The calibration of a code using engineering judgement requires experience. Such experience is usually obtained through years of engineering practice. Sometimes, using such an approach results in certain level of conservatism with little validation. Also under varying conditions where no experience exists both excessive conservatism or ever unconservatism may develop. Fitting ASD to LRFD Fitting ASD to LRFD includes using parameters from LRFD (i.e. resistance

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Unformatted text preview: factor) that result in equivalent physical dimensions of a substructure or superstructure as by ASD. It does not provide a better or more uniform margin of safety. In order to calibrate the ASD method, the first step is to rewrite equations 5-2 and 5-3 as 38 L D n Q Q FS R + ≥ (5-4) D D L L n Q Q R γ φ + ≥ (5-5) It should be noted that the loads only include dead and live loads. Environmental loads (i.e. wind, earthquake, etc) were not taken into consideration for the derivation of the ASD fitting equation. Solving both equations for R n we obtain ( 29 L D n Q Q FS R + ≥ (5-6) ( 29 D D L L n Q Q R + ≥ (5-7) Setting Equation 5-6 equal to Equation 5-7 and solving for φ ( 29 D L D D L L Q Q FS Q Q + + = (5-8) Dividing both the numerator and the denominator of Equation 5-8 by Q L + + = 1 L D L D L D Q Q FS Q Q (5-9)...
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