where f is the resistance factor, gi are the load factors, and h is the load modifier.
Load factors account for the uncertainties in magnitude and direction of loads, location
of application of loads, and combinations of loads.
On the other hand, resistance factors can be made to incorporate variability of soil
properties, reliability of predictive equations, quality control of construction, extent of soil
exploration, and even the consequences of failure. The main advantages of LRFD are that
it accounts for variability in both resistance and loads and provides a qualitative measure
of risk related to the probability of failure. However, LRFD also has the limitation of not
facilitating the selection of appropriate resistance factors to suit the design of different
foundation types. The LRFD-based evaluation of service limit state can be described by
Equation (3.1b).
Three different methods are adopted to select the resistance and load factors (FHWA,
1998):
1. Calibration by judgment (requires extensive experience)
2. Calibration by fitting to ASD
3. Calibration by the theory of reliability
The procedure used for the selection is known as the calibration of LRFD. The two latter
procedures will be discussed in this chapter.
where f is the resistance factor, gi are the load factors, and h is the load modifier.Load factors account for the uncertainties in magnitude and direction of loads, locationof application of loads, and combinations of loads.On the other hand, resistance factors can be made to incorporate variability of soilproperties, reliability of predictive equations, quality control of construction, extent of soilexploration, and even the consequences of failure. The main advantages of LRFD are thatit accounts for variability in both resistance and loads and provides a qualitative measureof risk related to the probability of failure. However, LRFD also has the limitation of notfacilitating the selection of appropriate resistance factors to suit the design of differentfoundation types. The LRFD-based evaluation of service limit state can be described byEquation (3.1b).Three different methods are adopted to select the resistance and load factors (FHWA,1998):1. Calibration by judgment (requires extensive experience)2. Calibration by fitting to ASD3. Calibration by the theory of reliabilityThe procedure used for the selection is known as the calibration of LRFD. The two latterprocedures will be discussed in this chapter.
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