274 In section C the formulas for calculating the depth to fixity for preliminary
structural design are included, which are referenced from Davisson and Robinson (1965). The estimation of nominal lateral resistance is discussed in section 10.7.3.12 which recommends using p-y curves, group effects accounted
for using P-multipliers, and a resistance factor of 1.0. Resistance of the pile cap is allowed if it is to be embedded. Section 10.7.2.4 allows the use of strain wedge model for large diameter, relatively
short piles or shafts, but notes that P-multipliers are not applicable due to the overlap of wedge zones. Minimum penetration to obtain fixity is relative to the applied lateral loads at the Strength Limit State as indicated in section 10.7.6. The majority of State DOT practice is consistent with the guidance presented in AASHTO LRFD (2014), with the DOTs occasionally providing additional guidance. In some cases, that DOT
guidance is more conservative, such as using resistance factors, and in other cases the DOT
guidance is simply different, such as using Broms method for final design or employing critical depth instead of fixity depth. A few of the other recurring differences include Defining the head deflection limits Different definition of the fixity depth Recommendations regarding head fixity Defining geotechnical and structural discipline responsibilities
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