Geoscience Reference
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Fig. 12.12. Influence ofpile bending stiffness(EI) on the results of static BNWF SD
pushover analyses: (a) computed crust load versus imposed crust displacement, (b)
computed piledisplacement profiles and imposed soildisplacement profile
EquivalentstaticBNWFanalyseswereperformedforthesamefourcasesanalyzedinthe
abovedynamicFEanalyses.Thelateralsoildisplacementsandinertialoadswereapplied
simultaneouslyaslinearlyincreasingwithtimetotheirfinalvalues.Thelateralsoilload,
whichisacomputedresponse,andtheimposedinertialoadareplottedversustheimposed
soil displacement in Figure 12.12. For the two stiffer pile cases, these equivalent static
analysespredictthatthepilecapwillmovelessthanthefree-fieldsoilandthusthelateral
spreadingsoilloadwillactinthesamedirectionastheinertialoads(i.e.,in-phaseloads).
For the two more flexible pile cases, these equivalent static analyses predict that the pile
cap will move more than the free-field soil and thus the lateral load from the crust will
actuallyberesistingtheinertialoads(i.e.,out-of-phaseloads).Thus,theequivalentstatic
BNWF analyses were able to predict the effect that pile bending stiffness had on the
dynamic phasing of lateral spreading and inertia loads (Figures12.11 and 12.12).
TheresultsofparametricanalysesshowedthattheequivalentstaticBNWFanalyseswith
the simultaneous application of ultimate lateral ground displacements and appropriate
fractions of peak inertia loads were consistently able to predict the dynamic phasing of
the lateral spreading and inertia loads, and that this phasing depends primarilyon:
•
Pilefoundation stiffness
•
Crust strength and stiffness
•
Inertiaload magnitude
•
Ground displacement magnitude
The ground motion characteristics and the superstructure period affected the phasing of
crust and inertia loads primarily through their influence on the ground displacement and
inertiaload magnitudes.
