Pseudo-static/dynamic methods for walls, which involve an assumed
distribution of internal earth pressure (e.g. Fig. 14.12), require that
each reinforcement layer carry a portion of the integrated earth pressure
over a tributary area, Sv, as illustrated in Fig. 14.15. The magnitude of
tensile force must not exceed the allowable design load in the reinforce-
ment based on tensile over-stressing, facing connection strength and pull-
out capacity of the layer. In North American practice, factors of safety
against these modes of failure are reduced to values that are typically
75% of static values. Figure 14.15 also demonstrates that the inertial
force due to the tributary portion of the facing column should be
added to the reinforcement forces under seismic loading in the case of
segmental walls. An important implication of the assumed earth pressure
distribution using the pseudo-staticM±Omethod described earlier, is that
the relative proportion of load to be carried by the reinforcement layers
closest to the crest of a wall with uniform reinforcement spacing increases
with increasing horizontal acceleration. This may require a greater
number of layers towards the top of the wall than is required for static
load environments. A similar conclusion was reached by Vrymoed
(1989) using a tributary area approach that assumes that the inertial
force carried by each reinforcement layer increases linearly with height
above the toe of the wall for equally spaced reinforcement layers. Bona-
parte et al. (1986) applied the tributary area method to walls and slopes
but recommended a uniform distribution for the dynamic earth pressure
increment (i.e. Hd 0:5H in Fig. 14.12).
Pseudo-static/dynamic methods for walls, which involve an assumeddistribution of internal earth pressure (e.g. Fig. 14.12), require thateach reinforcement layer carry a portion of the integrated earth pressureover a tributary area, Sv, as illustrated in Fig. 14.15. The magnitude oftensile force must not exceed the allowable design load in the reinforce-ment based on tensile over-stressing, facing connection strength and pull-out capacity of the layer. In North American practice, factors of safetyagainst these modes of failure are reduced to values that are typically75% of static values. Figure 14.15 also demonstrates that the inertialforce due to the tributary portion of the facing column should beadded to the reinforcement forces under seismic loading in the case ofsegmental walls. An important implication of the assumed earth pressuredistribution using the pseudo-staticM±Omethod described earlier, is thatthe relative proportion of load to be carried by the reinforcement layersclosest to the crest of a wall with uniform reinforcement spacing increaseswith increasing horizontal acceleration. This may require a greaternumber of layers towards the top of the wall than is required for staticload environments. A similar conclusion was reached by Vrymoed(1989) using a tributary area approach that assumes that the inertialforce carried by each reinforcement layer increases linearly with heightabove the toe of the wall for equally spaced reinforcement layers. Bona-parte et al. (1986) applied the tributary area method to walls and slopesbut recommended a uniform distribution for the dynamic earth pressureincrement (i.e. Hd 0:5H in Fig. 14.12).
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