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54
From these plots, the trend of increasing PGV with S1 is very Earthquake ground motion studies described in this chap-
evident; however, there is no discernible trend for PGA. ter are based on an earthquake with a 7 percent probability of
In addition to presenting the median PGV equation, Fig- exceedance in 75 years (that is, the 1,000-year return period),
ures 5-20 through 5-24 show the mean-plus and the mean- consistent with the recommendations adopted by AASHTO
minus one standard deviations. These lines use the standard in July of 2007. The 1,000-year earthquake ground motions
deviation coefficient of 0.38 as suggested by the Abrahamson are available in maps and from an implementation CD de-
PGV equation. The use of the standard deviation coefficient veloped by the USGS for AASHTO. As shown in this chapter,
of 0.38 implies that the mean-plus one standard deviation the recommended 1,000-year return period is a significant
and the mean-minus one standard deviation will be 1.46 and change from the existing AASHTO Specifications, in terms of
0.68 of the median PGV values. PGA and spectral shape for WUS and CEUS locations. These
From the five figures presented in this section, the follow- differences need to be considered when conducting seismic
ing relationship was selected for estimating PGV for design analysis and design for retaining walls, slopes and embank-
analyses, with the equation reduced to the following expres- ments, and buried structures, and therefore these ground
sion in log10 units rather than natural log basis: motion discussions form an important component of the
overall NCHRP 12-70 Project.
PGV = 0.3937 × 100.434C 1 (5-10) The information from ground motion review also was used
to update Newmark displacement correlations, as also de-
where
scribed in this chapter. Newmark displacement correlations
PGV = inches/sec and
will be used for estimating the displacement of retaining walls,
slopes and embankments, and buried structures, as discussed
C1 = 4.82 + 2.16 log10 S1 + 0.013[ 2.30 log10 S1 + 2.93]
2
in later chapters. The update in the displacement correlations
For design purposes Equation (5-10) was later simplified considered ground motions that will typically occur in CEUS
to the following equation. as well as WUS. Again both the PGA and spectral shape were
important considerations during the development of these
PGV ( in sec ) = 55 Fv S1 (5-11) correlations. Results of the Newmark displacement studies led
to two equations [Equation (5-6) for CEUS rock sites and
Equation (5-10) was developed by using the mean-plus Equation (5-8) for WUS soil and rock sites and CEUS soil
one standard deviation prediction (shown in heavy thick lines sites] and two charts (Figures 5-18 and 5-19) for use in design.
in the five figures for an M = 7.5 event). As a final component of the ground motion studies, a cor-
relation between PGV and spectral acceleration at 1 second
(S1) was developed. This information is needed within the
5.4 Conclusions
Newmark displacement correlations developed for this Proj-
The work presented in this chapter forms the basis of the ect, as well as for evaluating the transient response of buried
ground motion determination used during the seismic analy- structures. Equation (5-10) presents the correlation. Results
sis and design of retaining walls, slopes and embankments, of the equation are compared with records from the USNRC
and buried structures. The results of the ground motion stud- strong motion database to show the reasonableness of the rec-
ies were developed by interpreting existing strong motion ommended equation. For design purposes Equation (5-10)
data relative to recommendations that were made for the up- was later simplified to Equation (5-11). The simplified equa-
date of the AASHTO LRFD Bridge Design Specifications. tion provided a reasonable approximation of the data.
