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93
Distance (km)
""""--^Acc. (g)
Magnitude "*""~-~--—_
1
2
3
4
Magnitude 6.5 - 7.5 |g
10-30 30-50
0.2813
1.00 (10)
0.74 (2)
1.16 (64)
0.1355
1.00 (6)
1.51 (10)
0.78 (2)
1.18 (116)
50-100
0.1147
1.00 (6)
1.11 (12)
1.78 (16)
0.98 (72)
100-200
0.036
1.00 (2)
1.79 (2)
1.81 (14)
One can see from the table that the ratios vary with site condition. The ratio values are further
summarized into four groups according to the Ace. values ^O.OSg, 0.08~0.15g, 0.15~0.25g, or^
0.25g, the mean values of these four groups are listed in table 6 with the representative values O.OSg,
O.lg, 0.2g and 0.3g. From that table, one can find that, in general, soil site will amplify the ratio (the
maximum to 1.96 times), the rate of amplification may decreases smoothly as the soil gets softer and
the thicker the soil layers. The rate of amplification decreases obviously until less than 1.0 when the
Ace. is greater than 0.3g from the nonlinearity effect of soil. It is true that some values in the table vary
in unstable fashion, even jumpily, because of the insufficient and inhomogeneous data sample. Putting
the ratios for the soil sites together, a general trend of the ratio decreasing smoothly with the Ace. can
be recognized. From the above table and some other references, the suggested values of adjustment
coefficient are listed in table 7, where the values for Ace. 0.15g and 0.3g are estimated by
interpolation.
Table 6 The mean ratios of four Ace, groups
^^^"^•^A-cc (g)
Site Categories"--^^^
1
2
3
4
0.05
LOO
1.66
1.59
0.1
1.00
1.30
1.41 ^
1.06
0.2
1.00
1.47
1.96
1.35
0.3
LOO
0.77
0.95
""^^-^^Acc.Cg)
Site Categon&s--^^^^
1
2
3
4
Table 7 The suggested values of site coefficient
0.05
1.0
1.65
1.65
1.60
0.1
1.0
1.5
1.5
1.4
0.15
1.0
1.5
1.5
1.4
0.2
1.0
1.5
1.5
1.3
0,25
1.0
1.3
1.2
LI
0.3
1.0
1.2
LI
1.0
0.4
1.0
1.0
1.0
0.9
Ratio of vertical to horizontal component varying with period
As the accumulation of near field records has increased, some quite large vertical components of
ground motions have been reported, which are even larger than the horizontal components. To examine
if it is necessary to stipulate the ratio of vertical maximum amplitude to the horizontal one in the
design spectra for different distances, 1449 ratios of vertical to horizontal parrs of records were