Civil Engineering Reference
In-Depth Information
1.00
1.00
soft.pga
soft.SI
soft.pga
soft.SI
soft.SI lower
soft.SI upper
soft.SI lower
soft.SI upper
0.80
0.80
0.60
0.60
0.40
0.40
0.20
0.20
0.00
0.00
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0.00
0.50
1.00
1.50
2.00
2.50
3.00
Period (seconds)
Period (seconds)
1.00
1.00
firm.pga
firm.SI
firm.pga
firm.SI
firm.SI lower
firm.SI upper
firm.SI lower
firm.SI upper
0.80
0.80
0.60
0.60
0.40
0.40
0.20
0.20
0.00
0.00
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0.00
0.50
1.00
1.50
2.00
2.50
3.00
Period (seconds)
Period (seconds)
1.00
1.00
hard.pga
hard.SI
hard.pga
hard.SI
hard.SI lower
hard.SI upper
hard.SI lower
hard.SI upper
0.80
0.80
0.60
0.60
0.40
0.40
0.20
0.20
0.00
0.00
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0.00
0.50
1.00
1.50
2.00
2.50
3.00
Period (seconds)
Period (seconds)
Figure 3.20
Comparison of coeffi cients of variation (COVs) of spectral ordinates of a strong-motion data set scaled
by different spectrum scales and peak ground acceleration (PGA) for soft (
top
), fi rm (
middle
) and stiff soil condition
(
bottom
): elastic (
left
) and inelastic (
right
) spectra (
courtesy
of Pacifi c Earthquake Engineering Research Center,
USA)
The general observations from this study on scaling of earthquake records to minimize the coeffi cient
of variation in structural response characteristics are summarized in Tables 3.23 to 3.25. The artifi cial
records are signals derived to fi t a target spectrum. This is only indicative since the results will vary
when the target spectrum varies.
Based on the above study, it is recommended that Table 3.23 should be used to scale records in order
to minimize the dispersion of results obtained from using a proposed set of natural records. Tables 3.24
and 3.25 should be consulted when the objective is to acquire a close match between results of analysis
using spectrum-compatible and natural earthquake records.
Examination of Table 3.25 also provides physical interpretation of the results. Rock records are
dominated by high-frequency waves. Hence, scaling them using the lower-period range, i.e. 0.1 to 1.5
seconds, provides a close match in the period range up to 1.0 second. The opposite is true for soft soil
records that are best scaled using the upper-period range, i.e. 1.5 to 2.5 seconds. For scaling in the
long-period range, e.g. 1 to 3 seconds, amplifi cations are low on average because of the rarity of records
