Ground-Motion Parameters

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Ground-Motion Parameters
CEE 431/ESS465
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Ground Motion Parameters
Measured by triaxial accelerographs 2 orthogonal
horizontal components 1 vertical
component Digitized to time step of 0.005 - 0.01
sec For 60 sec record, N 3 x 60 / 0.01
18,000 values
Important Characteristics Amplitude Frequency
content Duration
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Ground Motion Parameters
Amplitude Parameters Peak acceleration Peak
velocity Peak displacement Sustained maximum
acceleration -3-cycle -5-cycle
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Ground Motion Parameters
Amplitude parameters
Highest amax
Rock site
Soil site
Highest vmax
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Ground Motion Parameters
Frequency content parameters Fourier
spectrum Plot of cn vs wn gives Fourier
spectrum cn
Example from ProShake
wn
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Ground Motion Parameters
Frequency content parameters Response spectrum
Examples from ProShake
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Ground Motion Parameters
Frequency content parameters Spectral
parameters Predominant period Bandwidth
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Ground Motion Parameters
Duration Bracketed duration Trifunac
duration
Td
95
Td
5
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Ground Motion Parameters
Other ground motion parameters rms
acceleration Arias intensity Spectral
intensity
All are influenced by amplitude, frequency
content, and duration
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Ground Motion Parameters
Effects of source parameters on ground
motions Magnitude
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Ground Motion Parameters
Effects of source parameters on ground
motions Magnitude
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Ground Motion Parameters
Prediction Predictive relationships (attenuation
relationships) Establish database Select form
of predictive equation Perform regression
analyses Evaluate uncertainty
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Ground Motion Parameters
Prediction Examples
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Ground Motion Parameters
Prediction Standard error - sln Y
Accounts for uncertainty in prediction of effects
of earthquake
ln Y
sln Y
ln Y
sln Y
M M
R R
log R
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Ground Motion Parameters
Prediction Standard error - sln Y
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Ground Motion Parameters
Prediction Standard error
ln Y
Y Y
ln Y
M M
R R
log R
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Ground Motion Parameters
Prediction Standard error
Most ground motion parameters are lognormally
distributed
ln Y
Y Y
ln Y
M M
R R
log R
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Ground Motion Parameters
Lognormal distribution
Median of x is less than mean of x
Median of ln x is equal to mean of ln x
x
ln x
The logarithm of a lognormally distributed random
variable is normally distributed
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Ground Motion Parameters
Standard normal distribution Standard normal
variate, z Mean z 0 Standard deviation
sz 1
Values of probability distribution for z
obtained from widely used tables
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Ground Motion Parameters
Prediction Standard error
PY gt Y MM, RR
ln Y
Y Y
ln Y
M M
R R
log R
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Ground Motion Parameters
Prediction Standard error
ln Y
PY gt Y MM, RR
ln Y
Y Y
M M
R R
log R
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Ground Motion Parameters
Prediction Common parameters Peak
acceleration Spectral accelerations
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Ground Motion Parameters
Prediction Common parameters Peak
acceleration Spectral accelerations
Sa
median s
median
0
T