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Effects of Strong Motion Processing Procedures
on Time Histories, Elastic and Inelastic Spectra
By Paolo Bazzurro, Brian Sjoberg, Nicolas Luco (AIR)
Walter Silva, Robert Darragh (Pacific Engineering and Analysis)
Presented at
COSMOS INVITED WORKSHOP
ON STRONGMOTION RECORD PROCESSING
Richmond, CA, May 2627, 2004
www.airworldwide.com
Motivation
To quantify on a statistical basis the effects on ground motion time
histories and elastic and inelastic spectra of
histories
and
elastic
and
inelastic
spectra
of
i. Causality of the filter
ii
Filter order
ii
.
Filter
order
iii. Selection of the highpass cutoff frequency
iv. Preservation or removal of residual displacement offset
We considered
¾Butterworth filter only
N
(di t R
17k )
d ti f th k ith
¾
N
ea
r
source
(di
s
t
ance
R
≤
17k
m
)
groun
d
mo
ti
ons
f
rom ear
th
qua
k
es w
ith
moment magnitude ranging from 6.5 to 7.6
¾Two components rotated faultparallel and faultnormal
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Earthquakes and Recording Stations
Rupture Distance
V
S30 HP LP
X
cos(
θ
) or DMF
Earthquake Year Mag Mechanism
(k
m
)
Station Name (m/s) (Hz) (Hz)
Y
cos
(
φ
)
Imperial Valley
1979 6.5 S 8.5 Brawley Airport 209 0.10 40 0.7 1.051.54
1El Centro Array #6 203 0.10 40 0.5 1.001.08
C#
0.6 El
C
entro Array
#
7211 0.10 40 0.5 1.001.08
14.2 Parachute Test Site 349 0.10 40 0.7 1.051.54
Loma Prieta
1989 6.9 R (oblique) 6.1 LGPC 466 0.10 0.8 1.041.17
Landers
1992 7.3 S 1.1 Lucerne 685 0.08 60 0.63 1.031.36
K
obe
1995 6.9 S 10.2
Amagasaki
256 0.10 40 0.57 1.02.123
obe
Amagasaki
0.2 Kobe University 1043 0.10 30 0.42 0.940.99
2.5 Port Island (0 m) 198 0.10 0.3 0.760.97
1.2 Takarazuka 312 0.13 33 0.64 1.031.39
Northridge
1994 6.7 R 6.2 Jensen Filter Plant 373 0.20 0.79 1.041.16
7.1 Rinaldi Receiving Stn. 282 0.10 0.77 1.031.15
Kocaeli, Turkey
1999 7.4 S 17 Arcelik 523 0.07 50 0.26 0.710.96
12.7 Duzce 276 0.08 15 0.51 1.101.10
17 Gebze 792 0.08 25 0.23 0.680.96
4.8
Izmit
811
0.10
30
0.02
0.46

0.92
4.8
Izmit
811
0.10
30
0.02
0.46 0.92
2.6 Yarimca 297 0.07 50 0.11 0.550.94
ChiChi, Taiwan
1999 7.6 R 4.4 TCU049 N/A 0.02 30 0.62 1.001.03
0.2 TCU052 N/A 0.04 50 0.61 1.001.02
1.1 TCU068 N/A 0.03 50 0.62 1.001.03
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Additional Records List
Kocaeli, Turkey
1999 7.4 S 3.1 Sakarya 471 0.04 40 0.19 0.630.95
Processing Techniques
2
pole
P
2pole/2pole
pole
a
ke
N
ame
A
causal 2pole/
2
A
causal  1.5xH
P
A
causal 2pole/3
4
pole
1.5xHP 4pole
5
pole
pole
1
.5xHP 4pole
pole
Legend:
Earthqu
a
Station
N
Cascade
A
Cascade
A
Cascade
A
Acausal
4
Acausal 
Acausal
5
Causal 4
Causal 
1
Causal 5
Static
Imperial Valley
Brawley Airport HBRA053.ATR HBRA053.ATR HBRA053.ATR HBRA053.ATR HBRA053.ATR HBRA053.ATR HBRA053.ATR HBRA053.ATR HBRA053.ATR
El Centro Array #6 HE06053.ATR HE060 53.ATR HE06 053.ATR HE06 053.ATR HE060 53.ATR HE060 53.ATR HE06 053.ATR HE06 053.ATR HE0 6053.A TR
El Centro Arra
y
#7 HE0 7053.ATR HE0 7053.ATR HE0 7053.ATR HE0 7053.A TR HE070 53.A TR HE0 7053.A TR HE07053.A TR HE07053.A TR HE07053.A TR
Available
Not Available
y
Parachute Test Site HPTS053.ATR HPTS0 53.ATR HPTS053.A TR HPTS053.ATR HPTS0 53.ATR HPTS0 53.ATR HPTS0 53.ATR HPTS053 .ATR HPTS0 53.ATR
Loma Prieta
LGPC LGP038.ATR LGP038.ATR LGP038.ATR LGP038.ATR LGP038 .ATR LGP038 .ATR LGP038 .ATR LGP038 .ATR LGP038 .ATR
Landers
Lucerne LCN175.ATR LCN175.ATR LC N175.ATR LCN175.ATR LCN175.ATR LCN175.ATR LCN175.ATR LCN175.ATR LCN175.ATR LCN175.ATR
Kobe
Amagasaki AMA230.ATR AMA230.ATR AMA230.ATR AMA230.ATR AM A230.ATR AM A230.ATR AMA230.ATR AMA230.ATR AMA230.ATR
Kobe University KBU2 30.ATR KBU230.ATR KBU230.A TR KBU230.ATR KBU2 30.ATR KBU230.ATR KBU230 .ATR KBU230.A TR KBU23 0.ATR
Port Island (0 m) PRI230.ATR PRI230.ATR PRI230.ATR PRI230.A TR PRI230.ATR PRI23 0.ATR PRI230.ATR PRI230.ATR PRI230.ATR
Takarazuka TAZ230.ATR TAZ230.ATR TAZ230.ATR TAZ230.ATR TAZ230.ATR TAZ230.ATR TAZ230.ATR TAZ230.ATR TAZ230.ATR
Nthid
N
or
th
r
id
ge
Jensen Filter Plan
t
JEN122.ATR JEN122.A TR JEN122.ATR JEN122.ATR JEN122.ATR JEN122.ATR JEN122.ATR JEN122.ATR JEN122.ATR
Rinaldi Receiving Stn. RRS122.ATR RR S122 .ATR R RS122.A TR RRS122 .ATR RR S122 .ATR RRS122 .ATR R RS122.A TR RRS122 .ATR R RS122.A TR
Kocaeli, Turkey
Arcelik ARC000.ATR ARC000.ATR ARC000.ATR ARC0 00.ATR ARC000.ATR ARC000.ATR ARC0 00.ATR ARC000.ATR ARC000.ATR
Duzce DZC180.ATR DZC180.ATR DZC180.ATR DZC180.ATR DZC180.ATR DZC180.ATR DZC180.ATR DZC180.ATR DZC180.ATR
Gebze GBZ000.ATR GBZ000.ATR GBZ000.ATR GBZ000.ATR GBZ000.ATR GBZ000.ATR GBZ000.ATR GBZ000.ATR GBZ000.ATR
Izmit IZT0 90.ATR IZT090.ATR IZT09 0.ATR IZT090.A TR IZT09 0.ATR IZT09 0.ATR IZT090.A TR IZT090 .ATR IZT090.ATR IZT004.ATR
Yarimca YPT000.ATR Y PT000.ATR YPT000.ATR YPT000.ATR YPT000.ATR YPT000.ATR YPT000.ATR YPT000.ATR YPT000.ATR YPT004.ATR
Sakarya
*
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
* Parallel component only
Sakarya
SKR090.ATR SKR090.ATR SKR090.ATR SKR090.ATR SKR090.ATR SKR090.ATR SKR090.ATR SKR090.ATR SKR090.ATR SKR090.ATR
ChiChi, Taiwan
TCU049 TCU049N.ATR TCU049N.ATR TCU049N.ATR TCU049N.ATR TCU049N.ATR TCU049N.ATR TCU049N.ATR TCU049N.ATR TCU049N.ATR TCU049N.ATR
TCU052 TCU052N.ATR TCU052N.ATR TCU052N.ATR TCU052N.ATR TCU052N.ATR TCU052N.ATR TCU052N.ATR TCU052N.ATR TCU052N.ATR TCU052N.ATR
TCU068 TCU068N.ATR TCU068N.ATR TCU068N.ATR TCU068N.ATR TCU068N.ATR TCU068N.ATR TCU068N.ATR TCU068N.ATR TCU068N.ATR TCU068N.ATR
Response to Butterworth Filters of Different Orders
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Inelastic Displacement Response Spectra – What’s R?
Earthquake
A
ccelerogra
m

0.6
0.4
0.2
0
0.2
0.4
0.6
Δmax (inelastic)
(R = 4)
Δ
max (elastic)
Displacement
Response
0.8
0.6
0246810121416
5
10
15
20
max
(elastic)
Δmax
Response
Time History
(T
n
= 1.0 sec)
10
5
0
0 2 4 6 8 10121416
Displaced
Structure
Base
Shea
r
dy =
Δmax (elastic)
/ R
Displacement
dy
Yield
Strength
Single

Degree

of

Freedom
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Δmax (elastic) Δmax (inelastic)
Single Degree of Freedom
Structure
Effects of Causality of the Filter
R=1 (Elastic)
Bandwidth upper bound
f l filt
f
or acausa
l
filt
e
r
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Bandwidth for cascade
acausal filter
Bandwidth upper bound for
causal filter
Effects of Causality of the Filter
R=8 (Severely Inelastic)
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Effects of Filter Order: 4pole vs. 5pole Causal
R=1 (Elastic) R=8 (Severely Inelastic)
R=1
(Elastic)
R=8
(Severely
Inelastic)
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Effects of Filter Order: 4pole vs. 5pole Acausal
R=1 (Elastic) R=8 (Severely Inelastic)
R=1
(Elastic)
R=8
(Severely
Inelastic)
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Effects of Filter Order: 2p2p vs. 2p3p Acausal
R=1 (Elastic) R=8 (Severely Inelastic)
R=1
(Elastic)
R=8
(Severely
Inelastic)
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Effects of HP cutoff frequency:
fHP vs. 1.5fHP  4poleCausal Filter
R=1 (Elastic) R=8 (Severely Inelastic)
R=1
(Elastic)
R=8
(Severely
Inelastic)
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Effects of HP cutoff frequency:
fHP vs. 1.5fHP  4pole Acausal Filter
R=1 (Elastic) R=8 (Severely Inelastic)
R=1
(Elastic)
R=8
(Severely
Inelastic)
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Effects of HP cutoff frequency:
fHP vs. 1.5fHP 2p2pCascade Acausal Filter
R=1 (Elastic) R=8 (Severely Inelastic)
R=1
(Elastic)
R=8
(Severely
Inelastic)
~5s 1.5s
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Effects of HP cutoff frequency:
fHP vs. 1.5fHP 2p2pCascade Acausal Filter
R=1 (Elastic) R=8 (Severely Inelastic)
R=1
(Elastic)
R=8
(Severely
Inelastic)
0.5s 2.0s
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Effects of HP cutoff frequency:
fHP vs. 1.5fHP 2p2pCascade Acausal Filter
R=1 (Elastic) R=8 (Severely Inelastic)
R=1
(Elastic)
R=8
(Severely
Inelastic)
1.0s 3.0s
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Effects of Residual Displacement
R=1 (Elastic) R=8 (Severely Inelastic)
R=1
(Elastic)
R=8
(Severely
Inelastic)
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
Notes: 1) normal components
2) 6 records only
3) Results for causal filters are similar
Summary of Effects of Processing Techniques on
Elastic and Inelastic Spectra
In general, effects are larger
¾for inelastic than for elastic spectra and
¾for longer periods at any given response level (i.e., R=1 through 8)
Causality of the filter does not systematically affect the amplitude of the spectra.
The statistical impact on spectra due to the filter order is negligible
I i th l f th HP t
ff f
f
t
ilti
t
I
ncreas
i
ng
th
e va
l
ue o
f
th
e
HP
cu
t
o
ff
f
requency,
f
HP, genera
t
es
i
ne
l
as
ti
c spec
t
ra
that are systematically lower at periods much lower than 1/ fHP regardless of the
causality of the filter. This can be in part explained by the lengthening of the
effective period of vibration of structures in the postelastic regime.
Records with residual displacement offset preserved generate inelastic response
spectra that are consistently higher than those caused by records with offset
removed. (Phenomenon observed for 6 faultnormal records only).
NOTE: See paper for effects on spectra caused by applying a filter to
simulated ground motion records
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP
simulated
ground
motion
records
Summary of Effects of Processing Techniques on
Ground Motion TH’s
In general, effects are significant for PGD and, to a lesser extent, for PGV. The
im
p
act on other
p
arameters
(
e.
g
., PGA, Arias Intensit
y
, and duration
)
is
pp(g y )
negligible.
Causally filtered records have PGV and PGD values that are, on average,
smaller (by 510% and 515%, respectively) than those of acausally filtered
ones.
Acausally filtered records generally display a more prominent ramp of
increasing displacement prior to the onset of strongmotion than causally
filtered records Peak

to

peak displacement amplitude however is similar for
filtered
records
.
Peak

to

peak
displacement
amplitude
,
however
,
is
similar
for
each processing technique.
The filter order does not affect the ground motion parameters considered here.
Increasing the value of the HP cut

off frequency
f
HP
generates records with
Increasing
the
value
of
the
HP
cut
off
frequency
,
f
HP
,
generates
records
with
lower PGV and PGD values (5% and 1520%, respectively), as expected.
The values of PGV and PGD are considerably larger (520% and 5060%,
respectively) in records with residual static offset preserved, as expected.
© 2004 AIR Worldwide Corporation COSMOS WORKSHOP