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1. INTRODUCTION
The 4.8 km long Jamuna Multipurpose Bridge connects the eastern and western parts of
Bangladesh. Being the only road and rail link between the two regions, the bridge bears
immense economic and strategic importance for the whole country. But the bridge is located
in a seismically active region that can be subjected to moderately strong earthquakes from a
number of sources and special earthquake protection devices have been used in the bridge.
The bridge has been designed for a peak ground acceleration of 0.2g due to a 7.0 magnitude
earthquake in the Bogra fault zone, which is about 25 to 40 kms from the west end of the
bridge, based on study by Bolt (1987).
Jamuna Multipurpose Bridge Authority (JMBA) took necessary steps for the installation of
seismic instruments on and around the Jamuna Bridge. JMBA employed Bangladesh
University of Engineering & Technology (BUET) as the technical consultant for this project.
The Installation of the seismic instruments on the bridge structure and six other free-field
(ground) stations was completed by Kinemetrics, Inc. USA on July 10, 2003 (BUET, 2003).
The Operating and Monitoring Phase of the project started on July 11, 2003. Earthquake on
26th July 2008 and on 16th June 2004 excited the Jamuna Multipurpose Bridge. The
excitations have been recorded by the sensors installed in Pier 10 which is at the end of
Module 1of the bridge. Module one is at the west bank of the river.
In this report the comparison of ground motion and the bridge excitation due to Earthquake on
26th July 2008 and on 16th June 2004 are presented. The excitations are recorded by the
sensors installed in Pier 10 which is at the end of Module 1of the bridge. Module one is at the
west bank of the river.
2. EARTHQUAKE DATA ANALYSIS
The report gives the complete processed data of the three components of motion at the three
free-field stations which recorded the earthquake. The data processing, which includes
necessary corrections and filtering, has been carried out using softwares SMA (Kinemetrics,
2001) and Origin 6.0. The earthquake data has been formatted using USGS format. The
acceleration, velocity and displacement time histories as well as Response Spectra and FourierSpectra have been evaluated.
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3. EARTHQUAKE PARAMETERS
The strong motion instruments record the time through GPS. Using the recorded ground
motions, the time of first arrivals of S and P waves, epicentral location, magnitude has beenestimated by BUET Consultants.
The estimated epicentral parameters for the earthquake 2004 are as follows:
Time: At 23:36:53GMT on 16/06/2004
Magnitude: ML=2.5
Epicentre: Approximately 50 to 60 km from the bridge site.
Depth: 33 km
The estimated epicentral parameters for the earthquake 2008 are as follows:
Time: At 18:52:11 GMT on 26/07/2008
Magnitude: ML=4.8
Epicentre: Latitude 24.8 Longitude 90.6
Approximately 120 km from the bridge site.
Depth: 39.3 km
4. GROUND MOTION DUE TO EARTHQUAKES
Figure 1 to 6 shows the time history and FFT of acceleration of Bridge west end ground
motion acceleration. Time history comparison figures clearly shows that the time period of
earthquake of 2008 was greater than that of earthquake 2004. Table 1 gives a list of peak
values of accelerations for the earthquakes of 2008 and 2004, recorded at the free-fieldstations of the east and west sides of the bridge.
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Table 1: Summary of Peak Ground Motion Acceleration and corresponding PredominantFrequency in Free Field Stations at the east and west side of the bridge.
Note. X represents East-West direction,Y represents North-South direction,Z represents Vertical direction
4.1 Ground motion in North-South direction
Earthquake in 2008 had a PGA of 36.46 cm/s2with a predominant frequency of 2.05 Hz, 3.28
Hz and in case of earthquake in 2004, this is 41.75 cm/s2 with 7.7 Hz (Figure 1-2). The
previous earthquake was 1.14 times stronger than the recent one.
Station ID# Direction
Latitude
&
Longitud
e
Earthquake on 26/07/08
At 18:52:11 (GMT)
Earthquake on 16/06/04
At 23:36:53 (GMT)
Ratio of
PGA of
the recent
earthqua
ke to the
previous
one
Peak groundmotion
Acceleration(cm/s2)
PredominantFrequency
(Hz)`
Peak groundmotion
Acceleration(cm/s2)
PredominantFrequency
(Hz)
BridgeWest-End
N-S
24.398N89.753
E
41.75 7.7 36.46 2.05 0.87
E-W 16.57 7.7 40.22 5.37 2.43
U-D 8.85 8.16 11.6 5 1.31
BridgeEast-End
N-S24.393
N89.805
E
-11.459 10.75 24.04 2.43 2.1
E-W12.615 8.28 26.78 2.75 2.12
U-D-4.4486 19.8 11.52 7.9 2.59
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(a) (b)
Figure 1: Acceleration at free field station in North-South direction, obtained from actual
response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake 16th
June 2004.
(a) (b)
Figure 2: Fifteen point FFT of Acceleration at free field station in North-South direction,
obtained from actual response along longitudinal direction, (a) Earthquake 26th July 2008, (b)
Earthquake 16th June 2004.
4.2 Ground motion in East-West direction
Earthquake in 2008 had a PGA of 40.22 cm/s2with a predominant frequency of 5.37 Hz and
in case of earthquake in 2004, this is 16.57 cm/s2 with predominant frequency of 7.7 Hz
(Figure 3-4). The recent earthquake was 2.43 times stronger than the previous one.
0 10 20 30 40 50 60
-50
-40
-30
-20
-10
0
10
20
30
40
50
Acce
leration(cm/s2)
Time(sec)
0 10 20 30 40 50
-50
-40
-30
-20
-10
0
10
20
30
40
50
Amp
litude(cm/s2)
Time(sec)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Am
plitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Am
plitude(cm/s2)
Frequency(Hz)
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(a) (b)
Figure 3: Acceleration at free field station in East-West direction, obtained from actual
response along longitudinal direction, (a) Earthquake 26thJuly 2008, (b) Earthquake 16thJune
2004.
(a) (b)
Figure 4: Fifteen point smoothed FFT of Acceleration at free field station in East-West
direction, obtained from actual response along longitudinal direction, (a) Earthquake 26th July
2008, (b) Earthquake 16thJune 2004.
4.3 Ground motion in Up-Down direction
Earthquake in 2008 had a PGA of 11.6 cm/s2with a predominant frequency of 5 Hz and in
case of earthquake in 2004, this is 8.85 cm/s2 with 8.16 Hz (Figure 5-6). The recent
earthquake was 1.42 times stronger than the previous one.
0 10 20 30 40 50 60
-50
-40
-30
-20
-10
0
10
20
30
40
50
Acce
leration(cm/s2)
Time(sec)
0 10 20 30 40 50
-50
-40
-30
-20
-10
0
10
20
30
40
50
Amplitude(cm/s2)
Time(sec)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
A
mplitude(cm/s2)
Frequency(Hz)
0.1 1 10 200.00
0.05
0.10
0.15
0.20
0.25
A
mplitude(cm/s2)
Frequency(Hz)
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(a) (b)
Figure 5: Acceleration at free field station in North-South direction, obtained from
actual response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake16thJune 2004.
(a) (b)
Figure 6: FFT of Acceleration at free field station in Up-Down direction, obtained from actual
response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune
2004.
4.4 Particle Size Distribution
Figure 7a shows particle size distribution of five records during the 2008 earthquake and
Figure 7b particle size distribution of three records during the 2004 earthquake.
0 10 20 30 40 50 60
-15
-10
-5
0
5
10
15
Acceleration(cm/s2)
Time(sec)
0 10 20 30 40 50
-15
-10
-5
0
5
10
15
A
mplitude(cm/s2)
Time(sec)
0.1 1 10 20
0.00
0.04
0.08
0.12
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.04
0.08
0.12
Amplitude(cm/s2)
Frequency(Hz)
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-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06
27/07/2008 Bogra FFS in NS direction
EW (cm)
NS(cm)
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15
27/07/2008 Bridge East FFS in NS direction
EW (cm)
NS(cm)
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5
27/07/2008 Mymensingh FFS in NS direction
EW (cm)
NS(cm)
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06
27/07/2008 Natore FFS in NS direction
EW (cm)
NS(cm)
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20
27/07/2008 Bridge West FFS in NS direction
EW (cm)
NS(cm)
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
East
EW (cm)
NS(cm)
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
-0.25 -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25
Mymensingh
EW (cm)
NS(cm
)
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5
West
EW (cm)
NS(cm
)
Figure 7a: Particle size distribution during the earthquake of 26.07.2008
Figure 7b: Particle size distribution during the earthquake of 16.06.2004
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5 EARTHQUAKE RESPONSE OF BRIDGE
The sensors and recorders installed on the bridge are listed in Table 2 along with location and
direction of measurement. Figure 8 and Figure 9 shows the sensor locations on the bridge. All
the sensors were placed in their designated positions and each of them were connected to one
particular channel of a recorder. Data is recorded in hard drives (PCMCIA cards).
Table 2: List of sensors and recorders installed on the bridge and bore-hole
K2 Data
Recorder Label
Sensor Type ChannelLabel
Orient-ation Sensor Location
JAMUNA
located inside bridgedeck near Pier P10
Displacement D1 X Across Isolation System atPier P10Displacement D2 Y
Displacement D3 Y Across Expansion Jointbetween Piers P7 and P8
EPI UniaxialAcceleromete
r
BR9 Z Pile Cap at Pier P9
EPI BiaxialAcceleromete
r
BR10 X Deck at Pier P9
BR11 Y
MEGHNA locatedinside bridge deck
near Pier P10
EPI UniaxialAcceleromete
r
BR4 Z Pile Cap at Pier P10
EPI UniaxialAcceleromete
r
BR8 Z Deck at Pier P10
EPI UniaxialAcceleromete
r
BR12 X Deck at Midspan betweenPiers P9 and P10
EPI UniaxialAcceleromete
r
BR13 X Deck at Midspan betweenPiers P10 and P11
SURMA locatedinside bridge deck
near Pier P10EPI Triaxial
Accelerometer
BR1 X
Pile Cap at Pier P10BR2 Y
BR3 Z
EPI TriaxialAcceleromete
r
BR5 X
Deck at Pier P10BR6 Y
BR7 Z
PADMA located at AB1 X
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Sensors on the bridge recorded the motion of the bridge. Time history and FFT of acceleration
are shown in figures 10 to 35. The peak values of all accelerometers are given in Table 3.
The West-End free-field station is nearest to the instrumented bridge module (7-span module
next to West-end module. Further analysis of the bridge structure will be done to study these
effects.
Table 3: Comparison of Sensor data of bridge
Channel ID Sensor Location
Max. Peak Ground Acceleration2
(cm/sec ) Multiplicationof bridge
response for
recent
earthquake
than the
previous one
Earthquake on
26/07/08
At 18:52:11 (GMT)
Earthquake on
16/06/04
At 23:36:53 (GMT)
BR-1X
Pile Cap at Pier P10
21.5 13.3 1.62
BR-2Y 28.16 5.7 4.94
BR-3Z 8.08 2.6 3.11
BR-4Z 4.03 2.5 1.61
BR-5X
Deck at Pier P10
15.96 4.6 3.47
BR-6Y 13.2 7.6 1.74
BR-7Z 4.5 3.06 1.47BR-8Z 3.75 2.65 1.42
BR-9Z Pile Cap at Pier P9 5.33 2.8 1.90
BR-10XDeck at Pier P9
18.2 3.7 4.92
BR-11Y 13.11 10.24 1.28
BR-12XDeck at Mid Span
28.3 7.4 3.82
BR-13X 28.2 10.43 2.70
Note: X means orientation across the bridge (transverse direction)Y means orientation parallel to the bridge (longitudinal direction)Z means vertical direction
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5.1 Comparison of Acceleration data of Pier at P10 along Transverse
direction(1X)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
21.5 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 17
th
June 2004 causedmaximum PGA of 13.3 cm/s2with a predominant frequency of 1.1 Hz in transverse direction
(Figure 10-11). Excitation for recent earthquake is 1.62 times stronger than the previous one.
(a) (b)
Figure 10: Acceleration at bridge deck, obtained from actual response along transverse
direction, (a) Earthquake 26th July 2008, (b) Earthquake 17thJune 2004.
(a) (b)
Figure 11: FFT of Acceleration at free field station in North-South direction, obtained from
actual response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake
16thJune 2004.
0 10 20 30 40 50
-25
-20
-15
-10
-5
0
5
10
15
20
25
Am
plitude(cm/s2)
Time(sec)
0 10 20 30 40 50
-25
-20
-15
-10
-5
0
5
10
15
20
25
Accelera
tion(cm/s2)
Time(sec)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Amplitude(cm/s2)
Frequecny(Hz)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Amplitude(cm/s2)
Frequency(Hz)
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5.2 Comparison of Acceleration data of Pier at P10 along Longitudinal direction (BR2Y)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
28.16 cm/s2 and earthquake on 16th June 2004 caused maximum PGA of 5.7 cm/s2 in
longitudinal direction. Excitation for recent earthquake is 4.94 times stronger than the
previous one.
(a) (b)
Figure 12: Acceleration at bridge pier, obtained from actual response along longitudinal
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 13: Fifteen points smoothed FFT of Acceleration at bridge deck, obtained from actual
response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune
2004.
0 10 20 30 40 50
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
Am
plitude(cm/s2)
Time(sec)
0 10 20 30 40 50
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
Amplitude(cm/s2)
Time (sec)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Amplitude(cm/s2)
Frequency(Hz)
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5.3 Comparison of Acceleration data of Pier at P10 along Vertical direction
(BR3Z)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
8.08 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 16
th
June 2004 causedmaximum PGA of 2.6 cm/s2with a predominant frequency of 1.1 Hz in transverse direction.
Excitation for recent earthquake is 3.1 times stronger than the previous one.
(a) (b)
Figure 14: Acceleration at bridge pier, obtained from actual response along Up-Down
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 15: Fifteen points smoothed FFT of Acceleration at bridge pier, obtained from actual
response along Up-Down direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune
2004.
0.1 1 10 20
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Amplitude(cm/s2)
Frequeny(Hz)
0.1 1 10 20
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Amplitude(cm/s2)
Frequency(Hz)
0 10 20 30 40 50
-10
-5
0
5
10
Am
plitude(cm/s2)
Time(sec)
0 10 20 30 40 50-10
-5
0
5
10
Acceleration(cm/s2)
Time(sec)
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5.4 Comparison of Acceleration data of Pier at P10 along Vertical direction
(BR4Z)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
4.03 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 16
th
June 2004 causedmaximum PGA of 2.5 cm/s2with a predominant frequency of 1.1 Hz in transverse direction
(Figure 16-17). Excitation for recent earthquake is 1.9 times stronger than the previous one.
(a) (b)
Figure 16: Acceleration at bridge pier, obtained from actual response along Up-Down
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 17: Fifteen points smoothed FFT of Acceleration at bridge pier, obtained from actual
response along Up-Down direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune
2004.
0 10 20 30 40 50
-5.0
-2.5
0.0
2.5
5.0
Amplitude(cm/s2)
Time(sec)
0 10 20 30 40 50
-5
-4
-3
-2
-1
0
1
2
3
4
5
Acceleration(cm/s2)
Time(sec)
0.1 1 10 20
0.00
0.01
0.02
0.03
0.04
0.05
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.01
0.02
0.03
0.04
0.05
Amplitude(cm/s2)
Frequency(Hz)
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5.5 Comparison of Acceleration data of deck at P10 along Transverse direction
(BR5X)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
15.96 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 16
th
June 2004 causedmaximum PGA of 4.6 cm/s2with a predominant frequency of 1.1 Hz in transverse direction
(Figure 18-19). Excitation for recent earthquake is 3.47 times stronger than the previous one.
(a) (b)
Figure 18: Acceleration at bridge deck, obtained from actual response along transverse
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 19: FFT of Acceleration at free field station in North-South direction, obtained from
actual response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake
16thJune 2004.
0.1 1 10 20
0.00
0.07
0.14
0.21
0.28
0.35
Acceleration(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.07
0.14
0.21
0.28
0.35
Amplitude(cm/s2)
Frequency(Hz)
0 10 20 30 40 50
-20
-15
-10
-5
0
5
10
15
20
Amplitud
e(cm/s2)
Time(sec)
0 5 10 15 20 25 30 35 40 45-20
-15
-10
-5
0
5
10
15
20
Accelerationincm/sec2
Time in sec
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0.1 1 10 20
0.00
0.05
0.10
0.15
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.05
0.10
0.15
Acceleration(cm/s2)
Frequency(Hz)
5.6 Comparison of Acceleration data of deck at P10 along Longitudinal direction
(BR6Y)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
13.2 cm/s2 and earthquake on 16th June 2004 caused maximum PGA of 7.6 cm/s2 in
longitudinal direction (Figure 20-21). Excitation for recent earthquake is 1.74 times stronger
than the previous one.
(a) (b)
Figure 20: Acceleration at bridge deck, obtained from actual response along longitudinal
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 21: Fifteen points smoothed FFT of Acceleration at bridge deck, obtained from actual
response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune
2004.
0 10 20 30 40 50
-15
-10
-5
0
5
10
15
Amplitude(cm/s2)
Time(sec)
0 10 20 30 40
-15
-10
-5
0
5
10
15
Accelerationincm/sec2
Time in sec
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5.7 Comparison of Acceleration data of deck at P10 along Vertical direction
(BR7Z)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
4.5 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 16
th
June 2004 causedmaximum PGA of 3.06 cm/s2with a predominant frequency of 1.1 Hz in transverse direction
(Figure 22-23). Excitation for recent earthquake is 3.47 times stronger than the previous one.
(a) (b)
Figure 22: Acceleration at bridge deck, obtained from actual response along Up-Down
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 23: Fifteen points smoothed FFT of Acceleration at free field station in Up-Down
direction, obtained from actual response along longitudinal direction, (a) Earthquake 26th July
2008, (b) Earthquake 16thJune 2004.
0 10 20 30 40 50
-5.0
-2.5
0.0
2.5
5.0
Am
plitude(cm/s2)
Time(sec)
0 5 10 15 20 25 30 35 40 45
-5.0
-2.5
0.0
2.5
5.0
Accelerationincm/sec2
Time in sec
0.1 1 10 20
0.00
0.02
0.04
0.06
0.08
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.02
0.04
0.06
0.08
Amplitude(cm/s2)
Frequency(Hz)
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5.8 Comparison of Acceleration data of deck at P10 along Vertical direction
(BR8Z)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
3.75 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 16
th
June 2004 causedmaximum PGA of 2.65 cm/s2with a predominant frequency of 1.1 Hz in transverse direction
(Figure 24-25). Excitation for recent earthquake is 3.47 times stronger than the previous one.
(a) (b)
Figure 24: Acceleration at bridge deck, obtained from actual response along Up-Down
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 25: Fifteen points smoothed FFT of Acceleration at free field station in Up-Down
direction, obtained from actual response along longitudinal direction, (a) Earthquake 26th July
2008, (b) Earthquake 16thJune 2004.
0 10 20 30 40 50
-4
-2
0
2
4
Amplitude(cm/s2)
Time(sec)
0 10 20 30 40 50
-4
-3
-2
-1
0
1
2
3
4
Acceleration(cm/s2)
Time(sec)
0.1 1 10 20
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
Amplitude(cm/s2)
Frequency(Hz)
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5.9 Comparison of Acceleration data of Pier at P9 along Vertical direction
(BR9Z)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
5.33 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 16
th
June 2004 causedmaximum PGA of 2.8 cm/s2with a predominant frequency of 1.1 Hz in transverse direction
(Figure 26-27). Excitation for recent earthquake is 1.9 times stronger than the previous one.
(a) (b)
Figure 26: Acceleration at bridge pier, obtained from actual response along Up-Down
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
.
(a) (b)
Figure 27: Fifteen points smoothed FFT of Acceleration at bridge pier, obtained from actual
response along Up-Down direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune
2004.
0 10 20 30 40 50
-6
-4
-2
0
2
4
6
Accleration(cm/s2)
Time(sec)
0 10 20 30 40 50
-6
-4
-2
0
2
4
6
Acceleration(c
m/s2)
Time(sec)
0.1 1 10 20
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Amplitude(cm/s2)
Frequency(Hz)
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5.10Comparison of Acceleration data of Deck at P9 along Transverse direction
(BR10X)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
18.2 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 16
th
June 2004 causedmaximum PGA of 3.7 cm/s2 with a predominant frequency of 1.1 Hz in transverse
direction(Figure 28-29). Excitation for recent earthquake is 1.62 times stronger than the
previous one.
(a) (b)
Figure 28: Acceleration at bridge deck, obtained from actual response along transverse
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 29: FFT of Acceleration at free field station in North-South direction, obtained from
actual response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake
16thJune 2004.
0 10 20 30 40 50
-20
-15
-10
-5
0
5
10
15
20
Acceleration(cm/s2)
Time(sec)
0 10 20 30 40 50
-20
-15
-10
-5
0
5
10
15
20
Acceleration(cm/s
2)
Time(Sec)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
Amplitude(cm/s2)
Frequency(Hz)
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5.11 Comparison of Acceleration data of Deck at P9 along Longitudinal direction
(BR11Y)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
13.11 cm/s2 and earthquake on 16th June 2004 caused maximum PGA of 10.24 cm/s2 in
longitudinal direction. Excitation for recent earthquake is 1.28 times stronger than the
previous one.
(a) (b)
Figure 30: Acceleration at bridge pier, obtained from actual response along
longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 31: Fifteen point smoothed FFT of Acceleration at bridge deck, obtained from actual
response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune
2004.
0 10 20 30 40 50
-15
-10
-5
0
5
10
15
Acceleration(cm/s2)
Time(sec)
0 10 20 30 40 50
-15
-10
-5
0
5
10
15
Acce
leration(cm/s2)
Time(sec)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.00
0.05
0.10
0.15
0.20
0.25
Amplitude(cm/s2)
Freqeuncy(Hz)
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5.12 Comparison of Acceleration data of deck at Mid-span of P9 and P10 along
Transverse direction (BR12X)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
28.3 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 16
th
June 2004 causedmaximum PGA of 7.4 cm/s2 with a predominant frequency of 1.1 Hz in transverse
direction(Figure 32-33). Excitation for recent earthquake is 3.47 times stronger than the
previous one.
(a) (b)
Figure 32: Acceleration at bridge deck, obtained from actual response along transverse
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 33: FFT of Acceleration at free field station in North-South direction, obtained from
actual response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake
16thJune 2004.
0 10 20 30 40 50
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
Amplitud
e(cm/s2)
Time(sec)
0 10 20 30 40
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
Accelera
tion(cm/s2)
Time(sec)
0.1 1 10 20
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Amplitude(cm/s2)
Frequecny(Hz)
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5.13 Comparison of Acceleration data of deck at Mid-span of P9 and P10 along
Transverse direction (BR13X)
In response to the earthquake on 26th July 2008 the bridge deck was excited with a PGA of
28.2 cm/s
2
with 1.025 Hz predominant frequency and earthquake on 16
th
June 2004 causedmaximum PGA of 10.43 cm/s2with a predominant frequency of 1.1 Hz in transverse direction
(Figure 34-35). Excitation for recent earthquake is 2.7 times stronger than the previous one.
(a) (b)
Figure 34: Acceleration at bridge deck, obtained from actual response along transverse
direction, (a) Earthquake 26th July 2008, (b) Earthquake 16thJune 2004.
(a) (b)
Figure 35: FFT of Acceleration at free field station in North-South direction, obtained from
actual response along longitudinal direction, (a) Earthquake 26th July 2008, (b) Earthquake
16thJune 2004.
0 10 20 30 40 50
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
Am
plitude(cm/s2)
Time(sec)
0 10 20 30 40 50
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
Accele
ration(cm/s2)
Time(sec)
0.1 1 10 20
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Amplitude(cm/s2)
Frequency(Hz)
0.1 1 10 20
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Amplitude(cm/s2)
Frequency(Hz)
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6. TRANSFER RATIO
Transfer Ratio (TR) is the ratio of the FFT of the displacement of the bridge deck to the FFT
of the ground acceleration due to the earthquake.
TR =
g
u
u
=iba
idc
+
+
=2
1
i
2
i
1
eA
eA
= )(i
2
1 12eA
A
= tiTe
= IR iTT + .......................................... (4.16)
Where,
T =2
1
A
A= Absolute value of TR = 2
I
2
RTT +
t = 21 = Phase angle of TR =R
I1
T
Ttan
RT = Real value of TR = tcos*T
IT = Imaginary value of TR = tsin*T
u = FFT of the displacement of the bridge at the deck at pier P10 in the NS
direction
gu = FFT of the ground acceleration recorded at the west-end free-field station in
the north-south direction
c = Real value of the FFT of the displacement of the bridge at the deck at pier P10
in the NS direction
d = Imaginary value of the FFT of the displacement of the bridge at the deck at
pier P10 in the NS direction
a = Real value of the FFT of the ground acceleration recorded at the west-end free-
field station in the north-south direction
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b = Imaginary value of the FFT of the ground acceleration recorded at the west-
end free-field station in the north-south direction
1A = Absolute value of the FFT of the displacement of the bridge at the deck at pier
P10 in the NS direction; i.e. at BR5X = 22 dc +
1 = Phase angle of the FFT of the displacement of the bridge at the deck at pier
P10 in the NS direction; i.e. at BR5X =c
dtan 1
2A = Absolute value of the FFT of the ground acceleration recorded at the west-end
free-field station in the north-south direction = 22 ba +
2 = Phase angle of the FFT of the ground acceleration recorded at the west-end
free-field station in the north-south direction =a
btan 1
6.1 Comparison of Transfer ratio of deck at P10 along Transverse direction
(BR5X)
Figure 36 shows the bridge deck transfer ratio vs frequency along transverse direction for the
earthquake of 2008 and 2004. The earthquake of 2008 has peaks at frequency 1.04 Hz, 3.49
Hz and 17.33 Hz. In case of the earthquake 2004 one main peak is at 0.99 Hz.
(a) (b)
Figure 36: Transfer- ratio of the bridge in transverse direction, (a) Earthquake 26th July 2008,
(b) Earthquake 16thJune 2004.
0.1 1 10 20
0
5
10
15
20
25Transfer ratio5 Point smoothed TR
TransferRatio
Frequency(Hz)
0.1 1 10 20
0
5
10
15
20
25Transfer Ratio5 Point smoothed TR
TransferRatio
Frequency(Hz)
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6.2 Comparison of Transfer ratio of deck at P10 along Longitudinal direction (BR6Y)
Figure 37 shows the bridge deck transfer ratio vs frequency along longitudinal direction for
the earthquake of 2008 and 2004. The earthquake of 2008 has the main peak at a very low
frequency 0.12 Hz. In case of the earthquake 2004 peak is at 1.09 Hz.
(a) (b)
Figure 37: Transfer- ratio of the bridge in longitudinal direction, (a) Earthquake 26th July
2008, (b) Earthquake 16thJune 2004.
6.3 Comparison of Transfer ratio of deck at P10 along Vertical direction (BR7Z)
Figure 38 shows the bridge deck transfer ratio vs frequency along UP-DOWN direction for
the earthquake of 2008 and 2004. The earthquake of 2008 has peak at frequency 0.98 Hz. In
case of the earthquake 2004 one main peak is at 1 Hz.
(a) (b)
Figure 38: Transfer- ratio of the bridge in up-down direction, (a) Earthquake 26th July 2008,
(b) Earthquake 16thJune 2004.
0.1 1 10 20
0
5
10
15
20
25
30
35
40
45
Transfer ratio5 Point smoothed TR
TransferRatio
Frequency(Hz)
0.1 1 10 20
0
5
10
15
20
25
30
35
40
45
Transfer Ratio5 Point smoothed TR
TransferRatio
Frequency(Hz)
0.1 1 10 200
5
10
15
20
25
30
35
40
45Transfer ratio5 Point smoothed TR
TransferR
atio
Frequency(Hz)
0.1 1 10 200
5
10
15
20
25
30
35
40
45Transfer Ratio5 Point smoothed TR
TransferR
atio
Frequency(Hz)
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7. SUMMARY
Earthquake of 2008 excited the bridge more severely than earthquake of 2004. There are
several reasons for this. Earthquake of 2008 had more duration and amplitude than earthquake
of 2004. More over, the shock absorbing system of the bridge has been detoured. The shock
absorbing system has suffered some permanent deformation at some points during the
earthquake of 2008. So, if the bridge would experience some more earthquakes like this in
future shock absorbing systems at some points may collapse. The transfer ratio of the bridge
for the two earthquake are different, which is caused by the directional effect of the two
earthquakes. Earthquake 2004 had stronger component in North-South direction. On the other
hand, earthquake 2008 has almost equal components in North-South and East-West direction.
REFERENCE:
1. Bolt, B.A (1987) Site Specific Seismicity Study of seismic Intensity and Ground Motion
Parameter for Proposed Jamuna Bridge, Bangladesh Report prepared for seismic design of
Jamuna Bridge.
2. BUET (2003) Final Report: Installation Phase, Jamuna Multipurpose Bridge Seismic
Instrumentation Project, report submitted to JMBA.
3. KMI Strong Motion Analyst, Version 2.4, copyright 1998-2001, Kinemetrics, Inc. 222,
Vista Avenue, Pasadena, California, USA 91107.