Report11 Ansary Sir

8/11/2019 Report11 Ansary Sir

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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


r

BR4 Z Pile Cap at Pier P10


r

BR8 Z Deck at Pier P10


r

BR12 X Deck at Midspan betweenPiers P9 and P10


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)


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


(a) (b)

Figure 13: Fifteen points smoothed FFT of Acceleration at bridge deck, obtained from actual


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)


8.08 cm/s

2


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


(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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(BR4Z)


4.03 cm/s

2


th



(a) (b)



(a) (b)



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)


15.96 cm/s

2


th



(a) (b)



(a) (b)



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)



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


(a) (b)

Figure 21: Fifteen points smoothed FFT of Acceleration at bridge deck, obtained from actual


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


Time in sec

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5.7 Comparison of Acceleration data of deck at P10 along Vertical direction

(BR7Z)


4.5 cm/s

2


th



(a) (b)

Figure 22: Acceleration at bridge deck, obtained from actual response along Up-Down


(a) (b)

Figure 23: Fifteen points smoothed FFT of Acceleration at free field station in Up-Down



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


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)


3.75 cm/s

2


th



(a) (b)

Figure 24: Acceleration at bridge deck, obtained from actual response along Up-Down


(a) (b)

Figure 25: Fifteen points smoothed FFT of Acceleration at free field station in Up-Down



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)

18


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(BR9Z)


5.33 cm/s

2


th



(a) (b)



.

(a) (b)



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)


18.2 cm/s

2


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)



(a) (b)



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)

20


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5.11 Comparison of Acceleration data of Deck at P9 along Longitudinal direction

(BR11Y)



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


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)

21


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5.12 Comparison of Acceleration data of deck at Mid-span of P9 and P10 along

Transverse direction (BR12X)


28.3 cm/s

2


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)



(a) (b)



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)

22


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5.13 Comparison of Acceleration data of deck at Mid-span of P9 and P10 along

Transverse direction (BR13X)


28.2 cm/s

2


th



(a) (b)



(a) (b)



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)

23


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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

24


25/27

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)

25


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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


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)

26


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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.

Report11 Ansary Sir

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