The document reports on bridge vibration monitoring tests carried out by SysEng Pte Ltd. A monitoring system was installed on the Henderson Foot Bridge but the data was corrupted. Further tests were conducted with 4 people simulating different loading conditions on the bridge such as jumping, walking, jogging, and groups crossing. Acceleration and displacement were measured in the X and Z axes. Analysis showed the Z axis was most sensitive, with peak acceleration around 1.6 Hz under all test conditions.

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Henderson Foot Bridge Monitoring
Introduction
The monitoring of the Henderson Bridge was carried out from 3 to 14 May 2008. It was expected that
there would be a large crowd during the opening of the bridge to the public. During the monitoring
period, a Micro G vibration data logger and a video recording system were placed near the bridge and
secured with a water proof locked IP65 casing. After the monitoring period, it was fund that the system
had malfunction due to possible vandalism on site. Hence the data was extracted and analyzed. It
was found that the data was too corrupted to be able to recover for analysis and reporting.
Another monitoring was carried out, but unfortunately it was not possible to reproduce the large
number of people walking through the bridge as that of the opening day. Hence it was decided to
have 4 people simulating the conditions.
Dr Tan Guan Hong
Date: 12 September 2008

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Objective: Bridge response with 4 persons
Field tests were carried out to measure the bridge vibration in the Z and X axes for different loading
conditions. The responses of the bridge were measured and analyzed for its behavior under these
conditions.
The test equipment measures accelerations in the XYZ axes while their respective displacements are
calculated by double integrating the acceleration results. The spectrum analysis are carried out on the
X and Z acceleration results for its peak amplitudes below 10 Hz.
Summary of measurement results
Under these test conditions, the results showed that the Z axis is the most sensitive and picked up
under 1 mg at the frequency of 1.6Hz with a calculated displacement of less than 0.7 mm movements.
The test showed very similar results and hence only typical results are shown here.
Bridge Vibration Measurement Conditions
Measurement conditions:
Weather: Normal with a slight wind present
Human Traffic: Visitors are moving around the bridge, with cars moving through the below road.
Schematic test layout
Figure 1: Axis directions

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Test 1: 4 persons jumping in Z axis (jumping frequency 0.5 Hz to 0.25 Hz)
Results in the Z Axis
Time [sec]
40
35
30
25
20
15
10
5
0
A
c
c
e
le
r
a
tio
n
[g
]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
40
35
30
25
20
15
10
5
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
The acceleration peak frequency is 1.613 Hz for the bridge. Those above 10Hz are the impact forces

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Results in the X Axis:
Time [sec]
40
35
30
25
20
15
10
5
0
Ac
c
e
le
ra
tion
[g]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
40
35
30
25
20
15
10
5
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
X axis Minimum Value 1 Hz, Peak Acceleration for below 10Hz is 1.613 Hz

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Picture was taken with the forth person behind camera.

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Test 2: 4 persons walking (about 1 to 2 Hz excitation)
Results in the Z axis:
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Acceleration
[g]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
The acceleration peak frequency is 1.613 Hz for the bridge. Those above 10Hz are the impact forces

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Results in the X axis:
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Acceleration
[g]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
X axis Minimum Value 1 Hz, Peak Acceleration for below 10Hz is 1.613 Hz

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Forth person behind camera

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Test 3: Visitors jogging through the bridge (a little wind is present)
Results in the Z axis
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Acceleration
[g]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
Z axis Minimum Value 1 Hz, Peak (below 10Hz): 1.601 Hz

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Results in the X axis:
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Acceleration
[g]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000

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Test 4: 3 or 4 groups of peoples moving through the bridge
Results in the Z axis:
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Acceleration
[g]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
Z axis Minimum Value 1 Hz, Peak (below 10Hz): 1.619 Hz

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Results in the X Axis:
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Acceleration
[g]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000

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Test 5: A group of 3 people crossing and 2 children are playing
Results in the Z axis
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Acceleration
[g]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
Z axis Minimum Value 1 Hz, Peak (below 10Hz): 1.62 Hz

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Results in the X axis:
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Acceleration
[g]
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
-0.0002
-0.0004
-0.0006
-0.0008
-0.0010
Time [sec]
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Displacement
[cm]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
Frequency [Hz]
80
70
60
50
40
30
20
10
Fourier
Amplitude
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
X axis Minimum Value 1 Hz,

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Appendix 1: Monitoring Equipment Specification
For Measurement of the bridge vibration, the system uses motion accelerographs with data upload to
a logging computer. The Motion accelerographs use is certified system from the Canterbury Seismic
Instruments Ltd, utilizing low-noise MEMS accelerometers. Following are the sensor specifications.
SENSOR
Type Triaxial MEM silicon accelerometers
Range ± 3g
Noise level < 0.65 mg RMS noise floor (80Hz
Bandwidth)
Temperature offset error ± 1 % over operating temperature range
Temperature gain error ± 1 % over operating temperature range
Temperature hysteresis ± 0.5 % over operating temperature range
Sampling Zero jitter, zero skew autonomous
sampling
Anti-Alias 8th order elliptic synchronized switched
capacitor anti-alias
filter (fc = 2x measurement bandwidth
(BW))
Extremely high linearity over 0-100 Hz
range
Sampling rate 800Hz
Conversion 16-bit data conversion

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SAMPLE SIGNAL PROCESSING
Filtering FIR digital anti-alias filter/decimator
Perfect linearity
Measurement Bandwidth 40 or 80Hz
Recorded dynamic range 108dB (80 Hz BW)
108dB (50 Hz BW)
TRIGGERING
Type STA/LTA AND or OR filtered level detection
STA/LTA - Independent thresholds on each channel
- Selectable channel AND or OR triggering
- Thresholds adjustable from 2:1 to 200:1
Level - Independent thresholds on each channel
- Selectable channel AND or OR triggering
- Selectable low pass, high pass and band
pass IIR filters or no filtering
- Level from 1mg to 3000mg in 1mg steps
Pre-event length 10 to 60 seconds in 1-second steps
Post even length 10 to 60 seconds in 1-second step

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STORAGE
Type Removable FLASH disc
Storage time 55 hours @ 200 samples/s
depends of FLASH disc size
SYSTEM
Processor Type Low power x86 based
OS Multi-tasking real-time Linux based
Supply voltage 10.5 – 24.0V DC
Power consumption 8 W typical 15W max
Temperature range 0 - 70°
C standard
Humidity 0 to 100% (non condensing)