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Vibration Data: Suspension Bridge Location 09

General Information

Contact: Gyorgy Szarka [additional processing by Dr Alex Weddell]
Institution: University of Bristol
Parameter: Vibration, 3-axis
Specific Location: At the beginning of the suspended bridge segment, Clifton side, logger is positioned on the metal of the lower railing
Data Duration: 00d 00h 04m 30s
Sampling Frequency: 2048 Hz

Description: The data was collected from 10 locations on the suspended segment of the Clifton Suspension Bridge. The suspended segment is in no contact with the land and the relative displacement between the ends of this section to the fixed pillars is visible, in excess of 10 mm. Generally, the vibration observed occurs in relatively short (few seconds) of transients as an effect of the cars passing by as well as entering and leaving the bridge segment. The peak acceleration levels are fairly small, in the region of 50-250 mg, depending on the location. In the frequency spectrum, there seem to be a main peak around 15 Hz, a slightly lower peak in the region of 38-40 Hz. There are some small local maxima at higher frequencies, in the region of 200 Hz as well but these are significantly less than the low frequency components. As the vibrations are not sustained by exponentially decay in time, the magnitude of these peaks vary. The maximum amplitudes are in the region of 10-50 mg depending on the location. The vibration magnitudes appear to be smallest in the middle of the suspended bridge segment and largest closest to the ends. The smaller metal structures, such as the metal cables connecting the lower railing (the ones support the road surface) to the chains, or the protective mesh along the sidewalk could potentially offer better energy harvesting locations.

The data streams are included in .mat file, titled with the location of each data segments. There are 7 columns of data that represent: time (in seconds), x-axis raw data (in mV), y-axis raw data (in mV), z-axis raw data (in mV), x-axis acceleration (in g), y-axis acceleration (in g), and z-axis acceleration (in g). The data segments are separated in the time domain by large amplitude motion that can easily be recognised, signalling the beginning and the end of the segment (data logging unit removed from location and rotated).

The length of each segment in time is around 3 minutes whilst the last two locations (9 and 10) offer slightly longer (approx. 5 minutes) of data streams.

The approximate distribution of the cars in time is shown in the graphic for the first seven locations for the first 2 minutes of logged data. The cars travelling right-to-left (bottom lane) are representing the cars that passed by on the side of the road where the data logging unit was mounted. Please note that the cars were not accurately timed, nor were their size and speed logged.

Acknowledgment: This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) under grant number EP/G067740/1 "Next Generation Energy-Harvesting Electronics: Holistic Approach"

Picture of test

Picture of test


Detailed Test Information

Original Filename: SuspensionBridge_Location_09.mat

Test Equipment:

Custom data logger based on ADXL325 MEMS 3-axis accelerometer

Calibration Parameters:

X: 210 mV/g, zero-g reading 1812 mV
Y: 210 mV/g, zero-g reading 1797 mV
Z: 210 mV/g, zero-g reading 1810 mV

Axis Directions:

X: horizontal, along the length of the bridge
Y: vertically down
Z: horizontal, along the length of the bridge

Downloads/Links

Data MAT file (zipped)
YouTube Video of FFT

Graphical Test Results

Peak Acceleration Frequency and Amplitude

Peak Acceleration Frequency and Amplitude

FFT at Maximum Vibration Amplitude

FFT at Max Vibration Amplitude

X-axis Vibration Characteristics

X-axis Vibration Characteristics

Y-axis Vibration Characteristics

Y-axis Vibration Characteristics

Z-axis Vibration Characteristics

Z-axis Vibration Characteristics

Automated Analysis

Processing Parameters

Sample rate: 2048 Hz
Duration: 270 s
Settling time: 15 s
FFT interval: 1 s
FFT length: 1 s
Number of FFTs performed: 255

Results

Highest mean vibration axis: Z

X-axis

Max Accel Ampl: 11.7 mgpeak at 247.0 Hz at 233 s

Time Peak Accel Ampl above 50% of Max Ampl: 22.0 s (8.6 %)
Peak Accel Freq Range (above 50% of Max Ampl): 240.0 ... 369.0 Hz
Mean Accel Freq (above 50% of Max Ampl): 313.0 Hz

Mean Peak Acceleration Ampl (whole test): 2.2 mgpeak
Mean Peak Acceleration Freq (whole test): 268.0 Hz

Y-axis

Max Accel Ampl: 4.9 mgpeak at 247.0 Hz at 233 s

Time Peak Accel Ampl above 50% of Max Ampl: 25.0 s (9.8 %)
Peak Accel Freq Range (above 50% of Max Ampl): 28.0 ... 363.0 Hz
Mean Accel Freq (above 50% of Max Ampl): 204.8 Hz

Mean Peak Acceleration Ampl (whole test): 1.1 mgpeak
Mean Peak Acceleration Freq (whole test): 221.2 Hz

Z-axis

Max Accel Ampl: 23.8 mgpeak at 247.0 Hz at 101 s

Time Peak Accel Ampl above 50% of Max Ampl: 7.0 s (2.7 %)
Peak Accel Freq Range (above 50% of Max Ampl): 29.0 ... 152.0 Hz
Mean Accel Freq (above 50% of Max Ampl): 47.9 Hz

Mean Peak Acceleration Ampl (whole test): 3.6 mgpeak
Mean Peak Acceleration Freq (whole test): 60.0 Hz

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