Traffic Speed Deflectometer - Results
Dedicated post processing software has been developed for use with the data produced by the Traffic Speed Deflectometer.
The software produces a file in text format that, among other information, contains:
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| | • | Temperature (air and road) |
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| | • | Structural Curvature Index 300, SCI 300 |
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| | • | Maximum Deflection under the load |
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The text file is based on a binary file created by the data acquisition software during measuring. Parameters such as filter lengths and output frequency can be changed by the user. The software also has a plot facility for quick viewing of the results. Extra files containing the raw data or information about data quality can be created.
Below the different results/parameters are discussed:
Chainage
The chainage is determined with an odometer using an optical encoder. The pulses from the encoder are also used to determine the driving speed.
Temperatures
The air temperature is measured using a standard PT100 sensor. The road temperature is measured using an infrared type of thermometer.
Deflection Velocity
To obtain the correct deflection velocities, the data from each of the Doppler lasers needs to be compensated for the sensors own movements. The fact the laser beams are not exactly perpendicular to the road and that the angle of incident varies also makes corrections necessary. This is done using data from an inertial unit consisting of 3 accelerometers and 3 fibre optic gyros. One laser Doppler sensor placed outside the deflection bowl is also important to the compensation of data.
Deflection Slope
The Deflection Slopes are obtained by dividing the Deflection velocities by the driving speed.
Structural Curvature Index 300 and Maximum Deflection
Close to the load we can assume, that the road behaves like an elastic beam on a foundation of linear springs. Based on the Deflection Slopes we can therefore use the Euler-Bernoulli Beam Equation to determine the Structural Curvature Index 300 and Maximum Deflection.
Curve fitting
The existing TSD devices has 4 Doppler lasers, which results in three slopes.
Based on a set of three slopes (the figure to the left) we can determine the best curve through the measuring points (the middle figure) and then integrate the found curve to obtain the deflection bowl (the figure to the right). From the deflection curve (to the right) we can simply read the values for the maximum deflection and also make a reading at 300 mm to obtain the Structural Curvature Index 300.
Readings further out are "not that reliable", because the curve fit is based on only three measurement points placed near the load, in 100 mm, 200 mm and 300 mm. If there is an interest of for example the Structural Curvature Index 900, more sensors can be added and a new model will be used to determine the deflection bowl.
Examples of results
The figure below shows SCI300 data from app. 100 m of the same section of road measured at 4 different driving speeds.
