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ABSTRACT
In recent years, there has been increased attention in the deterioration of civil engineering infrastructures like roads, building and bridges due to aging and usage beyond the design limits. Heavy duty vehicles that exceed the acceptable designed tonnage on the highway quickly lead to road failure before its service life. Abnormal excitation arising from this class of vehicle necessitates accurate measurement and monitoring of vibration which is essential for early detection of structural damage on the road. Technological advancement in photonics has led to the development in fibre optic sensor (FOS) for weight-in-motion (WIM). As the field of vibration sensor has advanced, fibre optic vibration sensors (FOVS) have emerged due to its cost-effectiveness, immunity to EMI and distributed sensing capability. This technique can be deployed to monitor excessive vibration from heavy duty vehicles which can lead to road failure on our highways across the country.
A multimode distributed FOS was placed across Ikpoba River Road by The Capitol in University of Benin, Benin City to measure the frequency of vibration caused by weight-in-motion. Phase Optical Time Domain Reflectometer (Φ-OTDR) is used to obtain millisecond snapshots of the signal arising thereof. A video shot was also recorded to match the exact timing of each excitation. An expression for forced vibration on the multi-mode fibre caused by external perturbation was used to obtain the phase shift and change in propagation of the signal. MATLAB 7.3 software was used to transform the signal from space domain into frequency domain and calculate the spectral analysis.
The results of the power spectra density (PSD) differential show that Camry at increasing speed have broader frequency peaks at 50ns when compared to that of 20ns, while the Truck at increasing speed had sharp frequency peaks at 50ns when compared to that of 20ns.
