Indirect Approach for Measuring the Bridge Frequencies from a Passing Vehicle

Conventionally, the bridge frequencies are measured directly from the dynamic response of the bridge, using vibration sensors directly mounted on the bridge. Such an approach is referred to as the direct approach. Recently, another concept for measuring the bridge frequencies, referred to as the indirect approach was proposed. The main idea of the indirect approach is to extract the bridge frequencies indirectly from the dynamic response recorded for a vehicle during its passage over the bridge, rather than from that recorded for the bridge. Compared with the direct approach, the indirect approach for measuring the bridge frequencies from a passing vehicle has the advantage that it is a movable technique; it can be conveniently applied to measuring the frequencies of a bridge with basically no instrumentation on the bridge. In the early stage of studies on indirect approach, focus has been placed on its feasibility. As such, only the first or fundamental frequency of the bridge has been considered in the investigation. The objective of this dissertation is to refine the indirect approach for extracting the bridge frequencies. The applicability of the indirect approach is extended to extracting bridge frequencies other than the fundamental one with higher reliability, taking into account the following factors: (a) to ensure resolution in the Fourier spectrum of the vehicle response, (b) to evaluate how each of the major parameters of the vehicle-bridge system may affect the dynamic response of a passing vehicle, (c) to enhance the indirect approach by combining it with the empirical mode decomposition (EMD) technique, and (d) to explore the feasibility of applying the Hilbert-Huang transform (HHT) as an alternative or joint tool for the conventional fast Fourier transform (FFT). Suggestions are made for later application of the technique in the field, along with further directions of research highlighted.