JOHN M. NICHOLS
Department of Construction Science, Texas A&M University
This paper presents the results of an experimental study investigating the frequency response of the Pont-Y-Prydd Bridge, near Cardiff, Wales as measured by an accelerometer accurate in the sub-milli-g range using the ambient signal noise in place of a large applied load required for less sensitive instruments. A new technique, termed the Variance Model, uses the statistical properties of a set of 51 Fast Fourier transform records to determine the relative strength of each FFT point in the range of 0 to 62.5Hz for the bridge. A set of most significant frequencies provides a set termed the FFT Spectrum. The FFT Spectrum results when compared to the set of natural frequencies of a simple arch finite element model for the Pont-Y-Prydd Bridge showed a tolerable fit below 20Hertz, although the first natural frequency difference suggests that a more refined FE model may be required. Whilst not proven, the results of the research work support the hypothesis, certainly to a point of requiring further experimental work on different types of structures. This is the first comparison of the Variance Model estimates for an actual bridge to a FEM of the bridge. The clear question for the future is whether the Variance Model can predict damage accumulation in buildings.