Vibration based damage detection is a nondestructive structural health monitoring approach that uses changes in the dynamic characteristics of a structure (bridge in this study) as an indicator of damage. Acquisition of vibration records with a high signal-to-noise ratio is important for such an approach, and the choice of sensors used to acquire the data is an important consideration. A geophone is a velocity transducer commonly used by seismologists for subsurface exploration, and their use for bridge vibration measurement provides some advantages over accelerometers which are commonly used for this purpose. Compared to accelerometers, geophones are cheaper, more sensitive, and do not require signal amplification. A possible drawback is the limited range of frequency response, but geophone frequency response it is not a problem for the majority of highway bridges. The objective of this paper is to summarize our recent study that used triaxial geophones combined with vibration based damage detection techniques to detect precisely controlled damage on two actual highway bridges. The results show that modal parameters obtained using geophones can be successfully implemented with vibration based damage detection techniques for the purpose of locating damage on full-scale bridges. We also discovered that the horizontal vibration response of bridges is particularly sensitive to damage, even more so than the vertical vibrations.

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