Using Geophones for Nondestructive Evaluation of Full-Scale Bridges

Nondestructive damage identification for civil engineering structures has received the attention of many researchers over the past several years. Vibration-based damage detection is a nondestructive structural health-monitoring approach that focuses on changes in the dynamic characteristics of a structure as indicators of damage. All vibration-based damage detection techniques require high signal-to-noise vibration data for analysis; thus the sensors used to measure vibrations are an important consideration. The objective of this study is to demonstrate the use of inexpensive geophones for determining the modal parameters of bridges to be used with vibration-based damage detection techniques. A geophone is a velocity transducer commonly used by seismologists for subsurface exploration. Researchers typically use accelerometers to measure bridge vibrations. However, compared with geophones, accelerometers are relatively expensive, have lower sensitivity, and require additional electronics for signal conditioning. To validate the use of geophones for modal parameter identification, a simple beam experiment was conducted, and the results were compared with theoretical values and a finite element model. Modal parameters identified from a full-scale bridge test are presented, and the effects of parapet rails and temperature change on the bridge's modal parameters are discussed. For successful implementation of the proposed methodology in a remote, wireless approach, a solar-powered, cell phone modem–based data acquisition system is demonstrated. This study makes an important contribution because the cost of the sensors needed for implementation of vibration-based damage detection on a large scale is substantially reduced with the use of high-sensitivity geophones.