Uncertainty in bridge mode shapes based on accelerometer location

In Structural Health Monitoring (SHM), modal analysis of a bridge structure is commonly used to aid in understanding the vibration characteristics of the structure under various loading conditions. These modal analyses are conducted by placing accelerometers along the length of the structure, for example, along the base of the parapet, or along the kerbside. This choice of accelerometer location has the potential to impact the modes shapes captured. This study presents modal analysis results for a bridge to determine if there is a significant difference in mode shapes based upon the location of the accelerometers on the structure. Initial tests were conducted with the accelerometers placed parallel along the kerbside. Subsequent tests were conducted with the accelerometers positioned parallel along the base of the parapet whilst maintaining the same longitudinal location as the previous test. Following the modal analysis of the data collected during the tests, the results indicate that for some modes there is a significant difference between the modal amplitudes captured for a given mode shape. This discrepancy derives from the differing locations of the accelerometers. The work conducted in this study provides evidence that sensor location can impact modal results, and that considering the location of sensors thoroughly during testing is crucial for effective SHM.